On Thursday morning last week we began releasing the centreboard from the mould. When we separated the two moulds halves we were very disappointed to see that one skin of the centreboard had torn its self from the foam core. Later it was found to be the electrical tape we had used to create a recess in the leading edge of the centreboard that had stuck heavily to the mould. This created a tensile force between the skin and core at the leading edge of board.
As can be seen from the image above the foam core failed in tension then the fracture propagated to the skin where the foam (not the foam / skin glue line) continued to fail in tension due to the peeling force. We then had to fill the void with straight epoxy resin and re-close the mould to rejoin the skin to the foam core.
This is what we learnt from it:
1. We should have put PVA or wax on the electrical tape and not just relied on the smooth plastic surface for a clean release.
2. That the foaming resin is a lot weaker than we first thought after two days of cure time. The data sheet recommends that the foam be post cured at 50 degrees for 16hrs to obtain the best properties.
Note: The board in the unpainted state weighs 3kg