Sealing EPS and XPS Styrofoam with polyester or epoxy

EPS (Expanded Polystyrene Foam) and XPS (Extruded Polystyrene Foam), better known by the names Styrofoam, Roofmate, insulation board or the like is an inexpensive material from which objects can easily be cut with, for example, a hot wire cutter, but also with a knife or saw or with sandpaper. Styrofoam, however, is quite soft, so it is easily damaged. It also does not have much strength.

To reinforce EPS/XPS Styrofoam or Roofmate, a glass fibre covering can be applied with polyester resin or epoxy resin. It is important to use a special polyester resin, as ordinary polyester resin will corrode or even dissolve the Styrofoam completely. Of course, we have this special polyesterhars for Styrofoam in our range.

Polyester or epoxy?

Working with polyester

The advantage of polyester is that it is easy and fast to use. Moreover, glass mats can be used, a type of glass fibre that is easy to work into awkward shapes. Polyester is therefore the first choice when it comes to objects with a lot of detail. Polyester can be finished with  polyester topcoat (this gives a small amount of structure), with  Double Coat Paint (applied to a sanded and filled surface, this gives a tight finish) or with various industrial lacquers or acrylic lacquers to give the object certain effects.

Working with epoxy

Epoxy can be applied in combination with glass fabrics. These are divided into plain (square) fabrics and twill fabrics. The plain fabrics are ideal for flat shapes, while the twill fabrics are easy to bend over curved shapes. Epoxy can be finished with Double Coat lacquer or various industrial lacquers or acrylic lacquers to give the object certain effects.

In general, an epoxy layer can be applied somewhat thinner than a polyester layer, which keeps the weight to a minimum. However, processing takes a little longer and curing also takes longer than polyester resin.

Covering EPS/XPS Styrofoam/Roofmate with polyester resin

Make sure the object is clean and dust-free. Mix the special polyester resin for XPS/EPS with sufficient hardener and brush or roll it over the Styrofoam object. Then apply a layer of glass mat. Now apply more resin. The glass mat will become transparent. Brush or roll the glass mat over so that it is all over the Styrofoam or Roofmate object. Shiny spots have too much resin, white spots need more resin. Next, use a vent roller to properly vent the glass mat. The fibreglass and polyester layer can now cure.

After curing, the object can be further coated with more glass mat and polyester resin. You no longer need to use a special polyester resin for EPS/XPS for this; you can now laminate with the standard polyester laminating resin.

The object can then be finished as desired (with polyester topcoat or Double Coat lacquer) or with any other desired finish.

Covering EPS/XPS Styrofoam/Roofmate with epoxy resin

Make sure the object is clean and dust-free. Mix epoxy resin with the corresponding hardener and apply it to the Styrofoam or Roofmate. Lay a glass fabric of your choice in the wet resin and apply more epoxy with brush or roller. The glass fabric should become completely transparent. Batten white spots again. Shiny spots have too much resin. It is easy to spread the resin with a laminating spatula. Now vent the layer with a vent roller. Roll over the laminate with the roller, pushing air bubbles out of the laminate.

Apply several layers in this way as required. The object can now be finished in various ways, such as with Double Coat DD Paint, or with other paints.

Frequently Asked Questions:

How many layers of glass mat or fabric should I apply?

This depends on the desired strength. An object that is not exposed to forces, such as an ornament, can be finished with one thin layer, for example 1 layer of fibreglass chopped strand mat 225 gr/m2 when working with polyester or 1 layer of glass fabric 300 gr/m2 when working with epoxy.

An object that has to withstand some forces can be finished with 2 layers of fibreglass chopped strand mat 450 gr/m2 and polyester resin, this gives 1 mm layer thickness per layer of fibreglass chopped strand mat 450 gr/m2. If working with epoxy, 2 to 4 layers of glass fabric and epoxy can be used. This gives 0.5 mm layer thickness per layer.

For objects subjected to high forces, such as playground equipment, several layers, sometimes up to 10 layers, can be applied, often fibreglass chopped strand mat 450gr/m2 with polyester resin.

Can I spray an image onto the polystyrene foam before applying glass fabric?

Yes, this is definitely possible. This is done a lot on surfboards and kiteboards. If you want to apply a transparent finish, choose the glass fabric 160 g/m2 or glass fabric 300 g/m2 and transparent epoxy coating.

 
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