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Bluestar Silicones & pathwaypolymers

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Por-A-Mold systems consist of two components; a curative and a urethane prepolymer. The ingredients of the Por-A-Mold system are compounded with extreme accuracy and subjected to stringent quality control before they are approved for shipment to our customers. The absorption of moisture by either side of Por-A-Mold will change the chemistry of the reaction and could result in improper cures. For this reason it is essential that the containers be sealed when not in use. The curative contains fillers which will settle out on long standing and requires thorough mixing before use.


Por-A-Mold is designed to be used in a ratio of one-to-one by volume for simplicity of measuring in the sculptor's studio or the foundry. Deviations from a one-to-one ratio could result in improper cures. Exercise reasonable care in measuring the quantities of each component. Large batches of Por-A-Mold react faster and have a shorter working life than small batches. We do not recommend mixing more than one half gallon of each side at any one time by hand.
For production mold makers or foundries that have a requirement for pouring large molds (250 to 2500 pounds at any one time), Pathway Polymers has developed the MCP 7200 dual component pump which blends the material through a static mixer with considerable savings in both time and material.

The normal working life of approximately 20 minutes will be substantially shortened if batches of more than one gallon (4 liters) are mixed at any one time by hand. Also be aware that room temperature affects working life. The warmer the material, the faster it will react. It is advisable to store Por-A-Mold in a cool dry place. The recommended procedure is to measure equal volumes of curative and prepolymer in two separate clean (preferably plastic or plastic lined) containers. The prepolymer container should have at least twice the capacity of the curative container. Transfer all the curative to the prepolymer container and stir gently but thoroughly.

Por-A-Mold curative and prepolymer are formulated with different colors. This is to enable you to tell when the two components have been thoroughly mixed. If you see color striations while blending the two components, you know that mixing has not been adequate.

Continue mixing gently, occasionally scraping the container side, until a uniform color develops. Stir slowly to avoid beating air into the mixture which will result in a porous mold and poor reproduction. The Por-A-Mold resins will adhere to the sides of the mixing vessels and must be gently scraped off the sides to insure that all the ingredients are equally mixed. Failure to do so could result in uncured tacky spots on the mold as a result of scraping unmixed material into the mold cavity when trying to get the last bit of mixture out of the container.

Por-A-Mold, like all urethane systems, is sensitive to moisture and will react with water to form carbon dioxide gas which on expansion causes the material to foam at the point of contact with the moist area. Por-A-Mold is a balanced formula and requires equal parts of curative to combine with equal parts of prepolymer. If a portion of the prepolymer reacts with water, it is not available to combine with the curative. Unreacted curative is a sticky resin. In addition to foam around the area of wetness, you will also have patches of uncured resin. Por-A-Mold cannot be used on wet plaster, wood or papier-mache. Masters must be dry, sealed and treated with a suitable release agent such that the cured Por-A-Mold can be removed intact from the master to give usable and perfect reproductions of the surface.

The surface of the master (and the mold box) must be dry and sealed with a thin coat of spray lacquer or fast drying enamel. Time should be allowed for the sealer to dry thoroughly before applying the release agent.

A good release agent should be used that can be applied in a very thin film such that the integrity of the surface to be reproduced is not destroyed. Por-A-Mold will reproduce the finest details in the master. If the releaseagent is applied in thick uneven layers with visible application lines or marks, they will be reproduced in the Por-A-Mold finished mold. We recommend Synlube 531 aerosol release agent from Pathway Polymers 
when using Por-A-Mold/Por-A-Kast systems.

These products have been tested in our laboratories with Por-A-Mold. We recommend that you test any release agent you select on the particular surface to which it is to be applied. One, to test the release agent compatibility with the sealer; and, two, to test the release characteristics with Por-A-Mold. See Product Bulletin Number 90-05.

If Por-A-Mold is to be poured into a mold box without degassing the blended material immediately after mixing, it is advisable to pour slowly into one corner of the box allowing the material to flow gently up the side of the master. Tapping the side of the box or applying a vibrator will move entrapped air to the surface.

When using a thixotropic mixture of Por-A-Mold to build up the model, it is recommended that for precise reproduction of the master model surface, an amount of regular Por-A-Mold sufficient to coat the entire surface be brushed onto the master model or instructions outlined in Product Bulletin Number 90-02 be followed. This will insure that the entire surface is covered and no air bubbles are entrapped. Allow this first application to gel before building up the thickness of the mold by troweling Por-A-Mold TA over the master model. See Product Bulletin Number 90-02.

If the temperature in the studio is below 70°F, it is advisable to warm both the material (before blending) and the master model. A small piece can be warmed in an oven, large pieces can be warmed with an electric blanket or a space heater placed at an appropriate distance from the master model.

Depending on the temperature of the material, Por-A-Mold systems can generally be poured up to twenty minutes after blending the two components. The curative and the prepolymer start reacting immediately upon being mixed and continue to increase in viscosity until the mixture gels, at which point it can no longer be poured. The mixture is at its lowest viscosity immediately after mixing.

Curing is a function of temperature. At normal room temperature, 72°F, allow the mold to cure 12 to 24 hours before demolding. The mold will reach its ultimate strength and hardness in two to three days. If you can tolerate a shrinkage of about 1%, curing time can be accelerated by heating the mold mixture at elevated temperatures up to 160°F for three hours.

Por-A-Mold is an excellent mold making system. Used with reasonable care it will give you long lasting molds that will not shrink or soften with age.


The conditions for your use and application of our products, technical assistance and information (whether verbal, written or by way of production evaluations), including any suggested formulations and recommendations, are beyond our control. Therefore, it is imperative that you test our products, technical assistance and information to determine to your own satisfaction whether they are suitable for your intended uses and applications. This application-specific analysis at least must include testing to determine suitability from a technical as well as health, safety, and environmental standpoint. Such testing has not necessarily been done by Pathway Polymers. All information is given without warranty or guarantee. It is expressly understood and agreed that customer assumes and hereby expressly releases Pathway Polymers from all liability, in tort, contract or otherwise, incurred in connection with the use of our products, technical assistance and information. Any statement or recommendation not contained herein is unauthorized and shall not bind Pathway Polymers. Nothing herein shall be construed as a recommendation to use any product in conflict with patents covering any material or its use. No license is implied or in fact granted under the claims of any patent.