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.

Tek-Tip: Painting with PlatSil® Gel-10 & Silicone Pigments

February 26th, 2015

Painting directly onto silicone can be challenging as there are not many paint materials that adhere well to silicone or stay in place when it stretches.

In this tutorial, we show you a painting technique that BITY Mold of Supply of Richardson, TX demonstrated when visiting our headquarters recently.
 
 
Supplies for Project

 

One benefit of this technique is that if you’re already making prosthetics or props out of PlatSil Gel, there is no need to purchase additional products.

In this tutorial , we paint a PlatSil Gel-10 face cast:

PlatSil-Gel-10-FaceCast

 

Measure & Mix PlatSil Gel-10

 
PlatSil Gel-10 has a mix ratio of 1A:1B by weight or volume. Carefully measure and mix a small amount.
 

PlatSil Gel-10_Painting
 

PlatSil Gel-10 Part A

[^Part A]

PlatSil Gel-10 Part B

[^Part B]

Mix PlatSil Gel-10

 

Carefully Mix in Naphtha

 
Add Naphtha to the mixed PlatSil Gel-10. We add the solvent at a 1:1 ratio, but you can add more or less depending on how thin you want the mixture to be.

Naphtha is a flammable solvent – care should be taken when handling. Make sure to use solvent-resistant mixing containers and tools.
 

Add Naptha

 
Very carefully mix the components – it is important to mix slowly as Naphtha is prone to splashing. Mix until the silicone breaks up and dissolves.

NOTE: The addition of Naphtha will increase working time. Standard working time for PlatSil Gel-10 is 30 minutes. The addition of this solvent could potentially double that time.
 

Mix Carefully

 

Combine with Silicone Color Pigments

 
Select the Silicone Color Pigments (the 8-color tray pictured below is available from BITY Mold Supply) desired for the project. Colors available from Polytek include: black, blue, green, red, yellow, fleshtone and white.
 

Silicone Pigments - Polytek

 
Place the desired pigment (or blend of pigments) into a mixing container and then add a small amount of the PlatSil Gel/Naphtha mixture to the pigment and mix.
 
Mix Silicone Pigments & Solvent

 
Mix Gel-10 & Pigments
 
 
Gel-10 Mixture & Silicone Pigments
 
 
Blue Silicone Paint
 
 
Gel-10 Silicone Paints

 

Begin Painting

 
The overall look is at the hands of the artist; this is just a basic demonstration using two colors.

Start painting with one color (for this demonstration, a combination of red and brown is used first to bring out detail).

Red & Brown Silicone Paint

 
Painting with Gel-10

 
First Color

 

Run a Hair Dryer Between Application of Colors

 
When finished with one color, make sure to run a hair dryer over the surface of the model for a few minutes before proceeding to the next color. If you add a second color before running the hair dryer, the colors will bleed together.
 

Use Hair Dryer Between Colors

 
A second color (blue) is then added.
 
Add Blue Silicone Paint
 
 
Blue PlatSil Gel-10 Mix

 
When application of the blue silicone paint is complete, the hair dryer is run again.
 
Painting Gel-10 face

 
Lastly, to produce the look of freckles, a brush is cut and used to “splatter” a bit of brown/red paint.
 
FreckleTechnique

 
A towel can be used to pull back color when necessary.
 
Blot if Necessary

 
The hair dryer is run once more.
 
PlatSil Gel-10 - Polytek

 
Repeat this process until the desired effect is reached. When the final touches are added, allow the silicone to fully cure before handling.
 
PaintingPlatSilGel10

 

Baby powder can be dusted on to the surface to reduce shine.
 
 
 
Do you have questions about this 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 Concrete Catalog: Liquid Mold Rubbers for Concrete Casting, Texturing & Stamping

February 11th, 2015

OuPolytek Liquid Mold Rubbers for Concrete Casting, Texturing & Stampingr newest “mini-catalog” features product recommendations for applications involving concrete casting, texturing and stamping:

 

  • Cast Stone Veneer
  • Form Liners
  • Decorative Surfaces & Decor
  • Hardscape
  • Architectural
  • Casting Plastics & Hardcoats
  • Accessories

 

View the catalog here. 

 

Do you need assistance in selecting an appropriate mold material for your next concrete casting project? Ask 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: Old-Growth Cypress Concrete TableTop

January 29th, 2015

SureCreteWe recently visited SureCrete Design Products, a decorative and specialty concrete manufacturer, at their headquarters in Dade City, FL. While there, we did some rubber mold making demos to showcase how flexible molds can be used to create a variety of unique, decorative concrete products. Typical applications include, but are not limited to:

  • full countertops & tabletops
  • individual countertop or tabletops elements such as sink inserts, decorative edging/trim strips and drain boards
  • decorative panels and tiles
  • outdoor and indoor furniture
  • planters
  • textured pool decks, walkways, patios, driveways, stairs, countertops with the use of rubber stamping and texture mats

 
For one demo, SureCrete provided us with a slab of old-growth cypress (pictured below). It was approximately 48″ x 20″ x 3″ and a “mold box” was already built around it using melamine-laminated particle board.
 

Old-GrowthCypress

 
UndercutsonCypressSlab
 
 
KnotsinCypress

 
Here are the basic steps that we took to make a mold of this model during the 90-minute demo:
 

Seal the Model

Porous models must be sealed prior to the mold making process. There are many sealing options available (view our Sealer & Release Agent Selection Guide here), but we chose Poly PVA Solution for this model. PVA is a water-soluble solution that can be washed off after the mold making process and is available in clear and green options.
 
We applied it by brush and then allowed it to dry.
 

PVASealer

 
PVASolution

 

Create Block-Outs

Because of the protrusions on one side of the slab, there are large empty spaces within the mold box.
 

UndercutsonCypressSlab

 
To cut down on the amount of rubber needed, we cut foam to block out those spaces.
 
ReducingWalls

 
CuttingFoam

 
We coated the foam in EasyFlo 60 liquid plastic (thickened with PolyFiber II) to give it a smoother, non-porous surface.
 
PlasticCoatedFoam

 
FoamCutoutsinPlace

 

Apply Release Agent

We applied Pol-Ease® 2300 Release Agent to the cypress, baseboard, mold box walls and foam, and then brushed it out with a dry brush to promote even coverage.
 

MoldMakingReleaseAgent

 
PolEase2300

 

Calculate Amount of Rubber Needed

We used Poly 74-45 Liquid Rubber to make this mold. It is a mid-range hardness, polyurethane mold rubber with a mix ratio of 1A:1B.
 
To following calculation was used to determine how much rubber was needed for the mold:

  • calculate the volume of the mold box (23″ x 50.25″ x 3.5″ = ~4,045 in³) and the approximate volume of the cypress (20″ x 48″ x 3″ = ~2,800 in³)
  • subtract the volume of the cypress from the volume of the mold box (4,045 in³ – 2,800 in³ = 1,245 in³)
  • take that result and divide by the specific volume of Poly 74-45 liquid rubber (1,245 in³ ÷ 27.5 in³/lb = ~45 lb of Poly 74-45 Liquid Rubber)

 

calculate rubber needed-01

 

Measure, Mix & Pour Liquid Rubber

We measured Part A & Part B separately by volume, then combined and mixed them thoroughly in a clean mixing container. We used a Poly Paddle mixing tool to mix by hand.
 

PartBPoly74-45

 
PartAPoly74-45

 
Mix74-45

 
MixRubberThoroughly

 
We poured the rubber into the mold box and allowed it to rise over to the model. It is best to pour rubber into rubber and avoid pouring it directly onto the model.
 
Poly 74-45 Liquid Rubber

 
PourLiquidRubberOverModel

 
PolytekLiquidRubber

 
AllowRubbertoFlow

 
AllowRubbertoCure

 
We allowed the rubber to cure overnight (~16 hours) at room temperature before demolding.
 

Demold

To demold, we began by removing the mold box walls and foam.
 

DeconstructBox

 
PryMoldBox

 
RemoveMoldBoxWalls

 
SidesofMold

 
We carefully loosened all edges of the mold with putty knives and crowbars.
 
LoosenEdgeofMold

 
LoosenEdgesandCorners

 
We peeled back the mold from the model, paying attention to areas where the rubber may have caught (i.e., in knots in the wood).
 
DemoldRubberMold

 
KnotsonWood

 
UrethaneRubberMold

 
We carefully freed the rubber from the knots using a utility knife.
 
Cut

 
FinishedMold

 
KnotDetail

 

Cast Concrete

SureCrete’s Xtreme Series precast mix was poured into the mold (a particle board block-out was used).
 

Concrete in Mold

 
Later in the day, we demolded.
 
TurnOverMold

 
DemoldConcrete

 
SureCreteConcrete

 
ConcreteCasting

 
ConcreteKnotDetail

 
The concrete was then stained with SureCrete’s EcoStain. 
 
MoldMakingProject

 
FinishedConcreteTabletop

 
Do you need assistance in selecting an appropriate mold 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.

Or leave a comment right here on the blog!

Mold Making: Poured Blanket Mold vs. Poured Block Mold

January 19th, 2015

In this blog entry, we will demonstrate two different mold making methods using the same plastic lion head model [pictured below] and the same silicone mold rubber. The methods are the poured blanket mold technique and the poured block mold technique.

Plastic Model for Mold Making

 
Based on the size and shape of this particular model, either mold making method could be used with success. The following information is designed to give you a better idea of the advantages and disadvantages of each technique as you decide which method to use for your mold making project. Below, we note the basic comparisons of each technique and then detail each method with pictures and instruction.
 

Basic Comparisons:

  • The poured block mold is considered the simplest type of mold, while poured blanket molds can take some time to master.

Mold Complexity-01

  • Poured blanket molds generally require less mold rubber than poured block molds.
    • In this specific tutorial, 4.3 lb of silicone mold rubber is needed for the poured blanket mold and 12.5 lb of silicone mold rubber is needed for the poured block mold (i.e., less money is spent on mold rubber). NOTE: Keep in mind that poured blanket molds do require construction of a mold shell (next bullet point), which requires more materials.
  • Poured blanket molds require construction of a “mold shell” or “mother mold”, while poured block molds require a containment area often referred to as a “mold box”. The following materials are often used to make mold boxes: melamine-laminated particle board, plywood, PVC pipe, plastic pails, metal flashing and many other options. The construction of mold shells take practice, while the construction of a box can be rather simple.
  • Removing castings from poured blanket molds can sometimes be easier because these molds are generally more thin and flexible compared to block molds. This depends heavily on the shape of the model, however.

 

Demonstration of Each Method:

The first step in both methods is to construct a containment area around the model. For the poured blanket mold method, a mold shell is constructed from liquid plastic. For the poured block mold method, a mold box is constructed from melamine-laminated particle board.

Rubber Blanket Molds vs Rubber Block Molds-01

 
Both methods are detailed below:
 

Poured Blanket Mold: Construction of Mold Shell

First, secure the model to the baseboard. We insert a wood screw through the bottom of the baseboard and into the plastic model. Another option is to adhere the model to the baseboard with epoxy. The baseboard in this tutorial is a piece of melamine-laminated particle board.
 

SecureModeltoBaseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Place plastic wrap over the model.

 

CoverModelwithPlastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

CoverModelwithPlasticWrap_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Form a uniform layer of clay over the model and plastic wrap. Make sure to use a sulfur-free, oil-based clay (we use plasticine clay) as sulfur can inhibit the cure of silicone mold rubbers.

The layer of clay should be approximately 1/2″ thick and should fill in any undercuts on the model. The clay represents the space that the mold rubber will later fill, so uniform thickness is important (i.e., you do not want thin spots or holes in your finished mold).

 

Clay over MOdel

Poured Blanket Mold: Construction of Mold Shell

 

Create a clay flange that extends ~1 to 1.5 inches beyond the model. Smooth out the clay as best as possible.

 

CoverModelwithClay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Build-up an area that will serve as the pour hole, which is where mold rubber will later be poured.

 

Build-UpPouredHole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

SmoothOutPourHole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Again, smooth out the clay as best as possible.

 

UniformLayerofClay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Spray Pol-Ease® 2300 Release Agent onto the clay and surrounding baseboard. This will help remove the plastic mold shell from the clay and particle board later in the process.

 

Pol-Ease 2300 Release Agent_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Apply Release Agent to Clay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Select a mold shell plastic such as Poly 1512X Liquid Plastic. This polyurethane plastic has a working time of 5 minutes and a demold time of ~30 minutes.

 

Mold Shell Plastic_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

Poly 1512X has a 1A:1B mix ratio and can be measured by volume or weight.

Measure Part A:

 

Measure Mold Shell Plastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Measure Part B:

 

Measure Poly 1512X Mold Shell Plastic_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Plastic Measured by Volume_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Thoroughly mix together Part A & Part B and then add PolyFiber II thickener to bring the mixture to a brushable consistency.

 

PolyFiberII Thickener_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

 

Mix Mold Shell Plastic with Thickener_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Add PolyFiber II thickener until a thick, non-sag consistency is reached.

 

PlasticBrushableConsistency_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Apply the thickened Poly 1512X to the layer of clay, leaving an opening at the top of the pour hole. Note: get the Poly 1512X plastic out of the mixing pail as quickly as possible; it will cure faster in larger masses (i.e., sitting in the pail).

 

Apply Mold Shell Plastic to Clay_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Spread the plastic evenly over the plasticine clay using disposable dry brushes or other tools like stainless steel spatulas.

 

Apply Plastic with Brush_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Mold Shell Creation_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Distribute Mold Shell Plastic Evenly_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Create a plastic flange that extends 1-2 inches beyond the clay on the baseboard.
 

Mold Shell_Poly1512X_BlanketMold

Poured Blanket Mold: Construction of Mold Shell

 

Before the plastic completely sets, add legs that will hold and level the mold and mold shell for casting later.

 

LevelWoodenLegs_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

AddWoodenLegs_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

When the Poly 1512X plastic has set (after ~30 minutes – this time will vary depending on temperature and humidity), create a reference point with a permanent marker indicating the location of the mold shell in relation to the baseboard for proper re-positioning later in the process.

 

Mark Location of Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Drill holes evenly throughout the plastic flange – the mold shell will later be re-positioned and screwed into place in these locations.

 

Secure Mold Shell to Baseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Loosen the edges of the mold shell and carefully remove it from the baseboard. CAUTION: Edges of the plastic mold shell can be very sharp.

 

PryMoldShell

Poured Blanket Mold: Construction of Mold Shell

 

 

Remove Mold Shell from Model_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Remove the plastic wrap and clay from the mold shell.

 

Clean Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Clean Interior of Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

If necessary, trim the top of the pour hole.

 

Clean Pour Hole_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

 

Finished Plastic Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Apply a release agent, like Petroleum Jelly, to the interior of the mold shell.

 

Apply Petroleum Jelly to Mold Shell_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Apply release agent to the model and surrounding baseboard before placing the mold shell back over the model. We have selected a silicone rubber as the mold material, so Pol-Ease® 2500 Release Agent is used.

 

Pol-Ease 2500 Release Agent_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Spray the release agent onto the model and then brush it out with a dry brush to encourage even and thorough coverage.

 

Brush Release Agent onto Plastic Model

Poured Blanket Mold: Construction of Mold Shell

 

Re-position the mold shell in its original position over the model. Align the marker and holes.

 

Reposition Mold Shell over Model_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Secure the mold shell to the baseboard with screws.

 

SecuretoBaseboard_Blanket

Poured Blanket Mold: Construction of Mold Shell

 

Seal around the screws and the edges of the mold shell with plasticine clay to help prevent rubber from leaking out.

 

SealEdgesofMoldShell-01

Poured Blanket Mold: Construction of Mold Shell

 

Construction of the mold shell is now complete.
 

Poured Block Mold: Construction of Mold Box

Start by securing the plastic model to the baseboard.

 

Bottomboard

Poured Block Mold: Construction of Mold Box

 

Seal the edges of the model with oil-based, sulfur-free clay (e.g., plasticine clay). Hot glue and caulk also work.

 

Caulk Edges with Clay_Block

Poured Block Mold: Construction of Mold Box

 

 

Smooth Edges_Block

Poured Block Mold: Construction of Mold Box

 

Smooth out and flatten the clay as best as possible.

 

Prevent Model from Floating_Block

Poured Block Mold: Construction of Mold Box

 

Apply Pol-Ease® 2500 Release Agent to the model and surrounding baseboard and then brush out with a dry brush. This step can be completed after the mold box is constructed; however, it is a bit easier to accomplish prior to construction.

 

Apply 2500 Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

 

Spray 2500 Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

 

Brush Out Release Agent_Block

Poured Block Mold: Construction of Mold Box

 

Construct walls around the model. We recommend leaving at least 1/2-inch of space between the model and mold box walls (sometimes more space is required, depending on the size/shape of the model and the casting material that will later be used).

We are using melamine-laminated particle board for the mold box. These adjustable mold boxes are available for purchase on www.polytek.com.

 

Construct Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

 

Particle Board Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

Secure mold box walls together. We use C-Clamps.

 

Secure with C-Clamps_Block

Poured Block Mold: Construction of Mold Box

 

Secure the mold box walls to the bottom board with screws; this will help to prevent rubber from seeping between them and lifting the walls.

 

Secure Baseboard to Walls_Block

Poured Block Mold: Construction of Mold Box

 

Seal the interior edges and corners of the mold box with clay (or hot glue or caulk) to help prevent leaking.

 

Seal Interior Edges_Block

Poured Block Mold: Construction of Mold Box

 

 

Smooth Clay in Mold Box_Block

Poured Block Mold: Construction of Mold Box

 

Here are the finished containment areas pictured side-by-side.

 

Finished Containment Areas_Blanket Mold_Block Mold

Mold Shell  /  Mold Box

 

Poured Blanket Mold: Pouring the Mold Rubber & Demolding

For both molds, we use PlatSil® 73-20 Silicone Rubber. It is a soft, platinum-cured silicone rubber with a 5-minute working time and a 1-hour demold time.

 

Polytek PlatSil® 73-20 Platinum Silicone Rubber

Poured Blanket Mold: Pouring the Mold Rubber

 

PlatSil 73-20 has a 1A:1B mix ratio. Carefully weigh out Part A & Part B and then combine and thoroughly mix. Scrape the sides and bottom of the mixing container several times.

 

Two-Part Platinum Silicone Mold Rubber

Poured Blanket Mold: Pouring the Mold Rubber

 

 

Mix Silicone Rubber

Poured Blanket Mold: Pouring the Mold Rubber

 

 

Poly Paddle Mixing Tool

Poured Blanket Mold: Pouring the Mold Rubber

 

4.3 lb of PlatSil 73-20 rubber is necessary to complete this mold (compared to 12.5 lb of rubber needed to complete the poured block mold).

Carefully pour the mixed rubber into the pour hole until it reaches the top.

 

Fill Mold Shell with Silicone Rubber_Blanket

Poured Blanket Mold: Pouring the Mold Rubber

 

 

Fill to Top of Mold Shell_Blanket

Poured Blanket Mold: Pouring the Mold Rubber

 

Allow the rubber to cure for about an hour at room temperature and then carefully remove the mold shell.

 

Remove Plastic Mold Shell from Mold._BlanketJPG

Poured Blanket Mold: Demold

 

 

Silicone Poured Blanket Mold_Blanket

Poured Blanket Mold: Demold

 

Loosen the edges of the silicone mold and then remove it from the model.

 

Peel Mold from Model_Blanket

Poured Blanket Mold: Demold

 

 

Loosen Edge of Mold_Blanket

Poured Blanket Mold: Demold

 

 

Finished Poured Blanket Mold_Blanket

Poured Blanket Mold: Demold

 

When ready for casting, place the mold back into the mold shell and align properly.

 

Place Silicone Mold in Mold Shell_Blanket

Poured Blanket Mold: Finished

 

 

Place Mold in Shell

Poured Blanket Mold: Finished

 

 

Poured Blanket Mold_Polytek_Blanket

Poured Blanket Mold: Finished

 

Poured Block Mold: Pouring the Mold Rubber & Demolding

Mixing procedure for the mold rubber is the same for both options.

12.5 lb of PlatSil 73-20 rubber is necessary to complete this mold (compared to 4.3 lb of rubber needed to complete the poured block mold).

Pour the mold rubber into one corner of the mold box and let it rise. Pour rubber into rubber and avoid pouring directly on the model.

 

Fill Mold Box with Rubber_Block

Poured Block Mold: Pouring the Mold Rubber

 

Fill the mold box to at least 0.5″ above the model.

 

Fill to Top of Mold Box_Block

Poured Block Mold: Pouring the Mold Rubber

 

Spraying release agent across the surface of the rubber immediately after pouring can help to release air bubbles.

 

73-20 block mold

Poured Block Mold: Pouring the Mold Rubber

 

Allow the rubber to cure for approximately 1 hour and then demold. Remove the screws that secure the baseboard to the mold box walls.

 

Remove Screws from Mold Box_Block

Poured Block Mold: Demold

 

Remove the C-clamps and mold box walls.

 

Remove C-Clamps_Blanket

Poured Block Mold: Demold

 

 

Remove Mold Box Walls_Block

Poured Block Mold: Demold

 

Loosen the edges of the mold and then remove it from the model. A prying tool may be helpful.

 

Remove Block Mold from Model_Block

Poured Block Mold: Demold

 

 

Lift Mold from Model_Block

Poured Block Mold: Demold

 

The mold is now ready for casting.
 

Resin Casting with EasyFlo 60

We prepare enough EasyFlo 60 Liquid Plastic to pour into both molds. EasyFlo 60 is a two-part, low-viscosity polyurethane plastic in the EasyFlo Series. This fast-setting plastic has a 2 to 2.5-minute working time and a 15 to 30-minute demold time.

Measure EasyFlo 60 by volume (1A:1B) or by weight (100A:90B) and mix thoroughly.

 

Fast-Setting Casting Resin_EasyFlo60

EasyFlo 60 Liquid Plastic

 

 

Measure Out EasyFlo Liquid Plastic

EasyFlo 60 Liquid Plastic

 

Carefully pour the mixed resin into the molds.

 

Poured Resin into Mold Cavity_BlanketMold

Poured Blanket Mold: Resin Casting

 

 

Pour EasyFlo Resin into Silicone Block Mold

Poured Block Mold: Resin Casting

 

Allow 15 to 30 minutes before demolding. This resin is a translucent yellow/amber color in liquid form, but cures to an opaque white color.

Allow EasyFlo to Cure
Demold the poured blanket mold by first removing the plastic mold shell.

 

Demold Poured Blanket Mold

Poured Blanket Mold: Demold

 

Peel back the blanket mold to remove the casting.

 

Peel Back Silicone Mold from Model_Blanket

Poured Blanket Mold: Demold

 

 

Demolding Plastic Model_BlanketMold

Poured Blanket Mold: Demold

 

 

Finished Casting_Blanket Mold

Poured Blanket Mold: Demold

 

To demold the poured block mold, loosen the edges and pull out the casting. This demold requires a bit more effort as the model has some undercuts and the mold rubber is thicker and less flexible compared to the blanket mold.

 

Demold Block Mold

Poured Block Mold: Demold

 

 

Remove Model from Mold_Block

Poured Block Mold: Demold

 

 

Demold Plastic Lion Head_Block

Poured Block Mold: Demold

 

We put some finishing touches on the plastic castings with black and green wax.

Apply Wax to EasyFlo Casting
 

EasyFlo 60 Plastic Head with Wax
 

Black and Green Wax Applied to Plastic Model
 

 

Poured Block Mold vs Poured Blanket Mold

left: casting from the poured block mold | right: casting from the poured blanket mold


 

Video Tutorial

This is one of the projects that we worked on with BITY Mold Supply (a distributor of Polytek products) when he paid us a visit back in December. Here is this video tutorial of the project:

 

 

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.

Or leave a comment right here on the blog!