Can I brush or feather a fresh coat into the old finish, to spot patch?

Q: I am trying to sell the house I grew up in. It was made in 1950 and the oak floors have been covered by carpeting from the beginning, so that almost all areas are near pristine with only minor cupping and gaping. However, there were 3 dark spots all less than 8 sq. ft. each; one adjacent to the bathroom, one adjacent the kitchen (both in the hall) and one in the middle of the living room. The larger one in the living room I managed to buff out, going through the overlying coating (I assume it’s polyurethane). I have sanded a little on one of the others and have removed the stain on the cupped edges and reduced it in the middle.

I assume the stains are water spots and think I can hand sand them out fully. I would like to just reapply polyurethane to the sanded and buffed areas and call it good, suggesting to the new owner that he have a couple more of coats of urethane applied over the apparently thin existing coat. The oak/finish is the common golden oak color with the bare oak not much lighter. Can I spot finish hardwood floor, brush on new oil-base urethane and feather it in to the old finish? If so, am I going to have a problem with agents/clients walking on it before it fully cures? Month? I can keep the house heated to 72 or a little above, but how long before I can cover the spots or allow traffic?

A: If you brush or feather the fresh coating into the old finish it won’t bond. I would lay down some green tape to indicate exactly where you will be coating. Abrade the existing finish with fine sand paper inside this marked area. Apply a thin coat and immediately remove the tape.

The finish should be dry to walk on with over night drying. Typical specs would say light traffic the first day. Normal traffic after 3. Most of the curing is accomplished in the first week under good conditions. Over night and you should be OK. I wouldn’t cover the fresh coating unless you intend to uncover it at days end. The finish needs exposure to air to help in the curing process.