Glass cloth and resin

Building an emergency rudder? After my abortive attempt to build a foam and glass blade for the last Longpac, I have a nearly full 5 gallon can of isophallic -- sorry, make that isophthalic -- polyester resin from Tap Plastics, and an appropriate quantity of catalyst. Since I don't have any major fiberglass projects coming up (I hope!), somebody else may as well use this stuff while it's fresh.

I also have a quantity of Knytex cloth cut into 78 x 30" pieces, plus a few remainders.

I'd like to get a little money for these materials, but not looking for anywhere near what I paid. Let's talk.

Max

Max,

Just curious....are there any lessons learned that you can you share regarding what NOT to do when building out of foam and glass?

Ummm ... basically, don't procrastinate so that you don't have time to do things right.

I went up to Svendsen's on a Saturday to get a piece of Divinycell for the core, only to find that with the shop closed they had no way to cut it. Thinking I had to get the blade pretty well built that weekend, I decided to go with Styrofoam building insulation. Yes, I know it's not right, but I figured it would be better than nothing. But for some reason, I couldn't even find Styrofoam, and I ended up with a plank of some other foam that was even weaker than Styrofoam and smelled a bit like dead animals. Not being a complete idiot, I found a piece of 2 x 3 rectangular aluminum tubing, cut a slot in the foam, and epoxied the tube into it to give the blade a little backbone. I got the blade nicely shaped and suspended it between two tables. When I gently laid the first piece of wetted out cloth on it, it broke at the end of the aluminum reinforcement. I think I said "Darn!" or something like that.

That's when I changed course and went to the wood and aluminum structure that I described in the other thread.

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Originally Posted by Critter

Thinking I had to get the blade pretty well built that weekend, I decided to go with Styrofoam building insulation. Yes, I know it's not right, but I figured it would be better than nothing.

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Were you using polyester resins on the foam? Polyester resins are incompatible with styrene-based products (e.g., styrofoam, blue board insulating foam) - the foams will effectively 'melt' as the polystyrene chain molecules that are the basis of the foam are broken up. If you want a really effective demonstration of this, hold a styrofoam cup in your hand and pour acetone or styrene into it - quite exciting!

Epoxy resins do not attack styrofoams. Polyurethane and polyvinylchloride (PVC) foams are compatible with polyester and epoxy resins. (Divinycell is a PVC foam.)

Bottom line is to experiment with the materials before going into full-scale production on a part.

- rob/beetle

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Originally Posted by tiger beetle

Were you using polyester resins on the foam? Polyester resins are incompatible with styrene-based products (e.g., styrofoam, blue board insulating foam)

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I didn't know that. Yes it was polyester resin, but no it wasn't Styrofoam. It was a fine-grained beige foam; I don't recall the name. It clearly broke from the weight of the cloth, not because of a chemical reaction. Really feeble stuff, it's good I didn't get any farther with it.