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When making tabletop gaming scenery from foam tiles (for example: XPS insulation tiles, or generic polyurethane foam sheets brought from a hobby store), is there a good way to make it more resistant to damage from general wear and tear, if heavy metal models are knocked over when the table is jogged, or during transport?

For example coating it in a particular type or resin, using a lacquer\varnish, or some other readily available substance.

Is it better to coat it and then paint over the top, or to apply a transparent coating after painting?

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    Can you be more specific about what kind of "foam tiles" you're using? I don't know what specifically would be a "foam tile," and there's a large variety of foams available, all of which may require a different answer.
    – Allison C
    Oct 4 '21 at 13:36
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    I've updated the question to specify PU or XPS tiles, and that the damage would be from heavy models or transport. Most foam tiles used in table top gaming fall into this range. Oct 5 '21 at 17:08
  • @fixer1234 If it were soft and spongy how would it dent?
    – rebusB
    Oct 5 '21 at 18:01
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PVA glue can make the foam much more dent-resistant. If you use polystyrene foam, many coatings and finishes will attack it. The usual method to protect the foam is to first coat it with a layer of PVA glue. A single paint-like coating of the glue will provide chemical protection if you get complete coverage. Multiple coatings (three or four generous coatings, waiting for each layer to dry before adding the next), will be thick enough to create a tough plastic shell on the foam that will be generally resistant to minor dents and dings.

PU is much more resistant to chemical attack by coatings and finishes, and is a lot tougher than PS foam, and less susceptible to dents and dings. But you can still use PVA glue to create a physically protective shell.

You can make the shell even stronger and tougher by reinforcing it. The question refers to foam tiles and sheets, so I assume the surface is flat.

Thin the PVA glue a little with water, saturate a piece of kraft paper or paper towel, and apply the paper to the foam (thin the glue enough so it soaks in and saturates the paper, but no more than an equal amount of water). One continuous layer of either of those kinds of paper should be enough for dent protection. Two layers of newspaper would also work (wait for the first layer to dry before applying the second).

This is paper mache, which is really tough stuff. When it's dry, coat it with another layer of glue.

Instead of paper, you can use a piece of cloth (natural fiber, like cotton), such as an old bed sheet, following the same process.

A shell reinforced with either paper or cloth will make the foam nearly immune to the kinds of dents and dings you're concerned about. You can paint the surface with almost any kind of finish.

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Another option is to use EVA foam. It will bounce back undamaged. That's what a lot of craft foam is. Cosplay foam is the same stuff but slightly denser (i.e. firmer) and comes in a wide range of thicknesses. You can also get floor mats made of EVA foam in 30cm/12" interlocking squares (and occasionally half that size). The "top" is usually textured, but the back is more often smooth.

EVA can be painted directly with acrylics, though priming can be useful as well. It's a little more expensive than PU foam, but if you're reusing the scenery repeatedly it would be well worth the extra cost.

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