Rockfall shelter progress

I did more rock carving on Sunday, but soon got a bit bored of that. It's a pretty slow and tedious process, although it's really starting to look the part now.

I decided instead to tackle the rock shelter. My masters had dried by now and were ready to be turned into molds.

Step one is to attach the masters to a smooth base, and build a fence around them. I'm making these molds upside-down, so the flat surface at the bottom will become the top where I pour in the resin. These are just simple one-piece molds.

The fences are cardboard, hot glued in position. As long as it's water tight that is all that matters.

Step 2 is to mix up some silicone. I have some highly accurate jeweler's scales which I use to measure out the precise ratios, and a 100 pack of disposable medicine cups and plastic spoons.

Unlike plaster or resin, the silicone has a good long working time so no need to rush here. I now take a cheap old paint brush and paint on the first coat of silicone directly onto the master; this makes sure no air bubbles get in the way. Once that's done I start pouring in the silicone. If I have any old molds I might cut then up and add them as I pour to bulk things up a bit; silicone sticks to nothing, except itself, which it sticks really well to.

Once poured I give it a good tap to get any bubbles out, then leave it for 24 hours.

A day later and it's all dry and ready to be turned into a mold. I removed the masters, breaking one in the process but never mind. Now that I have the molds it's time to cast them in resin.

Mixing up the resin follows a similar process of carefully measuring out equal weights of part A and B. I found 1.8g of each made enough resin to fill each mold and a couple of extras for my sky scraper project.

The resin I use is SuperCast, a 2 part urethane resin that is very strong, yet very easy to work with. Sadly it seems the NZ supplier has just gone out of business, so my stash is now highly prized.

From the moment I start mixing the resin I have about 3 minutes before it sets solid! So very quickly I drip in the right amount to each mold, flexing the mold as needed to get it into all the corners and make sure no air bubbles have got in.

That done I place a small square of waxed baking paper on top.

I then place a small flat weight on top of each mold to squeeze out the excess and ensure a perfect flat surface on the top of the casting. I find the plastic jewel cases that trains come in to be perfect for this.

I then wait about half an hour for the resin to set up and then they're able to be removed and the next batch made. They will continue to harden over the next day or so. At this rates it's quite easy to get a whole bunch made in a day; I'm up to my fourth batch so far today.

Here is how the completed bits will go together. It will be quite fun watching trains through the openings in the side.

Hopefully in the next few days I'll have enough bits and can start assembling it. Resin casting is fun!