A high-gloss finish can transform a tabletop or other flat surface. Besides protecting the wood, the highly reflective surface emphasizes the grain, color, and figure underneath.
But there's a difference between simply applying a gloss finish and creating a smooth, mirror-like surface.
Straight from the can, a gloss varnish or lacquer may be shiny, but the surface isn't perfectly flat. Small brush marks, dust nibs, and other irregularities scatter reflected light and can give the finish a slightly uneven or plastic appearance.
The solution is to rub out the finish.
This is essentially a two-stage process. First, you level the cured finish until it's uniformly flat. Then you polish that flat surface with progressively finer abrasives until the gloss returns.
Start with a Flat, Smooth Wood Surface
A high-gloss finish highlights imperfections rather than hiding them. So the process begins long before you apply the first coat.
A random-orbit sander works well for the early stages of surface preparation, but then switch to an extra-long sanding block for the final sanding. A long, wide block bridges low spots and helps remove subtle dips and ridges.
Sand the surface through 220 grit before applying the finish.
Inspect with a Raking Light
Once you've finished sanding, remove the dust and carefully inspect the surface.
A useful trick is to position a light low and just above the workpiece. This raking light casts shadows across tiny scratches, ridges, and depressions that can be difficult to see under normal shop lighting.
Wipe the surface with mineral spirits to make sanding marks easier to spot.
Don't move on until you're satisfied with the surface. Any flaw you can see now may become even more noticeable beneath a polished gloss finish.
Fill the Grain on Open-Grained Wood
If you're finishing an open-grained wood such as oak, walnut, or mahogany, sanding alone won't produce a completely flat surface. The pores need to be filled before building the finish.
Paste wood filler is designed for this job. It fills the open pores so subsequent coats of finish can build over a level foundation.
How to Apply Paste Wood Filler
The goal is to force filler into the pores without pulling it back out.
Use a plastic putty knife. Rather than working along the grain, pull the filler across the grain. This helps pack the material into the pores.
Allow the filler to begin drying, then use the edge of the putty knife diagonally across the surface to remove the bulk of the excess.
After additional drying, lightly rub the surface with the grain using a non-woven abrasive pad to remove the remaining residue without pulling filler out of the pores.
Inspect the surface again under a raking light. Open-grained wood may require a second application before the surface is completely filled. Allows the filled surface to dry for a day before moving on.
Build a Thick Film Finish
Now you're ready to apply the finish.
Use either lacquer or varnish. The specific finish isn't as important as building a film thick enough that you can flatten and polish it without sanding through to bare wood.
Lacquer and varnish behave differently. Lacquer dries quickly and allows multiple coats to be applied in a relatively short period. Each coat also melts into the preceding coat.
Varnish builds more quickly with fewer coats, but scuff-sand between coats to remove dust particles and prepare the surface for the next application.
Use four coats of varnish or eight coats of lacquer before rubbing out the surface. Those numbers are best viewed as our process rather than a universal formula—the important goal is having sufficient cured film thickness for the leveling process.
Woodsmith Tip: Let the Finish Cure. Don't confuse dry with ready to rub out. The finish needs time to cure before you start leveling and polishing it. Wait at least a week, while noting that temperature and humidity can affect curing time.
Wet-Sand the Finish Flat
Here's the part that initially seems backward. To create a high-gloss finish, you first need to make the glossy surface dull.
Wet sanding removes minor irregularities and leaves the entire surface flat with a consistent scratch pattern. Once the surface is truly flat, progressively finer abrasives can bring back the gloss.
Start with 800-grit wet-dry sandpaper wrapped around a flat cork block.
It uses mineral spirits as the lubricant over lacquer and water over varnish. The lubricant carries away sanding residue as you work.
Work with light pressure until the entire surface has a uniformly dull appearance.
Look for Shiny Spots
Shiny spots are important. If most of the surface is dull but isolated glossy areas remain, those spots are still lower than the surrounding surface. The finish isn't completely flat yet.
Once the surface is consistently dull, clean and inspect it. Then progress through 1200 grit and 1500 grit, repeating the process at each grit.
Woodsmith Tip: Be particularly careful around edges and corners. It's much easier to rub through the finish in these areas than across the middle of a broad, flat surface.
Polish with Pumice
Once the finish is flat, you can start bringing back the shine.
We traditionally use pumice followed by rottenstone. Both are fine powdered abrasives, with rottenstone being the finer of the two.
Because the surface has already been sanded through 1500 grit, the move directly to 4F pumice.
Combine a small amount of pumice with paraffin oil to create a thin slurry, then rub it over the surface with a felt block.
Work in small sections using circular motions and moderate pressure.
The goal isn't to polish one area completely before moving on. Try to give the entire surface roughly the same amount of attention so the sheen develops uniformly.
Continue until you've produced a consistent semi-gloss surface.
Polish to a Mirror Gloss with Rottenstone
Rottenstone is finer than pumice, making it the final step in the traditional polishing process. The technique is essentially the same: combine the abrasive with paraffin oil and rub the surface with a felt block.
But there's an important precaution.
Completely clean away the pumice and switch to a fresh felt block before using rottenstone. A stray pumice particle is coarser than the rottenstone and can leave visible scratches in the surface you're trying to polish.
Keep the pressure light and work methodically across the surface. Periodically wipe the finish clean and inspect the reflection.
At this point, the dull surface you created during wet sanding should develop into the smooth, reflective mirror finish you were after.
Modern Alternatives: Micro-Mesh and Polishing Compounds
Pumice and rottenstone aren't the only way to rub out a finish.
The principle remains the same regardless of the abrasive system: start with a flat film and progressively refine the scratch pattern until the surface becomes glossy.
Micro-Mesh
Micro-Mesh uses abrasive particles in a cushioned coating rather than conventional sandpaper construction.
The material is available in grits ranging from 1200 through 12,000 and can be used wet or dry to progressively polish a finish.
Automotive Polishing Compounds
Fine automotive polishing products can also be used for the final polishing stages on compatible cured wood finishes.
These products suspend very fine abrasives in a liquid or paste and can be applied by hand or with appropriate polishing equipment.
For either alternative, test the abrasive system on scrap or an inconspicuous area and verify compatibility with the finish manufacturer before polishing the project.
The Secret to a Mirror-Smooth Wood Finish
A professional-looking high-gloss finish is less about finding a magic finish in a can and more about creating a perfectly flat surface.
The process is straightforward: 1. Prepare the wood until it's flat and free of sanding marks. 2. Fill the pores if you're working with an open-grained wood. 3. Build enough film thickness to safely level the finish. 4. Allow the finish to cure completely. 5. Wet-sand until the entire surface is uniformly flat. 6. Progress through finer abrasives. 7. Polish the surface to the desired gloss.
The final polishing gets most of the attention, but the early steps are what make the mirror-like result possible. If the wood, grain filler, and film aren't flat, polishing alone won't produce the same effect.
Get Better Results on Your Next Finishing Project
A great finish can make all the work you've put into a woodworking project stand out. Learn more about surface preparation, choosing a finish, application techniques, and getting consistent results in our Home Shop Finishing online course.
