How do I fix a failed fiberglass repair?
Dear Boat Doctor,
I need some advice on a failing fiberglass repair at my keel stub joint. There is a crack that appears to be the result of repair that didn’t bond well. When I haul the boat, it appears to weep water for a bit, so there is water infiltration. To fix this I need to dry it out, but I am trying to figure out how far the crack goes. Where do I start?
Point Roberts, Washington
It is difficult to know how far a crack goes, but you can look for clues in the structure. Try tapping the area to detect any delamination. Good fiberglass will feel and sound solid and the bad glass will sound “dead.”
I think your best course of action is to chase that crack with a grinder. You need to grind out the bad repair and any damaged laminate to get back to good material. Make sure you flare the ground area out into the good fiberglass to get a good bonding surface. The flare needs to be pretty wide, I’d do at least 5-to-1: If your crack is a half-inch deep, flare out 2 to 3 inches.
I would use epoxy resin for this repair with good fiberglass tape. I like the 4-inch biaxial tape from West Systems. Start out by wiping down the entire area with acetone, this will remove any dirt and contaminants. From there, wet out the area with epoxy and lay up the area with small pieces of cloth. Since you are doing this under the boat, you’ll need to do this over a few days because the patch may get heavy and fall off before it cures if you do it all at once.
Once the epoxy hardens, sand down any high spots and assess. You’ll likely need to fair the area with a thickened epoxy, and this may take a couple of rounds of filling and sanding. After you are satisfied with the surface, I would recommend you roll on a few coats of epoxy barrier coat and finish up with bottom paint.
The key to doing a good job on this is to grind out everything pretty aggressively and flare the repair out. The epoxy has great adhesive properties, and the biaxial cloth will give a strong lamination. Good luck with your repair, take your time and it will turn out great.