Sometimes when you are surfing the snot out of big ocean waves in a fiberglass kayak, things break. Last weekend, I broke the seat in my NDK Pilgrim. I am going to pretend I am just stronger than the fiberglass, but whatever the real reason I needed to fix it.
The two cracks down each side made for a slightly technical fix, but fiberglass repairs are all pretty similar. For the seat I worry more about strength and comfort than appearance, but I still like things to look nice, so I took it home to fix rather than doing a field repair.
First, I removed the seat from the boat. I think it is always a good idea to get as much access to the break as possible without causing any more damage. Prep work will take the most time, but it pays off in the end.
Then I used a dental tool to dig out any loose fragments. These are not adding any strength, and can cause more problems farther down the road if they are left in place.
After all of the loose fragments are picked away this is where the real assessment of the damage happens. In my case, the break was from edge all the way down. So, I want to both replace the glass that broke and reinforce the entire seat so it dies not happen again.
I sanded down the cracks and so the glass can lay flat. For a hole or crack that goes all the way through the fiberglass, it is best to work on one side at a time while securing the other so it does not get warped. you can secure it by fuzing it with resin. For these fixes it is also best to sand half way through fiberglass on each side as you work so the new resin will fuse into one piece. Fully cured resin does not bond as strong with new resin as curing resin bonds to its self. (If you are only missing a chunk, only sand as deep as you need to in order to make the glass lay flat.)
Gel coat is a UV stable resin, but it is not reinforced with fibers. It is best to put glass on glass rather than glass on gelcoat in most cases. (A keel strip may be an exception.)
Deciding how thick to layer the glass is tricky. You can find strength formulas and really nerd out about breaking force, but it’s probably not a big deal. At the end of the day we are not taking our kayaks to space. I usually estimate the thickness of the rest of that area of the boat match it and add a bit extra.
In this fix I wanted to make it much stronger, so multiple layers of 6 oz cloth and 2 layers of some 2 oz cloth I had left over from another project. A 2 inch roll od 6 oz fabric is a pretty common in a small pre-assembled repair kit.
After sanding the area, wipe the surface with acetone to remove all excess dust and moisture. The surface needs to be clean and dry before applying glass. Premeasure and cut the glass cloth so it is ready to use. Some people recommend pre-saturating the cloth before applying it to the surface. I prefer to paint a thin layer of resin on to the surface being repaired. Then placing the dry cloth and saturating it in place. I make less of a mess. Be careful not to move the cloth as you apply the resin.
I prefer to use resin instead of epoxy in my repairs. Epoxy is supposed to bind better to a surface, but it takes much longer to harden and I don’t find it works as well for me. There are two main types of resin, polyester and vinyl ester. Vinyl ester is typically stronger, and less likely to absorb moisture, but realistically other factors are more important.
Resins do not fully cure when they are exposed to the air, so the last layer needs to have wax mixed in. Some resins are premixed. These are usually called surface resin. Laminating resin does not have pre-mixed wax. This is because wax reduces the strength. If you do not have surface agent (wax), you can spray a mold release over the area instead, but it must be cleaned off after.
The step many people mess up is mixing the catalyst into the resin. There are tables for the optimal mix for different temperatures, but for most reliable mix bring everything into the same climate controlled ish area and let it all balance out to the same temperature, ideally around 60 Fahrenheit. When stirring the catalyst into the resin, be sure to mix it fully, scraping the sides bottom and corners of the container. If it is not fully mixed the resin will never fully harden. Don’t mix to much either. It can kick before you finish applying it to the surface.
Lightly sanding between coats can help make a clean finish.
Applying the gelcoat should be applied in multiple thin layers. Spraying the gelcoat will make the smoothest finish, but paint brushes and rollers work too. When sanding the final coats, be carful not to sand all the way through the old gel coat when leveling it out. Repairs will likely not look like they just came out of a mold. My repair, I had black gel coat but no green, so I painted a larger area for a new look. i forgot to take a picture of the final coat, but part way through.
I hope this is helpful for your future glass work. If you are looking to try your first fiberglass repair, try to find someone who has done it before to help you. It is great to talk through all of the materials you will need with someone when you are buying the supplies. If you have questions let me know!
Now it is time to get back on the water!