Expanding RTV for mold making

[herrblatz]

Hello all,
I'm new to this great club. Please forgive me if this is a repeat question but does anybody know how to expand or enlarge a model from 1/92 or so. Maybe something to add to RTV to help it expands as it dries.
Thanks, Jeff

[only87]

I've done that several times but my technique lacks a bit of finesse. I made a casual RTV casting mold and threw it in a bath of lighter fluid (naphtha). Once the mold is soakeds full with the stuff the proportions of the mold should be back to normal only a size bigger.
But then comes the problematic part, casting with a wet, benzene sweating mold.... It's possible but you may lose some of the fine detail of the model.
The trick only works with rapid casting RTV and resin obviously as the lighter fluid will begin to evaporate from the RTV mold very quickly.
There are a few tricks like letting the resin set to a mximum degree before it turns solid and dabbing the inside of the wet mold dry right before you pour the resin in. I also would chose a single mold for solid casting.

I really wouldn't advise you to use rhis method, it's a real hassle and chances are against, I have however produced a few usable results with it.
I still have a few ideas to refine the technique like freezing the mold aftzer it's soaked full, but lack a bit of time to try those ideas out.
If you dig a little deeper in the forum and use the search you might find a few more tips, I think I have talked a bit about the method here and there.

Another way would be the HydroSpan from the Compleat Sculptor in New York.
www.sculpt.com/catalog_98/CastingMaterials/HydroSpan.htm
I don't really know if it's worth the money since I haven't tried it out but from what they promise basically it's exactly what you are looking for. From my experience they don't always stock the stuff, everytime I asked, they weren't carrying it for the moment, so there might be a little waiting period.

Here's a pic of a resin body I made the way I described. In the front the original, a 1/100th scale datsun by Kyosho. In the back a milled out solid casting in perfect 1/87th scale:


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And a Japanese Fuso truck cab, also from 1/100:




And a Nissan Silvia from Furuta in about 1/93:

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[herrblatz]

That's a good idea. I have the capacity to soak and dry a mold in my shop. I'm going to give it a try . Thanks. Jeff