Filling in two thru-hulls

[Bob L]

I'm going to remove my non-functional depth transducer and giant fairing block and possibly the thu-hull and fitting for the speed paddlewheel and need a little help on the "fill in the hole" process.

This is my first fiberglass experience. My idea is to:

Remove fittings
Grind the hull around the inner and outer orafaces
Grind the inside of the old hole
Cover the outside with wax paper, backed with cardboard, taped into place with duct tape (or prop it up with a 2x4)
Wet down the inside of the hole and wax paper with unthickend epoxy
Let that set up a bit
Fill with epoxy thickened with chopped glass (?) (or collidal silica? help!)

Thoughts, comments, suggestions?

Thanks,
Bob

[Tim]

That's basically the right procedure. I would use a mixture of epoxy thickened with microballoons and silica instead of chopped fibers. For such a small hole, you probably only need to tightly tape the outside with duct tape or even a couple layers of masking tape, just to prevent the epoxy fill from oozing out. You can certainly use cardboard and wax paper if you prefer.

Then, when the plug is cured, remove your "mold" from the outside and dish out (grind) a roughly circular area containing the repair, with the low point in the center, and install a couple layer of overlapping fiberglass to reinforce the repair--the first layer should be about 1/2" larger radius than the filled hole, and the second layer about 1" larger radius than the first. You don't have to go nuts with this step--you want a more or less consistently tapered "dish" that is perhaps 1/8" deep in the lowest point and about 5" overall diameter, to accommodate the thickness of the new glass.

When the fiberglass has cured, you can sand and fair the outside to suit and to match the surrounding contours. The epoxy plug is strong enough by itself, but the glass on the outside just ensures a strong bond on the outside, where it counts.