After seeing the pictures that Bruce Chandler posted of Jim Kottcamp’s RGS railway I got some mojo up to try rock casting. My thinking is the layout I’m planning will be a raised timber platform, but I still like the idea of ‘floor to ceiling‘ rock walls – or a cut down version.
Obviously real rocks are out due to weight…
I did plenty of internet research over winter, and the find of a good rock to work on was the final excuse gone. Time to experiment!
The plan is to make a latex rubber mold, a fibreglass ‘mother mold’ to hold the shape, and - at this stage - glass reinforced concrete (GRC) as the rock, That bit is still to come together, but it seems to reduce weight quite a lot - says the interweb.
I applied a sealer coat to the rock even though it probably didn’t need it, then a mold release coat.
First coat of latex next – it goes on pretty thin. Took about 12 hrs to touch dry as it was a cold day.
After that it was 1 coat a day for the next few days, all ‘normal’ latex that wasn’t thickened.
I realised after the third coat I might have a problem where I’d left an overhang or undercut or whatever it’s called so I tried to fix it by breaking off the rock that was sticking out. Time will tell how that bit is gonna end up.
Next two coats were thickened latex. This is where the learning really started. Latex isn’t like the videos I’d watched using SmoothOn 40. It flows, like, say melting icecream…
All attempts to stop the glacier flow in the lower left corner came to nothing. Gravity won.
Main learning was to keep the surface to be coated horizontal, and don’t try and do ½” thick layers. One side effect of the successful thick pours was shrinkage pulled the latex off the surface as it dried. Not a big deal for rocks but no good for other stuff where shape counts.
This is the latex at the end – a couple more not so thick coats of latex, and some attempts to fill in grooves and dents to help the mother mold release.
More to come.
Cheers
Neil