RE: Early eighties D&B Models P-51 D
Hi Jeff, the joint problems were obviously due to adhesive failure at the joints. The why of that would make an interesting discussion. My initial and many years belief was that the finishing resin attacked the foam through the glue joints but that proved false as the core was not dimpled at the joints. The more likely explanation for me now is that when wet sanding the finishing resin, moisture was absorbed into the glue joints of the sheeting and migrated 1/4 inch or each way to the water based bonding adhesive. At the same time, swelling of the wood added pressure and the joints were then the weak point to buckle up.
Did you use a finishing technique employing any wet sanding by chance? My joint problem did not show up however until after the epoxy finish coat but I'd used epoxy several times on sheeted foam wings but that was the first time to use finishing resin as the sealer.