Adding fiberglass and Gel Coat when it wears thin

I know Polepole is interested in reviving some old yaks, and I expect a few more are out there. This is some info for any other DIYers that have a lot of time to spend bringing worn out fiberglass back to life.

One of my old and treasured yaks was becoming see-thru thin late last year and water was leaking in at 3 different spots, maybe more. It was time to do some serious work. First step was to patch up the leaking fiberglass and make alterations to reinforce the wear spots. I won't go into this as there is a lot of good information out there on how to patch fiberglass. What I had the most trouble finding good information on was doing major gel coat repairs.

First step was to get the fiberglass in good shape and fix the leaks. I added many layers at the heavy wear spots, at least 5 layers to the keel and reinforced some of the serious spots with wood from the inside. I filled gaps, seams and holes with Marine Tex puddy and sanded this back until smooth. When it got to the 'good enuf' stage I gave it a final coat of resin, nice and thick. Once this cured I gave it a light sanding being careful not to sand thru resin to the cloth. This process took many days as each layer needs at least a day to cure up before sanding and/or adding more layers.

Spraying gel coat, especially in the backyard is tricky. The first thing I learned from reading is don't even try unless the temp is 65 f or better. Since that's not typical PNW weather I started tweaking the mixtures to find out if I could break this rule. The answer is you can bend it by about 8 degrees, but it's not ideal. If you have a nice heated shed then your set but this is a stinky process so doing it in an attached garage assures you'll hear about it unless you live alone.

Here's the best formula I came up with:
Gel Coat - 300 to 400 ml (about all I could spray out in the working time)
Styrene Monomer - 8% (a thinner that ensures the mixture will move thru the gun)
Pigment - 8 to 10% (assuming you want some color)
Surfacing Agent - 5% (a wax, also helps thin mixture, need to heat to 70 f to melt dissolved wax)
Catalyst - 1.5 to 1.7% (sets the whole mess off)

I found if I heated each of these compounds to above 70 f in warm water bath they were a lot easier to work with. They are thick and difficult to measure when at 50 f. But be careful, keep the mixture below 70 f before it goes into the gun or it will kick off in the gun early (lost a gun this way). With ambient temp about 57 to 60 f this mixture gives about 30 to 40 minutes of working time, and is tack-free in about 90 minutes.

The hardware: I used two types of guns, a standard can-type gun and a gravity feed 500 ml gun made by Vapor. The can-type guns are cheaper, as low as $10 at harbor freight tools on sale. The Vapor gun is about $40 but has less flow issues and is slightly easier to clean. Your compressor has to be dialed down to 40 pounds or less. With either type of gun the most important feature is the orifice, it should be at least 2 mm for viscous paints. My can-gun was 2.5 mm before it found a home in the trash can, the Vapor gravity feed gun is 2.3 mm.

Give the hull a good final sanding, wash it with soap and water and a soft brush to remove dust. If it has any sticky spots clean with acetone, or just give it a good wet-rag wash down with acetone. Let it dry well before spraying (30 mins in the sun), any left over acetone or water will really mess it up.

Mix reagents well, and add catalyst last after everything else is blended. Stir in catalyst for another minute, load gun tank and work fast. Test spray pattern on a piece of cardboard, work 6 to 12" away keeping gun the same distance away thru entire stroke. Less gel coat mixture is better, it should be mostly air or it will spit out in globs. If the flow stops and it's just air the mix has kicked off and you'd better clean fast or loose the gun. Have a couple jars of acetone ready to go and a pipe-cleaner type brush, toothpicks and rags at the ready. It should take about 20 minutes to spray out this amount of mixture. If it's warmer, 70 f or more I'd cut the catalyst down to 1.5%.

Hope this helps. Enjoy the smell of Styrene!

If you weren't running into big rocks on the river with the boat, you might not have to repair it so often. I was impressed with the work.

Wow, nice work! I love the smell of styrene in the morning

I agree, beautiful work. 

  mmmmmmmm, styrene





Nice work though!