Hi Henry, Thanks for your response. The floor is actually still at 3/4" in most places. I think a lot of the wood over the grooves may have lifted when I was prying underlayment off. The floor is solid, with only a few spots besides the gaps that I am really concerned about. Do you think it just best to leave the gaps instead of filling them? I have heard of people using a mixture of Polyurathane and saw dust to "slurry" in the gaps, but I think I may just be the safeist to leave them alone. I have two spots that need wood filler, I don't think I can get around it. If I do resort to a filler to you have one you recomend? And how about the type of sander????