I would have to say this process developed by Tony Johnson about 2 years ago is without a doubt the best way to repair scratches and gouges in plastic kayaks.
Some time ago, Tony and I were trying to figure out a way to extend the life of our kayaks. Because of the countless hours we spend playing in the rock gardens along our coast. Even some incidental contact with the sharp rocks in our area can add up to gouges shortening the life of our boats.
Tony and I had been exchanging emails on some of the products we had been trying (most testing done by Tony). We had tried everything from over the counter products like G Flex to just about everything Tony could find in his garage, including rope, plastic bottles and anything else that came to mind. Then one day Tony told me he had found something that worked very well, Poly Tarp. He explained the process and I also gave it a try on my boat……NOW after countless hours of testing I can safely say that there is no better way to make permanent repairs to scratches in your plastic kayak. This stuff is more abrasive resistant than the parent product and will not peel off.
– Bill Vonnegut

Tarp repair by Tony Johnson

Using the poly tarp color of your choice and a heated putty knife is all that’s necessary to do these repairs. Just heating the putty knife enough to melt the tarp into the hull (on a molecular level) will be a very strong
permanent repair for filling gouges. The tarp can also be used to armor areas that are prone to making contact with rocks. This process only heats the putty knife and when done properly with not deform the hull, there is no need to back up the repair area.

I use a torch, any torch will work as long as it can heat a putty knife red hot. Cut the poly tarp into two inch strips. You can fold the two inch strip, making a one inch strip two layers thick for deeper gouges. Place the tarp on the repair area and melt the tarp into the scratch/gouge using the hot putty knife. Work the tarp as the knife starts to cool, being careful not to heat the hull to the point it starts to deform. If you have two gouges work back a forth between the two, giving time for one gouge to cool as you work on the other. Tarp comes in many different colors and can be used to do designs also on your plastic boat. There is also the option of using a butane soldering iron/torch with an attachment similar to a putty knife, however any wind at all seems to cool this product and make it unusable.

Tarp repairs

Tarp used as armor on the keel.