How to Make a Rubber “Glove” or “Sock” Mold

July 15th, 2015

Example of Glove Mold

[^Example of a “glove” or “sock” mold]

Glove molds, also referred to as sock molds, are one-piece rubber molds that can be turned back on themselves and peeled off. These molds must be thin (~1/8″) and can only be done on bas relief or models with a pyramid shape.

One of the benefits of this mold type is that a cut does not need to be made in the mold, so seam lines in the reproductions are not a concern. Another benefit is that less rubber is needed to make the mold compared to block molds, for instance.

 
 
 
 
 
 
 
Materials & Supplies Needed for this Project: 

 

The Model

The following plastic model will be used for this project.

Model for Glove Mold

 
Model for Glove Mold - Side View

 
Model for Glove Mold - Rear View

 

Step 1: Prepare the Model

Perform a test cure on the model, if necessary.

The origin of this model is unknown, so a quick test cure is done to ensure that there are not any contaminants on the model that will inhibit platinum-cured silicone. Fast-setting PlatSil® 71-10 Silicone Rubber is used for this test. Read more about test cures here.
 

Test Cure with PlatSil 71-10

 
How to test cure silicone

 
The test shows that platinum-cured silicone will cure successfully against the model.
 
Test Cure - Platinum 71-10 Silicone Rubber

 
Adhere the model to a stable baseboard.
 
We use PolyPoxy Quick Stick Adhesive, a two-part (1A:1B), fast-setting (3-5 minute cure) epoxy adhesive, to secure the model to a piece of melamine-laminated particle board.
 
PolyPoxy Quick Stick Epoxy Adhesive

 
Adhere Model to Baseboard

 
Adhere Model to Baseboard with Epoxy

 
Allow Epoxy to Cure

 
Allow the adhesive to cure and then apply an appropriate release agent.
 
A silicone mold will be made in this tutorial, so Pol-Ease 2500 Release Agent is used. For polyurethane molds, use Pol-Ease 2300 Release Agent.
 
Release Agent for Silicone

 
Spray the release agent onto the model and baseboard and then brush out with a dry brush to ensure even coverage.
 
Apply Pol-Ease 2500 Release Agent

 
Brush Out Release Agent

 

Step 2: Measure & Mix the Mold Rubber

Mold rubbers used for making glove molds should be relatively soft with high elongation properties.

For this project, we select PlatSil 71-11 Silicone Rubber. It is a soft (Shore A10), platinum-cured silicone rubber with high elongation (751%).
 
PlatSil 71-11 Silicone Rubber: The Basics

  • Shore Hardness: A10
  • Mix Ratio: 1A:1B
  • Pour Time: 20 minutes
  • Demold Time (at room temp.): 4 hours
  • Color: Blue-Green
  • Mixed Viscosity: 6,000 cP
  • Specific Volume: 24.7 in³/lb

 

PlatSil 71-11 Silicone Rubber - Polytek

 
How Much Rubber is Needed?

A few layers of silicone will be brushed onto the model; to start, only measure and mix the amount of rubber needed for the first layer. The second layer will not be applied until the first layer has gelled.

The ultimate goal is to reach a mold thickness of ~1/8″. For an estimate of how much rubber is needed for the first layer, determine the surface area of your model and then multiply by 1/16″. Take that result and divide by the specific volume of the mold rubber (PlatSil 71-11 has a specific volume of 24.7 in³/lb). This number will give you an estimate of the amount of rubber (lb) needed for the first layer. It is a good idea to use a bit more rubber than estimated as some of the rubber may run off of the model. A flange should also be created at the base of model, so additional rubber is needed for that.
 
Accessories

Ensure that all needed accessories are ready to go before starting the mixing process.

PlatSil 71-11 is a low-viscosity silicone, so it must be thickened for brush-on application. This silicone can be thickened with either PlatThix Liquid Thickener, TinThix Liquid Thickener or Fumed Silica.

We select PlatThix as the thickener for this project.

PlatThix Liquid Thickener for Silicone

 
We would also like to speed up the cure time of the rubber, so we make sure to have PlatSil 71/73 Part X Accelerator on hand. Accelerator is not necessary for this project, but adding just 1% Part X decreases the gel time to ~1/3 the normal gel time.
 
Accelerator for Platinum-Cured Silicone

 
Weigh Components

When all accessories, mixing containers and mixing tools are ready, use a digital scale to measure out each component.

We recommend weighing Part B into the container first as it is generally lower in viscosity than Part A and less likely to cling to the sides of the mixing container.
 

Measure PlatSil 71-11 Part B
 
 
Measure out Part A into the mixing container.
 
Measure PlatSil 71-11 Part A
 
 
Mix Parts A and B together, scraping the bottom and sides of the mixing container several times.
 
Thoroughly Mix PlatSil 71-11
 
 
Add the thickener and mix thoroughly.

For this silicone rubber, ~3% PlatThix (by weight) of the total mixed weight is a good amount to thicken for brush-on application. TinThix Thickener is a more concentrated mixture and requires about half the amount of PlatThix (~1.5%).
 

Add PlatThix Thickener

 
Add the accelerator and mix thoroughly. We add 1% Part X. If you prefer to add the accelerator prior to mixing Parts A and B together, add it to Part B and then combine with Part A.
 
Add PlatSil Accelerator

 

Step 3: Brush Rubber onto Model

Using a dry brush, brush rubber onto the model working from bottom to top. Working from top to bottom can increase the chances of trapped air. Using short left and right movements while brushing upwards helps to work rubber into the details of the model.

Brush Silicone onto Model

 
Brush Silicone onto Figurine

 
Brush-On Silicone Rubber
 

Create a rubber flange around the base of the model.
 


Create Rubber Flange

 
After a thin layer of rubber has been applied to the entire model, allow the rubber to gel before moving on to the second layer. Application of the second layer should not disturb/move the first layer.
 
Allow First Layer of Silicone to Gel

 
When the first layer has gelled, measure and mix a second batch of rubber and brush it onto the model.
 
Apply Second Layer of Silicone

 
Brush On Second Layer

 
Second Layer of PlatSil 71-11

 
Allow Second Layer of Silicone to Gel

 
Allow the second layer to gel and then mix up another batch for the third and final layer. The amount of layers necessary will vary depending on individual technique.
 
Apply Third Layer of Silicone

 
Brush on Third and Final Layer of Silicone

 
Allow the final layer to cure.
 
Allow Final Layer to Cure

 

Step 4: Make a Mold Shell

Thin blanket molds must be backed with a rigid support shell or nest, otherwise they”ll deform during the casting process.

For this project, we choose to make a one-piece flexible foam “nest”.

To begin, trim the flange. We will be using a PVC pipe to cast the foam, we so we trim the flange to the same diameter as the pipe.
 

Trim Rubber Flange

 
Secure the two halves of the PVC pipe together with tape.
 
PVC Pipe to Make Foam Shell

 
Align PVC Pipe

 
Secure Pipe Together

 
Secure Two Halves Together

 
Foam Mold Shell Form

 
Coat the inside of the pipe with paste wax so it releases easily from the foam. Also lightly coat the silicone mold with paste wax.
 
Apply Paste Wax to Pipe and Mold

 
Apply Paste Wax to Inside of Pipe

 
Place the pipe over the mold and secure it to the baseboard with tape.
 
Place PVC Pipe Over Mold

 
Secure PVC Pipe to Baseboard

 

Secure Form to Baseboard

 
For a more dense, compact foam, close the top of the pipe with a board and make some vent holes.
 
We leave the top of the PVC mostly open.
 

Ready for Foam Shell

 
PolyFoam F-3 is a self-skinning, flexible polyurethane foam. It has a 1A:2B mix ratio (by weight), a 1.5-minute rise time and a 10-minute demold time. This foam has a free-rise density of 3 lb/ft³, but should be molded at 5 or 6 lb/ft³ for good results.
 
PolyFoam F-3 Flexible Casting Foam

 
To determine how much foam (lb) is needed, multiple the volume (ft³) of the space you’d like to fill by the desired density of the molded foam (5 lb/ft³).

Carefully measure out Parts A and B (1A:2B), combine and mix thoroughly.
 

Measure PolyFoam Flexible F-3 Foam Part B

 
Measure PolyFoam Flexible F-3 Foam Part A

 
Mix PolyFoam F-3

 
It is important to work quickly when using foam, especially in hot/humid environments. Immediately after mixing, pour the foam into the PVC pipe.
 
Pour Foam into the Pipe

 
PolyFoam F-3 Expanding

 
Because we did not close the PVC pipe, the foam rises out.
 
PolyFoam F-3 in PVC Pipe

 

Step 5: Demold

When the foam has cured, remove the tape and pipe.
 


Allow Foam to Cure Then Remove Pipe

 
Cut Tape on Pipe

 
Open PVC Pipe

 
Remove Foam Nest

 
Then remove the mold from the foam nest.
 
Remove Mold from Foam Nest

 
Remove Rubber Mold from Foam Shell

 
After removing the mold, it is a good idea to squeeze the foam with your hands. This will burst the cells and allow atmospheric air info the foam to prevent shrinking.
 
Massage the Foam to Prevent Collapsing

 
To remove the glove mold from the model, we recommend first applying a silicone release or soapy water to the exterior of the mold to allow it to slide easily against itself.

We apply Pol-Ease 2300 Release Agent. If you only have Pol-Ease 2500 Release Agent in stock, it will also work, but a larger amount may be required.
 

Spray Silicone Release onto Glove Mold

 
Spray Pol-Ease 2300 on Rubber Sock Mold

 
After application of silicone release or soapy water, begin to peel back the mold starting at the bottom.
 
Peel Glove Mold Off of Model

 
Peel Back Rubber Glove Mold

 
It may be helpful to place the mold on the corner of the table for leverage.
 
Peel Glove Mold Off of Model

 
PlatSil 71-11 Silicone Glove Mold

 
Remove Model from Mold

 
Trim the foam nest and make sure that it is level.
 
Cut Foam on Band Saw

 
To ensure alignment of the mold and foam nest when casting, create a simple notch in the mold and foam to properly align the two elements each time.
 
Key the Rubber Mold and Foam Shell

 
Key in Silicone Mold and Foam Nest

 
The mold is now ready for casting!
 
The Finished Mold with Foam Shell

 

Step 6: Casting

There are many materials that can be cast in silicone molds. Some examples include polyurethane resin, polyester resin, polyurethane foam, epoxy resin, wax, plaster and concrete.

The following example utilizes EasyFlo 60 Liquid Plastic, a fast-setting polyurethane plastic. This plastic has a 1A:1B mix ratio (by volume), 2 to 2.5-minute working time and 15 to 30-minute demold time.

To cast this figurine, we measure and mix the resin and then pour about half of it into the mold.
 

EasyFlo 60 Liquid Plastic Casting

 
We tilt the mold back and forth a few times to help release any trapped air bubbles and then pour the remainder of the EasyFlo 60.
 
Rotate Mold to Release Trapped Air

 
Complete Resin Pour

 
When the EasyFlo 60 has cured, we remove the figurine the same way that the original model was removed.
 
Demold EasyFlo 60 Plastic Casting

 
Peel Back Glove Mold to Remove Casting

 
PlatSil 71-11 Sock Mold

 
Remove EasyFlo Resin Casting from Mold

 
The EasyFlo 60 reproduction is pictured below next to the original.
 
Silicone Mold for Figurine Reproduction

 
EasyFlo 60 Resin Casting and Original Model

 
EasyFlo 60 liquid plastic can be dyed with PolyColor Dyes or the cured plastic can be painted after-the-fact.

The figurine below was colored with a small amount of Brown PolyColor Dye and then Sculpt Nouveau’s Black Wax was applied and wiped away with a paper towel to highlight the details of the casting.
 

EasyFlo 60 Plastic and Black Wax

 
Sculpt Nouveau Wax on EasyFlo Resin

 
Glove Mold - EasyFlo Plastic - Front View

 
Glove Mold - EasyFlo Plastic - Rear View

 
 
Do you have questions about your next mold making or casting project? Get in touch with our Technical Support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Rubber Mold Design for Wet Cast Pavers

July 1st, 2015

Mold design has a great impact on production efficiency and product quality. The following rubber mold designs are options for single-cavity wet cast pavers.

NOTE: This blog covers basic mold design; the shape and size of the original paver will affect mold design and mold rubber selection. For further assistance, please reach out to the Polytek Technical Support Team.

DESIGN #1

Block Mold on Simple Bottom Board

 
This design features mold side walls that are cast thicker in order to hold their shape when filled with concrete. Because of the thickness of the walls, there is no need to place a rigid mold box around the mold when casting.

This mold design is simple to construct and offers great stability; it is a good option for use in automated wet cast manufacturing.

Generally, these molds are more expensive to manufacture as they require more rubber compared to other designs.
 
 
The design:
 

block mold on simple bottom board

 
 
Examples are pictured below:
 
Rubber Mold Design - Block Mold for Pavers
 
 
Rubber Mold Design - Block Mold for Pavers

 
To learn the basics of making a paver block mold, refer to this tutorial.

 

DESIGN #2

Blanket Mold in a Mold Box

 
Generally, the term “blanket mold” refers to molds that are thin (resembling a blanket placed over the model). To learn about the basics of blanket molds, read this blog entry.

In this case, the mold box is placed around the rubber mold when casting; this is what allows the mold walls to be thin.

The downside to this method is that concrete and other debris may fall between the box and the mold which can cause distortion and quality issues.

This mold design is easy to construct and requires less rubber than the previous block mold option, but the sides may be unstable.

In general, this design is not very favorable for automated or manual wet cast operation.
 
 
The Design:
 

rubber blanket mold in mold box - polytek

 
 
An example is pictured below (without the mold box):
 
Rubber Mold Design - Wet Cast Pavers
 
 
Rubber Mold Design - Wet Cast Pavers
 

 

DESIGN #3

Blanket Mold with Flange in a Box

 
Like Design #2, this technique also has a thin blanket mold with mold box. The difference is the flange that extends along the top of the mold box walls.

The flange prevents concrete and other debris from falling between the box and the mold and also adds some rigidity and stability to the sides of the mold.

The mold may include a 5-degree draft angle on the outside of the mold wall for easier removal from the box.

The construction for this method is more complicated than the previous two designs, but is commonly used in manual wet cast operations.
 
 
The Design:
 

Rubber Mold Design - Blanket Mold for Paver

 
 
An example is pictured below (without mold box):
 
Rubber Mold Design - Blanket Mold for Paver
 
 
Rubber Mold Design - Concrete Pavers

 

DESIGN #4

Blanket Mold with Locking Flange in a Box

 
This design is very similar to Design #3; the only difference is that the flange locks around the mold box to improve stability and help to maintain overall size/dimensions.

This locking design has the most complicated construction of the four mold designs and can be challenging in a high volume production environment as it requires more effort to lock and unlock the flange repeatedly.
 
 
The Design:
 

Blanket Mold with Locking Flange in a Box - Paver Rubber Mold Design
 

Do you have questions about your concrete casting project? Get in touch with our Technical Support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

How to Make a Rubber Mold of a Corbel

June 16th, 2015

This mold making tutorial features the making of a poured block mold of a plastic corbel. It was one of the projects worked on at our October 2014 Mold Making & Casting Workshop.

If you prefer to make a brush-on mold with mold shell (for larger models), visit this blog entry.

A polyurethane mold rubber will be used to the make the mold because the intent is to eventually cast concrete (although we do show some resin casting in this tutorial). Polyurethane mold rubbers work very well for a variety of concrete applications.

 

Polytek Products Used

 

Other Supplies & Tools

  • Melamine-laminated particle board (or other material to make mold box)
  • C-Clamps
  • Drill
  • Wood screws
  • Dry Brushes
  • Putty knife
  • Digital Scale
  • Mixing Pail
  • Mixing Tool (Poly-Paddle)

 

Step 1: Prepare the Model & Containment Area

Because this corbel is plastic, the only preparation for the surface of the model is the application of a release agent. This will be applied once the mold box is constructed around it.

When working with a porous model (e.g., unsealed wood, concrete), it must be sealed prior to the mold making process. Some sealer options include paint, lacquer, paste wax and pre-packaged options from Polytek, including water-soluble Poly PVA Solution, Pol-Ease® 2350 Sealer & Release Agent and PolyCoat Sealer & Release Agent. View the Sealer & Release Agent Selection Guide for more information.
 

Corbel for Mold Making
 
 

Corbel_SideView

 
Secure the corbel to a baseboard. We use PolyPoxy® Quick Stick Adhesive, a two-part, fast-setting epoxy adhesive to secure this model to a melamine-laminated particle board. It could also be screwed to the baseboard.
 
When working with porous models, the baseboard should be vented from beneath to prevent trapped air from forming bubbles in the rubber.
 
Epoxy Adhesive for Mold Making

 
Adhere Corbel to Baseboard

 
Construct mold box walls around the model. They should be spaced at least 3/4″ beyond the model on all sides and the height should be at least 1/2″ above the model.
 
We use melamine-laminated particle board as the mold box wall material and secure them together with C-Clamps. The walls are also secured to the baseboard with screws.
 
Build Mold Box Walls

 
Corbel in Mold Box

 
Because there is quite a bit of empty space surrounding the thinner, bottom-area of the model, some block-outs could be added to take up space (pictured below in red) and reduce the amount of rubber needed to make the mold.
 
Mold Box Diagram

 
Seal the inside edges and corners of the mold box with clay (we use warmed plasticine clay). Hot glue or caulking could also be used.
 
Also seal the edges of the model that meet the baseboard (all clayed areas are marked with a dotted line below). Sealing the edges of the model is easier to do before the mold box walls are in place.
 
This step helps to prevent mold rubber from seeping beneath the model and out of the mold box.
 
Seal Edges of Mold Box and Model with Clay

 
Spray Pol-Ease® 2300 Release Agent onto the model, baseboard and mold box walls and then brush it out to ensure even coverage and no puddling. If a silicone mold is being made, use Pol-Ease® 2500 Release Agent instead.
 
Pol-Ease 2300 Release Agent

 

Step 2: Determine How Much Mold Rubber is Needed

To determine the amount of rubber needed for the mold, first start by estimating the volume of the original corbel.
 

Measure Corbel Height

 
Measure Corbel Width

 
Measure Corbel Bottom Width

 
Measure Corbel Depth

 
Based on the measurements, we estimate 88 in³.

Then, determine the volume of the mold box. This mold box is approximately 506 in³.

Next, subtract the volume of the original corbel from the volume of the mold box.

506 in³ – 88 in³ = 418 in³.

Divide the result by the specific volume of the mold rubber. The specific volume of Poly 74-20 Liquid Rubber is 27.5 in³/lb.

418 in³ ÷ 27.5 in³ = 15.2 lb

~15.2 lb of Poly 74-20 Liquid Rubber is needed to make this mold.

 

Step 3: Measure, Mix & Pour Poly 74-20 Liquid Rubber

Poly 74-20 Liquid Rubber is the softest (Shore A20) rubber in the 74-Series line of polyurethanes. It is selected because it is flexible enough to easily demold from the intricate sides of the original corbel.

The Basics of Poly 74-20

  • Mix Ratio: 1A:2B
  • Shore Hardness: A20
  • Pour Time: 30 minutes
  • Cured Color: Yellow
  • Mixed Viscosity (cP): 800

 
Measure Part A & Part B on a digital scale at the proper ratio (1A:2B) and then combine them (we recommend adding Part B to the pail first because it’s lower in viscosity). Mix thoroughly, scraping the sides and bottom of the mixing container several times.
 

Mixing Poly 74-20 Liquid Rubber

 
Pour the rubber into a low spot in the mold box and allow the rubber to rise.
 
Pour Poly 74-20 Liquid Rubber

 
Pour Rubber into Mold Box

 
Fill the mold box to at least 1/2″ above the highest part of the corbel.
 
74-20 Liquid Rubber in Mold Box

 
If needed, slightly tilt the box and baseboard back and forth to help dislodge any air bubbles that may be trapped against the model.
 
Release Bubbles

 
Allow the rubber to cure at room temperature for ~16 hours before demolding.
 

Step 4: Demold

Remove the mold box walls and then loosen the edges of the mold (a putty knife or stainless steel spatula are useful tools for this).
 

Demold

 
Loosen Edges

 
After loosening the edges, carefully remove the entire mold.
 
Finished Poly 74-20 Mold

 
The mold is now ready for casting.
 

Step 5: Casting

There are many casting materials that can be poured/brushed/sprayed into polyurethane molds, including:

  • Concrete
  • Plaster
  • Wax
  • Resin (polyurethane, epoxy, polyester), with the proper release agent
  • Foam, with the proper release agent

 
NOTE: Although it’s not necessary in this case, there are times when the mold box should be placed back around the rubber mold when casting so that the mold walls do not deform. Use of the mold box is most often needed when casting deep concrete objects.
 
In the example below, EasyFlo 60 Liquid Plastic, a fast-setting polyurethane plastic, is measured out by volume (1A:1B). Pol-Ease 2300 Release Agent is sprayed into the mold and brushed out and then the EasyFlo 60 is mixed and poured.
 

Measuring EasyFlo

 
Release and Pour EasyFlo

 
Although the mixed liquid is a translucent yellow color, this plastic cures to a white color. The demold time is 15-30 minutes.
 
Allow EasyFlo to Cure

 
EasyFlo Casting from Mold

 
The picture below shows the EasyFlo 60 casting next to the original.
 
Copy and Original Corbel

 
To make a cold cast bronze part, mix up a layer of EasyFlo 60, Brown PolyColor and Bronze Powder and slush/brush a thin layer into the mold. Again, Pol-Ease 2300 Release Agent must be applied prior to casting.
 
Cold Cast Bronze Process

 
Cold Cast Bronze Layer

 
Once this layer gels, it can be backed with EasyFlo 60 and Brown PolyColor (exclude the bronze powder this time) or a less expensive material like rigid polyurethane foam.
 
Once it cures, remove it from the mold.
 
Cold Cast Bronze before Burnishing

 
Burnish the casting with steel wool to expose the metal particles.
 
Cold Cast Bronze Corbel

 
Pictured below from left to right: EasyFlo Clear Liquid Plastic, EasyFlo 60 Liquid Plastic and EasyFlo 60 + Brown PolyColor + Bronze Powder.
 
Plastic Corbels - Mold Making

 
 
Do you have questions about your next mold making or casting project? Get in touch with our Technical Support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Spray-On PlatSil® Gel-25 Mold with Mold Shell

June 4th, 2015

PlatSil® Gel-25PlatSil Gel-25 is a platinum-cured silicone rubber that is used for theatrical prosthetics, lifecasting and mold making. It is a versatile system that can be used with a variety of accessories, including thickener, accelerator, deadener and hardener. This blog will focus on PlatSil Gel-25 as a mold rubber.

Without any additives, PlatSil Gel-25 is a pourable rubber that is great for making poured block molds or poured blanket molds. With the addition of TinThix or PlatThix liquid thickeners, it can be brushed or sprayed onto a model.

In this blog, we detail the process of making a spray-on mold with a PlasPak Spray Gun and then making an EasyFlo 120 mold shell. If a model is on a wall, ceiling or other location preventing it from being laid flat, spraying (or brushing) the mold rubber is a good option. Sprayable mold rubbers are also great when working on large models (like this one).

 

Step 1: Prepare the Original Model

The original model, shown below, is made of plastic. It is adhered to melamine-laminated particle board for the mold making process.

Mold Making Tutorial - Brush-On Mold

 
To prepare this non-porous model for silicone mold making, it is coated with Pol-Ease® 2500 Release Agent. After spraying, it is brushed out with a dry brush to ensure even coverage and no puddling. Release Agent is also applied to the surrounding melamine baseboard.
 
Porous models should be sealed prior to applying release agent (review our Sealer & Release Agent Selection Guide for more information).
 
Pol-Ease 2500 Release Agent

 
Step 2: Thicken Rubber & Load PlasPak Spray Gun
 
All necessary components for the spray system should be ready to go before preparing the PlatSil Gel-25.
 
Necessary equipment for the PlasPak system include:

 

PlasPak Cartridge Assembly

[PlasPak Cartridge Assembly]


 
PlasPak Spray Gun

[PlasPak Spray Gun/Regulator]


 
The mix ratio for PlatSil Gel-25 is 1A:1B. Part A and Part B are measured, by weight, and placed into separate mixing containers (this product can be measured by weight or volume). The 1:1 PlasPak cartridges hold 1500 ml of material in total.
 

Weigh PlaSil Gel-25

 
A small amount of TinThix liquid thickener is added to both Part A and Part B. 1% to 5% TinThix can be added, by weight, to PlatSil Gel-25. It may take some experimentation to achieve the right consistency for spray application.
 
TinThix Thickener

 
Pour thickened Part A into one side of the cartridge and thickened Part B into the other side of the cartridge.
 
Part A PlatSil Gel-25

 
Prepare Gel 25 - Part B

 
Close Cartridges

 
Step 3: Spray Silicone onto Model
 
The cartridges and static mixer are secured to the PlasPak Gun and then the gun is hooked up to an appropriate external air compressor. When everything is assembled correctly, the silicone is sprayed evenly across the surface and sides of the model. A rubber flange is also created around the outside of the model on the melamine baseboard.
 
*NOTE: This is a brief overview of the spraying process. For detailed instructions and use for PlasPak Spray Guns, review the PlasPak Technical Bulletin  or call Polytek Technical Support.*
 
It is important to keep the working time of the product in mind during this process. PlatSil Gel-25 has a working time of 6 minutes. After 6 minutes, the silicone will begin to set and will no longer flow through the static mixer.
 
Assembled Plaspak Spray Gun

 
Spray PlatSil Gel-25

 
A second person follows with a brush to work the silicone into the detail of the model and to ensure even coverage.
 
Follow with Brush

 
Because PlatSil Gel-25 is a milky white material, it is a good idea to add a silicone color pigment prior to spraying; especially if the model is an off-white color like this one. It is much easier to see coverage this way.
 
Spray with PlasPak Spray Gun

 
Blanket molds should be at least 1/4″ thick. Some molds may require multiple layers depending on the size of the model. If a second layer is necessary, allow the first layer of PlatSil Gel-25 to gel enough so that it won’t be disturbed when more silicone is applied.
 
In this case (pictured below), one layer has been sprayed on and is allowed to gel before application of a second brush-on layer to fill thin areas.
 
Finished Application of Gel-25

 
Close-up_spraymold

 
Step 4: Apply Another Layer of Silicone if Necessary
 
A batch of thickened PlatSil Gel-25 with blue silicone pigment is mixed up and used to manually fill thin areas in the mold.
 
Brush-on Second Layer

 
Apply Second Layer

 
Thickened Gel-25

 
Colored Gel-25

 
Allow to Cure

 
When the desired mold thickness is reached, the silicone is left to cure for ~1 hour before the next step.
 
Step 5: Construct Mold Shell
 
EasyFlo 120 Liquid Plastic is a fast-setting, polyurethane plastic. It has a pour time of 2 to 2.5 minutes and a demold time of 15 to 30 minutes.
 
EasyFlo 120 Liquid Plastic for Mold Shell

 
With the addition of PolyFiber II (pictured below), EasyFlo 120 can be brought to a thixotropic consistency for brush-on application.
 
PolyFiber II Thickener

 
Because this plastic has a fast working time, three batches are measured out in advance so they can be mixed quickly when needed.
 
EasyFlo 120 Liquid Plastic

 
One batch of EasyFlo 120 is mixed with PolyFiber II and then applied to the cured silicone with dry brushes and metal spatulas.
 
EasyFlo 120 Mold Shell

 
Plastic Mold Shell

 
Other batches of EasyFlo 120 and PolyFiber II are mixed as needed.
 
Mix up EasyFlo 120

 
Apply EasyFlo 120

 
Third Mold Shell Layer

 
Let EasyFlo 120 cure

 
The EasyFlo 120 is allowed to cure (~15 to 30 minute). When fully cured, the edges are carefully loosened and then the entire mold shell is removed.
 
Loosen Edges of Shell

 
Remove Mold Shell

 
Remove EasyFlo 120 Shell

 
The edges of the mold are loosened and then the entire mold is carefully peeled off of the model.
 
Demold Gel-25 Mold

 
Demold Gel-25 Spray-on Mold

 
Demold

 
Place Mold in Mold Shell

 
The mold is now ready for casting. Many materials can be cast in PlatSil Gel-25 molds, including polyurethane resin and foam, polyurethane rubber, wax, plaster, and concrete. Silicone can also be cast into this mold with the proper release agent.
 
Finished Gel-25 Spray-On Mold

 
 
 
Do you have questions about the PlasPak Spray System? Get in touch with our Technical Support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
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How to Make a Decorative Concrete (GFRC) Panel

May 13th, 2015

This tutorial shows the process of making a decorative glass fiber reinforced concrete (GFRC) panel using various Polytek® mold rubbers and casting materials.

 

STEP 1: Create an Original Pattern

The following pattern was constructed from wood. Ultimately, this small pattern will be repeated to form a large panel.

Pattern Making

 

 

STEP 2: Make a Mold of the Original Pattern 

A PlatSil® 73-25 silicone mold (not pictured) is made of the original wood pattern. Before making the mold, the wood is sealed and Pol-Ease® 2500 Release Agent is applied to the pattern so the silicone rubber will release easily.

Part B PlatSil® 73-25 Silicone Rubber

 

STEP 3: Cast a Plastic Copy of the Pattern to Finalize the Design (if necessary) 

Oftentimes, pattern makers will make a mold of an original pattern and then cast a copy (or copies) in order to clean-up and finalize the design.

EasyFlo 60 Liquid Plastic, used to make a the copy below, is a great option for fast replication. EasyFlo 60 has a 2 to 2.5-minute pour time, simple 1A:1B mix ratio by volume, and a 15 to 30-minute demold time. This plastic can be poured into silicone molds without any release agent.

 

EasyFlo Copy of Pattern

 

The plastic pattern is edited with various materials (e.g. bondo, primer paint) until a finalized design is reached. If primer paint is applied to the pattern, ensure that it is fully dry before moving on to the next step.
 
 

EasyFlo 60 Model Making Plastic

 

STEP 4: Make a Mold of the Finalized Pattern

A PlatSil® 73-25 Silicone Rubber mold is made of the final pattern. PlatSil 73-25 is a soft, platinum-cured silicone rubber with a 1A:1B mix ratio. This silicone has a 15-minute pour time and a 4 to 5-hour demold time.

Silicone Mold of Plastic Pattern

 

STEP 5: Cast Plastic Copies & Assemble a Larger Pattern

When the mold is finished, multiple EasyFlo 60 copies are cast and assembled into a larger pattern. The pattern is adhered to a baseboard, mold box walls are built around it and edges are sealed with plasticine clay where necessary. The baseboard and walls are melamine-laminated particle board.

For this pattern, we make sure to form mold walls that are least 1/2″ thick.

Plastic Pattern in Mold Box

 

A polyurethane rubber mold will be made of this new pattern, so Pol-Ease 2300 Release Agent is applied to the pattern, baseboard and mold box walls and then brushed out.

 

Pol-Ease 2300 Release Agent

 

Apply Release Agent to Plastic Model

 

You may be wondering why we used a silicone mold for the previous step and are going to use a polyurethane mold for this step. We’re merely doing it to showcase that either option can be used. Two of the main differences between these two options are:

  • Release agent does not need to be applied to silicone molds when casting polyurethane resin; however, release agent must be applied to polyurethane molds when casting polyurethane resin. The application of release agent may be a nuisance to some.
  • Polyurethane rubber is less expensive than silicone rubber.

 

STEP 6: Make a Mold of the New Pattern

FormRub 35, a medium-soft polyurethane rubber, is used to make the new mold. FormRub 35 has a 1A:1B mix ratio, 15-minute pour time and 16-hour demold time.

FormRub Series rubbers are specifically designed to stand up to the rigors of concrete casting.

FormRub 35 Liquid Rubber

 

FormRub 35 is measured, mixed and poured over the EasyFlo 60 pattern.


Measure FormRub Liquid Rubber

Mix FormRub 35

Pour Rubber Over Pattern

 

For this pattern, we make sure that the bottom of the mold is at least 1/2″ thick.
 
 

FormRub 35 Mold

 

The mold is removed 16 hours later. The edges of the mold are loosened before removing the entire mold.
 
 

Demold Mold

Demold FormRub 35

Finished Rubber Mold

 

STEP 7: Cast Plastic Copies & Assemble a Larger Pattern (if desired)

When the FormRub 35 mold is complete, multiple EasyFlo 60 copies are cast and then adhered to a baseboard to form the final panel.

Plasticine clay is used to seal small gaps between the individual elements and then mold box walls are constructed around the entire pattern.

20150512_144129

 

Pol-Ease 2300 Release Agent is applied to the model, baseboard and mold box walls and then brushed out to ensure even coverage.
 
 
STEP 8: Make the Final Mold

Poly 74-20 Liquid Rubber is used to make the final mold for casting concrete. Poly 74-20 is Polytek’s softest polyurethane rubber and often does not require release agent when casting concrete. We have found this rubber to be a good option when working with intricate patterns.


Poly 74-20 rubber

Poly 74-20 has a 1A:2B mix ratio, a low viscosity of 800 cP, a 30-minute pour time and a 16-hour demold time.

Pour Poly 74-20 over Pattern

Pour Mold Rubber over Plastic

74-20 liquid rubber

Pour Rubber Over Model

The mold is removed after 16 hours.

Finished Poly 74-20 Mold for Decorative Panel

Poly 74-20 Rubber Mold for Decorative Panel

 

Because the plastic pattern is not harmed during the mold making process, it can be used to make many more molds, if required.

 

STEP 9: Cast Concrete

A GFRC mix is manually worked into the details of the mold and allowed to cure (cure times vary depending on the product).

GFRC Concrete in Rubber Mold

Close-up_Concrete in Rubber Mold

The remove the concrete, the entire mold is first carefully flipped over. All of the edges are loosened and then the entire mold is slowly peeled off of the concrete.

Loosen Edges of Mold

Slowly Peel Off Mold

Carefully Demold

Remove Rubber Mold from Concrete

The concrete can then be sanded, colored and sealed as desired.

Decorative Concrete Panel from Rubber Mold

GFRC Decorative Panel from Rubber Mold

Decorative GFRC Panel

 

Do you have questions about your concrete casting project? Get in touch with our Technical Support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

 

Backfilling PlatSil® Gel-OO Skin with Flexible Foam

April 30th, 2015

If you’re using silicone to create props, it may make more sense to create a silicone skin backfilled with foam instead of a solid silicone part. Silicone skin backfilled with foam is much lighter and easier to handle and it costs less to manufacture.

This blog shows how to make a partial prop head with silicone and flexible foam. A big thanks to BITY Mold Supply for the demonstration.

 

PlatSil® Gel-OO & PolyFoam F-3

Prepare to cast PlatSil Gel-OO into a suitable mold.

The mold used in this tutorial (pictured below) is made of EasyFlo 120, a polyurethane plastic. No release agent is needed when casting platinum silicone in EasyFlo 120.

EasyFlo120 MoldMaking

 
EasyFlo120 Rigid Mold
 
 
PlatSil Gel-OO is an option in the PlatSil Gel Series. PlatSil Gels are platinum-cured silicone rubbers used for a wide variety of special effects applications, including lifecasting, theatrical prosthetics and mold making. Gel-OO has a Shore OO30 hardness, 6-minute working time, 30-minute demold time and can be easily colored with silicone pigments.
 
Measure out PlatSil Gel-OO Part A & Part B by weight or volume. We measure by volume below:
 
PlatSil Gel-OO

 
PlatSil Gel-OO Part B

 
PlatSil Gel-OO Part A and B

 
To make the silicone more life-like, color with silicone pigments (e.g., fleshtone, red and blue) before mixing Part A and Part B together. If you mix Part A and Part B together and then try to pigment the silicone, you may run out of working time.
 
Combine Part A and Part B and thoroughly mix, scraping the sides and bottom of the mixing container several times.
 
Mix PlatSil Gel-OO

 
Brush a layer of PlatSil Gel-OO into the mold, making sure to work the silicone into the details.
 
ApplyThinLayer_PlatSil_GelOO

 
PlatSil Gel-OO First Thin Layer

 
GelOO_FirstLayer

 
PlatSil Gel-OO Silicone Skin

 
While the first layer of silicone is gelling, prepare to mix up a second batch of PlatSil Gel-OO thickened with TinThix. TinThix is a liquid thickening agent that can be added to tin-cured and platinum-cured silicones (no more than 5%) to bring them to a brushable consistency. We did not add thickener to the first layer because we wanted it to be as thin as possible in order to capture detail. When the first layer has gelled enough that application of the second layer will not disturb it, brush in a layer of thickened Gel-OO.
 
SecondLayer_PlatSilGelOO

 
Immediately after application of this layer, add a layer of cotton or polyester fiber. PolyFoam F-3, a polyurethane foam, will not chemically bond to silicone; therefore, a mechanical bond must be made.
 
Add Cotton or Polyester Fiber to Silicone

 
Bonding Silicone and Foam

 
Put Cotton in Silicone

 
When the second layer of PlatSil Gel-OO has cured, pull the loose, excess fibers out of the silicone.
 
Pull Excess Cotton from Silicone

 
Prepare to backfill the silicone with PolyFoam F-3.
 
PolyFoam F-3 is a flexible, polyurethane foam with a free-rise density of 3 lb/ft³. It has a mix ratio of 1A:2B by weight, a 25-second cream time and a 10-minute demold time.
 
PolyFoam F-3 Flexible Foam

 
Carefully weigh out PolyFoam F-3 Part A and Part B. Once these parts are added together, work quickly to mix and then pour the foam into the mold. If too much time elapses, the foam will rise in the mixing container and the mix may be lost.
 
We recommend packing PolyFoams to a minimum of 2 to 3 lb/ft³ above their free-rise density to achieve good surface detail. PolyFoam F-3 should be packed to 5-8 lb/ft³.
 
Mix Flexible PolyFoam
 
 
Pour the PolyFoam and brush around to thoroughly coat the silicone.
 
Brush in PolyFoam

 
Brush in PolyFoam F-3

 
Allow the foam to rise and cure. Some may choose to add a lid (with vent holes) to close the mold – doing so will provide better compaction and produce a better part in most cases. If using a lid, it should be securely clamped down to the mold before the foam begins to rise.
 
Allow Foam to Cure

 
After ~10 minutes, the piece can be demolded. Carefully loosen the edges of the silicone before removing the whole casting.
 
Demold Silicone and Foam

 
CarefullyDemold

 
Demold

 
Silicone Skin with Foam

 
Silicone Head

 
The polyurethane foam can be trimmed to better fit the silicone skin around the edges.
 
Another Option: PlatSil® Gel-OO & PlatSil® SiliFoam
 
PlatSil SiliFoam is a platinum-cured silicone foam with a free-rise density of 15 lb/ft³. This product has a 1A:1B mix ratio, ~45-second cream time and ~30-minute demold time.
 
Unlike polyurethane foam, silicone foam will bond to silicone rubber.
 
Silicone Foam

 
The same process for applying the PlatSil Gel-OO skin is used (i.e., one thin, detail layer and one thickened layer); however, the addition of cotton or polyester fiber is unnecessary. After the second layer of PlatSil Gel-OO has been applied, PlatSil SiliFoam can be mixed up and poured into the mold. Casting the foam before the silicone has fully cured is the most effective method.
 
Mix Silicone Foam

 
Silicone pigments, like Fleshtone, can easily be added to the foam before mixing Part A and Part B together.
 
Fleshtone Silicone Pigment

 
After mixing thoroughly, pour the silicone foam into the mold and brush around.
 
PlatSil Silicone Foam

 
Backfill Silicone with Silicone Foam

 
Silicone Skin Backfilled with Silicone Foam

 
Allow the silicone foam to cure before loosening the edges of the silicone and removing the casting.
 
Loosen Edges and Remove

 
SiliconeSkin with Silicone Foam

 
Silicone Head Backfilled with Silicone Foam

 
Ready to move on to the next step? Learn how to paint on silicone with PlatSil Gels and silicone pigments here.
 
Do you have questions about this casting process? Reach out to our technical support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

New Lifecasting Video: PlatSil® Gel-25 Face Cast

April 14th, 2015

Our latest video features the making of a PlatSil® Gel-25 face cast.

PlatSil® Gel-25 is a skin-safe, platinum-cured silicone that is most often used for lifecasting and for making prosthetic appliances.

 
Steps in the lifecasting process:

Step 1: Prepare Model

Step 2: Measure & Mix PlatSil Gel-25

Step 3: Apply PlatSil Gel-25 to Model

Step 4: Construct Plaster Shell

Step 5: Demold

 

 

PlatSil Gel-25, PlatSil Gel-OO and PlatSil Gel-10 make up the PlatSil Gel Series, which is widely used for specials effects in television, theater and film. All of these options can be used for lifecasting, for creating prosthetics and for mold making.

PlatSil Gel-25 is similar to Gel-10 & Gel-OO, but varies in its versatility and physical properties. Gel-25 offers lower mixed viscosity (6,000 cP compared to Gel-OO and Gel-10’s 15,000 cP viscosity) and greater versatility in Shore hardness. Using PlatSil Deadener LV and PlatSil Part H Hardener, PlatSil Gel-25 can be made as soft as Shore OOO30 and as hard as Shore A40.

ATTENTION: Polytek® products are intended for professional use only.

 

Do you have questions about this lifecasting silicone or other Polytek lifecasting products? Reach out to our technical support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Mold Making Tutorial: Silicone Mold of Clay Sculpture

April 2nd, 2015

John Cannon of The Whimsical Gardens brought his clay sculpture to our facility to make a mold of the figure and then reproduce it in plastic on a rotational casting machine. The detailed sculpture is pictured below from different angles.

This blog details the steps that we took throughout the mold making and casting process:

Step 1: Select a Mold Making Method & Mold Rubber
Step 2: Construct Mold Box & Prepare Sculpture
Step 3: Measure, Mix & Pour Silicone Mold Rubber
Step 4: Demold
Step 5: Cut the Mold
Step 6: Rotational Casting

ClaySculpture_MoldMaking
 

ClaySculpture_SideView
 

ClaySculpture_Detail_MoldMaking
 

ClaySculpture_BackView_MoldMaking
 

ClaySculpture_BaseDetail_MoldMaking

Step 1: Select a Mold Making Method & Mold Rubber

Mold Making Method

For this sculpture, we select the “poured block mold” method (for an introductory tutorial on this method, visit this blog entry).

Here are the reasons that we are eliminating other methods:

Brush-on Mold: We are concerned that air bubbles may form in the intricate details on the base of the sculpture. Also, brush-on molds tend to have thick and thin spots – thin spots end up being weak points in the mold.

Poured Blanket Mold: One of the steps in the poured blanket mold process is to form a layer of clay on top of the original model (review a poured blanket mold tutorial here). This step would most likely deform the clay original.

Based on the shape of the sculpture, we also know that the mold will require a cut in order to remove the original sculpture and subsequent castings.

 

Mold Rubber

For this particular project, we also know that we want to use a silicone mold rubber because it does not require release agent when casting polyurethane resin. Release agent can be difficult to apply in intricate areas and it may be difficult to remove from the casting. Residual release agent can prevent paint from sticking to castings.

 

Platinum-Cured vs. Tin-Cured Silicone Rubbers

Polytek silicone falls into two general categories: platinum-cured and tin-cured. Basic comparisons between the two options are in the table below:

Rubber Type Advantages Disadvantages Casting Materials Methods
Platinum-Cured Silicone Mold Rubbers No shrink on cure, cured rubber has long storage life Liquid rubber can suffer from cure inhibition by some materials (e.g., sulfur clay, tin silicones, Bondo, some 3D-printed plastics, latex rubber). Most materials, especially resins, foams and some low-melt metals. Pour, Brush, Spray.
Tin-Cured Silicone Mold Rubbers No cure inhibition, slightly less expensive than platinum-cured systems Shrinks on cure (~1%), shorter library life (2-5 yrs.) than platinum-cured systems. Most materials, especially resins, foams and some low-melt metals. Can inhibit polyurethane rubber, platinum-cured silicone, and 14-Series Poly-Optic Resin castings. Pour, Brush, Spray.

 

Platinum-cured silicone rubbers have advantages compared to tin-cured silicone rubbers (e.g., no shrink on cure, longer library life), but can suffer from cure inhibition when exposed to certain materials. Sulfur, for instance, is a known inhibitor and is present in some modeling clays.

We are unsure if John’s sculpture contains sulfur, so we perform a small test cure.

To do the test, we mix and pour a fast-setting platinum silicone rubber (PlatSil® 71-10) into a clay containment area against a small section on the backside of the sculpture.

Platinum Silicone Test Cure-01
 

TestCureonSculpture
 

After 30 minutes, we remove the silicone rubber to determine if it has cured properly. We find that the rubber that touched the sculpture remained gummy while the sides of the rubber exposed to air and clay cured properly. This indicates that there is a contaminate within or on the clay that would prevent any platinum-cured silicone rubber from curing properly.

 

SiliconeTestCure_Clay
 

Based on these findings, we select a tin-cured silicone rubber as the mold material:  TinSil® 80-15 Silicone Rubber. We choose a soft silicone (Shore A15) due to the deep undercuts on the sculpture. A harder rubber could be more difficult to remove without damage.

 

 

TinSil 80-15 Silicone Mold Rubber
 

TinSil 80-15 Silicone Rubber: Specifications
Hardness: Shore A15
Mix Ratio: 1A:10B
Pour Time: 30 Minutes
Mixed Viscosity: 12,000 cP
Demold Time: 24 Hours
Cured Color: Peach
Specific Volume: 25.3 in³/lb

Step 2: Construct Mold Box & Prepare Sculpture

To begin, a plywood mold box is constructed at the proper dimensions (i.e., at least 1″ beyond the sculpture in all directions) and then sealed with petroleum jelly.

 

NOTE: It is a good idea to taper the inside of the mold box so the mold can be removed more easily when the mold box is turned upside-down.

PetroleumJelly_SealMoldBox

 
SealMoldBox_PetroleumJelly

 
Pol-Ease® 2500 Release Agent is then applied to the clay sculpture.

NOTE: Use Pol-Ease® 2300 if making a polyurethane rubber mold.

PolEase2500_ReleaseAgent

 
ApplyPolEase2500_ReleaseAgent

 
The mold box is placed around the prepared sculpture to verify that the dimensions are suitable.
 
Put Sculpture in Mold Box

 
We estimate the amount of rubber needed for the mold with the following calculation:

Volume of Mold Box = ~1,716 in3

Volume of Sculpture = ~84.78 in3

Volume of Mold Box – Volume of Sculpture:  1,716in– 84.78 in3 = 1,631.22 in3

1,631.22 in3 ÷ 23.7 in3/lb (specific volume of TinSil 80-15) = 68.8 lb of TinSil 80-15 Silicone Rubber

Mold Rubber Calculation

 
68.8 lb is a large amount of rubber and we realize that there is opportunity to reduce that amount by adding corner inserts and other block-outs.
 
Add Block-Outs to Mold Box-01

 
3CornerInserts_MoldBox

 
Block-Outs_MoldBox

 
ConstructingBlockOut_MoldBox

 
We add a number of block-outs, but still maintain at least a 1″ space between the sculpture and mold box walls/block-outs.
 
All_Blockouts_Installed_MoldBox

 
Once all of the block-outs are secured, the mold box is removed to seal the new plywood additions with petroleum jelly and caulk all edges with warmed plasticine clay. Caulking the edges helps to prevent leaking when liquid silicone is poured into the mold box later.
 
Warmed Plasticine Clay

 
Seal Edges with Plasticine Clay

 
The sculpture is placed back into the mold box and then the mold box is secured with screws.
 

Step 3: Measure, Mix & Pour Silicone Mold Rubber

Based on the new dimensions of the mold box, we determine that approximately 40 lb of TinSil 80-15 Silicone Rubber is needed to make the mold.

As mentioned previously, TinSil 80-15 has a mix ratio of 1A:10B. The components are measured by weight and then mixed thoroughly.

NOTE: Do not attempt to measure products with 1A:10B mix ratios by volume – always measure by weight.

Weigh TinSil 80-15 Silicone Rubber

 
Because of the quantity of rubber needed for this project, we mix two separate batches using a turbo mixer.
 
Mix with Turbo Mixer

 
The rubber is mixed until a uniform color is reached.
 
NOTE: Avoid hitting the sides of the mixing pail with the turbo mixer as this can introduce air into the mixture.

Mixing Silicone Mold Rubber

 
Mixing Silicone Mold Rubber

 
Mixing Silicone with Turbo Mixer

 
The batches are then mixed by hand with a Poly Paddle.
 
NOTE: It is important to scrape the sides and bottom of the mixing container several times, as this is where unmixed material tends to cling.

Hand Mix Silicone Rubber

 
The silicone is poured into the lowest point of the mold box and allowed to rise.
 
Hand Mix Silicone Rubber

 
Pour Silicone Mold Rubber

 
Pour Silicone Mold Rubber

 
Pour Silicone Mold Rubber

 
The rubber is poured until it reaches at least 1.0″ above the highest point on the sculpture.
 
Pour Silicone Mold Rubber Over Model

 
We allow the rubber to cure at room temperature for ~24 hours. Heat lamps can help speed the cure.
 
NOTE: Demold times vary by product. Check product Technical Bulletins for this information.

Pour 0.5" Over Model

 

Step 4: Demold

Before demolding, the locations of the mold box walls and block-outs are marked with a pen. This is done so that the mold box can be put back together correctly for casting later.

Mark Locations on Mold Box Walls & Inserts

 
Mark Mold Box Walls

 
All mold box walls and block-outs are carefully removed.
 
Remove Mold Box Walls & Inserts

 
Remove Mold Box Walls & Clay

 
All edges of the mold are loosened from the baseboard with a putty knife before the entire mold is removed.
 
Loosen Edges from Baseboard

 
Upon removal of the mold from the baseboard, the sculpture splits in half, leaving the top half in the mold.
 
Part of Model Removed from Mold

 

Step 5: Cut the Mold

To remove the remainder of the sculpture and subsequent castings, we prepare to make a cut on one side of the mold. Pictures of the sculpture are printed to determine a good location for the cut.

NOTE: If possible, it is best to cut along a line that already exists on the sculpture or in an inconspicuous location (i.e. avoid the face).

Reviewing Photos for Cut

 
A scalpel is used to make the cut.
 
NOTE: It is important to create an irregular cut pattern (i.e., tongue and groove or zig-zag cut) so that the two sides align well for casting (for general information on cutting rubber molds, visit this blog entry).

Cutting Silicone Mold with Scalpel

 
Cutting Silicone Mold with Scalpel

 
Cutting Silicone Mold with Scalpel

 
Cutting Silicone Mold with Scalpel

 
The remainder of the sculpture is removed from the mold and any clay left behind in the mold is cleaned out.
 
Remove Remainder of Sculpture

 
Sculpture After Mold Making

 
Clean Clay from Mold

 

Step 6: Rotational Casting

The mold is placed back into the mold box and then secured.

Silicone Mold for Sculpture Reproduction

 
Reassemble Mold Box Around Mold

 
Secure Mold Box Around Mold

 
Because we plan to use the rotational casting machine, we create a mold box lid with a pour hole. This hole is where the fast-setting resin is poured once the mold box is on the rotational casting machine.
 
Create Pour Hole in Mold Box Lid

 
Wooden bars are added to the sides of the box in order to mount and attach it to the rotational casting machine.
 
Mold Box for Rotational Casting

 
A silicone plug will later be used to plug the hole when casting.
 
Silicone Plug for Rotocasting

 
The mold box is loaded onto the rotational casting machine and secured with C-Clamps.
 
Place Mold Box on Rotational Casting Machine

 
Secure Mold Box with C-Clamps for Rotational Casting

 
EasyFlo 120 Liquid Plastic is the product that we most often recommend for rotational or slush casting. It is designed to gradually solidify over its working time, as opposed to “snap-set” (like the curing characteristics of EasyFlo 60, another product with the EasyFlo Series). This gradual thickening over the last 30-45 seconds of the working time helps to provide an even coat.

EasyFlo 120 Casting Resin - Polytek

 

EasyFlo 120 Liquid Plastic: Specifications

Hardness: Shore D65
Mix Ratio: 1A:1B by volume, 100A:90B by weight
Pour Time: 2-2.5 minutes
Mixed Viscosity: 120 cP
Demold Time: 15-30 minutes
Cured Color: White
Specific Volume: 26.9 in³/lb

 

Approximately 2 lb of EasyFlo 120 is thoroughly mixed and poured into the mold.

NOTE: Ideally, this resin should be mixed and poured in under a minute.

 

Resin for Rotocasting

 
The pour hole is plugged with the silicone plug and then the machine is turned on.
 
Run the Rototational Casting Machine

 
Rotational Casting - Sculpture Reproduction

 
After ~30 minutes, the mold is removed from the rotational casting machine and then the casting is removed from the mold.
 
Plastic Casting - Rotational Casting

 
Hollow EasyFlo 120 Plastic Casting

 
For the next run, we mix EasyFlo 120 + Brown PolyColor Dye + Bronze Powder to produce a cold cast bronze copy.

Bronze Powder for Cold Cast Bronze

 
Here are some photos of the cold cast bronze piece prior to burnishing with steel wool (steel wool is used to expose the bronze powder on the surface of the casting). Initially, castings will appear chocolate brown; you will notice a small spot on his cheek that has been burnished.

Cold Cast Bronze Casting - Sculpture Reproduction

 
Cold Cast Bronze - Sculpture Detail

 
EasyFlo 120 Casting Resin - Great Detail

 
Penny Detail on Casting

 
Hollow castings such as these can be backfilled with a number of products, including less expensive resin or polyurethane foam.
 
Do you need assistance in selecting an appropriate mold making method and material for your next project? Ask our technical support team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

Tek-Tip: Tools & Techniques for Cutting Rubber Molds

March 19th, 2015

Some rubber molds require one or multiple cuts in order to remove the original model and subsequent castings.

Poured Blanket Mold with Mold Shell
 

Cutting_RubberMold
 

Here are some tips regarding the tools and cutting techniques that we use here at Polytek:
 
 
Tools that we use: 

A tool like your kitchen paring knife will not work well for cutting rubber molds. At Polytek, we most often use the following:

  • Mold Key Knife
  • Scalpel
  • Razor Blade (one-sided for safety)
  • X-Acto Knife

Cutting Rubber Molds - Tools
[in order from left to right: mold key knife, scalpel, razor, X-Acto knife]

 
 
 General notes about these tools:

  • Mold Key Knives automatically create a tongue-and-groove pattern.
  • Scalpels, razor blades and X-Acto knives can fit into tighter spaces/corners than mold key knives. Often, a mold key knife is used to create the first cut (this cut should not reach the model) and then a scalpel/razor blade/X-Acto knife is used to make the final cut.
  • Depending on the rubber being cut, blades can degrade rather quickly (i.e., after cutting 2-3 molds), so it’s a good idea to keep multiple on-hand.

 
 
General notes on cutting rubber molds: 

  • It is very difficult to cut mold rubbers that are harder than Shore A45 (read more about Shore Hardness here).
  • Silicones are generally easier to cut than polyurethanes.
  • To avoid damaging the model, the first cut should not go completely through to the model. As mentioned in the previous section, the final cut should be made with a scalpel or X-acto knife as these tools are more precise.
  • Avoid making a straight cut in the mold; make a zig-zag/tongue-and-groove pattern for better alignment when casting.

 

ZigZag_CutinMold
 

Planning ahead:

  • If you are planning on cutting a mold, it is a good idea to create a thicker section of rubber in the area that you intend to cut (~0.75″). An example is shown on the far right below. You can also see this technique in a video tutorial on our YouTube Channel.

 

Rubber Flange for Cutting-01
 

For brush-on blanket molds (like the mold pictured above), we make these thick pieces of rubber by casting the rubber in strips (we have a silicone mold that we made specifically for this purpose) and then applying them to the mold:

 

Casting Rubber Strips-01
 

  • When selecting a location for the cut, choose an area where seam lines will not be as noticeable if they appear on the casting (e.g., avoid the face).
  • Repetitive opening and closing of the mold can cause tears over time. Embedding Tietex® Fabric in the area where the cut ends can improve strength. The red arrow below indicates an area where TieTex would be beneficial.

 

TieTex next to cut-01

 
TieTex Fabric for Cut Molds
[^TieTex Fabric]
 

Are you working on a mold making project and have a question about technique?

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.

New Product Announcement: FormRub Series Liquid Rubbers

March 3rd, 2015

FormRub 50 Liquid Rubber - 80-lb Kit

FormRub Series Liquid Rubbers

Use FormRub Series liquid polyurethane rubbers to make high-performance molds that stand up to the rigors of high-production casting and forming of concrete.

The product options within this series offer simple, 1A:1B mix ratios (measured by weight or volume) and low-viscosity mixes that flow easily across original models.

Popular uses include molds for casting concrete veneer stones, architectural elements, edge and trim strips, decorative panels, tiles, countertops, tabletops, sinks, pavers, slabs, patio stones, fences, sound barriers and more.

 

 

FormRub Series Features

  • Shore A35 to A65 hardness mold rubbers
  • Low viscosity
  • 1A:1B mix ratios
  • High-strength, abrasion-resistant, long-lasting molds
  • Reproduces fine details
  • Pourable or brushable (brushable with the addition of PolyFiber II)
  • Can be accelerated for rapid cure
  • Economical & versatile
  • Ideal for the most demanding mold making applications
  • All rubbers can be demolded after ~16 hours

 

Individual Options

FormRub 35Shore A35 Hardness – ideal for models with deep relief or irregular undercuts that require a flexible, yet durable mold option.

FormRub 50Shore A50 Hardness – this low-viscosity option is very suitable for pouring large molds or molds with challenging flow conditions.

FormRub 60 Shore A60 Hardness – provides a longer working time compared to other Shore A60 polyurethane mold rubber options that we offer.

FormRub 65Shore A65 Hardness – ideal for casting larger parts where dimensional stability is required.

 

Accessories

A range of additives can be used to adjust the characteristics of FormRub Series liquid rubbers, including accelerators, thickeners and softeners. View accessories on the FormRub Series page on www.polytek.com. 

 

Do you have questions about this new mold rubber line? Reach out to our Technical Support Team:

Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online form.