Using Epoxy Resin For Making Molds – Good or Bad

In general, epoxy resin laminates are considered to be superior when compared to polyester resins. That being stated, epoxy does not produce as hard a surface as polyester tooling gel coat so it is not quite as suitable for mold making. If you are planning on turning out even a small volume of parts, you really want the mold to carry the harder surface provided by polyester resins and gel coats.

Epoxy is also not compatible with ordinary mat so needle mat has to be used in the build up instead. If you don’t have needle mat, you could use cloth but cloth always carries the risk of pattern transfer to the surface of the mold.

I like to spray my resin on larger jobs. While epoxy resin does not carry the foul odor that is associated with polyester resin, it is much more toxic and therefore should not be sprayed. If you are not spraying epoxy you are rolling or brushing it which can be quite time consuming.

Epoxy resins also take longer to cure. Increased cure times combined with the excessive cost of epoxy results in slow production times with increased costs.

The only times that epoxy molds would be preferred to polyester molds are when the production pieces will generate extreme heat during curing. Epoxy is more heat resistant than is polyester. The other situation in which epoxy molds would be preferred over a polyester mold is when fumes are a concern. If you are sharing a shop with others or if there is exposed flame in the shop epoxy would be the better choice.

Keep in mind that many times we default to the more expensive material thinking that using a less expensive material will degrade the quality of the final product. In this case, your mold. That is not always true. I think that by describing the cons of the more expensive material we have show this to be true in this case.

I hope this clears up some of the many questions that I have had regarding the use of epoxy resins for mold production.

Fiberglass Radio Controlled Model Boat

Fiberglass Radio Controlled Model Boat

Happy Glassing


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