Hardwood Floors October/November 2024

AT THE SITE Dark Spots Mysteriously Appear in Red Oak (Again) (Continued)

Your first thought usually is that you or your helper must have sharpened the scraper over the floor (or hit a nail), and these are the resulting iron deposits from the errant shavings. But look closer. From where do you see the spots emanating from? If they’re our mysterious dark spots, they’ll be board-specific and all originate in the soft grain vessels, elongating in the same direction as the grain (though some can spread a bit sideways as if smeared). So, what are these spots, and can we The scenarios and chemical reactions that make up these spots have been around for as long as red oak. While there are various theories as to their exact origin, the general consensus is that the dark, gum-like substance that is the basis for these spots is formed by the tree’s defensive reaction to damage and/or the colonization of one or more microorganisms in that particular tree. This substance forms and is stored in the open vessels of the soft grain to help prevent the spread of any fungal, yeast, or bacterial attack resulting from any damage or colonization. During kiln-drying, it does stabilize and becomes somewhat brittle, but the temperature used to kiln-dry wood flooring (160-180°F) is not high enough to make the substance insoluble (>212°F); thus, when alkaline and polar solvents (common in many sealers and finishes) are applied to the wood’s surface, the substance has a tendency to bleed out from the vessels. IS THERE A WAY TO PREVENT THEM? Since the “spot” substance originates in a “standing tree,” it can’t be remedied in the tree itself. Given that, and the fact that flooring isn’t kiln-dried to a temperature to eliminate the problem, you must discuss the possibility of these spots appearing with the floor owner when talking about their floor project from Day One. The biggest challenge is the spots are only readily visible when the flooring is brand new (photo 1, previous page). If you’re good at spotting affected boards, you could separate them out during installation. Just don’t miss any because you won’t know until sealer/finish is applied when they’ll pop back out of the grain (which, of course, is too late). If an existing floor is stained a wood tone, it will be hard to pick out affected boards as the spots will look more like character marks than prevent them from showing up? WHAT ARE THEY?

PHOTO 2 – SANDED

PHOTO 3 – WHITE STAINED

PHOTO 4 – WATER SEALED

PHOTO 5 – FINISHED

PHOTO 6 – WATER POPPED

PHOTOS COURTESY OF BONA

70 hardwood floors hardwoodfloorsmag.com