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I recently bought that stiff pink foam insulation board to use for a armies on parade board. Do I need to put a primer paint over it? If so, what kind would work best for that? Additionally, what is the best knife for carving this stuff?

So I have done a lot of terrain work with foam. If you are going to paint it with rattle can be careful not to melt it. Make sure you seal it with some watered down pva glue. (This won’t completely protect it from spray paint). But it will give the foam a measure of protection from bumps etc.

As far as cutting. A good xacto knife works well or a wire cutter I have used both. I have even gone so far as to use a good 9 inch kitchen knife. I was trying to match some previous terrain and had to carve huge swathes out of the foam.

I wouldnt say you need a primer to get your paint to stick. That gak is really porus and adhesion shouldnt be a problem. But you might want to prime just to stop it from soaking up the paint.

Spray primer will melt foam, so you will need to use some brush on paint to seal it before you use any spray can paint. You can get fairly cheap small cans of paint at a hardware store, and you can even get it matched to a color you already have. The paint is pretty thick, so it's only really good for terrain or big projects.

Alternatively, you could use an airbrush to put on the primer coat, but avoid spray cans at all costs until you seal it with a primer coat.

For cutting foam, three options:

1) a hot wire cutter. Neat, tidy, smells a little. Costs a bit.

2) a REALLY sharp meat carving knife. Use a gentle sawing motion and little pressure to get cleaner cuts. Resharpen knife with a whetstone very regularly, it will blunt like crazy. Pointless unless you know how to sharpen a knife. Likely to make a bit more mess as the knife blunts.

3) coping saw. Very fast, very, very messy.

You'll need to seal the foam prior to painting. A couple of good coats of PVA should do it, then texture as normal before priming. Don't forget to seal up side edges.

winterdyne wrote:
For cutting foam, three options:

1) a hot wire cutter. Neat, tidy, smells a little. Costs a bit.

2) a REALLY sharp meat carving knife. Use a gentle sawing motion and little pressure to get cleaner cuts. Resharpen knife with a whetstone very regularly, it will blunt like crazy. Pointless unless you know how to sharpen a knife. Likely to make a bit more mess as the knife blunts.

3) coping saw. Very fast, very, very messy.

You'll need to seal the foam prior to painting. A couple of good coats of PVA should do it, then texture as normal before priming. Don't forget to seal up side edges.

I was a little confused when you said hot wire cutters cost a bit. Mine is basically 2 D-cells in a tube with a wire and a support arm, and can’t have cost me more then $20 when I picked it up (which admittedly was a while ago)



But a quick google shows that they do make some much nicer ones that plug in and have options which are in the $100+ range. But also a cool little one that only costs $35, plugs in, and has a straight wire, without the frame to get in the way. I’m sure some more in depth research would yield more options. So getting an entry level tool is not unreasonable.

When I was working my foam project I used knives, both serrated and straight, and the hot wire cutter. The wire was hands down the best tool for the job.

I paint my foam buildings/terrain with wall emulsion! It’s cheaper, doesn’t melt the foam, then you can work details in with acrylics and finally I spray with clear laquer.
I have a tin of black and one of eggshell blue, which mix to a nice grey, so I do an undercoat with black (which sticks to the foam fine) then dry brush with mlifhter and lighter mixes of grey.
Admittedly I’m almost entirely doing stone outcrops and stone buildings, but it would work fine with greens and browns too.

I cut my foam with a Stanley knife and a scalpel, but I’m after clean edges mostly. Sometimes I attack it with a really coarse file or even claw at it with my nails haha!

The aerosol/solvent present in spray cans will corrode the foam. It can actually work for you if you're going for bumps, but in the end, the finish is messy (as in it doesn't get primed well).

Your options are as suggested:
1. airbrush
2. tempera paint w/ paint roller
3. wall paint w/ paint roller

As for cutting, for square cuts, I prefer blades over heat wire. Just make sure the blade is sharp and angled as low as possible to prevent the foam from 'biting'. Heat wire, although convenient, is hard to maintain the straightedge over long spans (say, you're trying to cut a 4'x4' board) and has a very little tolerance to errors. You gotta go in one shot with 0 shaking or else the edge will be ruined.

For free hand for cliff edges, get yourself a handheld heated wires - it costs $15~$30 depending on the type/brand.

What kind of scene are you trying to make with the foam?

Cutting foam you can pretty much do it with one of those cheap snap off knife or even a serated bread knife though the last one will leave a giant mess.

You can glue foam together with PVA though iv seen a lot of rail road people use the expanding gorilla glue using books to keep the pieces together

You can rough cut the foam with the knife and if you want to smooth or texture it down you can use a metal wire brush to smoothing out parts really quickly then go over that with sand paper (also makes a massive mess)

The classic way of sealing and painting foam would be to coat it in a layer or two of PVA (you can also add your texture then) after which you should be able to prime and paint as normal. (dont forget the edges.)