A depression where the grain shows

Q: We just had our oak hardwood floor refinished and are not happy with the finish. It looks like the polyurethane is uneven. You can especially notice it when squatting down and looking forward. Wherever the wood grain is showing it looks like there is a bit of a depression. Overall instead of getting a flat smooth looking floor it seems to have undulations.

We also had a new section of floor which looks the same. Our installer says its the nature of the wood, but it didn’t look that way before we had it refinished. Any idea what is causing this and how to fix it?

A: It is the nature of the wood actually. That heavy grain in plain sawn oak is quite a bit softer than the surrounding material. When it is sanded more wood is removed from the heavy grain in what is called dish-out. This softer grain also tends to absorb the finish to a greater degree than the rest of the wood. Though not as pronounced as it is after sanding, you can look closely at such a board straight from the mill and never sanded. The heavy grain is slightly depressed on those boards too. If you don’t like this natural look of plain sawn oak, perhaps you should have selected quartered and rift sawn…