all the hdu was 1.5" 15# precision board. I think the material left beneath the wood planks was about .15 thick, but this was epoxied to a 4" core with mas epoxy. simply drill a few holes into the core with a 1/2" bit about 1/2" deep every so often. that gives the epoxy a little extra holding power_ so I've been told. I do it and it has worked so far.