- Fibreglass Resin.
- Sanding Discs.
- Orbital Sander.
- You could also use a Fibreglass Repair Kit
Fixing a Hole: The first thing to do is to sand or grind the edge of the hole, so it's a gradual transition into the hole. By doing so it will give a nice area for the fiberglass to lay in and give it more area to bond with, if there's any loose fiberglass around, remove it to get it as smooth as possible.
Fixing Any Cracks: When you have a crack that is cracked through the fiberglass, we’re not talking about a small crack, we’re talking about a crack that's deep; what you need to do is you need to grind a “V” in that crack. Again, making a transition or a puddle area to lay the fiberglass in.
The next step is to use an orbital sander with some 80 grit (at least 80g) sandpaper on it. Sand the area around the crack and in the crack just to smooth everything out, make sure there's no loose fiberglass, you may not be able to get it all but do the best you can. You should now have a nice area that's all prepped out for the fiberglass resin and the fiberglass matting.
Fibreglass Resin: It's time to mix up a little resin and get your matting ready to lay in the fiberglass. Be sure to follow the mixing instructions on the can. Make sure you have cleaned the repair area with some automotive prep solvent, you can also use rubbing alcohol. This is to remove any dust or debris. Take your fiberglass resin and a brush and spread a liberal coat around the area you're going to be repairing in the hole or crack. Make sure that whole area is covered, anywhere that you’re going to lay the fiberglass matting.
Take your pre-cut fiberglass matting and soak it really well in the resin then spread it as smooth you can because you are going to have to sand this off. Take another piece, lay it over top, put some resin on the brush and soak that thoroughly and smooth it in. Continue this process until that hole is filled, it's probably going to take three or four coats of matting. Continue over that cracked area that we ground out and fill that up until its level.
Once the fiberglass is dried after an hour to two sand off the excess resin. Your goal is to get it flat. You can do it by hand or whatever method you have of sanding. Repeat this on a cracked area.
To finish off the sanding process, you can use an orbital sander and some 80 grit sandpaper. You can also use a hand block with some 80 grit on it and block it in an X pattern over the fiberglass, this will get it straight. The goal is to get this flat and straight in preparation for primer.
If you take a closer look at this spot you can see how flat that is, the flatter the nicer the finish. If there are a few waves and imperfections in the fiberglass sometimes you may have to put a little bit of body filler or polyester putty over it to fill any pinholes or air pockets that are in that fiberglass. There are a lot of different products out there that you can use. The filler process is very similar to sanding the fiberglass, actually it should sand a lot easier. Once this is smooth, you’re ready for primer.
The sandpaper being used here is 180 grit, it's not super coarse but it's not really fine either. What this will do is knock down the heavy stuff (with the 180 grit) and then go over it with a finer sandpaper like a 320 grit. When painting over, or priming over, you don't want to prime over anything coarser than a 320 grit, so with 180 grit you don't want a prime or paint over that, it should be at least 320 grit or below. The higher the number in the sandpaper, the finer the sandpaper is.
Now you’re ready to prime!