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I have recently been interested in terrain modeling, to make something similar to the stuff at dwarven stone and castlemolds. I have found plenty of information on how to cast terrain models, but I can't seem to find any information on how to make master models for terrain, and how to create molds for them. Can anyone help me?

It is fairly easy to make one piece moulds for casting resin.

Two piece moulds are a bit more difficult but the main barrier is not the mould so much as creating a good master piece to create it.

There is an article here... http://www.dakkadakka.com/wiki/en/Simple_Two-Piece_Mold_for_Casting_with_Resin

I cast the bases of my Termagants using a one piece mould I made with silicon rubber liquid moulding materials. I used a two part silicone rubber for the mould -- Rapimould Addition Cure RTV Silicone. The resin was Polyurethan Fast Cast. It is very runny and fills the mould easily, and sets quickly.

I got my rubber and resin from Tomps, a UK company (I am in the UK). I am sure there are plenty of companies in the USA who supply similar materials.

http://www.tomps.com/

Here are my top tips for moulding and casting.

1. Mix the mould silicone carefully and don't get air bubbles into it. If using the liquid type which takes equal amounts of both components, you can judge the amount by eye.
2. Make sure the mould is completely dry, as water reacts with the resin and makes it foam.
3. If the resin needs to be weighed for mixing, get an electronic bathroom scales so you can weigh accurately.
4. When mixing the resin, do it thoroughly but gently, to avoid air bubbles.

I found I needed to mix a minimum of 40g of resin materials, to be accurate enough to let it set properly. This was enough resin to fill five of my small moulds and have a bit left over.

Lastly, remember that these moulding and casting chemicals can be poisonous, so make sure to read the safety precautions.

Go to Hirstarts.com. There is a world of info there on casting and making molds. I have used Smoothon
Moldmax 30 an it works very well.

Hirstarts has a bunch of good articles and tips on hobby casting in plaster and resin. Like Kilkrazy said, it seems making a suitable master is more problematic than actually making a decent mold. Be aware of the limitations of your mold material - some are quite flexible but relatively weak, while others will last forever, but are rather stiff - this will govern how deep and numerous the undercuts it can handle are.

oadie wrote:Hirstarts has a bunch of good articles and tips on hobby casting in plaster and resin. Like Kilkrazy said, it seems making a suitable master is more problematic than actually making a decent mold. Be aware of the limitations of your mold material - some are quite flexible but relatively weak, while others will last forever, but are rather stiff - this will govern how deep and numerous the undercuts it can handle are.

are there any common sizes that should be adhered to for these masters?

I don't think size is as much concern as the design of the piece and the extent of undercuts.

I made my Termagant base with very little undercutting, and was able to cast easily from the flexible silicone rubber mould. I think I could have got away with more undercutting that I did.

I imagine the OP wants to make items like window sashes, eagles and other bits of flat decoration. These should be simple to make as one piece masters with little or no undercuts.