Wednesday, January 21, 2015

Structural Fiberglass Repair

With the window replacement on hold awaiting new glass and another nice weather day in store, I decided to turn my attention to my fiberglass repair. This all started when I was showing a fellow Leopard 38 owner my cool new Mantus anchor and noticed that the anchor roller and bail were loose. Looking closely, the roller itself wasn't loose but the fiberglass it was mounted to had cracked and was flexing quite a bit.

So, after removing the anchor roller, the first step in repairing the area was to determine how bad the crack was. From the surface, it appeared the crack was pretty large, but I couldn't tell for sure. So, instead of cutting out the area I thought might be cracked, I decided I would just try grinding it down. I'm glad I did this approach, as I found part of the area I thought was cracked was actually in good shape and there was just a small surface crack and a roughly corresponding stress crack in the gel coat on the other side. Since I wasn't worried about the stress crack in the gel coat, I just ground down the area that actually needed to be repaired, tapering the area out about 9 inches (where possible) to give the 12:1 taper recommended for this type of fiberglass repair. I did leave a thin layer of the existing fiberglass and gel coat for a couple smaller cracks in order to help preserve the existing shape of the area.

Learning from my practice on the anchor locker tray, I came up with another idea for creating the mold around the missing chunk of the curve. I used a piece of one of my flexible cutting boards (a thin polyethylene sheet) for the mold surface and backed it up with a block of the green foam used for flower arrangements that I cut it into an L shape. I taped the poly sheet as tight as I could over the cutout area and then taped the foam over it to provide support.

Just as I did in my practice, I brush applied a thick layer of gelcoat to the inside of the mold and let it cure until it was reasonably solid. Before the gelcoat set, it kept running down the vertical part of the mold, so I periodically brushed it back up until it started thickening up.

While the gelcoat was setting up, I cut 4 pieces of fiberglass, starting with the one just slightly larger than the mold area and increasing the radius by about 1/2 inch on each subsequent piece. For the bottom two layers, I used the biaxial cloth with the chopped strand mat backing and the other two were standard 17 oz. biaxial cloth. I then mixed up a little of the epoxy resin (the metered pumps for the resin I'm finding to be quite handy) and applied a little bit to the repair area. I applied each layer of cloth, wetting it out with the chip brush until I had all four layers in place.

Apparently epoxy (and polyester) resin can get quite hot while curing, so they recommend you don't do more than four layers at a time. Excess heat can cause cracking and, in extreme cases I've heard it may even catch fire. Once the four layers were in place, I went back and cut 3 more pieces of fiberglass continuing my 1/2 inch or so size increase with each successive piece, adjusting as needed to keep the resulting surface relatively flat. After the first four layers had cured to the point that it wasn't sticky but I could leave an imprint with my fingernail (most of the heat has been generated but it isn't completely cured), I mixed up more resin and applied the next three layers. I used a small plastic squeegee/spreader and fiberglass laminating  roller to smooth out and compress the layers together to create a good structure. 

By this time it was getting dark (ok, in truth it was already dark and the last layer I had to use a flashlight to lay it up), so I left just a tiny bit more resin on the top. I did this because, once you get past the "fingernail" stage, you need to let everything cure and then clean and sand (or Scotchbrite) the surface before you can continue the layup. Since I have more layers to apply I didn't want sanding to cut into the glass fibers and compromise the structure. If you do this, you want to be careful not to leave the area too "resin rich" as that is as bad as cutting into the glass fibers.

Guess I'll be finishing up this job after I find my replacement salon windows. Nothing like having a couple big projects going at one time on the boat.  Wheeeee.

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