Before applying the barrier coat we had some work to be done. We had some hull reinforcements and repairs we wanted to do, and we also wanted to replace the old thru hulls to new ones. This means glasfiber work, grinding, sanding, fairing and some more sanding. In the previous post, we described how we prepared the surface of the hull for this work. If you have missed this you can read about it here.
We had got the advise from the boat yard to check the area just infront of the keel for cracks or moisture, and to add some glassfiber for future precaution. Our moisture meter actually gave a very small indication that the hull was not entirely dry there, so after drying it all out (just being out of the water was enough) we grinded the gelcoat away and started reinforce it.
Update Nov 13, 2021:
The epoxi treatment we did in 2020 failed due to a series of unknown events and had to be redone in 2021. This post about how we used epoxi and glasfiber to reinforce and repair the hull still applies and contains some good tips if you are to do this yourself. If you are doing an epoxi treatment, or just have a general curiosity for boat stuff, we really recommend that you read our summary about the epoxi failure and what we learned, described here.
We grinded the surface with an angle grinder to clear it from gelcoat. This is done so that the new glassfiber gets a really good adhesion against the GRP surface. Our hull is constructed of two halves that are put together lengthwise. If we ever run aground cracks could start to build where the two halves meet on the outside. The inside already has these reinforcements, so the risk is not to “break” the boat but rather to get cracks and moisture in the laminate. To minimize the risk of this ever happening, we decided to do the reinforcement all the way to the bow. This way, we have an extra layer of glassfiber protecting the joint, just in case.
We decided to do the glassfiber work with epoxi and not polyester. This we did because of the more adhesive properties when putting epoxi to old polyester GRP. Epoxi also results in a stronger reinforcement. Another very important aspect for us is the curing time. Since we are putting epoxi barrier coat over the glassfiber work the polyester would have needed to cure for a very long time (weeks to months) to not affect the barrier coat. With the epoxi, a few days is enough.
To reinforce in all directions we used a combination of biaxial tape and rowing mat (300-400 g/m2). We cut the rowing mat into different shapes that covered the area infront of the keel using larger and larger pieces. To get the right shape we used a large plastic bag that we cut and then used as a template. All together we added 8 layers of differently shaped and sized pieces of the rowing mat.
Once cured we lightly sanded the irregularities and sharp edges from the glassfiber. Then we used the same epoxi as before, just adding fairing additive (low density filler) to make a faring compound. We were prepared to do this in multiple steps, but it turned out that twice were enough. We managed to smooth out the entire area and after sanding it was ready for the epoxi barrier coat. We also took the opportunity to fill out a few scratch marks that we had from scraping and sanding the hull. The goal was to make the entire hull completely smooth.