I used Divinnycell H-80 3/4" thick cut into 1" squares wigh a scrim backing. Because of the favorable location and great price I used advanced-plastics.com. Installl with scrim side up. I used ATC-72 core adhesive but had to buy a 5 gal bucket but I have found many other creative uses so as not to waste it. It does require the same catalyst as polyester resin and when mixed has the consistency of thick mud and cures in about 4 hours. Apply it with a notched trowel like you would lay tile and when you install the core put some weights on to ensure a firm bond as the core will want to float. When the core adhesive has cured pour a generous amount of resin on it and roll it out. The objective here is to fill all those vertical grooves in the core with resin. This does 2 things - 1) builds a honeycomb type structure - 2) isolates each square in the event of water intrusion. Then lay the cloth and wet it out with resin. It is critical to have the core completely encased in glass to prevent water intrusion. Have lots of resin on hand as this step will use more than any other part of a restoration. 2 other notes - 1) you may want to leave a small area at the stern un-cored to install a bilge pump and another small area for a thru-the-hull depth gauge transducer. 2) - The techniques described above also apply to an end-grain balsa core.
