Sunday, September 27, 2009

Arnica: Vacuum Chamber Report

As many of you may recall, we recently bought a 3-gallon vacuum chamber for degassing resin and silicone rubber. I just thought I'd give you a quick report and let you know that I'm VERY happy with this purchase.

We're using both 5-minute and 10-minute curing resin, and so far I'm thrilled with the results. I can mix as aggressively as I want without fear of working air into the mix. Once it's all mixed (and looking quite milky), I pop it in the chamber and in less than 3 minutes it rises (bubbling ferociously), then collapses back down. Then it quickly starts a rolling boil (this happens when the chamber achieves a complete vacuum registering -30 inches), at which point I turn it off and slowly let the air vent back in. I remove the lid and my resin looks like crystal clear honey. I'm amazed at how clear it is. I pour it into the molds, run a thin stick or blade through some very tight spots (the cross bar on windows, deep & thin areas around door frames) and then sit back and watch it quickly cure. When I demold, there are no bubbles against the surface, and very seldom any on the back.

The resin is nice, but this is what I really bought it for. I'd been having lots of trouble with bubbles in my silicone. Right now I'm using silicone with a 45-minute pot life, so I've got plenty of time to pour, mix, and pour on the master, and mix more if I need it. Again, I can mix as aggressively as I like. I've tried using an electric mixer, but have not been satisfied with the results.

Now, the resin only doubles in size during the degassing process, so I can really do a lot if I want to (but I don't because I like to take my time pouring). But the silicone more than triples its size. Since I'm using 16-oz disposable plastic cups right now, I've found that I can put in about 130-140 grams of rubber and catalyst. More than that risks a serious mess because the rubber would overflow the container. Even at this amount I've occasionally had to vent the chamber (open the valve to let in a little air) to keep it from overflowing.

I'll tell ya, when the silicone is degassing, it's incredible to watch. It looks like some sort of mutant alien sponge that throbs and pulses with something that looks like it's got a heartbeat. It's really creepy looking, but in a cool way. If I were filming a movie, this is exactly what I would use for some sort of alien life form.

When it's degassed, I add I carefully pour it into the corner of the prepared mold box. Following a variety of advice I've received (including Michael over at, I take the time to carefully brush the rubber over the master, pushing the rubber into thin and tight spaces. I also work it up in corners and other tight locations. Once I'm sure I've done a good job of pushing the rubber into the details, I think add more rubber. Because I'm using 45-minute pot life rubber, I can easily pour a second (or third) cup of rubber, degas it and then add it to the mold box. This helps me get the proper thickness I want for each mold.

So far, the molds have been amazingly bubble free. In fact, I've only seen three bubbles so far, and I know they came from me pouring the rubber too fast.

I know many of you have not had problems with bubbles, and there's been some speculation that I'm getting them because I live in a very humid part of Texas. I also know that $400 is an expensive tool for anyone's budget. But the fact remains, so far I'm thrilled with the vacuum chamber we bought and I fully believe it will pay for itself by helping prevent bad molds and bad resin pours.

By the way, if you're interested in looking at the vacuum chamber we bought, here's a link to the seller on ebay: