Sea Kayak Repair: my attempt to fix my carbon fibre kayak

On one disasterous day trip along the coast four calamities hit me. First a helpful collegue pulled my kayak up a gravelly beach, the gravel jammed my skeg and in attempting to release it, the skeg broke. Seondly, my beautiful, red and white, carbon fibre, Norse Idun Sea Kayak inadvertently made contact with a rock which resulted in a fracture and leak. On capsizing and rocks getting in the way of my poor attempt at a roll, I discovered that thirdly, my dry suit was no longer dry. Finally my "waterproof" VHF radio packed up, the charging point cover had undone and water had entered, killing the device. Its replacement travels in a waterproof pouch, although some people recommend taping the chargong cover instead. On the bright side, one of my fellow kayakers gained some rescue practice.

This post describes my attempt to repair the hole in my boat.

My poor fractured kayak. View of gel coat on outside of hull. The blue stuff at the top is a soft plastic release film ready to be applied across the resin I was about to apply in Stage 2.

Stage 1. Applying a patch inside.

I discovered from kindly, helpful fellow kayakers that if you have damage penetrating beyond the “gel coat” that covers the outside of the boat, that leads to breakage of the carbon fibres and maybe leakage of water into the boat, the first stage is to apply a carbon fibre patch inside of the kayak to restore the strength of the hull. For other types of kayak, slalom or polo kayaks maybe, you might apply a patch on the outside as shown in https://www.easycomposites.co.uk/learning/composite-kayak-repair-tutorial and https://www.youtube.com/watch?v=cigKOIf-HDU . I was kindly loaned a box of carbon fibre material and epoxy resin belonging to the Poole Harbour Canoe Club, which I used for stage 1 of the proceedure.

First I cleaned up the area around the fracture using sandpaper (120 grit) to removed damaged carbon fibres and form a key for the epoxy resin to stick to. I sanded an area perhaps 2” beyond the edge of the damaged carbon fibre, to accommodate the patches that I later applied. To ensure it was grease free I cleaned the area with acetone and did not touch it again with my greasy fingers.

Fracture viewed from the inside of the kayak after sanding.

Next I cut out a patch of the carbon fibre material that would cover the damaged area and an inch more, then cut out a second, larger patch that would extend an inch beyond the first patch. I used a normal pair of scissors which had no problem cutting the material but the edges of the patch kept fraying leaving short lengths of carbon fibre on the floor of my garage for weeks after.

When I had everything ready I mixed the epoxy resin. There were two bottles, one for the resin and the other for the hardener. Here I made a major error. There was nothing on the bottles supplied by the club and I stupidly assumed the ratios would be the same as for the gel coat repairs I had completed before, in which 2% catalyst was added to the (polyester) resin. Use of 2% hardener meant the epoxy failed to set and I had to pull off the patches I had applied with it, clean off the unset resin and start again!!

I bought new epoxy resin and carefully followed the instructions supplied with the products. For the ER1 Epoxy Rapid Repair Resin Pack I ordered from Easy Composites the ratio was 3:1, resin to hardener by weight. I mixed the epoxy resin in a paper cup using a wooden spatula that came with my gel coat repair kit. To ensure I had the right ratio I weighed the cup and mixture while adding the components on a small electric scales (apparently of a type also used by drug dealers based on my television viewing of Police reality TV). After vigorously stirring in both directions I applied the resin immediately before it started to set.

I first applied the epoxy resin mixture to the inside of the kayak, on and around the damaged area, covering the area on which the patches would be placed. To apply I used a small paint brush bought especially for this purpose which would not be useable once the resin mixture had set, so I chose an inexpensive one. Then I placed the smaller patch over the damaged area and added more of the epoxy resin mixture on top of it, dabbing it on top of the patch with the paint brush (brush strokes caused the carbon fibre textile to fray, strands start to come off). This was also an opportunity to make sure the patch was fully in place, using the paint brush to push the patch firmly into the bend formed by the "chine" of the kayak.

Once satisfied, I covered this first patch with the larger patch so that it extended an inch or more beyond the first patch. Then I dabbed more epoxy mixture on top.

Then I had to wait, leaving it to set overnight, however it was evident from the stuff left in the bottom of the paper cup that it was hard within a few hours. Next day I sanded off bits of fibre that stuck up to stop my equipment being caught on them.

Patch in place, note the strands of carbon fibre that became dislodged from the patch as it was put in place.

Stage 2. Repair of the white gel coat on the outside of the kayak.

To repair the white gel coat covering the outside of my kayak, I used a kit from ECF Composites. They are available in a variety of colours to match your kayak. Instructions were provided with the kit and the ECF Composites website had a video. Note that the gel coat repair uses a polyester resin, which requires only 2% catalyst, very different ratios to the Epoxy resin. Some people also add styrene (also at 2%) to give a better finish. I have in the past but have read that it means a second coat, should it be necessary, will not stick. I felt results were satisfactory without the styrene.

First I used a screwdriver and knife to prose off bits of gel coat loosend by the damage. Then I sanded the area with 120 grit sandpaper to remove any loose bits of carbon fibre and form a key for the new resin, ending by cleaning the area with acetone.

I had two types of release film, one more rigid than the other. For my first attempt I used the softer material, although I discovered this did not give the best finish. I used drafting tape to hold one edge of the release film in place before mixing the resin.

On my scales I placed a paper cup and "zeroed" the weight reading. Then I added resin to the cup using the wooden spatula provided. Next I calculated what the weight 2% was equivalent to, this I added to the weight reading on the scales. I wrote this figures down and checked my calculations. Then I added the catalyst drop by drop until the weight equivalent to 2% was reached. Immediately after I stirred the mixture vigorously before applying it to the damaged area. I then stretched the release film over it, pushing out any bubbles. Unfortunately if I pulled the film too tight, black carbin fibre became visible at the edge of the chine, consequently I had to leave the film a little loose.

On removing the release film 24 hours later I found there were still tiny patches of the black carbon fibre visible and the surface was uneven. Consequently I sanded down the first layer to remove the higher parts and form a key for a second coat. This time I used two pieces of the more rigid release film that came with the repair kit, one each side of the chine (the corner of the hull), such that they joined at the edge formed by the chine. Once set, the results this time were far better (see photos below). I only sanded down this second layer slightly as I felt additional sanding would not improve the finish, and I was worried about accidently exposing the carbon fibe again, something that had happened on a previous repair.

After first coat and sanding, preparing to apply second coat with stiffer release film seen at the top and bottom of photo

After second coat and a little sanding

See also my experience of repairing the skeg.