To the ends of the foam 'box' I epoxy'd on scrap pieces of wood that will be used to support the ends of the canopy holder. Two slanted troughs were added along one side to allow topping off the silicone since the canopy holder covers most of the cavity.

The canopy was then coated with Vasoline which was buffed smooth with a soft towel. Vasoline was also wiped over the filler block at the back of the canopy – as thick as the silicone is, it will key into the wood pores and I didn't want that to happen on a part that has to slip out of the mold vertically!

Finally a couple of pieces of double sided 1/32" foam tape were attached, one at each end of the canopy frame, to hold it in place on the wood strips while the silicone set. (Since the canopy will be filled with water there is no tendency for it to float and so the tape just needs to hold the canopy centered in the cavity.)

Finally it was time to mix and pour the silicone. Two batches were used, each with about 6 oz of material. The first batch was poured into the cavity and most of the second. Then the canopy was lowered into it and water added to the inside of the canopy until it was full to with 1/16" of the top. Silicone was added via the troughs until the cavity was filled to top.

Then all one can do is sit around and wait.


If you haven't used this stuff, it's thick, slimy and very messy to handle. On the other hand it forms around almost anything and will replicate #600 sanding marks perfectly. And it releases mixing bubbles very well in all but areas where they can't rise to the top.

It's a curative silicone – as opposed to the hardware stuff which is a condensate silicone – and uses a curative additive. It's pure white and the curative is deep blue, which turns it a baby blue color when it's well mixed. Pot life is about an hour and it takes at least 24 hours before de-molding.

There are a lot of formulations on the market for mold making silicone, some with widely varying characteristics. I use a Silpak product I get from Fiberlay which is a local fiberglass retailer. It's farily stiff cured, yet has a lot of give without breaking. This makes it easy to get molded parts out of it that wouldn't be even close to possible with rigid molds.

Neat stuff.