What causes white spots on our floors?

Q imported from our old site, Face Lift Floors: I recently had the hardwood floors in my 1950’s house professionally refinished (sanded, stained, and polyurethaned). The floors were previously covered with carpet and had some stains, thought to be from carpet cleaning chemicals. A couple of months after the floors were refinished, white spots on some areas of the first floor started appearing and keep on getting worse. The floor is above a crawl space. The contractor said he thinks it’s from moisture; however, not all areas are affected and it seems the white spots are in the areas that were previously stained. (- from an Environmental Scientist)

A: First, I don’t recall ever seeing staining from carpet cleaning chemicals, except that around the perimeter, the moisture will cause black rings around the nails of the smooth edge that holds the carpet in place. Other than that, I have never seen “stains” from carpet cleaning on the floor in general. None the less, such chemicals would be or can be a concern. If it cannot all be removed from the floor, how will it react with the solvent based finish? It is likely that such finishes will “activate” existing residue from old finish or cleaners.

I have seen white spots in the past with products that are not compatible when not fully cured and mixed together. Are these light areas on the board joints or all over the surface?

Since this floor is over a crawl space, do you have this area vented and covered with a tarp? How far above the ground is the floor? I don’t suspect this is a problem with moisture at this point. If it was, the floor would swell and cup! Wood always expands or shrinks with more or less moisture.

So, I think this must surely be a chemical reaction between incompatible substances. As the workers went through the process of sanding and finishing the floor, did they allow sufficient time for each coat to dry? Given that there is a crawl space, it is likely cold under the floor. So, each of the products would likely require longer dry times, for stain and finish.

Original / moved link https://faceliftfloors.com/q-and-a/whitespotsstains.php

White spots on exotic woods

White spots can also be caused by compounds in the wood. See here.

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