Can I build perpendicularly over existing fiberglass?

[pillowfort]

I pulled out a porthole to restore and rebed it and found that the builders cut holes that were too large. As a result, the interior screw holes all along the top of the porthole are along the edge of the hole, not actually solidly holding onto glass. (See photo)

However, the glass along the rim of the cutout is intact. I am wondering if I can grind out what's there and layer glass along the cutout's lip. (Probably the easiest thing would be to use a filler for the existing holes and move the porthole up slightly, building up the lower lip of the hole?)

Any suggestions are most welcome. It's lasted 40 years, so perhaps I'm overthinking it, but the porthole is definitely leaking. If it's not an insane project, I'd rather fix it correctly while I already have it disassembled.

[tkeithlu]

Yes, you can fill in the entire mess, and basically start over. Given the configuration, use polyester or epoxy with imbedded fiber for strength. Lots of boaties make their own, but (dare I say it?) Bondo will do the job. Squeeze it into the existing layers around the port for a good grip, don't worry too much about making a mess, and then sculpt it with a grinder after it hardens. Redrill, bed with butyl tape, and move on to the next problem.

Good luck with it.

[coopec43]

Originally Posted by tkeithlu

Yes, you can fill in the entire mess, and basically start over. Given the configuration, use polyester or epoxy with imbedded fiber for strength. Lots of boaties make their own, but (dare I say it?) Bondo will do the job. Squeeze it into the existing layers around the port for a good grip, don't worry too much about making a mess, and then sculpt it with a grinder after it hardens. Redrill, bed with butyl tape, and move on to the next problem.

Good luck with it.

I would second what tkeithlu has to say.
Overfill it and grind it back to shape.


(If you move all the portholes up you are just making work for yourself)

[Spot]

I could see taping up a small piece of angle iron with packing tape or coating it with mold release and then hanging it on the upper edge with the L sticking out and the inside corner at the desired edge height. Fill in using resin thickened with fumed silica, cloth fibers, and a pinch of glass microspheres (to taste). Have a second piece of angle or wood also taped to help dam the materials in. Let cure fully, carefully demold, sand, and finish to suit.

You could also clean or freshen up the other holes too, countersink them a bit and fill with thickened resin.