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I'm considering building darkroom sinks out of thick plexiglass mounted in an al uminium frame. Does anyone have any positive or negative experience doing this? I live in Israel and the guy who's building this for me is having trouble locati on fiberglass. Also he hasn't worked in fiberglass before. Any comments or hel p would be much appreciated. Yaakov Asher Sinclair
Hi YA - Fiberglas cloth comes in a roll and is a very easy to work covering over a plywood sink frame. There is a 2-part epoxy that gets painted on [couple of coats] over the fiberglas. In fact, the epoxy is so good, that I've even eliminated the fiberglas and just used the epoxy over playwood. Plexiglas cracks with stress and is hard to seal watertight againt the aluminium frame. In your place, I think I'd stick to a good, solid plywood sinks sealed up with epoxy. It should last forever. -D
Plain epoxy resin is fairly brittle; there's a marine epoxy resin/sealer called Gluvit that stays flexible enough to avoid stress and impact fractures etc.
I wouldn't build a sink out of plexi without very good support underneath the entire bottom and if the plexi cost very little.
The comment about giving full support to the bottom is a good one. Plexi is a brittle material, and I wouldn't want to be standing there when the bottom lets go all over your feet.
I have built several sinks using plywood (3/8" -- 1/2") and fiberglass cloth and resin. The fiberglass should be available at any place that sells marine and boatbuilding supplies. The only tools needed for working with the fiberglass are a pair of scissors, some disposable paint brushes, and some plastic or rubber gloves. The cloth adds strength to the plywood, but I have made some smaller sinks without using the cloth and had good results. It will certainly be easier than cutting and fitting all those plexi pieces.
Make the sink tray using normal woodworking techniques for plywood.
Plexiglass is acrylic plastic. Its resistance to chemicals is not the best it could be for the purpose you intend, and also, it is a brittle material. As others commented, epoxies can be brittle also. Depending on the type of hardener and cure process, their chemical resistance can vary a great deal. Some epoxies can be water sensitive. Elevated temperature cure epoxies, which you are not likely to find in the consumer market, have excellent chemical resistance. Instead I suggest that you use polyester resins of the type used for auto body work, -without the filler. These resins can be used to impregnate fiberglass cloth on a plywood base, and provide a chemical resistance surface. In this way I made cheap, large paper developing trays. Better yet, use formica covered plywood. The Formica surface has excellent chemical resistance and is more than adequate. Some chemicals will stain it though. Formica makes many types of high pressure laminates, some may be more suitable for your purpose than the consumer types. Give them a call. Hope this helps.