Super-Smooth Poly Finish Groton CT
New London, CT
M-SA 6 am - 10 pm
SU 8 am - 8 pm
Super-Smooth Poly Finish
Super-Smooth Poly Finish
A Defect-Free, Even Finish with a Brush
by Eric Smith
Polyurethane is a tough, high-quality finish, ideal for tabletops and other surfaces that take a lot of abuse. But no matter how clean your finishing area or how good your brushing technique, a few bubbles, dust particles and streaky spots always manage to sneak into the final coat (Photo 1). Directions on the can don’t say anything about it—leaving you to assume a less-than-perfect finish must be your own fault. However, the solution is quite simple—rub out the finish with fine sandpaper and synthetic steel wool. Sanding removes defects and levels ridges.
Photo 1: The Problem: A few dust nibs, broken brush bristles and bubbles are almost inevitable on big horizontal surfaces finished with slow-drying polyurethane.
Synthetic steel wool creates an even, silky smooth finish that’s a joy to look at and feel. This age-old two-step technique is commonly used on shellac and lacquer finishes, but it can work well on water- and oil-based polyurethane, too. The only drawback with poly is that it is difficult to bring up to a high gloss. If a satin or semi-gloss look is what you’re after, this technique will give you great results.
Materials and Supplies
SandpaperSandpaper is used to flatten the finish and remove dust nibs and brush marks. Stearated aluminum-oxide sandpaper is by far the best product for sanding a finish. Stearated paper has dry lubricants that help prevent “corning” or the balling up of finish on the paper. Wet-dry silicon-carbide paper balls up like crazy if you don’t use water as a lubricant. The trouble with wet sanding is the water slurry can make it difficult to see your progress.
Synthetic Steel WoolI used synthetic steel wool on both water- and oil-based polyurethane. Traditional steel wool is not recommended for water-based finishes; it sheds steel particles that leave a mess and give the user steel wool slivers. Synthetic steel wool pads equivalent to 00 steel wool are widely available at home centers and hardware stores. Fine synthetic wool equivalent to 0000 steel wool is harder to find. I had good luck at auto-body supply stores and mail-order woodworking suppliers (see Sources, below).
Powdered AbrasivesPumice and rottenstone are sold at some paint stores and at woodworking suppliers. Pumice is ground volcanic glass that comes in grades from 1F (coarse) to 4F (fine). Rottenstone is even finer than 4F pumice. It’s made of ground limestone (see Sources, below).
Build a Good Foundation for the Finish1. I use 220-grit sandpaper for final sanding on raw wood. I always sand a little bit longer than I think is necessary. Then I vacuum thoroughly and wipe the wood with a clean, soft cloth until I stop getting dust on my fingers when I run them over the wood.
2. Use grain filler on open-pored woods, such as oak or walnut....