Plastic coating foam and expanded polystyrene pieces

Plastic coating your Plastazote / EVA / Polystyrene foam / cardboard props and costumes

Foam building is great because it’s quick and clean, and you can get compound curves in the foam by heating it, which saves a lot of trouble sanding and filling paper based Pepakura props. However, once the foam is painted it still looks a bit like painted foam which is ok for some props, and I’ve seen some good foam suits, but it would be ideal to coat the foam with a rigid plastic coating so it can be finished and painted like a plastic or fibreglass suit.

I’ve used a lot of Polyurethane resin for casting costume pieces, but I’ve found that it doesn’t stick to Plastazote foam well, and it will melt Expanded Polystyrene foam. So we need some sort of primer that you can coat the foam with, which will also stick to the Polyurethane. The answer is PVA.

PVA is white glue/wood glue which can be purchased cheaply from most DIY/home stores and craft shops. It will stick to Expanded Polystyrene, Plastazote, EVA foam, cardboard, and many other materials. This acts as the perfect primer for Polyurethane fast cast resin. Here is some testing I did with a sample of Plastazote and Expanded Polystyrene.

Firstly, three coats of PVA were applied to the samples, note that PVA dries clear:

Once it had dried, I brushed two coats of Smooth-on 65D over the top surface. PVA is water soluble so if you touch it with a wet finger it gets sticky again. I’m pretty sure this means that Polyurethane resin applied in liquid form will bite into the surface and stick fast.

You can see here that it has run off the edges, if I’d continued to rotate the piece as the resin set, then it would have evenly coated the piece – you can see a better example in the YouTube video below.

After a light sand, priming and painting with standard rattle cans, you can see the results below along with a comparison of the finish with painted foam from by Iron Man foam build. Obviously, since the surface is plastic you can fill any gaps with car body filler and sand it smooth to finish it as perfectly as you like:

Here’s a YouTube video showing the entire process of plastic coating a more complicated piece: