Moulds for rocks & rock walls

[James_Scott]

I have done plenty of sculpting out of polystyrene in the past and have been reasonably happy with the results. However, after seeing some of the results from docroc and the like, I have been doing some research into making rock moulds and how to paint them. Interestingly enough, the best information I have been able to find are on taxidermy websites.
For a step by step run through of how to make a rock mould and then the fake rock go to:
Taxidermy.Net Forum - Making a Simple Rock Mold with Silicone Caulk

For steps on painting these rocks so that they look real go to:
Joshua Knuth

I really hope this makes the job easier for everybody. I have done a couple of tests so far with good results. I did learn quickly not to use granite or quarts as the silicon will stick to it and wont come off. Sand stone is a great rock base to do a mould from. I have estimated to do a 2'x1' flat wall it would take around 6 tubes of silicon, but one the mould is done you can make as many as you like. The material you use to make the rock is up to you. I am about to trial plaster of paris and will see how it goes.

Good luck and I would love to see some results for anybody who wants to give it a go.

Cheers
James

 

[saximus]

Awesome mate thanks for sharing. Have you tried/considered trying expand foam?

 

[James_Scott]

The issue I had with expand foam is the time it requires to set completely. I wanted a material that would set relatively well in a 6-8 hour time frame and then be removed. If I am taking a casting from a rock in a national park etc. I don't want to be there overnight or leave equipment there overnight. I have found that small castings can be done in around 4 hours, and I am yet to do a large one.

You do require 100% silicon for the mould so I would be interested to find brands that are cheap. The brand I'm using now is around $8 a tube. The cheaper tubes of silicon dont say 100% so I'm not sure how they would go.

 

[Just_Plain_Nuts]

You can buy moulding silicone, but it too is very expensive.....

 

[melluvssnakes]

I don't know what kind of expanda foam you've been using, but the stuff i've got sets in 30 minutes...

 

[MathewB]

Can you use plaster Cloth?

 

[James_Scott]

Good question. I don't know if you can use plaster cloth. I suggest giving it a go and post your findings.
As for the expanding foam that sets in under an hour, what brand is it. Do you intend on using it as a mould casting material or as the final cast itself?

 

[MathewB]

When I try it I will

 

[James_Scott]

Here is a sample run I did on a very small rock. This is three copies put together and roughly painted.
The end result in this sample run is 3 plaster tiles that can be glued with liquid nails to a ply wood back board and installed in the enclosure.
I am trialing latex to do a large mold that would measure over 1.5m long and 60cm high.
If anyone else has had a chance to give this technique I would love to see the result.

 

[slide]

Thanks Jamie. Did you experiment with other methods/materials?