Covering EPS and XPS Foam With Epoxy
EPS (Expanded Polystyrene) and XPS (Extruded Polystyrene), often referred to as styrofoam, Roofmate, or insulation board, are cost-effective materials that are easy to work with. They can easily be cut with a hot wire cutter, knife, saw, or even shaped with sandpaper. Because styrofoam is soft, it is vulnerable to damage and lacks structural strength.
To strengthen EPS/XPS styrofoam or Roofmate, a fiberglass skin can be applied in combination with epoxy resin. In this article, we explain how to reinforce styrofoam with epoxy resin.
Please note: Do not use polyester resin, as it will attack or even completely dissolve the styrofoam.
What are EPS and XPS?
EPS (Expanded Polystyrene) and XPS (Extruded Polystyrene) are two commonly used types of insulation materials that both belong to the polystyrene family. They are characterized by their light weight, thermal insulation properties, and versatility. Both materials are widely used in construction, shipbuilding, and DIY projects.
- EPS
EPS, commonly known as expanded styrofoam, is made by expanding small polystyrene beads using steam. These beads are then fused together into a lightweight foam material with an open-cell structure. The material is easily recognized by the individual foam beads that form it. EPS is frequently used for packaging, insulation panels, and decorative objects.
- XPS
XPS is produced by extruding polystyrene under pressure into a closed-cell structure. This process results in a smoother, stronger, and far less water-absorbent material. XPS is popular in applications requiring higher strength and water resistance, such as foundations, floor insulation, and protective structures.
What is the difference between EPS and XPS?
Although EPS and XPS are made from similar base materials, there are key differences that determine their suitability for various applications:
-
Cell Structure and Strength
- EPS: Open-cell structure, making it less strong and more susceptible to water absorption.
- XPS: Closed-cell structure, providing higher compressive strength and superior moisture resistance.
-
Moisture Resistance
- EPS: Can absorb water over time, which may reduce its insulating performance and make the material vulnerable during prolonged exposure to moisture.
- XPS: Significantly lower water absorption, making it far better suited for damp or underground applications.
-
Insulation Value
- EPS: Good thermal insulation, but often slightly less efficient than XPS per unit thickness.
- XPS: Higher thermal insulation value per cm of thickness thanks to its closed-cell structure.
-
Cost
- EPS: Usually cheaper, making it an attractive option for budget-conscious projects.
- XPS: More expensive due to the extrusion manufacturing process and improved material properties.
Working with Epoxy Resin and Reinforcement Fabrics
Epoxy resin is commonly used with fiberglass fabrics, which are available in different weave styles: plain weaves and twill weaves. Plain weave fabrics are ideal for flat surfaces, whereas twill weave fabrics drape better over curved and complex shapes. Once cured, epoxy can be finished with Double Coat paint, industrial coatings, or acrylic paints to achieve the desired finish.
An advantage of epoxy resin is that it can be applied in a thinner layer compared to polyester resin, resulting in a lighter finished product.
Coating EPS/XPS/Styrofoam/Roofmate with Epoxy Resin
Follow these steps to coat styrofoam with universal epoxy resin:
- Ensure the object is clean, dry, and free of dust.
- Mix the epoxy resin and hardener at the correct ratio and thoroughly stir for 3 minutes.
- Apply the mixed resin onto the styrofoam or Roofmate.
- Lay your choice of woven fiberglass fabric into the wet resin and apply additional epoxy using a brush or roller until the fabric turns completely transparent. White patches indicate dry spots — apply more resin there. Shiny pools mean too much resin — spread excess resin using a laminating squeegee.
- Use a washer roller (bubble buster) to remove trapped air bubbles from the laminate.
- Apply additional layers as required.
Once the epoxy has fully cured, you can finish the object with Double Coat DD Paint or another suitable topcoat of your choice.
Need More Information on Coating Styrofoam?
Do you have questions about reinforcing styrofoam with epoxy? Feel free to contact our product specialists. We are happy to provide expert, honest, and tailored advice with no obligation.
