2016 Mold Making & Casting Workshop Dates

November 25th, 2015

OctoberMoldMakingSeminar_15Polytek® Mold Making & Casting Seminar/Workshops are held twice a year at our Easton, PA facility. Attendees are invited to bring their own mold making projects to work on over the course of the two-day class.

Our 2016 Workshops are on the following dates:

March 17 & 18, 2016

October 20 & 21, 2016

To see the general itinerary or to sign-up for the workshop, visit our website.

To see pictures from our past workshops, click on one of the options below:

October 2013

March 2014

October 2014

October 2015

Mold Making & Casting Seminar & Workshop: October 2015

October 29th, 2015

On October 15 & 16, we held our fall Mold Making & Casting Seminar/Workshop. Attendees of this two-day class are invited to bring their own project (as long as the project can be realistically completed in two days).

A variety of mold making techniques were used at the workshop, including poured block molds, two-piece block molds, poured blanket molds and brush-on blanket molds. Take a look at some of the projects below:















































































Check the Polytek website for upcoming workshop dates or get in touch with us:

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


How to Make Wood-Textured Concrete Stools

October 13th, 2015

Concrete Log StoolsThe following tutorial details the process of making a polyurethane rubber mold of a log that will be used to cast concrete stools.

A list of supplies and tools used for this project are provided at the end. If you prefer to watch the video tutorial of this project, it is also provided at the end of this blog entry.

The Process:

Step 1: Prepare the Original Model
Step 2: Construct a Containment Area
Step 3: Measure, Mix & Pour FormRub 35 Liquid Rubber
Step 4: Demold & Cut the Mold
Step 5: Cast Concrete


Step 1: Prepare the Original Model

Preparation of the original model is a very important step in the mold making process. Improper preparation can lead to the rubber bonding to the model or improper cure of the rubber [for general information on how to prepare models when making polyurethane rubber molds, read this blog entry.]

For porous models that are brought in from the outdoors, it’s important to allow them to fully dry as moisture can affect the cure of polyurethane rubbers.

Porous models, such as this log (below), must be thoroughly sealed to prevent rubber from penetrating the pores and becoming stuck. Many sealers can be purchased through local home improvement stores while others are available directly from Polytek.

How to make a mold of a log

In some cases, a couple of layers of primer spray paint will be enough to seal the model; however, this log is extremely textured and porous, so we decide to paint on a layer of paint by hand. Brushing on the paint allowed us to “push it” into the texture better and seal the surface more thoroughly.

Apply Primer Paint to Log

Once the model is thoroughly painted, a release agent must be applied. Again, since this log is extremely prous and the bark texture is very deep, we decided to use PolyCoat. PolyCoat is a silicone-based, semi-permanent sealer and release agent.

PolyCoat Sealer and Release Agent

The log is turned onto its side to help prevent runoff and allow the PolyCoat to fully penetrate the irregular surface. In total, four layers of PolyCoat are applied.

PolyCoat should be allowed to cure in between application of each layer and the final layer should be allowed to cure before application of any liquid rubber.

Sealer & Release Agent for Porous Models

When the PolyCoat has cured, a large crack in the bottom of the log is filled with warmed plasticine clay to help prevent rubber from seeping into it (the side of the log pictured below will be the bottom of the finished concrete stool.) A clay “snake” (i.e., clay that has been rolled out into a long, thin strip) is also placed around the outside edge of the bottom of the log to act as a gasket when the log is mounted onto the baseboard.

Prepare the Model for Mold Making


Step 2: Construct a Containment Area (a.k.a. Mold “Box”)

The log is about 12″ in diameter, so we manufacture a plywood baseboard with a 14″-diameter recess. A 14″-diameter cardboard concrete tube (e.g., Quik-Tube® or SonoTube®) will fit snugly into the recess and will act as the containment area. The recess is only about 1/2″ deep, but it will help to keep the tube stable when the mold rubber is poured.

A 14″-diameter tube is selected so that the mold walls will be about 1″ thick.

Baseboard with 14-Inch Recess

The baseboard is placed onto the bottom of the stool and secured with screws. It is important to make sure that the work surface and log are level throughout this process.

Mold Making Tutorial

Vent holes are made in the baseboard so that air in the model may escape. Without vent holes, this air may become trapped in the rubber.

Drill Vent Holes in Baseboard

Screws and Vents in Baseboard

The edges of the log are sealed with plasticine clay to help prevent rubber from seeping beneath the log. The mold rubber will pick up the clay texture, so the clay is flattened/smoothed out as best as possible.

Seal Edges of the Log

Clay is also placed around the edge of the recess to help prevent rubber from leaking outside of the containment tube.

Clay Gasket

A cut is made down one side of the tube; this will make the demolding process easier, but will also weaken the tube.

Cut 14-Inch Diamater SonoTube

Before placing the tube around the log, we tape the inside and outside of the cut.

Tape the Cut in the Tube

Vaseline is then applied to the entire inside of the tube with a dry brush. The exterior side of the bottom of the tube is also coated just in case rubber leaks outside of the tube.

Coat Inside of Tube with Vaseline

Tape is wrapped around the tube and then the tube is placed snugly into the recess. Mold straps are used to secure the tube and baseboard together.

Place Tube Around Log and Secure


Secure Mold Straps and Tape


Step 3: Measure, Mix & Pour FormRub 35 Liquid Rubber

FormRub 35 Liquid Rubber is a two-part (Part A & Part B) polyurethane system that cures to a Shore A35 hardness.

Basic Specifications
Mix Ratio: 1A:1B
Initial Mixed Viscosity: 600 cP
Pour Time: 15 minutes
Demold Time: 16 hours
Cured Color: Turquoise

Mold Making Polyurethane Rubber


To determine how much rubber is needed to make this mold, we do the following calculation:

  • Determine the volume (in³) of the containment area.
  • Estimate the volume of the log and subtract it from the volume of the containment area.
  • Take that result and divide by the specific volume of the mold rubber (the specific volume of FormRub 35 is 27.2 in³/lb).
  • This final result is the amount of rubber, in pounds, needed to complete the mold.

This log mold requires approximately 65 lb of FormRub 35 Liquid Rubber.


FormRub Series rubbers can be mixed by weight or volume, but we highly recommend weighing on a digital scale.

Because these mixing pails only hold 40 lb of material, we mix three separate batches of rubber.

Part B is added to the mixing pail first because it is lower in viscosity and less likely to cling to the sides.

Measure Part B - FormRub 35

Part A is then weighed into the bucket.

Meaure Part A - FormRub 35


The components are thoroughly mixed. It’s important to scrape the sides and bottom of the bucket multiple times during the mixing process.

Keep the pour time of the product in mind when mixing. FormRub 35 has a pour time of 15 minutes, but this time varies from product to product.

A Poly Paddle, used below, is a good tool for hand mixing.

Thoroughly Mix FormRub 35

The rubber is poured into one side of the mold. We continue to pour the rubber into the same spot and allow it to rise.

Pour Mold Rubber into Tube

When working with multiple batches, pour the next batch as soon after pouring the previous batch as possible.

FormRub 35 Mold Rubber

Generally, mold rubber should be poured to at least 1/2″ above the top of the model. For this mold, we pour the rubber about 1″ over the top of the log.

Allow FormRub 35 to Cure


FormRub 35 can be demolded after 16 hours at room temperature.


Step 4: Demold & Cut the Mold

The tape that covers the cut in the tube is cut and then the tube is removed from the mold.

Demold FormRub 35

Remove Tube from Rubber Mold

The screws are removed from the baseboard and the edges of the mold are loosened with a flat tool (e.g., putty knife). The mold is then turned over (this may require two people) so that the bottom of the log is exposed.

Remove Log from Baseboard

Remove Mold from Baseboard

Flip Mold Over


A cut will be made down one side of the mold to remove the log and subsequent castings. A sharp scalpel or blade is a good tool for cutting soft, polyurethane rubbers.

It can be helpful to have a second person pry open the cut; this gives a better view of where the model is. The location of the cut of this mold is not incredibly important because a seam line in the final casting is well-disguised in the deep textures of original model. Seam lines can be more noticeable depending on the shape and texture and original model, so cutting the mold along an existing line in the model is important in those instances.

Cut Rubber Mold with Scalpel

Cutting in a zigzag pattern (compared to a straight cut) is helpful for realignment of the mold when casting.

Cut in ZigZag Pattern

If rubber has seeped into any deep knots in the log, it can usually be cut away easily with a scalpel.

Make Cut in Rubber Mold

While one person holds the mold apart, a second person removes the log.

Polytek - Rubber Mold of a Detailed Log

FormRub 35 Rubber Mold - Pollytek


Step 5: Cast Concrete

To cast concrete, the tube is placed back around the mold and secured with a mold strap; this will help to prevent deformation of the mold from the weight of the concrete. It is situated so that the cut in the tube is on the opposite side of the location of the cut in the rubber mold. This will provide more stability during the casting process.


Realign Mold and Tube for Casting

The mold is coated with Pol-Ease® 2650 Release Agent. Pol-Ease 2650 is a silicone-free, oil-based release agent that does not require any drying time before casting concrete. There are a number of other concrete release agents that are suitable for use with polyurethane mold rubbers.

Concrete Release - Pol-Ease 2650 Release Agent

The concrete is mixed and poured into the mold.

Mix Concrete

To reduce the weight of the finished stool, a small amount of concrete is poured into the mold and then a 6″-diameter foam plug is inserted.

Pour Concrete into Mold

Foam Insert in Concrete Stool

A weighted pail is placed on top of the foam insert so it doesn’t float and then the remainder of the concrete is poured into the mold.

Pour Remainder of Concrete

Once cured, the concrete is removed from the mold.

Demold Concrete

Open Rubber Mold

Remove Concrete from Rubber Mold

Excess foam is trimmed from the insert.

Trim Foam Insert

Concrete Casting - Mold Making Rubber

If desired, the concrete can be stained.

Concrete Log Stools

Concrete Casting Tutorial

Wood-Textured Concrete Stools


When properly taken care of, this mold can be used to cast hundreds of concrete stools.

Video Tutorial



Supplies and tools used for this project: 

  • Original Log Model
  • FormRub 35 Liquid Rubber
  • PolyCoat Sealer & Release Agent
  • Pol-Ease® 2650 Release Agent
  • Primer Paint
  • Baseboard
  • Cardboard Concrete Tube
  • Plasticine Clay
  • Mixing Containers & Mixing Tools
  • Dry Brushes
  • Tape
  • Mold Straps
  • Wood Screws
  • Drill
  • Digital Scale
  • Utility Knife
  • Scalpel or Sharp Blade
  • Prying Tool
  • Concrete Supplies


Would you like to speak with Polytek Technical Support about your concrete casting project?

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


New Video Tutorial: How to Make a FormRub 35 Concrete Log Mold

September 28th, 2015

concrete log stoolsOur latest video tutorial details the process of making a FormRub 35 rubber mold of a log in order to cast concrete stools. The original log is sealed and released and then placed in a cardboard concrete tube. The mold rubber is poured around and on top of the log to make the mold. FormRub 35 is very low in viscosity which allows it to easily flow into the deep textures of the log.

1. Prepare Original Model (i.e., the log)
2. Construct Containment Area Around the Log
3. Measure, Mix & Pour the Mold Rubber
4. Demold
5. Cast Concrete


Watch the Video Tutorial:


Do you have additional questions about mold rubbers for concrete casting projects? 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.

Tek-Tip: Reduce Bubbles in Clear Casting Resin

September 9th, 2015

Without the proper equipment, it can be difficult to achieve bubble-free castings with clear polyurethane casting resins such as Polytek Poly-Optic® 14-Series resins. These clear resins are two-part polyurethane systems formulated specifically for applications where optical clarity is needed.
Poly-Optic1411 Clear Casting Resin - Polytek

[below: an example of Poly-Optic casting (left) next to the original model (right)]

Example of Poly-Optic Clear Casting Resin


In this blog entry, we discuss three different methods for casting Poly-Optic® 1411 Clear Casting Resin. Each method produces varying levels of bubbles in the final casting.
Casting Methods

NOTE: Some of these methods require special equipment; always seek the advice of a professional when sourcing and using this type of equipment.

In each method, the first step is to measure and mix the resin. Poly-Optic 1411 has a mix ratio of 1A:1B by volume (100A:90B by weight).
Mixing Poly-Optic 1411 Clear Casting Resin


In all three method examples below, a small polyethylene container will serve as the mold.


Open Pour Method

The open pour method does not involve any special equipment. After mixing Parts A & B together, simply pour the resin into a properly prepared mold and allow it to cure.
Open Pour into Cup - Poly-Optic 1411
Open Pour - Clear Casting Resin


Vacuum Degassing

Vacuum degassing requires a vacuum chamber, which can be expensive. To degas, the mixed resin is placed inside a container and then placed inside the vacuum chamber. The container holding the resin should have enough headspace to accommodate three times the original volume of the resin.
Vacuum Degas Clear Casting Resin
Vacuum is pulled to 29 inches of mercury.
29 Inches of Mercury - Vacuum Degassing Clear Resin
The air is sucked out of the resin which causes the bubbles to rise up and then collapse. This process typically takes a couple of minutes. NOTE: Resins with short working times should not be vacuum degassed.
Poly-Optic Resin in Vacuum Chamber
When the resin is removed from the chamber, it appears bubble-free.
Vacuum Degassed Clear Resin


The resin is then poured into the mold. Although the resin has been degassed, bubbles may be generated in this step.

Vacuum Degassed Resin Poured Into Mold

Pressure Casting

To pressure-cast a part, the resin should be mixed and poured into the desired mold prior to placing it in the pressure pot. Pressure casting essentially crushes the air bubbles in the resin.

NOTE: Molds must be made under the same pressure or deformation may occur.
Prepare Pressure Pot for Resin Casting
We recommend setting the pressure pot at 60 psi; the closer to 100 psi, the better.
60psi Pressure Pot - Resin Casting


The mold should remain in the pressure pot for the length of the demold time.


The Results

3 Casting Methods - Clear Resin
The open pour method results in hundreds of tiny air bubbles which are quite obvious in the final casting.
Open Pour - Poly-Optic Clear Casting Resin
The vacuum-degassed casting is an improvement, but the act of pouring the degassed resin into the mold produced some air bubbles.
Vacuum Degas - Poly-Optic Clear Casting Resin
The resin cast under pressure resulted in the casting with the least air bubbles.
Pressure Cast - Poly-Optic Clear Casting Resin
The recommended casting method for bubble-free, clear parts is pressure casting.
Do you have additional questions about Poly-Optic casting resins? 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.


Kiln-Casting with Glass: The Process

August 25th, 2015

Anna Boothe, former faculty member in the Glass Program at Tyler School of Art (Temple University) and current freelance artist, provided us with a behind-the-scenes look at her lead crystal kiln-casting process. You can find Anna’s bio at the end of this blog entry or view her work at www.annaboothe.com.

Photo Credits: Anna Boothe


Step 1: Create the Original Model

From wax, Anna hand-carves a form that she wishes to transpose into glass. All details and surface textures will be replicated.

Glass Casting - Rubber Molds

Original models do not necessarily need to be carved from wax. They can be made from any number of materials. The composition of the original may affect which mold material (i.e., silicone or polyurethane) is used in the next step.


Step 2: Fabricate a Flexible Rubber Mold

To create multiples of the original wax model, Anna fabricates a polyurethane rubber mold. Silicone mold rubber is also an option.

In this case, she utilizes Poly 74-24 Liquid Rubber, a relatively soft, two-part polyurethane rubber. The mold making process is not detailed here, but Anna made this mold by using a “poured block mold” technique. For a tutorial on this process, visit the How to Make a One-Piece Rubber Block Mold blog entry or browse our entire Block Mold category.

Rubber Mold for Glass Casting Process

Step 3: Make Wax Copies of the Original Model

The original wax is removed and archived; future waxes of this model are generated by pouring molten wax into the mold.

Wax Casting in Polyurethane Rubber Mold

Step 4: Prepare to Make Refractory Mold

In preparation to pour a refractory (heat-resistant) plaster-based mold, Anna places the wax model on a clay base and then secures a tar paper coddle (cylinder into which the liquid refractory will be poured) around the model and base.

Prepare to Make Refractory Mold

Tar Paper Coddle - Lead Crystal Casting

Step 5: Make the Refractory Mold

A refractory mixture predominately comprised of silica, plaster and fiberglass is mixed with water and poured into the coddle.

Refractory Material Poured Over Wax Model

Step 6: Remove Coddle & Melt Wax

When the plaster has cured, Anna removes the coddle. In the photo below, the mold has been turned over to expose the sprue (i.e., the opening into which glass will be poured once the wax has been removed).

Refractory Molds for Glass Casting

The wax-filled mold is placed upside down inside an industrial pressure pot, atop a grate that is suspended above a water bath. Pressurized steam created by heating the pot over a propane stove causes the wax to melt out of the mold and into the water bath.

Melt the Wax - Glass Casting

Step 7: Kiln-Casting the Glass

Anna fills the empty mold with leaded glass frit (crushed glass) and places it in a special kiln. The glass is melted at 1500°F degrees and cooled slowly. Anna explains that for molds this size, the whole firing process takes approximately 3 to 4 days.

Fill Mold with Leaded Glass Frit - Lead Crystal Casting

Step 8: Break Away Mold

Once cooled, Anna carefully breaks away the mold from the cast glass object. This type of mold is called a “waste” mold because it can only be used one time.

Break Away Refractory Mold - Glass Casting

Step 9: The Glass is “Cold-Worked”

After the glass has been washed of mold debris, it is “cold-worked” (i.e. cut, ground and polished using a variety of machinery and hand tools that rely on diamond and other abrasives).

The Glass is Cold-Worked

Step 10: The Finished Sculpture

Anna’s finished sculpture incorporates multiple “hand flower” forms, all of which have been cast individually and assembled.


“Release” 2008
17” ht. x 17” top diameter x 8.5 bottom diameter
Assembled kiln-cast lead crystal.

Anna Boothe - Assembled Kiln-Cast Lead Crystal - Release

More on Anna Boothe:

With a BFA degree in sculpture and MFA in glass from Rhode Island School of Design and Tyler School of Art (Temple University), respectively, Anna Boothe has worked with glass since 1980. Her primarily kiln-cast and pate de verre work has been exhibited at the Tittot Glass Art and Bergstrom-Mahler Museums, Museum of American Glass, and Kentucky Museum of Art and Design, and is in the permanent collections of the Corning Museum of Glass and the Tacoma Museum of Art. Comprised of both sculptural and decorative objects, her works are shown in galleries throughout the US.

A member of Tyler’s glass faculty for 16 years, Anna also helped to develop and  institute Salem Community College’s (NJ) AFA glass art degree program in 2004 where she also chaired the school’s International Flameworking Conference. She has taught and lectured extensively at other schools that include the Corning Museum of Glass, the Pittsburgh Glass Center, Urban Glass, Pilchuck, and venues in Belgium, Switzerland, Turkey, and Japan. In recent years, the artist has presented her work at the Rochester Institute of Technology, Virginia Commonwealth University, the University of Wisconsin at Madison, Illinois State University, Illinois-Wesleyan University, Sheridan College (Toronto) and the Everhart Museum (Scranton, PA).  In 2012, Anna was awarded a Corning Museum of Glass Collaborative Artist Residency with NY area sculptor Nancy Cohen, the result of which was exhibited at the Accola Griefen Gallery in Chelsea, NYC in 2013 and reviewed in Glass Quarterly Magazine.

From 1998-2006, Anna served on the Glass Art Society Board of Directors and as the organization’s President (’04-’06). Until recently, she was the Director of Glass at Philadelphia’s National Liberty Museum where she curated glass exhibits and was in charge of organizing the museum’s annual Glass Now auction. Currently, Anna is a freelance artist and maintains a studio northwest of Philadelphia.

For more information on rubber mold materials for use in glass casting processes, get in touch with the Polytek technical support team:

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

Tek-Tip: Shelf Life & Storage of Polytek® Polyurethane Products

August 12th, 2015

Poly 74-45 - 16 lb Kit - HiResShelf Life

The shelf life of all Polytek® liquid polyurethane products (rubberplastic, foam) is six months from the date of shipment in unopened containers. After this time, the product may either cure improperly or may begin to solidify in the container.

Only purchase as much rubber, plastic, or foam needed for six months and use all of the product as soon as possible once opened (i.e., avoid keeping partially filled containers).



Exposure to Atmospheric Moisture & Water

A primary concern with liquid polyurethane components is exposure to atmospheric moisture and water, which can cause irreversible solidification, especially in Part A. Even if the product has not visibly hardened, it may have absorbed moisture which can cause foaming or an improper cure when the A and B components are mixed together.

Exposure can occur when the lid is left off of the product container, when the lid is placed back onto the container but not sealed well, when there is too much “headspace” in the container and when the product is exposed to water.

Here are some tips to help reduce the risk of moisture contamination:

  • Always tightly reseal lids immediately after using the product (it is a good idea to also clean the rim of container after the product has been poured and before resealing the lid; you can use a solvent like ethanol/denatured alcohol on a clean paper towel).
  • After dispensing the product, spray PolyPurge into the open container before replacing the lid. PolyPurge is a heavier-than-air dry gas blanket that displaces moist air. When the product is in drums, use Drierite® Cartridges.

PolyPurge Dry Gas Blanket_Polytek

  • If there is a large amount of headspace in the container after dispensing, consider transferring the liquid to a smaller container (i.e., a clean metal or plastic container, excluding PVC) with less headspace. As always, use proper personal protective equipment when handling liquid components.
  • Ensure that any fillers added to polyurethanes products are completely dry.
  • Always work at room temperature (~77°F). Working in cold temperatures can slow the cure of the product (or may prevent the cure altogether) which may increase the likelihood of exposure to ambient moisture.



For best results, store liquid products indoors at temperatures between 60°F and 95°F. Long-term exposure to temperatures below and above this range may cause the product to act improperly. Polytek polyurethane products should always be at room temperature before use.


Do you have additional questions about storing Polytek polyurethane products? Ask our technical support team:

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

Marbled Effect in Polyurethane Resin

July 30th, 2015

Marble Resin SwatchAn intrinsic “marbled” look can be a challenge to achieve with resin. It takes experimentation and it is extremely difficult to reproduce the same look/pattern every time.


General recommendations:

– use a fast-setting resin (this may prevent the color dyes from migrating/settling too much)

use a resin that cures to a white/off-white color

 experiment with PolyColor Dyes

 experiment with thickeners to achieve varying effects


In the example below, we show you a general method of achieving a marble pattern in polyurethane plastic.

Supplies needed for the following example:


Step 1: Prepare the Mold

Properly release the mold prior to pouring the casting resin. This PlatSil® 71-30 Silicone Mold does not require any preparation prior to casting because release agent is not necessary when casting polyurethane resin in silicone molds.

Silicone Mold

This mold is of a stair runner architectural detail (typically found on the side of steps). The following is an example of a polyurethane resin cast in this silicone mold without any PolyColor Dyes or fillers.

Stair Rubber - Architectural Detail Casting

Step 2: Prepare All Components

EasyFlo 60 Liquid Plastic has a very short working time (2 to 2.5 minutes), so it’s important to prepare all components ahead of time.

First, measure out Parts A & B of EasyFlo 60 by volume (1A:1B) or weight (100A:90B).

EasyFlo 60 Casting Resin

Next, prepare the PolyColor Dyes desired for marbling. Some may choose to only use PolyColor Black for natural-looking marble striations. Others may choose to use a variety of colors.

PolyColor Dyes are available in black, brown, blue, green, red, yellow and white.

Polyurethane Color Dyes

Pour a small amount of each desired color into individual cups. In this example, we use blue, purple (a combination of PolyColor Red and PolyColor Blue), and yellow.

Prepare PolyColor Dyes for Marbling

Ensure that you have a mixing tool for each color.


Step 3: Mix Primary Batch of Resin

Combine EasyFlo 60 Parts A and B and mix thoroughly.

By mixing in a thickener, you may be able to gain more control over the marble pattern. Thickened resin will not flow as easily, allowing more control of its placement and dispersion. In the following example, we do not add any thickener, but we will show some examples of marbled resin with thickener later in this blog entry.

Part A & Part B - EasyFlo 60 Liquid Plastic

Mix A & B - EasyFlo 60

Keep in mind that the working time of this product is 2 to 2.5 minutes once these components are mixed.
Step 4: Dispense Small Amount of Resin into PolyColor Containers

PolyColor Dyes are reactive; if they are not thoroughly mixed in with the A & B components of the primary casting material, they will not cure properly and may “bleed” out of the cured casting. Do not pour PolyColor Dyes directly into the primary batch.

Dispense small amounts of the primary EasyFlo 60 batch into each of the containers that contain the PolyColor Dye.


PolyColor Dyes - Purple, Yellow, Blue

Add Resin to PolyColor Dyes

Then, individually mix each color.

Mix Resin and PolyColor Dyes

Step 5: Pour PolyColor Mixes into Primary Batch & Pour Into Mold

Pour each PolyColor mix back into the primary EasyFlo 60 batch but do not mix

Dyes for polyruethane resin

Pour the mixture into the mold. Some may choose to pour into one spot and allow the resin to flow across the mold while others may pour the resin into different spots in the mold. The technique used to pour the resin will affect the final look of the casting.

We choose to pour the resin in one spot and allow it to flow across the mold.

Pour Marbled Resin into Mold
Let EasyFlo 60 Cure

When EasyFlo 60 begins to set, it turns from a transparent yellow/amber color to an opaque white color; therefore, the liquid mixture that you pour into the mold will change color quite significantly as it cures.

Allow the Resin to Cure

Let EasyFlo 60 Cure Before Demolding

Close-Up Marbled Resin

Step 6: Demold

After 15-30 minutes, the casting can be removed from the mold.

You’ll also notice that the front of the casting can look quite different compared to the back.

Demold the Casting

Finished Marble Plastic

Close-Up Front of Marbled Casting

Using Thickeners for Marbling Resin

EasyFlo 60 and PolyColor Dyes are both very low in viscosity; some may choose to add thickeners to the resin in order to gain more control of the striations. We show some examples below of the results we got when using thickeners in varying scenarios.

The thickener used in the following examples is PolyFiber II. This product is traditionally used to thicken polyurethane rubbers and plastics for brush-on application.

PolyFiber II Thickener

In the example below, we thicken a batch of mixed EasyFlo 60 with PolyFiber II and then divide that mixture among the cups that contain PolyColor Dyes. Then we add those individual PolyColor Dye mixtures into a batch of EasyFlo 60 that does not contain thickener.

Pouring Resin with Thickened PolyColor Dyes

The colors appear to be more concentrated with this method.
Marbled Resin with Thickened PolyColors

Marbled Resin with Thickened PolyColor _CloseUp

In the example below, we use PolyFiber II to thicken both the PolyColor Dye mixtures and the primary batch of EasyFlo 60. The thickened PolyColor Dye mixtures are added to the thickened EasyFlo 60 primary batch and then poured into the mold.

Pouring Thickened Marble Mixture

Thickened Marble Mixture Casting

Thickened Marble Mixture Casting

In the example below, we pour mixed EasyFlo 60 resin into the mold and then drizzle the EasyFlo 60 + PolyColor Dye mixtures into the resin.
Pour EasyFlo 60 into Mold

Drizzle PolyColor Dyes

As you can see in the final casting, the color dyes did not make their way to the front of casting very well.

Drizzled PolyColor Casting

Drizzled PolyColor Casting Closeup

An important takeaway is that even though the same PolyColor Dyes and base resin are used for each casting, they turn out quite different based on the thickeners added to the resin and the pour technique as it’s poured into the mold.

How to Marble Polyurethane Resin

Marbling Clear Resin

A very different look is achieved by using a clear resin instead of a white resin. In the finished casting, it’s difficult to see the striations without holding it up to light.

Marble Clear Resin\

PolyColor Dyes in Clear Resin

Marbling Poly-Optic Resin

Do you have questions about coloring polyurethane resin? Get in touch with our Technical Support team:

Call us at 800.858.5990.
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How to Make a Rubber “Glove” or “Sock” Mold

July 15th, 2015

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

Rubber Glove Mold-01

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

Materials & Supplies Needed for this Project: 


The Model

The following plastic model will be used for this project.

Model for Glove Mold

Model for Glove Mold - Side View

Model for Glove Mold - Rear View


Step 1: Prepare the Model

Perform a test cure on the model, if necessary.

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

Test Cure with PlatSil 71-10

How to test cure silicone

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

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

Adhere Model to Baseboard

Adhere Model to Baseboard with Epoxy

Allow Epoxy to Cure

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

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

Brush Out Release Agent


Step 2: Measure & Mix the Mold Rubber

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

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

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


PlatSil 71-11 Silicone Rubber - Polytek

How Much Rubber is Needed?

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

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

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

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

We select PlatThix as the thickener for this project.

PlatThix Liquid Thickener for Silicone

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

Weigh Components

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

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

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

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

Add PlatThix Thickener

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


Step 3: Brush Rubber onto Model

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

Brush Silicone onto Model

Brush Silicone onto Figurine

Brush-On Silicone Rubber

Create a rubber flange around the base of the model.

Create Rubber Flange

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

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

Brush On Second Layer

Second Layer of PlatSil 71-11

Allow Second Layer of Silicone to Gel

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

Brush on Third and Final Layer of Silicone

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


Step 4: Make a Mold Shell

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

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

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

Trim Rubber Flange

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

Align PVC Pipe

Secure Pipe Together

Secure Two Halves Together

Foam Mold Shell Form

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

Apply Paste Wax to Inside of Pipe

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

Secure PVC Pipe to Baseboard


Secure Form to Baseboard

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

Ready for Foam Shell

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

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

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

Measure PolyFoam Flexible F-3 Foam Part B

Measure PolyFoam Flexible F-3 Foam Part A

Mix PolyFoam F-3

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

PolyFoam F-3 Expanding

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


Step 5: Demold

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

Allow Foam to Cure Then Remove Pipe

Cut Tape on Pipe

Open PVC Pipe

Remove Foam Nest

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

Remove Rubber Mold from Foam Shell

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

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

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

Spray Silicone Release onto Glove Mold

Spray Pol-Ease 2300 on Rubber Sock Mold

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

Peel Back Rubber Glove Mold

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

PlatSil 71-11 Silicone Glove Mold

Remove Model from Mold

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

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

Key in Silicone Mold and Foam Nest

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


Step 6: Casting

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

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

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

EasyFlo 60 Liquid Plastic Casting

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

Complete Resin Pour

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

Peel Back Glove Mold to Remove Casting

PlatSil 71-11 Sock Mold

Remove EasyFlo Resin Casting from Mold

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

EasyFlo 60 Resin Casting and Original Model

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

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

EasyFlo 60 Plastic and Black Wax

Sculpt Nouveau Wax on EasyFlo Resin

Glove Mold - EasyFlo Plastic - Front View

Glove Mold - EasyFlo Plastic - Rear View

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

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

Rubber Mold Design for Wet Cast Pavers

July 1st, 2015

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

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


Block Mold on Simple Bottom Board

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

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

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

block mold on simple bottom board

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

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



Blanket Mold in a Mold Box

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

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

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

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

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

rubber blanket mold in mold box - polytek

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



Blanket Mold with Flange in a Box

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

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

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

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

Rubber Mold Design - Blanket Mold for Paver

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



Blanket Mold with Locking Flange in a Box

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

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

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

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

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