I’ve been using polyester resin since the 70’s but this is my first time using epoxy resin for fiberglass repairs. I had been hearing how much nicer epoxy was to work with. The plan is to use the boat with the recommended 100 hp, so making the boat stronger the stock was not an issue. If someday I up the hp or weight it’s ready. The choices of epoxy brands online seemed endless.
Why I chose MAS, I went to the closest supply store, a BOW just a couple blocks away. They had West & MAS systems on the shelf, the staff said both were good but the MAS is preferred here if temp & humidity were 90 plus. I asked at a couple local boat yards and they said MAS performs much better when used in high heat/humidity. In addition they recommended stitched mat and explained to me when using epoxy resin with styrene coated glass mat the mat reacts different than with polyester resin. The epoxy does not dissolve the styrene used to hold the strands of the mat together and will be stiffer to work, and gave me a few pointers to work around this. Also the epoxy needs to be thickened to prevent flowing out thinner than the mat. Epoxy works the same as other resins in cloth. They had some hybrid fabrics, as they called em. These multi-layered fabrics needed to be vacuum bagged and use the low viscosity resin with slow hardener to insure penetration / saturation and, prevent delaminating. So far I’ve been able to do what I needed using the mat and cloth with MAS epoxy.
When mixing I put the fillers in the cup first then added the resin, mixed well, then stirred in the hardener. For gluing pieces together I thickened the epoxy with Q-Cell and added some ¼” chopped 16 oz fiberglass to act as a spacer preventing the resin from squeezing out, worked like a charm. For fairing I thickened the resin with Cab-O-Sil and 1/32” milled fiber then added ¼” chopped 16 oz fiberglass. I used the rounded end of the stir stick to shape. Picture hard candy with shredded coconut inside. I was working with this outside, the temps and humidity both over 95 with slow hardener, below 95 I used a 50/50 medium & slow hardeners. Pots were very consistent and user friendly to work. Almost zero waste, no smell and with the pump measuring no mess. I mixed the resin with micro-balloons to fill some small non-structural voids, keep bugs from building a home. The mix also worked very well to brush out and self level areas. The micro-balloons make sanding a breeze.
Lots of how to and projects to look at on their site.
Great for beginners, loved by professionals