Q. I sanded and finished an
older wood floor and applied four coats of water- based urethane. Now the
floor has cloudy or white stripes along the separations of the boards. Why?
Remember that the floor has had a lot of wear and tear and may have
been abused-improper maintenance products may have been applied for years.
There could be wax, furniture polish or other household cleaners that are
not intended for hardwood floors present on the floor. If left behind in the
seams or wood cells, these contaminants could cause white lines to appear in
the finished floor. This could occur throughout the entire surface or only
in heavy traffic areas. The white or cloudy stripes or lines that you now
see can happen to any refinish job that has a surface finish, whether it's
water-based, oil-modified or another type. When sanding and refinishing an
older or existing wood floor, there are many precautions to take. Proper
choice of sandpaper and proper sanding procedures are critical. Knowing what
grit of sand-paper to start and finish with could prevent problems in the
finishing stages. The floor must be cut properly each time it is sanded. Different grits of sandpaper (coarse, medium and
fine) should be used on succeeding cuts. If these procedures are not
followed during the sanding process, problems can occur. Most people get
into trouble when the floor sands easily and the old finish cuts right off,
because they then take shortcuts by eliminating a sanding step. When you
eliminate a sanding step (i.e., skip a grit), you leave contaminants on the
floor. Following all sanding steps ensures sufficient wood is cut to
eliminate or at least minimize the amount of contaminant left in the floor.
In some cases, trowel-filling with latex filler between the medium cut and
fine cut, or grain filling after the fine cut and before screening may
eliminate some of the problems. Improper screening between coats may also
contribute to the problem. Inter-coat adhesion is very important. In the
finishing stages of the job, it is critical that you follow the finish
manufacturers' recommended procedures for applying finish and preparing the
floor between coats. Too often when a floor is coated, there is not enough
time spent on preparation between coats.
Buffing with an
abrasive pad or a screen to smooth and abrade the finish between each coat
is a very important part of the finishing process. Some manufacturers'
finish products can be coated without padding or screening between certain
coats. The finishers must have good judgment up front. On all finishes, dry
time is very important to the coating process and how the job looks and
performs after it is complete. If you know that you will be using a water
based product on a refinish job, you must consider extra dry time. Just
because a finish is dry enough on the surface doesn't mean it will be dry in
the seams or side matches of the hardwood floors. Finishes or stains will
aggravate or loosen any contaminants that are present, so pay particular
attention to finish in end-joints and side-matches. Remember that
contaminants are not seen or detected until after the first, second or third
coat is applied. Old floors also move more than new floors. They have been
exposed to the elements longer and the structure has settled over the years.
A floor that is tight, with minimal cracks, is deceiving. Even though it
looks tight, it may move up and down. In this case, it will cause the finish
to stretch at the seams, resulting in the white or cloudy lines in the
floor. This appearance can worsen over a period of time. The best prevention
against this stretching of the finish is to keep a constant humidity level,
thereby keeping floor movement to a minimum. Dark floors such as mahogany
will show the effects much more than a lighter floor. When sanding and
refinishing an older floor, keep in mind what problems that may occur. Good
job-site inspection should be done at the time of the estimate and all
findings written on the contract or job order. When a floor such as this is
refinished, it is the responsibility of the wood flooring contractor to
educate the customer. Don't hang yourself out to dry in this situation !