First thing to do was sort out the "small crack" which had never let any water in , apparently I could just sikaflex it. Not that the seller was any the wiser than me, he was a nice fellow, I think , right Neil ?? I got a wire brush and drill and just started to remove the old repair, which started off as a 3 inch crack.
Each layer of the deck has to go back as was, you cant just fill it with glass as it will create a hard point which will crack.
Firstly I put back the gellcoat layer in the hull, I used a bit of hard plastic off an old TV, this forms a seal and a base to put the rest of the deck material onto. I used eastcoast fibreglass marine grade epoxy and glued it and then used fibre strips where it met the edge of the hull.
then I cut out some ply and put that layer back which layed on a "thin" level layer of resin. I only left this to go solid enoguh to lay the firbreglass so it could co-cure with the next layer.