I've roughed out a foam plug for some new bodywork working off cad drawings. I've used celotex type low density insulation and i'm now looking to start coating and filling. I was considering covering the foam plug in a fibreglass skin and then building up the finish in layers of polyester primer filler. Can you recommend a suitable cloth and a whether I can use a polyester resin or ?. I have made the plug approx. 3mm smaller than the finished item to allow for a finished build up. ( I attach a photo pre sanding to give an idea of curvatures. Thanks

Always better to do a test using the stuff you've got, there's so many different types of foam it's easy for us to say it will work and then you go and put polyester resin on and it all melts away. Or what I have found with some foams is that the appear to withstand the resin, but 2 days later you are sanding it and the resin just gives way and you find the foam has gone extremely brittle and crumbly. 

Perhaps I'm missing something but why are you going to sand, surely if you have cnc you can finish straight of the mill.




A cool way to work IF POSSIBLE would be to coat the foam in filleting wax and then cnc that as the finished shape then take a mould straight off the wax, anyone tried this?

He didn't mention anything about a cnc? CAD drawings don't mean he is using a cnc machine. 

i've used a cad model and sliced it into sections. Im not using cnc just finishing by hand. Really looking for the simplest and tightest way to form a hard skin on the foam so that i can build my finish on. I had heard about mixing micro balloons with resin and painting it on rather than using matting but not sure if this would form a hard enough skin to work off? Thanks 

I would think about a single light layer of fibreglass, either a tissue/vale fibre glass, a light CSM or a light glass cloth.

If your foam is a ridged polyurethane then you can use polyester or epoxy resin.

If your foam is something like a polystyrene or Styrofoam then you can only use epoxy. Styrene resins will dissolve it.

Like Hanoldo said, test a bit of your foam first.




It's a bit risky to try and paint straight onto foam as you need to sand the surface, if it gets too thin then it just digs into the foam and makes a hole. Better or safer/easier to have a hard surface behind the paint.

Hi

Thanks, it looks like a light cloth and epoxy resin might be the safest option if not the cheapest. If i was to use the polyester pattern coat system does it give a hard enough surface to work off or do i need to combine it with some matting? Thanks for the replies .

p.s the foam is celotex insulation , a low density polyurethane foam.

Hi