bubbles on plywood hull with fiberglass

This is my first boat built from kits. Everything seems smooth until I put fiberglass on plywood hull. The instruction of kits does not include fiberglass the hull and said it is not necessary. But I felt that since other boat designers suggest fiberglass the hull, I would better do it.

Since there is no instruction from the kits manufacturer, I found it is hard to avoid bubbles. The 14' skiff has many bubbles hardened. Most of the bubbles are on the edge, where the fiberglass cloth has extra hanging. I thought afterwards, I should be better cut the extra fiberglass cloth off when apply the epoxy resin. Anyway, it is hardened. Some other bubbles are formed because uneven surface, such as stitches gathering extra resin and form lumps that I overlooked.

Now I face a problem, there are many bubbles around. How do I handle the situation? Anyone have suggestions?

 

It sounds like you applied the epoxy and glass directly over the plywood in one step?

If you did, or applied the resin onto bare plywood and the temperature was rising you have bubbles that developed from what is called out gassing.

Since the resin is already on there I don't believe you have any other choice but to sand the bubbles out of the cured surface and apply an additional thin coat or two of slightly thickened resin until you get a fair surface. Probably one would be sufficient.

 

Pictures would help. I had a similar problem when I glassed my hull during rising temps. In some instances, small bubbles, a wire brush on a die grinder popped the tops off the bubbles and I was able to fill them without removing much of the fiberglass. Some larger ones I slit the tops open, pried them open with a piece of wood and filled them with epoxy. I then screwed them back down till they cured. Filled the screw holes later. I had two large ones that I had to completely grind out and back to good glass then epoxy in a patch. On a 14' skiff I don't think it would be that much of a problem with a few small bubbles. Anything below the water line has to be fixed though.

 

Thank you

I thought about the same solution last night. But since many of the vacuums are on the edge, between the bottom of the hull and side. It was formed because there is over hanging bottom. side of the boat was about 1/4" inside. air trapped under the over hanging boat bottom. I cut open the glass and use filler mix to fill it up and lay fiberglass over it. But any way, thank you for your information.

 

Got it. Yeah, fiberglass cloth, even very light cloth doesn't wrap around a sharp edge very well. You'll learn as you work with cloth and resin to sand or route a radius on those edges.

 

Any wood glassed over should be coated first and let cure, If glassing directly over plywood without coating first not only will you get out gassing but the plywood will soak some of the resin out of your first laminate making it easier to delaminate. It is very important to always coat wood first.

 

I did coat the plywood with epoxy resin.

I did as you said. The plywood was coated with epoxy resin before fiberglass. But I think because I am inexperienced with the epoxy resin, the fiberglass drops hanging on the side. I should have cut off the extra hanging fiberglass to make it smooth. I did not cut off the extra, instead, I tried to squeeze in the extra, that's where the bubbles form.

To make up the mistake, I sanded the bubbles off to the bare plywood and apply another coat of fiberglass. The second coat of fiberglass is smooth but still can see the previous mistake because when sanding off the bubbles, the fiberglass showed. Under the fiberglass has void space. the fiberglass edge stick out cannot be sand off. I use knife to cut as much as possible. But after second coat of fiberglass, the mistake still show.

 

Resin doesn't dry, it cures.

 

Resin does dry, usually part way through the cure . . .

If you are looking for a natural finish under the cloth and have made repairs, you're not going to hide these, without putty and paint. This is the nature of clear finishes, you can't screw up or it'll show (we all know this particular pain). If you're not shooting for a clear finish, then don't worry about it, as some putty and paint will fix any and all ills, caused by a wood butcher.

 

Par is right on! a grinder, sander, some putty etc. makes errors and bubbles water under the bridge.

Getting it right for a clear coat finish takes experience, skill, etc. My last stitch and glue was an attempt to 'do it right' - I failed and it is all paint now.

paul - progressive epoxy polymers inc.