Hi there folks. Having some issues with my Alumifoam cranks and hope someone can help. This is my process: pour Alumifoam in a 2 part mold. After it dries, there's a mushroom of excess foam where my pour holes were. I sand those down flush and fill in the "scar" with wood putty. Sand that, prime, paint, and do 3 coats of etex on a drying wheel. What happens next is what I believe is off-gasing. My paint bubbles under the etex and then cracks or splits(see pics). I just did a batch and sealed the foam with spar urethane like my cedar lures. Haven't painted or applied etex yet. Any help or suggestions?