Why Does This Wood Floor Finish Have a Milky Cast and Uneven Sheen?

Why Does This Wood Floor Finish Have a Milky Cast and Uneven Sheen?

The Problem

I got a call about a floor with finish that showed a definite milky cast—sometimes described as a hazy look—in the overall appearance of the floor. In addition, there were differences in luster throughout the floor.

The Procedure

The 2¼-inch red oak floor was installed and sanded. A catalyzed water-based finish in a satin sheen was applied. The first two coats were applied and dried normally. They were clear and even in appearance.

When the final coat was applied, the floor was normal looking. A day later, the contractor received a complaint that the floor was hazy-looking. When he went back and looked at the floor, there was a definite white, hazy cast to the floor, and he noticed the floor had an uneven luster.

The Cause

In discussing the finishing process with the contractor, it was discovered that on the day the final coat was applied, it was raining outside, so the contractor couldn’t open any of the windows. The humidity was high and the air was cool, although the house had heat and the floors were not cold. By not opening windows or adding ventilation, the moisture from the water-based finish was trapped in the house. The finish could not dry properly, as the drying process of the co-solvent and water in the finish were slowed down dramatically.

Additionally, the extra trapped water hydrolyzed the catalyst in the coating, preventing it from curing the finish.

In cases like this, not only is the film hazy, it also is usually soft enough to put a fingernail into the surface. Trapping the water and co-solvent would also keep the film wet longer, allowing it to soak in differently in different places on the floor. This would account for the uneven luster when the finish dried.

How to Fix the Floor

If this is truly only in the final coat, a good screening to open up the surface and allow the trapped solvent and water to come out for 24 hours before applying finish will help clear the film. Then, a good wet coat of finish should be applied, allowing the proper drying conditions and ventilation.

Remember that with satin finishes, the heavier the coat, the shinier the finish, and the thinner the coat, the duller the finish. So, apply the finish very evenly and with a uniform wet film thickness, and make sure there is good ventilation for drying.

If the haze is in more than one coat, the contractor must start over by sanding off the finish. Screening deep enough to take out more than one coat is possible but is not an efficient use of time. Also, screening that deep is hard to do without leaving severe scratches that would have to be removed by starting over anyway. So, it’s best to bite the bullet, dig out the drum, and start sanding.

In the Future

On those cold wet days when the windows cannot be opened for proper ventilation, there are two ways of preventing this condition from happening (sometimes both may be necessary):

1) Set some 20-inch box fans around the house on timers set to turn on slow speed a half hour after you leave. This circulates air throughout the house and helps pick up moisture everywhere in the building.

2) Relative humidity is just that—relative to the temperature. Turning the heat up to 90°F would allow the air to pick up more water, since the warmer the air, the more water it will hold.