Q: I have recently installed tongue and groove spruce floors. The boards shrunk a bit so there are grooves between most of the boards. I have applied a mixture of 1/2 stain 1/2 Waterlox to the wood but am wondering what you would suggest to use as a final coating that would give a harder finish and also fill in the grooves?
A: I have used Waterlox several times including staining a very large pine floor with stain mixed with the oil coating. It worked really well. Waterlox is meant to be a finish coat and there is no need to screen it between coats if you need to freshen it up. That is a big plus. However, it isn’t a hard surface coating. If you want that sort of finish I would use Poloplaz Primero. Great polyurethane and applies beautifully well with a roller. You will likely need two coats over the Waterlox but you will have to judge yourself after applying one coat. 500 Sq. feet per gallon.
It isn’t unusual the spruce shrunk and left gaps. I’d give it a full 4 seasons to see if some of them close up. There isn’t a fail safe wood filler I’ve used or heard of. If there is any movement between boards or even vibration, it will eventually crack and start falling out.