The first step is to clean up the edges of the carbon fiber. I start by trimming off the fabric with a sharp utility (box-cutter) knife. I try to trim as close to the wood as I can, but inevitably I leave a little edge sticking up. This edge can be quite sharp, especially as the epoxy gets harder. I generally trim this off with a block plane, but a bit of coarse sandpaper on a block will work as well. I trimmed both the sheer edge and the cockpit edge.
Next the rough surface of the coaming needs to be sanded smooth and fair. Wrap the coarsest sandpaper you have around a cylinder of foam or other soft material. Sand aggressively. When the surface is smooth start moving up to finer grits of sandpaper. While you are at it, round over the corner between the coaming and the deck. Also sand about 1/2" onto the inside deck surface to help promote a good epoxy bond.
I'll want a clean edge to my fiberglass, so I will do the masking tape trick. First I ran tape around the perimeter of the coaming about 1/2" (1 cm) from the edge.
Before laying fiberglass on the surface apply a heavy coat of epoxy. This helps hold the cloth in place as you lay it down. I used 4" (10 cm) wide "bias-cut" cloth. Since the bias cut cloth distorts easily, handle it with care. Lay it onto the sticky surface while avoiding pulling on it.
With the fabric in place dab at it gently with a resin-wet brush to form it to the surface. At this point stroking the fabric will cause it to bunch up and wrinkle. Continue to brush down the cloth until it is fully saturated.
All this brush work may leave a fair amount of air trapped in the cloth. This is not a significant structural problem but will effect the clarity of the layup. A quick warming with a heat gun will lower the viscosity of the resin and cause the air bubbles to expand and rise to the surface and then pop. Over heating will force air out of the wood and cause more bubbles, so use this technique with care.
After the resin has set up for a few hours I trim off the glass that overlaps the masking tape. I use a very light touch to avoid cutting into the carbon fiber.