Reply by gfadvm

That finish is aluminum oxide and will KILL planer blades in a big hurry (voice of experience here!). I use a lot of flooring for my boxes and have found a drum sander with 50 grit paper the best tool to remove this finish fast. 80 grit also works well but require a couple more passes. I do use my planer to remove the grooves on the back side. If you can swing a drum sander, DO IT! I have 2 and they get used on every project.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm