job wrote:

Hi. I am looking for ways to fix Velcro straps to the hull of a Kevlar Sea
Kayak.
The straps would be to secure lead ballast and other gear
I am thinking of using thickened epoxy or contact cement.

The hook side of Velcro is very difficult to bond to. I don't know for
certain, but it appears to be made of polyethylene, which would explain
the bonding difficulties. Also, Velcro on it's own is not all that
strong and I wouldn't trust it to hold ballast weights without some
reinforcement. Your best bet is to sew the velcro to polyester webbing
(or nylon if you can't find polyester), then epoxy the webbing to the
hull. The webbing will bond well with epoxy. Contact cement will also
work, but it's best used in areas where it's not constantly wet.