The transom looked really ugly since we bought the boat and needed some attention. The red gelcoat faded, with badly done hole repairs and there was a small vertical crack in the middle. The original plan was to just widen the crack a bit with a Dremel tool and apply a gealcoat filler. But when I started opening up the crack, it turned out that it's deeper than expected. Probably the water got into the laminate at the top of the crack and worked its way all the way down. So I decided to sand all the damaged laminate out.
I widened it to a ca. 10cm patch and removed quite a bit of it on the sides to have a good angle for the new fiberglass to stick to. The laminate underneath was healthy though and the crack didn't went through (there is no crack from the inside of the boat), so it's more of a cosmetic issue, but we thought it's good to reinforce it anyway.
We laid 2 layers of 800g triaxial fiberglass and one layer of chopped strand mat on top of it and repaired all holes with thickened epoxy. Then we applied 4 layers of 407 low density epoxy fairing with sanding in between to get a nice smooth finish. Next is a primer, then 2-3 layers of finish. We're going to use Epifanes 2 part polyurethane primer and paint. The weather is getting cold, wet and humid though so we might need to delay the finish until the spring.