I’m working on a new garage roof. After installing 18mm plywood, do I need a primer before installing self adhesive underlay+ felt? Yes, a primer should be used when installing an IKO self-adhesive underlay onto plywood. We would recommend either the IKOpro Easyseal Bonding agent or IKOpro SA primer for such an application. How do I install easyseal underlay and cap sheet felt I want to use IKO Super Shed Felt for my 10 ft x 8ft shed. What size clout nails should I use? I will also need to overlap the felt, how much overlap should I use and is it necessary to use adhesive?