LDPE plastic shaving

20 g of LDPE plastic shavings that come from finishing and drilling the kayaks once they've been moulded in one piece (to insert hatches and rod holders).

This is the same plastic, and it's a good thing it's the only one that sticks well.

Clean up, heat the area, melt some shavings, reform, be careful with the thermal driver, you need a regulable and or *be far enough away, the melting temperature of ldpe is around 110/120 ºC - the work is best done at 80-90ª C.
It's fairly easy to do a cosmetic repair or a repair on the emerged part of the kayak, but for large repairs or repairs under the hull, you need to be sure, there are other techniques for reinforcing before repair (heated staples...) - If you're not sure, have it done by a professional.