Hardwood Flooring
Hardwood Flooring

Hardwood finish and adhesion, the overlooked but critical factors

The tremendous range of hardwood floor finishes available these days has become almost exhausting to keep pace with any more. In the previous blogs we have discussed wood floor finish options and pro and cons. This blog has less to do with actual chemistry and understanding mechanisms of adhesion.

There are pretty much two ways by which hardwood floor finishes adhere to a floor, chemical or mechanical bonding. Chemically bonded finishes integrate into previous layers and essentially fuse into one layer of finish. Acid curing “Swedish” finishes will chemically bond to a wood floor and merge into one finish layer. The significant advantage of this type of bond is that it is virtually impossible for the finish to have adhesion problems to a wood floor regardless of the final burnishing steps or the species of the hardwood. Some species of hardwood contain a high content of oil and sometimes silica and this may create potential adhesion problems for a finish.

The second form of bonding of finish to a wood floor is a mechanical bond. A mechanical bond of a finish requires a roughed up surface so that finish can literally fall into the texture of that surface and “grab” the substrate. The layers of finish in a mechanically bonded system are much more sensitive to compatibility as they are applied in succession. For example, if you stain a wood floor with a penetrating stain, and then apply a weakly bonding quick dry oil sealer, followed by coats of waterborne urethane, there is a real chance for the finish layers to be torn off the floor following application of tape or some other sticky substrate. I have witnessed this firsthand and received many phone calls from distressed colleagues.

The final finishing grit of the sanding process can also affect adhesion. I know that there are sanding machines present that rotate with such significant speed that they may close down the grain of the hardwood floor at certain sandpaper grits so that a mechanically bonded finish will have problems sticking to the floor. In this case I recommend re-opening the grain by wetting or “water-popping” the floor.

A final and overlooked factor affecting finish adhesion occurs during abrasion of a finish coat layer in order to accept a new finish coat. The abrasives used to abrade the floor will typically become dull within a suggested square footage for usage. If a contractor continues to abrade the finish layer with a dull abrasive, the surface may again become too slick for the new finish layer to hold on. The result is that the finish will peel off the floor in big sheets.

Although this blog may not be particularly intriguing to all, it may serve as a reminder that there are sometimes questions to ask your contractor that go well beyond the price of the job.

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