4sp wrote:
I'm a house painter, not a flooring person-so I would think that if the white paint has seeped into cracks and holes that can't be sanded or scraped with a pointed scraper (like a caulk remover scraper) or something finer line a dental pick, or nail in a vise grips, I would "paint" them too, as Kevin suggested. But, instead of paint, if you have a coat of poly on there(which will stop the stain from soaking into the surface of the floor boards), I would take a dark stain(oil, but latex might work well also), apply it to the cracks and gaps with a rag or small brush, and then wipe off the surface of the boards with rags and paint thinner (or water if you go with latex). Latex products might offer better filling. Maybe a dark "polyshade" product.
A heavy-bodied exterior house paint (Aura from Ben Moore or Duration from Sherwin-Williams) would offer good filling with less shrinkage/cracking(good flexibility) then oil stain. Might work well, all you need to do is hide the white so that your eye isn't drawn to it and you will never notice.
Maybe you could take a dry paintbrush to remove excess product, because you don't really want to fill the cracks, just coat them with something dark. Maybe even clean the cracks out with compressed air after you have filled them with stain?
ps: Just re-read the post, sounds like you need to paint the gaps between boards. Could use an airbrush with black paint/stain, or devise some sort of paint-pad (like a rag wrapped on a putty knife)you can slide between the board gaps. Then you can wipe the surface off and continue finishing the floor.
Thanks for the suggestions. Using the exterior paint sounds like a good idea.