Tuesday, March 15, 2016

Targa Support Repair

After buying LUX, we started to see cracks forming at the top of the hard top targa supports. (See Google for a definition of ‘targa’.) Some unexpected jibes seem to have taken a toll on the supports. We found a blog by Mike Boyd in which he described repairing a similar set of cracks.

The cracks were growing in length and were becoming a concern. Each of the supports had cracking, with the starboard a bit more than the port. We did our repair during the summer 2015.

We started by removing the gelcoat along the crack so we could more closely examine the crack, using one of our favorite boat working tools, the Rotary Tool (Dremel). One concern was creating a repair that would not concentrate loading of the structure and create “hard spots” that would subsequently fail in a storm or emergency jibe. So we extended the repair about eight inches beyond the bottom of the crack.

It was possible to insert a small screw driver into the crack. Interestingly, the screw driver came out sticky!? We ask Troy Bethel about the cracks and stickiness. He indicated that sometimes the mixing gun isn’t set properly, resulting in a resin mix that doesn’t set correctly. It looks like the cracks started in the uncured resin due to the stresses that the mainsail put on the hard top. Looking closely, you may see a difference in color running down the center of the support flange. The targa supports are built of two C-shaped fiberglass halves that are nested inside one another with resin to glue the two pieces together along the flanges.

The resin is less than an inch deep along the joint. So we used a set of drills to remove most of the uncured resin. Different size drills are necessary as the flange gap isn’t constant. The drills easily removed the resin easy and minimized the chance of damage to the flanges.

The rotary tool with a large fiber disc was used to remove the remaining pieces and to clean up the edges of the fiberglass flanges. Once the flanges were clean, we mixed West Epoxy, thickened with microfibers and colloidal silica (also known as cabosil or fumed silica). Measuring the gap allowed us to determine the approximate amount of epoxy to mix.

The mixture was put into a caulking tube and slowly squeezed into the gap, making sure to wet down the sides of the flanges in the process. Tape was applied over the result and pressed down slightly to form a concave surface along the length of the cut. The tape keeps the epoxy from sagging out of the gap and creates a nice shape for finishing.

When it cured, the tape was removed and the epoxy surface was cleaned with acetone and lightly sanded for the next step. Finishing was done by mixing epoxy with colloidal silica to thicken it to mayonaise consistency and adding some white epoxy tint. The tint imparts a translucent white color to the epoxy because the recommended mix is a maximum of 10% tint by volume. This nearly white mix was put into the groove left by the tape and smoothed flat. This provides a base white coat for the final gelcoat.

The final step was to clean and lightly sand the white epoxy coating, then apply a layer of gelcoat. We used the Everlast gelcoat, which we’ve found doesn’t need an air barrier coating. As an experiment, we used a foam brush to apply it while it was still thin. We worked quickly so that the brush didn’t collapse. Just like applying varnish, brush back onto the wet surface. It worked like a charm and didn’t need a second coat. We didn’t even need to touch up the edges! You have to look very closely to notice the difference in gelcoat color.

The whole job was done over the course of four days, one step at a time. It is now early spring 2016 and there is no evidence of cracking. On to the next project...


Yachtdynamics said...

Hi Terry ,
A good alternate to your white epoxy and finished gelcoat is white Marinetex epoxy available at most US marine stores . It cures quick , is very easy to work and apply , and if you want a glossy finish , spray a little WD40 onto the uncured epoxy and give the surface a wipe with a rubber glove or a piece of plastic . It is UV safe and does not yellow like most other epoxies .

Terry said...

Thanks for the tip. It is good to know about UV safe alternatives. I'll look for Marinetex epoxy. The tough part of any finishing job is matching the gelcoat tint. I'm improving in my ability to match, but still have a ways to go.

Mike Boyd said...

Hi Terry,
Thanks for the shout-out. Glad that post helped. Although our targa's are different (I just had the arch, the hardtop was something I made recently) my repairs are holding well. Epoxy is supposed to be much better than the polyester resin they tried to use to glue the halves together at the factory...or that was what I was told when I did the fix.

As for gelcoat matching, here is a trick I stumbled upon. I had a guy do some repairs right after I bought the boat and he had gelcoat matched to our propane locker lid (not sure where...but I assume you can find places to do this anywhere there are lots of boats around). The lid sits in the shade of the cockpit so the gelcoat wasn't as sun bleached and a bit darker than the more sun exposed areas. When I matched the arch, I took some of that leftover gelcoat and added white gelcoat until I was happy with the result. As long as you don't catalyze the mix, you can dab a small bit on an adjacent surface to test the color match and just wipe it back off. This technique worked well for me.

Wish I had thought of tinting the epoxy, oh well. Your repair looks great in the pictures.

Terry said...

You're welcome! I read your blog first. I wasn't happy with the thought of spraying gelcoat so I tried the brush and it worked well in the small area I had to cover.
I've tried the trick of working with un-catalyzed gelcoat and my eye still doesn't get it quite right. I've gotten better at matching colors after getting some brown pigment. It only takes a very small amount of pigment to make a big difference. A toothpick is useful for getting a very small amount of pigment.