Fin­ish Well with Water­bornes

Water­borne fin­ishes over­come old ob­jec­tions


To­day’s wa­ter-based top­coats ap­ply eas­ier and look bet­ter than ever.

Look­ing for a crys­tal-clear fin­ish that’s durable, easy to ap­ply, and doesn’t fill your shop with fumes? Water­borne (WB) clear wood fin­ish may be the ticket.

Early WB fin­ishes proved trou­ble­some to home wood­work­ers, of­ten due to their un­fa­mil­iar­ity. But man­u­fac­tur­ers kept im­prov­ing their prod­ucts to meet users’ ex­pec­ta­tions. Now those old ob­jec­tions—they add mois­ture to the wood, don’t re­sist wa­ter and damp­ness when dry, mar eas­ily, and im­part a hazy tint to the wood—no longer hold wa­ter.

Note: The wa­ter in water­borne fin­ishes evap­o­rates quickly af­ter ap­pli­ca­tion; it doesn’t soak into the wood, so it doesn’t in­crease mois­ture con­tent.

Chem­istry makes it clear

Water­borne fin­ishes (also re­ferred to as wa­ter-based) be­have like tra­di­tional polyurethanes—a sol­vent evap­o­rates and leaves a tough film of in­ter­locked resin par­ti­cles— but the chem­istry is more com­plex with WB fin­ishes be­cause the resins are not dis­solved di­rectly into the wa­ter.

The fin­ishes work well for in­te­rior and fur­ni­ture fin­ish­ing, and, gen­er­ally, equal the dura­bil­ity of tra­di­tional prod­ucts. They re­sist wa­ter, but heat can mar the sur­face. Some fin­ishes are sus­cep­ti­ble to sol­vents, which are usu­ally spec­i­fied on the la­bel.

Pluses and mi­nuses

The ab­sence of VOC (volatile or­ganic com­pounds) fumes leads the list of ad­van­tages for WB fin­ishes. Hazardous from health and fire-safety view­points, VOCs found in oil-based and lac­quer prod­ucts make fin­ish­ing risky in home work­shops that lack ad­e­quate ven­ti­la­tion. WB fin­ishes, on the other hand, prove safer to ap­ply, even in a base­ment workshop in win­ter. And you can clean up with soap and wa­ter [Photo A].

Gen­er­ally WB fin­ishes dry more quickly than oil-based polyurethanes and dry as close to crys­tal clear as any fin­ish avail­able, ad­ding only slight col­oration to the wood [Photo B]. That clar­ity also counts as a draw­back: Many wood­work­ers value the warm am­ber tone that oil-based fin­ishes cre­ate.

Note: Even though there are no VOC fumes, it’s still a good idea to pro­vide ad­e­quate ven­ti­la­tion when ap­py­ing WB fin­ishes in­doors.

Tip! Add tra­di­tional fin­ish am­ber col­oration by ap­ply­ing a coat of shel­lac be­fore fin­ish­ing with a clear water­borne prod­uct.

Us­ing water­borne fin­ishes

Even though a larger can may be more eco­nom­i­cal, buy just enough fin­ish for your project. That way, you won’t have to store so much left­over ma­te­rial that may de­grade and have to be dis­carded. Be­fore ap­ply­ing water­borne fin­ish over oil-base stain, al­low the stain to dry at least 48 hours. A coat of shel­lac over the stain im­proves fin­ish ad­he­sion.

Most deal­ers carry WB fin­ishes in pints (some­times half-pints), quarts, gal­lons, and aerosol sprays, usu­ally in gloss, semigloss, satin, and flat sheens. Ex­pect cov­er­age sim­i­lar to tra­di­tional fin­ishes, about 400 sq. ft. per gal­lon. Stir it be­fore ev­ery use [Photo C]. Strain ma­te­rial to re­move dried or clumped fin­ish if the can has been par­tially used.

Sand and pre­pare the wood, as for other clear fin­ishes. Some fin­ish­ers sug­gest rais­ing the grain by ap­ply­ing wa­ter to bare wood first and lightly sand­ing, but let­ting the first coat of fin­ish raise any grain works just as well. Then, sand to 220 grit or finer and ap­ply a se­cond coat [Pho­tos D and E]. Sand to 220 grit for sub­se­quent coats.

Ap­ply WB fin­ish with a syn­thetic-bris­tle brush; nat­u­ral bris­tles tend to ab­sorb the wa­ter in the fin­ish and be­come too limp to brush well. Many fin­ish­ers pre­fer bris­tles made of Tak­lon, a polyester fil­a­ment [Open­ing photo]. Foam brushes work sur­pris­ingly well for WB fin­ishes, too, and can be thrown away af­ter use.

Lay on the fin­ish with long, wet brush­strokes along the wood grain, main­tain­ing a wet edge. Min­i­mize brush­ing: Let the fin­ish sit on the sur­face rather than try to scrub it into the wood. If the sur­face looks rough or un­even right af­ter ap­pli­ca­tion, leave it alone. The fin­ish dries quickly once brushed on, so go­ing back over it just makes it look worse. Brush marks dis­ap­pear and the fin­ish self­levels as it dries.

Sand­ing and ap­ply­ing an­other coat will re­pair any flaws that don’t go away with dry­ing. Ap­ply at least three coats to achieve a high-qual­ity fin­ish. (With reap­pli­ca­tion time as lit­tle as two hours, you can eas­ily put on three coats in a day.)

To ap­ply WB fin­ish over an ex­ist­ing fin­ish of any type, clean and scuff-sand the sur­face first. A lightly sanded shel­lac seal coat en­hances ad­he­sion.

You can also ap­ply WB fin­ishes with a con­ven­tional or high-vol­ume, low-pres­sure (HVLP) spray gun. Most prod­ucts need no thin­ning for spray­ing, al­though ex­ten­der (avail­able from a paint dealer) may be re­quired in hot or dry con­di­tions. Check the can la­bel or the man­u­fac­turer’s web­site for noz­zle and pres­sure rec­om­men­da­tions.

Clean brushes or spray equip­ment with soap and wa­ter [Photo F]. Rags used dur­ing fin­ish­ing and cleanup pose no fire haz­ard and can be thrown in the trash—an­other ad­van­tage over oil fin­ishes.

Stor­age and dis­posal

Store fin­ish in its orig­i­nal can or a tightly lid­ded glass or plas­tic con­tainer marked to show its con­tents. Keep the prod­uct from freez­ing. If it does freeze, put some drops on a piece of glass or me­tal to see if the fin­ish dries within an hour or so. If it doesn’t, dis­card the fin­ish. Dis­card fin­ish that’s stringy, gummy, or smells sour.

Dis­pose of empty, dried cans in house­hold trash. If a small amount re­mains in a can, leave the lid off to let the con­tents dry; or spread the left­over fin­ish on news­pa­per or card­board and let it dry. Check with lo­cal waste dis­posal au­thor­i­ties about dis­pos­ing of larger un­dried quan­ti­ties.

Foam brushes

Water­borne fin­ish can im­part sev­eral looks, shown on beech­wood. The un­fin­ished wood at far left and the fin­ished panel next to it (three coats of satin sheen ap­plied with a foam brush) ap­pear sim­i­lar in color. The third panel shows three coats over su­per-blonde shel­lac. At the far right, three coats over dark-cherry wa­ter-based stain.

Cleanup in­struc­tions on the can la­bel quickly iden­tify WB fin­ishes. Soap and wa­ter cleanup in­di­cates a WB fin­ish; mineral spir­its, an oil-based prod­uct.

Sand be­tween coats to give the sur­face tooth for the next coat. Sand­pa­per, sand­ing sponges, and ny­lon pads work fine, but do not use steel wool with water­borne fin­ish.

Al­ways stir WB fin­ish; shak­ing cre­ates bub­bles that take a long time to dis­si­pate. Milky-white ap­pear­ance is nor­mal in the can; the ma­te­rial dries clear on the wood.

Dish deter­gent Clean brushes with dish deter­gent and wa­ter. Work the suds into the bris­tles, rinse the brush thor­oughly with run­ning wa­ter, and pat it dry with pa­per tow­els.

Larry John­ston

Pro­duced by

Thor­oughly clean off sand­ing dust to en­sure a smooth fin­ish. Rely on a tack cloth or damp rag to pick up the par­ti­cles rather than just spread them around.

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