I asked these questions on my WIP thread already, but I am hoping on buying the rest of the supplies needed for my terrain piece, tomorrow. So I am also posting them here.

Will PVA glue dissolve expanded foam? Will it be strong enough to glue together layers of foam? If yes, then will slightly watered down PVA be adhesive enough? And finally does the black spray paint have an unwanted effect on expanded foam?

The pieces of foam I'll be gluing together are pretty big, and I want permanent adhesion.

I am very very grateful for your replies. The project I will be working on is an Erebor mountainside. You will can find pictures of my progress so far, i my WIP if you are interested.

Thanks again for your time. (All advice given in this topic will benefit the everlasting kingdom of stoic Dain and/or Durburz the magnificent.)

PVA won't dissolve Expanded Polystyrene but spray paint certainly will - creating some rather unsavoury fumes. I wouldn't recommend using PVA for gluing Polystyrene together. I used No More Nails and a Hot Glue Gun (the later melts the foam slightly but it's just melting, not dissolving.)

Hmm, so I will just paint it the regular way. Is PVA not strong enough for layers of expanded foam? I would wish to minimize my project's cost as much as possible and due to past experiences, I am a bit timorous when it comes to buying new modeling products.

Isn't there an alternative that will not affect the foam in any way?

Thank you. You saved me, I was planning of buying spray paint lol.

By score you mean pinning them together? I was considering using toothpicks for that.

And one final question, (forgive a terrain-making newbie), I will prime the whole piece black. In order to economize I will obviously not be buying GW black paint. I am planning on buying a black primer from the local supplies store.
Are all primers safe to use on expanded foam? The last thing I want to happen is buying a cheap primer only to find out that the foam reacts badly to it.

Go but the cheapest black paint you can find. As long as it is not spray paint. The propellent in spray paint will eat right through the foam. Go to a home supply store and buy a quart of cheap black paint. Pour some into a mixing cup and add a few ounces of sand into the paint. Mix it up throughly. If you are adventerous, buy some Woodlands Scenics (or any brand) model railroad ballast and mix that in, too. It will give your terrain the appearance of a rocky area. Use a large disposable brush and slop it all over. The hardest part of this project is waiting for everything to dry throughly. After painting the foam, let it dry for 24-36 hours. This will create a hard shell over you terrain boards.

PVA will not hold large pieces of foam. PVA needs air to dry and if the glue is covered by foam it will never set completely. If you are stacking foam, one on top of another, you need the Liquid Nails glue that is made especially for foam. You can usually pick up a tube at the same place that you purchased the quart of paint. One tube will last you forever.

I have made hundreds of terrain boards and I have found that this is the best way to go. Others may have a better way, but this works for me.

Thanks for your advice mate. It was most enlightening. I hadn't thought of mixing the paint with the sand. My only concern is that since I leave in Greece I may not be able to find the brands of glue that all you folks are recommending.

I more question if I may. I am planning on basing the whole piece on thin styroboard for extra protection. The last time I glued little pieces of foam on styroboard, for some reason the styroboard curved. The base (of the wall I was making) actually became a bit convex! I do not want the same thing happening again. Is there a way to avoid it?

Thank you again,

Styroboard = foamcore?
You must use something that wil not warp. Use MDF or hardboard. Make sure that you paint BOTH sides of the MDF or hardboard first. This will prevent any kind of warping.

There is a product called GATORBOARD, which is a heavy duty foamcore, that will not warp. It cost a few bucks more than regular foamcore, but it is well worth the extra money.

I know you live in Greece, so do a search and see if you can get Gatorboard
locally or have it shipped to you.

Yeap, by styrofoam I meant foamcore.
I will follow your advice and use hardboard. Just out of curiosity, do you know the reason why paint prevents it from warping, and why foamcore warps?
Thank you so much for your advice!

The quick answer is that paint shrinks as it dries. So, as the paint shrinks it tightens and casues the foamcore to warp. That's why you need to paint both sides, so that you have equal shrinkage and no warps. Even MDF or hardboard will warp if you don't paint both sides.

Hmm the foamcore I used warped after I glued foam on it but before painting it. Then the glue must shrink as well, causing the foamcore to warp. But if this is the case the side of the hardboard which has glue+paint will still receive more pressure than the side which just has paint.

Yes, the glue shrinks and causes warping. Foamcoare will warp because it is not rigid. MDF or hardboard will warp if you glue foam to it also, but not as much. If you paint both sides of the Hardboard, you are coating both sides. Wood is porous. Once you paint the wood, it is no longer porous and therefore what casues the wood to warp, has been defeated. It won't warp as badly, if at all.

Nevinsrip, and everybody else, once again thank you for your advice. It has been invaluable.

The couple times I've done this sort of thing, I've been sure to paint both sides of the MDF at the same time, thinking that if you did only one at a time you'd risk warping still.

Was that overkill or was it really needed? I'll admit, it was more messy. Also, I don't worry about this for any MDF base smaller than about 6" - 8" across.

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Wait ye the finish! The fight is not yours.
Beowulf

http://TacticsInMiniature.com

Better safe than sorry. My hardboard base will be much larger than this, about 60cm x 50cm.

I think it's very sensible to paint one side and then the other with PVA. This balances out the warp (if there is any) and seals the whole thing at the same time. I think Beowulf and Nevinsrip are right about this.

I've never done a large board for hobby use but I imagine the extra size makes any warping worse just like a large sheet of wood used for DIY will warp easier than a smaller piece.

It's always better to prepare properly for terrain making just like you would for a mini. There is no rush if you want a top class result - just chill and take your time.

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Careful with that axe of yours... Dain!

Azog

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