When we decided to pull the mast to rebuild the mast step the need for some additional work was easy to see. The original construction of the mast collar left the deck core open to water intrusion. The tie rod fitting was in poor condition and the bolts attaching it to the deck were bent. So the nice work installing the new header and varnished trim had to be removed temporarily.
Although we expected to find plywood in the core for this area it was mostly end-grain balsa. The only plywood was 1/2" thick 2" square pieces around the upper part of the collar. The rest was end-grain balsa.
We also found that the inner layer of laminate thickness was variable and much thinner than the outer laminate layer.
Fortunately the core (made of small rectangular sections) was heavily bedded in a polyester fairing compound. This limited the water intrusion from going further into the core.
Access to excavate the wet core material was relatively easy using a set of old wood chisels. Once the area had dried a wire brush on an electric drill was used to clear out the last bits and clean the polyester surfaces.
A 1/2" marine plywood backing was cut using the SS collar as a template. We thought of using G-10; however, the inner laminate surface is so irregular that we felt it would be better to use a material that will compress slightly and conform to the shape of the surface. This was glued into place using a flexible epoxy adhesive.
The void between the fiberglass layers was then filled with thicken epoxy and faired to make a solid structure. The holes for the stainless steel collar were re-drilled. The collar was dry fitted and then bedded using butyl rubber tape.
A new SS fitting will be made for attaching the tie rod on the two aft bolts of the mast collar. We are not sure it was very effective in the condition we found it. At the moment we have ordered a small piece of 316 SS angle stock 1.5" x 1.5" x 0.25".