Can my epoxy part be used outdoors for exterior applications?

Article courtesy of Smooth-On, Inc.

Smooth-On Epoxy products that are fully cured (and do not contain additional additives) are suitable for interior and exterior use.

These materials are not UV resistant and for exterior applications will need to be primed and painted for best results. Testing for compatibility with your specific paint is recommended. Castings can be displayed outdoors after painting with an aliphatic urethane clear coat (such as Axalta Imron 3.5 Plus High Gloss Polyurethane Topcoat available at

Exterior parts require a minimum thickness of 3/8 inches.

There are many variables and challenges that can contribute to the success of an exterior application and it will be up to you to determine suitability for your project. A small scale test is always recommended to determine suitability for you environment and project needs.

An awareness of the extreme temperatures (highest and lowest temperature) that your installation site or exterior location can reach can be critical to success. You will need to know these values to select a product for testing with an appropriate heat deflection temperature under the maximum temperature for your location. Some Epoxy products offer a higher useful temperature range which may be better suited to your unique environmental conditions. The observed tested values for each Epoxy material can be located on the Technical Bulletin at our document library at and on the Material Specification Charts at

Freezing and thawing conditions are also a potential challenge for exterior applications. To reduce the potential for moisture to enter the interior of your part, make sure your part is closed off and any interior supporting substrates are completely encased in Epoxy. Interior Armatures can expand/contract during freeze thaw conditions. Do not allow moisture inside the interior the part as this can cause cracks and break the piece over time due to expansion during freezing and thawing.

Another challenge for exterior applications is that rigid Epoxy materials are brittle and can break, crack, or easily shatter in high wind environments without additional reinforcement for added strength. For a stronger (or thin section) Epoxy part the EpoxAmite Series can be used to laminate Fiberglass, Kevlar, and Carbon Fiber reinforcement. You can learn more about these Epoxy Laminating Systems at the following link:


This FAQ article is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Safety Data Sheets (SDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.