Boat Building Forum

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What is the cloth actually doing?

The desire to wrap cloth around thin edges comes up a lot over the years. I think it comes from the idea of things made from fiberglass are strong. The cloth we put over out boats acts mostly as a binder or girdle holding thngs together. It has some abrasive resistant quality but not a lot. Without epoxy or polyester, its just a fabric with strong tensile strength.

When glass fabric is not filled (fill the weave) its abrasive resistance is very weak. Try sanding into glass cloth unfilled vs. filled. A sander will rip right through the unfilled cloth surface fast.

My point here is, just epoxy coat your fine edges. Epoxy is super strong in itself. It can't bridge things together like the glass and epoxy combination does but as an abrasion resistant surface its like iron. To go through all kinds of gymnastics to get cloth to wrap around a thin edge is not necessary and if you do it and achieve it, you get 10 points.

Heres where cloth is great. If you coat a piece of plywood and leave it out to the weather, the epoxy thickness would have to be quite thick to prevent cracking, whereas glass cloth/epoxy could be used thinner and not crack because of the binding fabric. Want to drag it down the road carrying bricks? Then pile on the coats of epoxy, because the fabric will just get ripped apart. I'm not an expert, - just trying to shed some light on the misunderstanding of what the cloth does.