2nd Coat of polyurethane rough and grainy

Q: We sanded, stained and oil based polyurethaned a wood floor with 2 coats. We did not sand between 1st and second coat. 2nd Coat dried rough and grainy looking. We sanded second coat. Smooth but still grainy looking. Do we need to start over?

All 5 rooms look like this (put 1st coat down day 1 and put 2nd coat down the next day). Have not applied 3rd coat. Can this be fixed without sanding down to bare wood again. Would attach picture if I could.

A: Roughness can be caused by rough preparation in sanding, grain raise or debris in the finish for example. A light but thorough sanding with fine abrasive should take care of this issue. The floor needs to be completely vacuumed and wiped down to remove all dust and debris. I’m not certain what you mean by grainy. I’ll take a guess. If you are working with oak for example that has a heavy grain pattern the finish will soak into that much more than the surrounding wood. The grain is much softer. Finishes have a spread rate they should be applied at, generally about 500 sq. feet per gallon. Applying thick coats is a bad idea. The heavy grain is really part of the wood species. If you are trying to duplicate the look of a factory finished floor where they boast multiple coats of finish, don’t. The process is much different and all done by machine.

One more coat should make a difference if you follow what I said above. I wouldn’t use rougher than 120 grit to rub the edges. If you have access to a polisher, I would try 180 grit screens and work down if you need to. Be careful not to cut through and remove the stain.

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