Rubbing OutComments (0)
This article is from Issue 41 of Woodcraft Magazine.
The basics of “finishing a finish”
By Jeff Jewitt
Every woodworker enjoys completing projects, but few enjoy finishing them—often because the initial results fall short of spectacular. In an ideal world, you might think that properly applying a finish—whether by wiping, brushing, or spraying—would produce a perfect result. However, application is only half the story. In truth, even a flawless application may result in a finish that’s too dull or too shiny for your taste. Rubbing out the finish is an important follow-up step, because it allows you to create the sheen of your choice. In the process, you also smooth the finish and correct any defects.
The three basic steps involve flattening the finish with fine sandpaper to remove imperfections, leveling it to remove dips and humps, and then polishing it to your desired sheen. This can be done by hand using traditional materials, or you can speed up the process by using various modern products and tools. Whatever approach you choose, expect to ratchet up your finishing expertise a few notches while producing professional quality work
Some finishes rub out better than others. Those that respond best are hard, film-forming finishes like lacquer, shellac, varnishes, and polyurethanes. Thicker applications allow you more latitude in leveling, smoothing, and polishing, because there’s more material to work with. Although wipe-on varnishes don’t typically have the “build” of a brushed or sprayed finish, they can still be rubbed out, only less aggressively. In that case, the goal is usually to remove minor defects or to change the sheen. However, don’t expect results on thin penetrating finishes like pure oils and shop-made oil/varnish concoctions.
Materials and Supplies: (A) pumice and rottenstone, (B) compounding and polishing pastes, (C) abrasive papers, (D) abrasive pads, (E) lubricants, (F) abrasive backers.
Materials and supplies
Materials for rubbing out include abrasive papers and pads, backer blocks, steel wool, polishing powders and pastes, and lubricants (Photo A). Your choice depends on the thickness of the finish and your desired sheen.
Abrasive papers in grits of 400 and 600 are used to remove imperfections and to level the finish. Stearated papers can be used dry, while “wet/dry” silicon carbide papers are best used with a lubricant like rubbing oil, mineral spirits, or soapy water. I use stearated papers on water-based finishes, which may suffer from wet-sanding. Stearated papers tend to clog when rubbing out lacquer, shellac, and solvent-based varnishes, so I usually wet-sand these with silicon carbide sandpaper, using soapy water as a lubricant. When leveling a finish, wrap abrasive papers around a cork- or felt-backed block.
Micro-Mesh offers ultra-fine cloth-backed sheets that can replace abrasive papers and rubbing compounds for the entire rubbing out process. It’s available in discs for larger surfaces, and small sheets for edges and detailed work.
Steel wool and synthetic abrasive pads are used for smoothing and preliminary polishing. Stick with 0000 steel wool and ultra-fine gray abrasive pads. To attain a satin sheen, steel wool can be lubricated with either rubbing oil or “Wool-Lube” (a commercial water-based paste made for the purpose.) Abralon is a form of abrasive pad with wet/dry sandpaper affixed to an absorbent hook-and-loop disc for power sanding with a lubricant. Its 1000, 2000, 3000, and 4000 grits are much finer than steel wool.
Abrasive powders and pastes let you polish to a desired sheen. Traditionally, 4F pumice or rottenstone (the finer of the two) are combined with rubbing oil to make a paste. Or, you can use a 2- or 3-step liquid suspension or paste available at automotive supply shops, applying them by hand or machine.
To make lubricant for wet-sanding, mix a capful of dishwashing soap into a pint of water.
Coarser scratches produce a flat finish (left). Finer scratches result in a satin finish (center), while a scratch-free surface displays gloss
Types of sheen
Sheen is the quality of a finish’s reflectivity (Photo B).
It is determined by the size of the abraded scratches. Those produced by 400- or 600-grit sandpaper create a flat sheen. As finer abrasives are used, the scratches become smaller, diffusing less light and creating a glossier sheen.
Many flat and satin finishes contain small bits of silica to hinder reflectivity, so choose gloss if you want to create any sheen you like. (You can convert a glossy sheen to satin, but not the other way around.)
Dry-sand a thin finish with hand-backed stearated paper, using light pressure.
Instead of abrasive paper, use small pads of steel wool to rub profiled edges and other detailed shapes.
After sanding, rub broad, flat areas with a folded pad of steel wool, bearing down with both hands.
Rubbing a thin finish
Rubbing out a thin finish requires special care to avoid abrading completely through it. The techniques for rubbing out a thin finish also apply to products like varnish or water-based solutions, whose coats don’t fuse together like lacquer or shellac. With these finishes, cutting through one layer into the next will create visible “witness lines.”
To rub out a thin finish, start with 600-grit paper backed only with your hand. Dry-sand along the grain using stearated paper, as the sanding powder will help you gauge your progress. (If the paper gums up, let the finish dry longer.) Apply just enough pressure to remove any brush strokes and dust pimples. In most cases, one or two passes should be enough (Photo C). At the edges, hold the paper perfectly flat against the top surface to prevent cutting through at the corner. When you’re done sanding, wipe away the dust with a cloth dampened with mineral spirits or naphtha.
Avoid using abrasive paper on profiled edges, moldings, turnings, or carvings. Instead, use steel wool, applying just enough pressure to knock down the gloss a bit (Photo D). Tear away pieces of steel wool to create small pads that will better conform to the shape being worked.
Finally, unravel a steel wool pad, fold it into quarters, and dry-rub broad, flat areas (Photo E). Follow up with a series of short, quick strokes around the perimeter until its sheen matches the rest of the surface. Then blend all the areas together with a couple of quick passes over the entire surface.
Flatten a thick finish with 600-grit wet/dry paper backed by a block. Soapy water is the lubricant here
Gingerly wet-sand squared edges, backing the paper with your hand only.
Finish up by rubbing the surface with 0000 steel wool, using the residual soapy water for a lubricant.
Rubbing a thick finish
With a thick finish (6 to 10 or more coats), start with 400- or 600-grit abrasive paper torn into quarters and wrapped around a backing block. Begin by sanding just enough to flatten the finish, removing any nibs, drips, or other defects (Photo F). Wet-sand solvent-based finishes using soapy water, rubbing oil, or mineral spirits as a lubricant. For water-based finishes, dry-sand with stearated sandpaper. You can wet-sand flat edges (Photo G), but avoid sanding profiled edges or shapes. After wiping the surface clean, it is acceptable to see a few unsanded shiny spots when backlit.
Next, level the surface using one grit finer than you employed in the previous step. When the paper starts clogging, shift it to expose fresh grit or change the paper. After you’ve gone over the entire surface, wipe it clean and inspect it under backlighting. It should show mostly a dull scratch pattern, although some areas will probably still be shiny. Continue to work slowly and deliberately until the entire surface is dull or nearly so, without worrying about any small shiny areas. Finally, use steel wool to create a consistent flat sheen, which will blend in any remaining shiny spots at the same time (Photo H). You can now rub to gloss or satin if you like.
For wet-sanding, rubbing oil is a great nontoxic, odor-free alternative to mineral spirits.
Apply the coarser polishing compound first. For efficiency, use a buffing pad (like the Surbuf shown here) attached to a random-orbit sander.
After following up with the finer compound, remove the excess with a fresh pad or cloth to reveal the gloss finish.
Rubbing to gloss
To create a gloss finish, use polishing compounds. I prefer two-step products (or else pumice followed by rottenstone). However, a one-step product like Behlen Deluxing Compound will also work. After leveling to 600 grit as explained above, continue through a sequence of successive grits through 2000 grit. Then smear the coarser of the two-step compounds on the surface and rub it vigorously in any direction, either by hand with a soft cloth or with a power-buffing pad (Photo I). When done, wipe the surface clean, and repeat the process with the finer compound, using a fresh applicator. When done, remove all excess compound with a clean dry cloth or pad (Photo J).
After leveling the finish, rub it with long, even strokes, using 0000 steel wool and Wool-Lube.
Rubbing to satin
After leveling (as discussed in “Rubbing a thick finish”), rub the finish with 0000 steel and Wool-Lube. (Photo K). After three passes, unfold the pad to expose a fresh surface; then make three more passes. Repeat twice for a total of 12 passes. Go lightly at edges and on legs and other narrow surfaces, using a small portion of the pad backed up with only one or two fingers.
For a sheen somewhere between satin and gloss, use wax thinned 50/50 with mineral spirits instead of Wool-Lube. The wax fills in the tiny hairline scratches left by the steel wool pad, creating a higher sheen.
About Our Author
Jeff Jewitt is a professional finisher who has been teaching and writing on the subject for over 17 years. Owner of Homestead Finishing Products, he has developed finishing products sold worldwide under the Homestead brand name.
You must be logged in to write a comment. Log In