Polyurethane did not exist during the civil war era.
What do a oak bookcase, a walnut clock and a cherry table have in common?
Besides being constructed of natural wood, they all look especially nice with a
clear finish. In fact, most natural woodworking jobs call for one or more topcoats
of a clear finish. That's not to suggest that they can't be stained, they can.
An antique walnut clock will look stunning and last for a very long time, with a
hand-rubbed oil stain. The oil stain will feed the wood fibers keeping them moist and
supple. There is only one problem, there is no UV protection. On the other hand, an
old oak table that is used primarily for daily dining will last longer, look better and be
easier to keep clean with a hard, clear finish. Wood and water do not mix. If the object
will be exposed to water from time to time, go for a clear finish.
One of my favorite clear finishes is marine polyurethane. Essentially a marine base paint
without pigment, polyurethane is an extremely durable clear plastic finish that is ideal
for tabletops, wet bar tops, doors, hardwood flooring, etc. Although there are
water-base urethanes, I prefer marine polyurethane because of the way it flows and the
super-hard finish that it achieves.
You don't have to be a pro to have a finish that looks like glass. With a little patience
and the right tools and materials, you can have professional-looking results.
How to use Polyurethane?
Begin by making sure the surface is clean, dry and smooth. Sand the surface with
progressively finer paper beginning with medium (100-grit) sandpaper, then 150-grit and
finish with 220-grit. Use a vacuum cleaner with an upholstery brush, along with a tack
cloth to remove all the sanding dust. Then wipe the surface with a clean cloth dampened
with denatured alcohol.
If you will be staining the object, now is the time to apply the stain.
Wipe on the stain using a soft, clean cloth. Apply evenly, being careful to remove
excess. Gel based stains give you the most uniform coverage.
Allow the stain to soak in overnight before applying the first coat of polyurethane.
Since heavily grained wood -- such as oak -- absorbs stain unevenly, you may need to first
apply a clear sealer. Some stains are self-sealing and, thus, don't require sanding
sealer. The label directions should specify what you are using.
If you will be skipping the stain, the first coat of clear finish should be thinned as
follows:
three parts polyurethane and one part mineral spirits.
This will help the polyurethane penetrate the wood more easily and reduce the number of
brush marks. The thinned polyurethane should be brushed over the entire surface to be
finished. For best results, use a China or natural bristle brush designed for use
with oil-base stains and paints. Synthetic brushes tend to leave brush marks.
After the initial coat has dried (at least 4 hours), lightly sand it smooth using 220-grit
sandpaper. Use the vacuum and upholstery brush along with a tack cloth to remove all the
dust, and prepare for the next coat. Unlike the first coat, the second coat of
polyurethane doesn't need to be thinned. In fact, if the material is too thin, or if too
much is applied, it will usually run, which can be quite a chore to repair. If a run does
occur, allow it to dry and cut it away using a razor blade. Be careful not to cut into the
surrounding finish. Small drips will disappear when the finish is wet-sanded.
Repeat the process for the third coat and any subsequent coats. Be sure to sand between
coats using a wet 400-grit wet and dry sandpaper to remove imperfections in the surface.
Two to three coats should be sufficient for a previously finished surface. Your furniture
kit usually will require three to five coats.
After the final coat has dried completely, use an automotive rubbing compound first, and
then a polishing compound to remove minor scratches and to achieve a glasslike finish.
Finish the job by buffing the surface with a clean cotton cloth.
What is the drawback of Polyurethane?
Polyurethane can be toxic. If you have small children or pets that could chew on the Finish, Polyurethane is a not good choice. It is a not good choice to finish baby furniture or childresn toys with.
Why use Polyurethane?
Polyurethane can even be used successfully to finish an exterior piece of furniture provided that it has reasonable protection from the elements, such as on a covered porch. A better bet for exterior furniture is a marine spar varnish. Spar varnish is a tougher, more durable finish that will hold up to prolonged exposure to sunlight and water. However, it, too, will require regular upkeep.
How do I apply Polyurethane?
Well, you have three choices. Brush it on, spray it on or wipe it on. Spraying it on
works best with an HVLP type sprayer. The nozzle must be one for thicker materials though.
Be sure everyone in the room wears a respirator. Brushing it on is what most people do. A
2 or 3 inch china bristle brush works best. Clean the brush with denatured alcohol or a
mixture of one part ammonia to one part water. Remember, use long full even strokes. To
wipe it on start with an old, clean T-Shirt that is 100 percent cotton. Fold it into a
palm sized pad and dip it into the Polyurethane. Again, take long strokes, please. Avoid
rubbing in circles because it will result in an uneven finish. Toss the T-shirt pad in the
trash when you are done. Which ever method you choose, be sure to apply thin coats
following the wood grain. Being sure keep a wet edge. Use long strokes from one to the
other end of the furniture.
Back
