Poured Blanket Mold of Architectural Element for Concrete Casting

July 23rd, 2014

Two times a year, we hold a Mold Making & Casting Seminar & Workshop. Attendees are invited to bring their own models (there is a size limit because the workshop is only two days long).

At our March 2014 Workshop, this decorative architectural element was brought in:

Architectural Decor Model for Mold Making
 

Architectural Element - Concrete Casting
 

This particular attendee wanted to make a mold of this plaster element to later cast concrete.

 

After a discussion with Polytek staff members, a strategy was decided for the making of the mold:

  • Mold Making Method: Poured Blanket Mold – this technique is backwards from most mold making methods; the mold shell is made first and then the rubber mold is made.
  • Products: Poly 74-20 Polyurethane Liquid Rubber (for the mold) & Poly 1512X Liquid Plastic (for the mold shell).

 

The following steps were taken to complete the mold:

 

Step One: Cover the Model with a Uniform Layer of Clay

Apply a uniform layer of clay (e.g., plasticine clay) to the entire model (often, plastic wrap is placed over the model prior to clay placement). This clay represents the space that the mold rubber will eventually fill – it should be approximately 1/2″ thick and should fill any undercuts on the model so the mold shell does not lock onto the rubber mold.

Applying Clay for Blanket Mold
 

Applying Clay - Blanket Mold
 

Mold Making - Blanket Mold
 

After a uniform layer has been applied, add a clay extension that will later be used as the pour hole for the liquid rubber. Also build-up a thick parting line in the clay that will later serve as the area where the finished rubber mold is cut. When possible, situate this line in an inconspicuous area of the model – along the corner, for instance, so parting lines are less obvious on castings.

 

Pour Hole and Shims on Blanket Mold Making-01

 

Step Two: Construct Shims to Separate Mold Shell Sections

This particular model required two mold shell pieces. To define the parting lines, shims were constructed from flashing and duct tape:

Constructing Shims - Blanket Mold

 

Step Three: Apply Release Agent to Clay & Shims

Apply Pol-Ease® 2300 Release Agent to the clay and shims and then brush out with a dry brush to ensure even coverage. Release agent is applied to prepare for the construction of a plastic mold shell.

Pol-Ease 2300 Release Agent - Mold Making
 

Brush Out Release Agent

 

Step Four: Construct Plastic Mold Shell

Poly 1512X, a fast-setting polyurethane plastic, was used in conjunction with PolyFiber II, a fibrous thickening agent, to make the mold shell in this instance:

Plastic Mold Shell Construction
 

Poly 1512X Plastic Mold Shell
 

When the first side is complete and cured, remove the shims, apply release agent to the clay and mold shell (only the parts of the mold shell that will touch the second half of the mold shell) on the opposing side, and construct the second half of the mold shell:

 

Plastic Mother Mold - Polytek

 

Step Five: Remove Clay from Model, Place Mold Shell Back Over Model & Add Hardware

Once the second half of the mold shell has cured, mark the location of the mold shell on the base board (so you can return it to that exact position when the liquid rubber is poured). Remove the mold shell from the model and then remove the clay from the model.

Blanket Mold - Mold Making
 

Once all of the clay has been removed, apply a proper release agent to the model (e.g., Pol-Ease 2300 Release Agent) and reposition the mold shell over the model making sure the positioning is the same as when it was initially created. NOTE: this plaster model was sealed by the attendee before arriving at the workshop – if it had not been sealed beforehand, we would have applied a sealing agent (e.g., mold soap, paste wax) prior to applying release agent.

Add hardware (e.g., nuts and bolts) to secure the two mold shell pieces together and add hardware securing the mold shell to the base board. Caulk possible leak points with plasticine clay:

 

Insert Hardware into Mold Shell-01

 

Step Six: Measure, Mix & Pour Mold Rubber into the Mold Shell

Poly 74-20 Liquid Polyurethane Rubber, the mold rubber used in this instance, has a 1A:2B mix ratio, a 30-minute pour time, and a ~16-hour demold time.

One way to estimate the amount of rubber needed is to weigh the clay that was removed from the model (the rubber will be filling the same space as the clay). Once weighed, calculate the volume of the clay by multiplying its weight by its specific volume (18.4 in³/lb), then divide the clay volume by the specific volume of the liquid rubber (27.5 in³/lb).

Example:
If 5 lb of clay was removed from the model:
5 lb x 18.4 in³= 92 in³ of clay
92 in³ ÷ 27.5 in³/lb = ~3.34 lb of Poly 74-20 liquid rubber

Carefully weigh and mix the rubber and then pour it into the pour hole located at the top of the mold shell.

To decrease cure time, we applied heat:

Heat Lamps on Rubber Mold

 

Step Seven: Demold

Poly 74-20 can be demolded after ~16 hours (less when heat is applied). Remove hardware and separate mold shell halves.

Poly 74-20 Blanket Mold with Mold Shell
 
 

Rubber Blanket Mold with Mold Shell
 

While the mold is still on the original model, make a cut through the thickened part of the mold created earlier with clay. We used both a mold key knife and scalpel for this process.

 

Polyurethane Rubber Mold - Polytek
 

The mold is now ready for casting!

 

Original Model with Rubber Mold and Mold Shell
 

Not sure if the poured blanket mold technique is best for your mold making 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!

Customer Project: Cast Stone Magnolia Buds for Tattnall Square Park

July 16th, 2014

West Side Stone Works of Macon, Georgia took on a mold making and casting project to create cast stone magnolia buds that would serve as finials on the columns situated at the entrance of Tattnall Square Park in historic Macon. Local artist Amy McCollough Hellis sculpted the magnolia buds from clay and West Side Stone Works took over from there. The original sculptures are approximately 3 feet tall and 20 inches in diameter.

Here are pictures of the original magnolia buds at varying angles:
 

[all photos are courtesy of West Side Stone Works]

Magnolia Bud_Clay Sculpture_3
 

Magnolia Bud_Clay Sculpture_4
 

Magnolia Bud_Clay Sculpture_5
 

Magnolia Bud_Clay Sculpture_6
 

Magnolia Bud_Clay Sculpture_1
 

Magnolia Bud_Clay Sculpture_2
 

Because of the significant undercuts on these models, West Side Stone Works utilized our most flexible polyurethane mold rubber, Poly 74-20.

 

Basic Specifications: Poly 74-20 is a Shore A20 polyurethane rubber with a 1A:2B mix ratio, 30-minute pour time and 16-hour demold time (see other popular uses for this rubber here).

 

Poly 74-20 is a pourable rubber with low viscosity. To make it suitable for brush-on application, they thickened the liquid rubber with PolyFiber II, a shredded fiber thickening agent. They also accelerated the cure and demold time by adding Poly 74/75 Part X Accelerator.

 

Prior to brushing on the liquid rubber, Pol-Ease® 2300 Release Agent was applied to the models so the cured rubber would release well from the clay when demolded:

 

Release Agent for Clay Sculpture
 

This is a picture of one of the cured Poly 74-20 brush-on molds prior to mold shell construction:

 

Poly 74-20 Brush-On Mold
 

Because brush-on blanket molds are thin, a mold shell is required for support. West Side Stone Works decided to use Poly 1511 Liquid Plastic with PolyFiber II thickening agent to make their multi-part mold shells. They used clay to make shims for this process.

 

Brush-On Plastic Mold Shell
 

Liquid Plastic for Mold Shell
 

Removing Mold Shell from Polyurethane Mold
 

Upon cure of the plastic, the rubber mold and mold shell were removed from the model to prepare for casting. The picture below is a view of the interior of one of the finished Poly 74-20 molds:

 

Mold for Clay Sculpture
 

After cleaning the molds and placing them back in their mold shells, a concrete mixture was poured into them. The final pieces are shown below prior to installation:

 

Cast Stone Sculpture
 
Artificial Lime Stone from Rubber Mold
 

Finally, the cast stone magnolia buds were installed atop these columns in Tattnall Square Park as part of a revitalization effort:

 

Cast Stone Magnolia Buds Finished
 

West Side Stone Works is located in Macon, GA and can be reached at 478-474-8585.

 

Do you have an upcoming mold making or concrete casting project you would like to discuss with a Polytek Technical Support staff member?

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!

Customer Project: Indianapolis Fabrications Assists Sopheap Pich – “A Room” Installation

July 9th, 2014

Commissioned to assist Sopheap Pich with the “A Room” installation at the Indianapolis Museum of Art (IMA), Polytek customer Indianapolis Fabrications (iFab) was asked to produce artificial bamboo elements to be combined with natural bamboo for this meditative space. They also assisted in finishing cast aluminum elements (cast at the Herron School of Art and Design Sculpture Departments) for the installation.

According to IMA:

Cambodian artist Sopheap Pich’s “A Room” fills the Efroymson Family Entrance Pavilion with nearly 1,200 real and artificial bamboo strips extending 40 feet from the atrium’s ceiling to floor. The 26-foot space inside the bamboo is a place for contemplation, allowing visitors to experience natural light bouncing off of and piercing between the bamboo strips to evoke the sense of light within Cambodia’s bamboo forests. In using bamboo, Pich creates a contrast between the aluminum, glass, and cement structure of the Pavilion, the warmth of the bamboo and the various bright and subtle colors of the different bamboo castings.

This exhibit runs from February 27 – August 24, 2014.

Sopheap Pich - A Room

 [All photos are courtesy of Indianapolis Fabrications.]

iFab used bamboo supplied by Sopheap to create silicone rubber molds and then cast 2,800 colored polyurethane plastic reproductions using EasyFlo Clear casting plastic and PolyColor Dyes. EasyFlo Clear is a fast-setting polyurethane plastic that cures to a translucent light amber color – it can be colored with PolyColor Dyes (available in black, brown, blue, green, yellow, red, and white) to achieve a variety of colors. iFab also used Polytek tin silicone mold rubber and release agents.

 

Sopheap Pich - A Room - Bamboo
 

Sopheap Pich - A Room - Silicone Molds
 

Sopheap Pich - A Room - EasyFlo Clear
 

Brian McCutcheon of iFab made a 3-week trip to Cambodia to assist Pich with the project, give instruction on mold making, and set-up a small foundry for Pich to cast scrap aluminum. iFab also helped the Indianapolis Museum of Art assemble the installation.

 

Sopheap Pich - A Room - Clear Plastic Bamboo
 

Indianapolis Fabrication - A Room - EasyFlo Clear
 

Indianapolis Fabrication - Sopheap Pich - A Room
 

The following video, detailing Sopheap Pich’s work on this installation, can be found on IMA’s YouTube Channel.

 

Would you like to discuss your next mold making or casting project with a Polytek Technical Support staff member?
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!

New Product Announcement: PlatSil® Gel-25 with New Accessories

July 1st, 2014

We are happy to announce a new addition to the PlatSil® Gel product line-up. PlatSil Gels are primarily used to create prosthetic appliances and for life casting. PlatSil Gel-OO and PlatSil Gel-10 have been the industry standard for special effects in television, theatre, and film for years, but now there’s a new player.

 

PlatSil® Gel-25: Industry Tested, Versatile, Low Viscosity

PlatSil Gel-25 is a new platinum silicone gel system 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 new 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.

New PlatSil Gel-25 Silicone_Polytek-01

^By Imaginarium FX.

PlatSil Gel-25 was introduced and featured at IMATs London by Neill Gorton (Neill Gorton Prosthetics Studio) & Mouldlife. Photo courtesy of Mouldlife.

 
If you juggle several projects at once and they each require platinum silicones with varying hardness, PlatSil Gel-25 is a great option. With the use of one silicone product, you can create a theatrical prosthetic with a Shore A10 skin, make a Shore A40 mold for casting prosthetics, and make a super soft gel as an appliance filler.

Gel25 16 lb kit

^PlatSil® Gel-25 is available in 2 lb, 16 lb & 80 lb kits

 

View PlatSil Gel-25 on the Polytek website.

Scroll down to view more photos of PlatSil Gel-25 demos from IMATS London.

 

New Accessory: PlatSil® Deadener LV

Like Smith’s Theatrical Prosthetic Deadener, PlatSil Deadener LV can be used to soften PlatSil Gels without oil leaching. The major difference between Smith’s Deadener and PlatSil Deadener LV is that Deadener LV has a lower viscosity (1520 cP compared to 5800 cP). Either Deadener can be used with any PlatSil Gel for maximum versatility.

DeadenerLV 1.8
 

You will also notice that the demold time decreases with the additional of Deadener LV. The table below details the effects of PlatSil Deadener LV on PlatSil Gel -25:

 

Effects of PlatSil® Deadener LV on PlatSil® Gel-25

Mix Ratio 1A:1B:0D 1A:1B:0.25D 1A:1B:0.5D 1A:1B:1D 1A:1B:2D
Pour Time (min) 5 7 8 10 10
Demold Time (hr) 1 0.5 0.5 0.5 0.5
Shore Hardness A25 A15 A4 (OO45) OO20 (OOO60) OOO30
Tack No No No Yes Very

 

New Accessory: PlatSil® Part H Hardener

PlatSil Part H Hardener can be used to increase the Shore hardness for any of the PlatSil Gels. For PlatSil Gel-25, a mix of 1A:1B:1H has a 7-minute working time and cures to a Shore A~40 rubber in under two hours.

PlatSilHardener 2 lb
 

All other existing PlatSil Gel accessories can also be added to Gel-25 to achieve varying effects:

Accessories
Pigments Use Silicone Color Pigments to create custom colors in silicone rubber. Available in fleshtone, red, blue, green, yellow, black and white.
Thickener Add PlatThix liquid thickener to PlatSil Gels to thicken the mix to a light-bodied, non-sag gel.
Retarder Add PlatSil® 71/73 Part R Retarder to slow the cure of PlatSil products.
Accelerator Add PlatSil® 71/73 Part X Accelerator to accelerate the cure of PlatSil products.
Thinning Agent/Softener Add Silicone Fluid 50 cSt to the mixed rubber to thin the mix. More than 10% fluid addition may exude from the cured rubber. To soften without oil leaching, use Smith’s Theatrical Prosthetic Deadener.

 

More photos, courtesy of Mouldlife, from IMATS London:


Neill Gorton _ PlatSil Gel 25

 ^By Neill Gorton [photo below from Neill Gorton Prosthetics Studio Facebook page]

PlatSil Gel-25_MouldlifePhoto_1

 ^By Gary Christensen

PlatSil Gel-25_MouldlifePhoto_2
 

PlatSil Gel-25_MouldlifePhoto_7
 

PlatSil Gel-25_MouldlifePhoto_3

 ^By Anthony Davies

PlatSil Gel-25_MouldlifePhoto_4
 

PlatSil Gel-25_MouldlifePhoto_5
 

PlatSil Gel-25_MouldlifePhoto_6

 ^By Leigh Cranston

PlatSil Gel-25_MouldlifePhoto_8
 

PlatSil Gel-25_MouldlifePhoto_9

Danny Marie Elias

PlatSil Gel-25_MouldlifePhoto_10
 

For questions about this new addition to the PlatSil Gel Series:

Call us at 800.858.5990.

Email us at sales@polytek.com.

Fill out this simple online contact form.

Gary Christensen

 

Tek-Tip: How to Store Rubber Molds to Extend Library Life

June 24th, 2014

The Library Life of a rubber mold is the length of time a rubber mold will remain useful after being placed in storage. When properly taken care of, molds can have a library life of up to 10 years or more.

 

Rubbers with Long Library Life

If long library life of a rubber mold is required, consider polyurethane rubber or platinum-cured (addition-cure) silicone rubbers. Avoid tin-cured (condensation-cure) silicone rubbers as they only last two to four years depending on conditions. Also avoid Poly-Fast 72-40, a polyurethane rubber that degrades quickly in storage.

Polyurethane and silicone mold rubbers-01

 [a small sample of Polytek polyurethane and platinum silicone rubbers]

 

Store in a Cool, Dry Area

Store molds in a cool, dry area and out of sunlight. These mold rubbers are not UV-resistant and will chalk and yellow when exposed to sunlight.

 

Store Molds in Original Shape

Store molds in their original, undistorted shape. If rubber is left in a distorted position (e.g., a corner is curled up, the mold is placed over top of another object, an object is laying on top of the mold) for any length of time, it may never recover to its original shape.

Store block molds flat and do not stack them on top of or underneath other molds or objects:

Store Rubber Molds Flat
 

Store brush-on or poured blanket molds in their mold shells (also known as mother molds):

How to Store Rubber Molds
 

Some complicated blanket molds should be stored with the original model in place as the mold may collapse in on itself over time and in certain circumstances. In these cases, and depending on the material, the model may need to be sealed to prevent migration of oils between the model and mold. For instance, when you have a blanket mold that is stored in a mold shell made of porous material (e.g., bare plaster), the mold shell surface that is in contact with the mold should be sealed (e.g. with shellac). Distortion can occur from migration of oil between the two.

 

StoringMolds
 

Two-piece mold shells should be secured together with the proper hardware for storage:

 

StoreRubberMoldsinShell
 

Don’t Mix Rubbers in Storage

Do not allow molds made of one type of rubber to remain in contact with molds made of other rubbers when in storage. This even applies to rubbers within the same series; for instance, don’t allow one polyurethane rubber (e.g, Poly 74-20) to rest against another polyurethane rubber (e.g., Poly 75-80) in storage. This may cause migration of oils or plasticizers which can cause swelling, shrinking, or distortion.

 

If you have questions about the best way to store your rubber molds or if you have a question about an upcoming mold making or casting project:

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!

 

Casting Concrete in Polyurethane vs. Silicone Rubber Molds

June 18th, 2014

Here at Polytek, we often recommend the use of liquid polyurethane rubber to make molds for concrete casting (e.g., concrete tiles, panels, statuary, pavers, bricks, countertops, edging, etc.). Platinum silicone mold rubbers can be appealing because of their great release properties (tin-cured silicones should not be considered for concrete as they shrink over time and deteriorate with age), but overall, we find that the advantages of polyurethane rubber outweigh the advantages of silicone rubber for this particular application. Here are some of the major points of comparison:

 

RubberMolds_Concrete-01

 [Polyurethane mold rubbers were used for all of the concrete casting projects in the above photo]

 

Efflorescence & Color

We have found that efflorescence, which produces salt deposits on the surface of concrete, more often occurs when silicone rubber molds are used for casting (in comparison to polyurethane rubber molds). This white residue can be aesthetically displeasing and sometimes requires the use of solvents or other chemicals to remove.

In line with this, the overall color quality of the cast parts seem to differ depending on the mold material; concrete cast in polyurethane rubber molds tend to display more vivid color, where colors may appear muted when cast in silicone rubber molds.

 ConcreteSteppingStone-01
[A concrete casting of a section of a tree made with a Poly 74-20 polyurethane mold]

 

Cost

Liquid silicone rubber costs about twice as much as polyurethane rubber.

By weight, it would require more silicone rubber than polyurethane rubber to create the same mold because silicone is more dense (our platinum silicone rubbers range from 21.3 in³/lb to 26.0 in³/lb, while our polyurethane rubbers range from 26.0 in³/lb to 27.5 in³/lb).

7420 Barkman Stone Veneer 030
[Poly 74-20 polyurethane rubber is being poured over veneer stone models]

Durability

Cured polyurethane rubbers exhibit physical properties that are generally “tougher” than silicones, so they are more resilient to wear and tear when molds are used repeatedly for years.

 

Release Properties

One advantage of silicone mold rubbers is that they have better release qualities than polyurethane rubbers – release agents are generally not necessary when casting concrete in silicone molds.

In most cases, release agent (e.g., Pol-Ease® 2650 Release Agent) should be applied to polyurethane rubber molds before casting concrete. Some softer polyurethane mold rubbers may not require release agent (e.g., Poly 74-20); however, it depends greatly on the concrete mix itself.

Veneer Stone Demolding
[Poly 74-20 molds can often be used without release agent]

 

Hardness Range

Polyurethane liquid mold rubbers offer a greater range of options. The hardest Polytek silicone option has a Shore hardness of A60 (click to read up on “Shore hardness”), while Polytek polyurethane rubbers are available up to a Shore D45. These harder rubber options are very useful for making tools like stamping and texture mats, block-outs, and form liners.

 

StampingMat_Polytek

 [This brick-textured stamping mat was made from Poly 75-80, a Shore A80 rubber]

 

Video Tutorials

Some do find success in casting concrete with silicone mold rubbers. The video tutorial below features the use of a platinum silicone mold rubber (PlatSil® 73-40 Silicone Rubber) when making a mold of a decorative tabletop:

 

This video tutorial features the making of a polyurethane rubber (Poly 74-45 liquid rubber) Travertine panel mold:


As a follow-up to the previous video tutorial, concrete is cast in the Travertine panel mold:

 

Would you like to discuss your concrete casting project with a Polytek technical support staff member?

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

How to Prepare a Model When Making a Polyurethane Rubber Mold

June 11th, 2014

A model, also called a “master”, should be prepared according to the model material & mold material.

Models being used to make a polyurethane rubber mold often need to be prepared differently than models being used to make a silicone mold. Generally, silicone rubbers have better release properties than polyurethane rubber.

Polyurethane Rubber Mold

 [Poly 74-20, a polyurethane rubber, being poured over a prepared clay model]

 

What Can Go Wrong

Incorrectly preparing a model for mold making can result in the rubber bonding to the model or the rubber not properly curing against the model.

 

Determine if the Model Requires a Sealing Agent

Porous models, such as wood, concrete, plaster, stone, pottery or masonry, must be sealed before applying any release agent or rubber.

[p.s. porous models should also be vented from beneath to prevent trapped air from forming bubbles in the rubber]

VentMoldBox_Polytek
 

Sealing agents are designed to create a barrier so that liquid rubber does not penetrate pores in the model. Sealing pores reduces the chance that rubber can stick or mechanically lock on to the model. Generally, sealing agents are available in removable, semi-permanent, and permanent options.

 

Examples:

This very porous concrete stepping stone is sealed with two coats of a sealing agent before the mold making process:

Seal Concrete Paver-01
 

This non-porous plastic model does not require a sealing agent:

Non-Porous Model
 

Other popular non-porous model materials include metals, wax, glazed ceramics, fiberglass, polyurethanes, and plasticine (even sulfur-containing clays do not generally require a sealing agent when working with liquid polyurethane mold rubbers).

 

Popular Sealing Agents for Porous Models

Some sealing agents can be purchased from your local home improvement or hardware store. Multiple coats of paste wax, dried and buffed, will seal most surfaces. Lacquer and paint are also used. For plaster, Potters soap works well (do not use soap on other model materials). The following sealing agents are available from Polytek (some of them serve as both a sealing agent and release agent):

 

Poly PVA Solution

Poly PVA Solution - Clear-01This alcohol-based sealer has one major advantage over many other sealing agents: it is water-soluble. This can be appealing for those that would like to return the model to as close to original condition as possible (NOTE: Even though Poly PVA can be removed, we cannot guarantee that the model will be in the same condition it was at the start of the mold making process).

If this sealer is not washed off with water after the first mold is made, it should continue to act as a sealer if a second mold is made.

A release agent should be used in conjunction with this sealing agent; however, it should not be water-based. Release agent should not be applied until the PVA solution has dried, which takes approximately an hour after application (depending on temperature & humidity).

Poly PVA Solution is available in clear and green varieties.

 

Pol-Ease® 2350 Sealer & Release Agent

Pol-Ease2350_ReleaeAgent_PolytekThis semi-permanent sealer and release agent is white petrolatum dissolved in mineral spirits. It is considered semi-permanent because small amounts of the sealer can come off when the mold is cured and removed.

When applied correctly, additional release agent is not needed before making the polyurethane mold.

It is important to allow the solvent to evaporate before applying rubber; insufficient evaporation will cause cure issues in the polyurethane rubber.

 

 

PolyCoat Sealer & Release Agent

PolyCoat Release & Sealer PolytekWhen this semi-permanent sealer & release agent is applied to a model, it leaves behind a thin silicone coating. Liquid polyurethane rubber can be applied directly to this coating without the use of additional release agent.

After applied, the solvent typically evaporates in ~5 minutes and the silicone cures in about 30 minutes (depending on temperature and humidity). Do not apply polyurethane rubber until it is completely cured.

Multiple molds can usually be made from one application of PolyCoat (multiple coats may be required if the model is very porous).

 

 

 

Apply a Release Agent

PolytekReleaseAgents-01Release agents are coatings that are designed to prevent liquid rubber from sticking to surfaces.

Polyurethane rubbers naturally stick to a variety of a materials; therefore, release agent should almost always be applied to the model before applying liquid polyurethane rubber.

Pol-Ease® 2300 Release Agent is the release agent that we most often recommend for this process. As a reminder, if Pol-Ease® 2350 Sealer & Release Agent or PolyCoat Sealer & Release Agent have been applied, there is no need to apply this additional release agent.

Liquid rubber can be poured over the model immediately after this release agent is applied – there is no wait time. In most cases, we recommend brushing out Pol-Ease 2300 with a dry brush after it is applied; this promotes even coverage. Applying too much release agent can cause pinhole surface defects in the mold.

 

Test Cures

If there is ever a question concerning compatibility between liquid polyurethane rubber and the prepared model surface, we recommend performing a small test cure on an identical surface to determine suitability.

 

Sealer & Release Agent Selection Guide

For an overview of all sealing and release agents available from Polytek (as well as a matrix that recommends which product to use for certain applications), view our Sealer & Release Agent: Selection Guide

Sealer&ReleaseAgent Selection Guide
 

Review Product Technical Bulletins

All product Technical Bulletins, available at www.polytek.com, have a “Model Preparation” section. We recommend reading this section carefully before beginning your mold making project. If you have additional questions:

Call Us at 800.858.8620
Email Us at sales@polytek.com.
Fill out this simple online form.

“Communities In Schools of the Lehigh Valley” – Chemistry Demo with Polytek Products

June 4th, 2014

Polytek® was happy to be a part of Communities In Schools of the Lehigh Valley last week. This organization is dedicated to helping children stay in school, overcome obstacles, and thrive in life:

Communities In Schools is the nation’s largest dropout prevention organization bringing coordinated, integrated student services into public schools to meet the needs of at-risk students.  Our mission is to surround students with a community of support, empowering them to stay in school and achieve in life.  To help our students achieve their greatest successes, we determine students’ needs and establish relationships with local businesses, social service agencies, health care providers, and parent and volunteer organizations to provide needed resources. - cislv.org

David Salisbury, a chemist and the President of Polytek, spent part of the afternoon with students at Easton Middle School. After introducing the basics of chemistry via whiteboard, David got started on showing the students how chemistry applies to products that we use or see every day. Armed with a variety of Polytek products, including liquid rubbers, plastics, and foams, he demonstrated that the right combination of chemical compounds can create a useful, new material (e.g., mixing two liquid components together can create a hard plastic). The best part: the kids got to help. Here are some of the highlights:

We had many volunteers eager to help:

Communities in School_1

This student volunteered to have a mold made of her hand. David applied a skin-safe silicone rubber (PlatSil® Gel-10) to her hand and then she sat back down to wait for it to cure while other demonstrations were done:

Communities in School_2

Communities in Schools_20

Our next volunteer helped David mix some EasyFlo plastic and pour it into a few molds:

Communities in Schools_19

Communities in Schools_3

Even the teachers wanted to take a good look at the plastic parts he made:

Communities in School_21-01

This student helped by dusting some bronze powder into a rubber mold and then mixing and pouring some EasyFlo plastic to produce a bronze-like part:

Communities in Schools_5

This student burnished the bronze part with steel wool to bring out the metal particles and then showed the completed piece to his classmates:

Communities in Schools_18

David demonstrated how quickly EasyFlo plastic cures. As the liquid plastic begins to fall out of the cup, it quickly solidifies and stays put:

Communities in Schools_6

Communities in Schools_7

Our next volunteer helped demonstrate how polyurethane foam works:

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Meanwhile, the silicone mold was removed from our volunteer’s hand and shared with the rest of the students:

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EasyFlo plastic with red dye was poured into the silicone hand mold, allowed to cure, and then shared with the class:

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We had a great time at the Easton Middle School as part of Communities In Schools of Lehigh Valley and we hope to return again.

Looking Back: Hanks & Spielberg Receive Cold-Cast Bronze Statues

May 28th, 2014

Looking back through the archives of Developments, a Polytek® printed newsletter covering a variety of mold making and casting topics, we are reminded of decade-old customer projects that deserve to be revisited.

PolytekDevelopmentsNewsletter
 

The following article features the story behind the making of a cold cast bronze bust that was gifted to Tom Hanks, Steven Spielberg and Dale Dye. This story appeared in the Winter of 2003 edition of Developments, although the actual project was completed in 2001:

 

Hanks & Spielberg Receive Cold-Cast Bronze Sculpture Made with Polytek® Products

Cold Cast Bronze BustWho among us has not been taken to the edge of our seat by the intensity and realism displayed in military action movies of the past few years? The special effects, cinematography, and overall artistry make us feel as if we were firsthand witnesses to these dramatic and often historic events. Movies such as Platoon, Saving Private Ryan, and Band of Brothers are just a few that top the list. The daunting job of directors like Steven Spielberg and Oliver Stone is to orchestrate the numerous disciplines within the movie industry, relying upon the expertise of technical advisers to organize the endless combinations of effects that go into making these stunning film experiences.

Captain Dale Dye is one such senior technical assistant who has written, acted in, and advised on dozens of action movies. In 1986, Dye met Ron Petitt, a sculptor well known for his military- and history-themed pieces, and shortly thereafter Dye began collecting Petitt’s work. Dye was captivated by Petitt’s highly detailed and historically accurate 20th-centry military sculpture. Petitt himself had served in the military during the Vietnam War and began creating combat artwork at the time.

While working as senior technical advisor during the filming of the immensely popular HBO miniseries Band of Brothers, Dye approached Petitt to create a distinctive commemorative sculpture to be presented to actor Tom Hanks and director Steven Spielberg in appreciation from the staff and crew for their extraordinary efforts on Saving Private Ryan and Band of Brothers. Dale thought it appropriate to do several hot bronze castings of a 14-inch-tall sculpture of a 101st Airborne Division soldier.

Petitt decided to do a prototype casting of his sculpture in cold-cast bronze using Polytek EasyFlo 60 polyurethane liquid casting plastic as the resin binder. He made a rubber mold over his microcrystalline wax master using one of Polytek’s 1:1 mix platinum silicone mold rubbers. PlatSil 71-15 (no longer available – for a similar product, see PlatSil 71-20) was chosen because of its easy 1:1 mix ratio and its super-elongation and tear resistance. Since a silicone mold rubber was chosen, Petitt would be able to cast repeatedly in this mold either with EasyFlo 60 filled with bronze powder or with wax, as would be required for the lost-wax process leading to a hot bronze reproduction.

Upon completion of his EasyFlo 60 cold-cast bronze prototype, Petitt took it to show friends and colleagues in several art foundries who cast hot bronze. To his amazement, no one could tell this was not an actual hot bronze casting! As a result, he chose to forgo the lengthy and more expensive process of creating the hot bronzes and make three cold-castings using EasyFlo 60 and bronze – one for Tom Hanks, one for Steven Spielberg, and one for Dale Dye. This process allowed Pettit to create the sculpture without the aid of a foundry, making each a truly unique piece created entirely by the artist. The “Airborne” castings were a tremendous success and were greatly appreciated, as evidenced by the special thank-you letter from Tom Hanks.

TomHanksSculptureLetter

The success and notoriety of this project led the National Association of the 101st Airborne Division to ask Petitt to create a life-size monument in hot bronze that will commemorate the heroic service of American soldiers in World War II, Vietnam, and Desert Storm, as well as those currently in uniform. This sculpture will be the only one of its kind designed exclusively for the 101st Airborne. Polytek mold rubbers will be created to cast wax positives, which will then be sectioned, shelled, and fired to create the refractory molds needed to withstand the temperatures of molten bronze.

Petitt, who has been a Polytek customer for many years, admits he has tried competitive products, but he always comes back to Polytek because of superior product performance, consistency, and support both from Polytek and from his local Polytek distributor in Loveland, CO, Sculpture Depot. Petitt has a studio in Loveland. For more information on the 101st Airborne Division, visit www.screamingeagle.org. To view more of Ron’s work, visit www.ronpetitt.homestead.com.

 

More Information on Cold Cast Bronze

For more information on this cold cast bronze technique, start here by learning three different casting methods. To speak with a Polytek technical support staff member:

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

Tek-Tip: Repairing Torn Rubber Molds

May 21st, 2014

If a tear develops in your polyurethane rubber or silicone rubber mold, one of the following options may help to repair it.

 

General Tips & Notes

  • Before applying adhesive to torn molds, clean the affected area thoroughly. Denatured alcohol is a good option for this, but care must be taken with respect for health and flammability hazards.
  • Generally, block molds are easier to repair than thin blanket molds because there is more surface area.
  • When repairing thin blanket molds with adhesive, consider adding a layer of fabric (e.g., TieTex® Fabric) to better reinforce.
  • If a tear occurs within 24 hours of creating the mold, you may be able to use the same mold material to repair it.

 

Repairing Polyurethane Rubber Molds

For polyurethane rubber molds, like 74-Series, 75-Series, and Polygel® rubbers, the ideal option for repairing tears is PolyBond. PolyBond is a two-part, flexible, polyurethane adhesive that has a 1A: 3B mix ratio (by weight), a 3-minute pour time, and a 15- minute cure time.


PolyBond_Adhesive
 

Epoxy adhesives, like PolyPoxy® Quick Stick Adhesive, could also be used to repair a tear; however, they are non-flexible and will begin to crack if they are situated in a position on the mold that is frequently flexed. It will also hinder the flexibility of the mold in that location.

Polypoxy Quick Stick 2lbs.

 

Example of Repairing a Block Mold with PolyBond

This Poly 74-20 polyurethane rubber coaster mold has a tear in the corner:

Torn Polyurethane Rubber Mold-01

Cut around the tear to expose clean rubber (PolyBond will adhere much better to clean rubber, as opposed to rubber that is contaminated with release agent, casting materials, etc.):

Cutting Mold to Repair

The new cut:

Cut Corner of Mold

Either position the original model in the mold or use a different material to recreate the shape of the model to prevent PolyBond from leaking. Plasticine clay is used here:

Position Clay in Corner

Carefully weigh and mix PolyBond at a 1A:3B mix ratio. It has a 3-minute working time, so application of this adhesive should be done quickly after mixing:

Weigh PolyBond

Apply PolyBond to the interior of the cut:

Apply PolyBond to Corner

Remove excess PolyBond and allow it to cure (~15 minutes):

Let PolyBond Cure

Cured PolyBond:

Cured PolyBond on Block Mold

 

Example of Repairing a Poured Blanket Mold with PolyBond

Blanket molds are generally thinner than block molds and can be more difficult to repair.

Torn Blanket Mold

Clean the affected area with a solvent cleaner, like denatured alcohol (be aware of health and flammability risks with these solvents):

Clean the Mold

Situate the two sides of the tear so they are level with each other and are in the proper position. Clay was used here to prop the two sides up:

Level Sides of Mold

Apply PolyBond to the interior of the tear:

Apply PolyBond to Interior Tear

Remove excess PolyBond:

Clean Excess PolyBond

Apply PolyBond to the exterior surface of the tear:

Brush On PolyBond

Before mixing the PolyBond, a piece of Tie-Tex® Fabric was cut to position over the tear for increased reinforcement:

TieTex Fabric for Mold Repair

Ensure that the Tie-Tex® Fabric fully covers the tear:

Layer TieTex Fabric

Apply PolyBond over the fabric:

Cover TieTex with PolyBond

Allow PolyBond to cure:

Allow PolyBond Adhesive to Cure

 

The flexibility of PolyBond makes it ideal for repairing flexible polyurethane; however, it does have a Shore hardness of ~A50, so if you’re working with a very soft rubber (Shore A20), it may interfere with the flexibility of the mold depending on the location of the tear.

 

Repairing Silicone Rubber Molds

If a small tear occurs in a platinum-cured silicone rubber or tin-cured silicone rubber, a good product to use for the repair is TinSil® 80-30 Silicone Rubber. Traditionally used to make molds, this two-part, Shore A30 silicone also serves as a great adhesive. TinSil® 80-30 has a mix ratio of 1A:10B, a pour time of 45 minutes, and a cure time of 24 hours. Because the cure time of this product is 24 hours, it is important to situate the ends of the tear in a stable position that will remain unchanged for at least 24 hours.

The techniques used on polyurethane molds, as shown above, can also be used when repairing silicone molds.

TinSil 80-30 Silicone

Repairing Torn Silicone Mold
 

Do you have a question for Polytek Technical Support?
Call us at 800.858.5990.
Email us at sales@polytek.com.
Fill out this simple online contact form.

Or leave a comment right here on the blog!