Yes, You Can Still Coat Floors in Winter

Pete’s is based in Minnesota where the floor refinishing market all but dries up by the beginning of January. But it shouldn't be that way.
 

All of our customers are convinced (not without cause, mind you) that the floor-coating process will be unendurably smelly during the closed-window season.

And sure, compared to coating in the ideal month of June where the days are warm and breezy, but not humid, coating in the winter is slightly more challenging.  But by managing your heat source and choosing the right products, the winter months can be the ideal time to refinish or recoat floors: you’re already cooped up inside, so you might as well be doing something!  Think about how romantic it would be to have a refinished dining room floor by Valentine’s Day…

Heat, Humidity and Air Exchange

No matter what the season, modern floor finishes need three conditions to cure properly and quickly: dry air that is above 65ºF and a source of fresh, outside air. The air has to be dry because damp air literally blocks the solvent from evaporating.  It needs to be warm because the chemical reaction that cross-links and cures the finish will not proceed below 65°. That chemical reaction will also stop or slow if the solvent-laden air hovering above the wet finish is not regularly replaced with fresh air, a process known as air exchange.

The curing process may sound finicky, but it’s worth it because finishes that cure are tougher and less permeable than finishes that merely dry.  Finishes that dry by evaporation of their solvent can actually be re-dissolved by an application of that solvent. For example, if you rub hardened shellac with denatured alcohol (or a bit of gin) it starts to soften and dissolve. Polyurethanes, however, cannot be re-dissolved, no matter how much solvent you wipe on them, because their solids have irreversibly cross-linked.

 This is a long-winded way to say that the conditions under which you apply finish are crucial, no matter what the season.  July and August are actually the most challenging months for coating, because of humidity levels.  Even in an air-conditioned home, maintaining a reasonable balance between heat and humidity is challenging, so the smelly solvent lingers and the finish never seems to dry.  Applying finish between November and April is actually easier because the air is naturally dry. So all you need to worry about are temperature and fresh air.  One window per coated room cracked to a height of 3” supplies enough air exchange for most finishes, but air movement is important too.  Finishes should be allowed to level for 45 minutes to 1 hour before circulation is reintroduced.  Slow-turning ceiling fans,  HVAC fans set to ‘on’ or a fan on low in an adjacent room will make the air move and allow those polymer chains in the finish to entangle each other.

But what about the SMELL? 

Even with air exchange adequate to allow curing, the odor of that solvent laden air can hard to live with.  In cold weather, we tend not to open windows in non-affected rooms, and this can cause coating smells to linger.  Most solvents are heavier than air, which concentrates vapors in the lower floors, but in winter the solvents ride the rising warm air, so the upstairs can be just as bad.  Here is where choice of finish can make a difference.  Finishes with lower levels of volatile organic compounds (VOCs) will be less offensive, even in winter.  Since most oil-modified finishes have high VOCs, we steer customers toward waterborne polyurethane between November and April.  The only drawback of that recommendation is that traditional waterborne finishes don’t give floors that warm, amber color that the oil polyurethanes do.  Some companies, including Basic Coatings and the Swedish company Bona have developed waterbornes that contain some color, though not quite as much as the oil polyurethanes.  We have been skeptical of tinted waterbornes in the past because the color can appear uneven on the floor. But we have tried Bona’s Deep Tone Sealer (only 170 g/L VOC) and have been pleasantly surprised. The Deep Tone Sealer acts as a primer coat and is followed by two layers of any Bona brand waterborne poly.  We carry Bona Mega (in gloss, semi-gloss and satin) or the commercial strength Traffic (semi-gloss or satin).  The biggest drawback of the Deep Tone Sealer option is cost, largely because waterbornes tend to be more expensive than oil-modified polyurethanes and they don’t cover as much per gallon.