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I recently acquired some plaster or paris and mould making materials. I have always wondered about casting some nice castle, ruins, terrain, or even a few bitz and needed some advice on how to go about it. I looked around the site and either found info on the resin or pump needing versions but couldn't find any on the sit-an-set variety. It appears that the pour and wait method isn't optimal for making things but that is what i have to work with. If anyone has any advice, comments, or direction on this it's greatly appreciated. Note: This is not the area for legal advice or criticism, don't go there .

Resin casting (more than simple single sided moulds, requires more and different methods than plaster-casting.

As far as mould* making goes, the principle is the same.

You also shouldn't have the same issues with bubbles as resin (which is partly a chemical thing and partly from mixing).

* We use 'U's in these words the same way we use that extra 'I' in aluminium. You Americans spell this 'mold' (which my spellchecker tags as 'wrong'.

You might also check out Hirst Arts website. A lot of really good moulds and casting advice there.

Thanx for the nice links so far, really helping with the mold part.

Does anyone know of any thickening agents that could be added to the plaster of paris to make it stronger or less brittle?

Plaster is brittle there is in my recollection any way to strengthen it but you might try Durhams rock hard water putty if you want something stronger.

chromedog wrote:the same way we use that extra 'I' in aluminium.

but you are supposed to say the extra I in Aluminium... "Aluminum" is a lazy word...

I don't think there is a way to make Plaster of Paris less brittle to the point that it is appropriate for making wargaming scenery - it would suck to make a great piece, and paint it, only for it to look awful a month later with chips and scratches. I'd suggest using the PoP for filler as well as "proof of concepts" to see how a piece might look, and using dental plaster for the actual gaming pieces.

http://www.hirstarts.com/casting/dental.html has some info.

As Ouze points out, you're better off using dental plaster - I have some terrain made from the stuff and it's very resilient. I also have some terrain cast in plaster of paris (dragons teeth tank traps moulded from an ice-cube tray) and it requires a lot more careful handling.

Whichever way you do it, do colour your plaster, because it will be much easier to hide chips and scratches that way.

I heard once (and have never tried it, so you will want to test it) that adding PVA glue to plaster of paris made it harder (although it takes AN AGE to dry). And, yes, tint your plaster.

A good option for a castle might be to mix up a batch of gray-tinted plaster and pour it into a shallow tray (about an inch deep) and then - while it is still soft - cut it into "blocks o' stone" and let these dry fully. You could then use these to build an actual castle, like Legos. We did this for a display board once, and it works quite well if you time it just right. If you let stuff set too long, you break it up with a hammer and make rubble.

You'll want to grease the tray with something, and possibly have a tray with removeable sides.

Most of the questions are already answered:
-plaster of paris is too weak for gaming terrain
-Durhams is a good (if expensive) substitute
-Look for Hydrostone/Ultracal30 at your local concrete supplier
-order dental plaster/Excalibur/Merlin's Magic if you can't pick up Hydrostone locally
-no need for a vacuum chamber/pressure chamber when working with plaster
-Hirst arts will have all of this info and more

If you don't have RTV molds, cast your plaster in large sheets 1/4 to 1/2 inches thick. Cut it, score it, carve it. Plaster is a very willing material to work with. With the harder plasters, just be sure to use fresh cast plaster (24 hours old) to insure workability.

Project example start to finish:
http://chicagoterrainfactory.wordpress.com/2007/04/05/ruin-stone/
http://chicagoterrainfactory.wordpress.com/2007/04/24/ruin-stone-5/