Sprayer selection for finishing projects is really a simple matter, which has only become complicated by the fantasy of having one type of tool technology that can do it all. This dream doesn’t just apply to sprayers, but all tool types in general. Everyone wants to find the one tool that can “do it all”. It’s a nice thought, but really doesn’t coincide with the realities of finishing.
Because I deal mostly in the realm of professional paint contracting, I see a lot of cases where people try to drag that dream into existence by misusing that archaic weapon of mass atomization called the airless sprayer. If a painter has just one sprayer, it is most likely an airless pump, and they try to do everything with it. There was a time when you just about could, but that time has passed.
In the past decade, paint products have changed dramatically. Because of heightened VOC regulations, we have all witnessed the long drawn out swing of the formulation pendulum back around to waterborne finishes, and away from oil/solvent based products. As a result, the fine finish limitations of the airless sprayer have become glaringly apparent in the realm of fine finishing. This time around, the waterborne finishes are really good, viable replacements for oil. They are here to stay, which leaves many a finisher struggling with the failure of applying outdated tools and processes to new finish technologies.
Specifically, painters have an odd tendency to spray .5 gpm (or higher) sprayers wide open at 3300 psi (or more) on interior ceilings and walls, or even exterior facades, in production mode. This has long been a benchmark or “standard” for spraying, because it produces results on large, open road tasks. But then, there is the odd desire to turn right around, put a “fine finish” tip on the same airless machine and want so badly to believe in a magical transformation into a cabinet grade finishing sprayer.
What Happens When you put a Fine Finish Tip on an Airless Sprayer?
It would be nice, but real life doesn’t really work that way, and neither do sprayers. The old “airless with fine finish tip” trick kind of worked ten years ago when products were different. Oil trim paints were thinner, stayed wet longer and could be run through airless sprayers at reduced enough fluid pressures to do small tasks fast and get out of the space before the overspray/airborne mist gremlins set in to compromise the finish. Oils were thinner and easier to spray. With the new generation of waterborne finishes, a fine finish tip on a low transfer efficiency gun tied to a large pump results in neither efficiency nor high quality finishes.
It is the nature of the airless sprayer to require high fluid pressures, and to “shear” the material, resulting in a coarse atomization in comparison to the finer fluid droplets delivered by HVLP turbine units. This directly impacts the way products “lay down.” Add a roomful of airborne mist settling into the wet finish, and airless results become even more coarse. My own professional observation has been that the smaller the orifice of the “fine finish” tip on an airless sprayer, the more the fluid is sheared during atomization. This just doesn’t result in a fine finish on any type of scale, because latex doesn’t shear well. At least not well enough to meet generally accepted fine finishing standards.
The bottom line on the airless/fine finish tip myth is that painters who attempt cabinet grade finishes with this set up are for the most part plagued by inefficiency and overspray due to the poor atomization that results in airborne mist settling in the wet finish as it attempts to lay down, in turn yielding a less than smooth finish.
In fact, the larger the fine finish project, the worse the result usually gets when running an inefficient technology. And, of course, the act of just setting up a typical airless requires about a gallon of paint just to fill up the 50’ of hose and the piston pump.
Get More Quality “Bang” Out of a Bucket of Finish
As noted above, with the paint industry shift to waterborne finishes, my paint company has adapted its small scale fine finish program around HVLP, for a number of reasons. While waterborne finishes require high fluid pressure to pass through a small orifice in an airless machine, they happen to respond very well to high velocity and lower pressure (HVLP) spraying.
In very simple and practical terms, I (or just about anyone), can produce a 6” fan by running a 5 stage turbine at 9.5 psi through an HVLP gun that will produce a flawless cabinet grade finish. Meanwhile, a 6” fan through an airless machine requires about 3000 psi, a whole lot more material and yields a poor result.
A More Efficient Delivery
HVLP systems routinely deliver materials (conservatively) in the upper 80% range, 86-90% transfer efficiency seems to be the standard range of quality turbine systems. Airless guns are so much lower by comparison that manufacturers generally don’t share airless gun transfer efficiencies, focusing instead on the production value of the technology. While airless are solid production machines, it is a bit of a guessing game as to where in the 50-70% efficiency range they might actually measure.
In three decades of spraying airless systems professionally, there have been many times when I have personally observed as much material landing on the floor and on the operator as on the walls or ceilings being sprayed.
By way of quick summary, the obvious advantages of HVLP over airless for fine finishing include:
- Less materials consumed
- Quicker set up and breakdown
- Better quality finish
Misconceptions About HVLP
In my opinion, and this ties back to the desire of all consumers these days to find “the one that can do it all,” HVLP is sometimes overlooked by finishers because it is perceived as a specialist. And, to an extent, in the big picture of painting, it is. You probably won’t paint an entire home interior with an HVLP. Large scale production of many thousands of square feet at a time is not its strength. That’s fine, there are other machines built for exactly that.
However, it is possible to find enough variety of finishing tasks for an HVLP to become a general solution to a whole range of specialized task types that would otherwise be best suited to manual (brush and roller) application. HVLP shines in projects that are too small, complex or detailed for larger technologies, and too large or intricate to attempt manually by brush.
A great example of this is exterior spindle and rail systems on decks and porches. We have done many new spindle/rail systems in our shop and just as many onsite in exterior repaint situations. Another example would be a small quantity of interior or exterior doors. Take a quantity of 5-6 interior doors. Not worth setting up a pump and hose style sprayer, but quick and easy with an HVLP system. Custom cabinetry and millwork applications are another specialty.
The bulk of this discussion has centered around using HVLP as a more qualified replacement for airless sprayers in waterborne primer and paint grade situations for fine finish applications. One last strength I would mention is the absolute mastery that HVLP demonstrates in waterborne clear finishes. This is a realm where airless spraying is mostly incompetent, because airless pumps just aren’t happy operating at low pressures in thin viscosity materials.
So, it is possible to “have it all”, at least within the discipline of small scale fine finishing, and HVLP is the solution.
Glue seepage, or glue on your fingers that’s transferred to the wood, blocks stain penetration. This usually results in a lighter area. The same can happen with wood putty because it doesn’t accept color the same as wood does. In both cases, you have a lighter area or spot that you want to color in to match the surrounding wood.
Here’s how to do it.
As shown in the accompanying picture, the better method is usually to first seal the wood, then paint in the grain. Connect the grain lines on either side of the lighter area. When this has dried, apply a washcoat (a highly thinned coat of finish) to seal in what your have done, then color in the areas between the grain lines.
When you’re happy with the result (which is rarely an exact match), apply the topcoats.
For the coloring medium, ideally you want to use something that can be removed without disturbing the color underneath if you should want to begin again. The best medium is usually shellac because it can be removed by wiping with denatured alcohol. It won’t lift an oil stain. But it could lighten a water-based stain, so wipe very lightly.
Shellac also dries rapidly, so all steps can be accomplished in a short time.
Universal color pigment, the same as the paint store uses to tint latex paint, can be used with the shellac.
For the washcoats, aerosol sprays are widely available and work well.
Instead of shellac you could use thinned varnish and oil- or Japan-color pigments, but the drying time will be extended to a day or more.
Stripping veneer is no different than stripping solid wood, with a few exceptions.
First, avoid using lye or a stripper that contains water. Because of the thinness of the veneer, these might work through and loosen the glue bond. Solvent-based strippers shouldn’t cause any problem that didn’t already exist.
Second, if you sand after stripping, which is usually a good idea to check that you have removed all the finish, do so lightly and with fine sandpaper. Otherwise, you might sand through, and a sand-through is almost impossible to fix.
I recommend doing this sanding by hand with just your fingers backing the sandpaper. Using a hand-held sanding machine is more risky because it is more aggressive and you can’t see what’s going on under the sander. Using a flat block to back the sandpaper, even on supposedly flat surfaces, can also lead to sand-throughs if there is any unevenness, which is common on old surfaces.
You know, that wooden or big steel monstrosity with the rusty, peeling Bilco doors that swing up and open to your basement. As a residential painter, I usually find the bulkhead to be one of the ugliest items around the outside of my customer’s homes.
So if you have one, here is how you can turn that big frown upside down. Here’s how I handle the steel monstrosity. The first key is to properly clean the bulkhead with a stiff brush. Maybe give it a good scrub down with damp rags. A quick scuff sand at 220 grit, and then remove all dust. Already, this is a great excuse to break out some power tools to accelerate the process.
This is where it starts getting good. If you have a 5 stage HVLP, there are some great new product technologies that are entirely sprayable through your unit. Waterborne Direct to Metal (DTM) paints are a life save. They are rust inhibitive and require no primer. Check your local Sherwin Williams or Benjamin Moore dealer and pick up a gallon. It is a pretty quick dial in with your gun, and easy clean up. Just be sure to properly mask (exterior blue tape and plastic) where the bulkhead attaches to the house.
In the old days, we used to do these with brush and roller. HVLP has been a game changer, turning ten hours of frustration into about 3 hours of excitement with a much better result.
As with any technical field, understanding the terminology of finishing is critical. It’s also critical that we all mean the same thing with the terms we use.
With that in mind, here are some of the most common finishing terms, in alphabetical order, and their definitions.
Bleach is a chemical that removes stains and, sometimes, the natural color from wood. The three types of bleach are chlorine (sodium hypochlorite), which removes dye color without changing the color of the wood; oxalic acid, which removes rust marks and lye stains without changing the color of the wood; and two-part bleach (sodium hydroxide and hydrogen peroxide), which removes stains, and also removes the wood’s natural color.
Dye is a chemical that dissolves in a liquid solvent. Typical solvents include water, alcohol and toluene. Dye can be applied to wood dissolved in the solvent alone, or dye can be added to a finish and thinner (with or without pigment included) to make a wiping stain or toner. Dye is transparent.
Film Finish is any finish that can be built up on the wood (by repeated applications) to a noticeable thickness. The key requirement for a film finish is that it cures hard.
Varnish(including polyurethane varnish), shellac, lacquer, water-based finish and a number of two-part finishes are all film finishes.
Finish is a substance that changes from a liquid to a solid after it’s applied to the wood. The purpose of a finish is to protect the wood from moisture and to enhance the wood’s appearance. The term “finish” can also refer to all the steps in a built-up finish. These steps could include a stain, several coats of transparent finish, and coloring steps (glazing and toning) in between the finish coats. The context usually makes it clear which definition of “finish” is being referred to.
Gel stain is a stain that has been made thick and resistant to flow, similar to glaze. Because of the resistance to flow, gel stains don’t penetrate well, so they are used primarily to reduce blotching on blotch-prone woods such as pine and cherry.
Glaze is a stain that has been thickened enough so it stays where you put it. It doesn’t run on vertical surfaces or flatten out on horizontal surfaces. Glaze is used to decorate (graining, antiquing, highlighting, etc.) and to add the appearance of age and depth.
Glazing is the application and manipulation of a stain or glaze between coats of finish with the purpose of adding decoration. Typical effects include graining, antiquing, distressing and highlighting recesses.
Paste wood filler (or “pore filler”) is a finish (usually varnish or water-based finish) with a pigment colorant and a solid filling substance added. The filling material is usually silica (resembles fine sand) in varnish-based fillers and wood dust in water-based fillers. Paste wood filler is used to fill the pores of porous woods such as oak, mahogany and walnut before the application of topcoats. The filler can be applied directly to raw wood to fill and stain in one operation, or it can be applied over a washcoat or sealer coat to add color only to the pores (the best procedure). All excess paste wood filler has to be wiped or sanded off the surface to avoid muddying the wood.
Patina is the mellowing and color change that occurs in wood over time due to oxidation (from exposure to air) and bleaching (from exposure to light). Patina is also the dings, scratches and wear in the wood or finish that give old furniture and woodwork character.
Penetrating finish is any finish that cures too soft to be functional if built up on the wood. The excess finish has to be wiped off after each application. All oil and oil/varnish blend finishes are penetrating finishes. By this definition, wax is also a penetrating finish, but it isn’t usually referred to as such because it doesn’t penetrate much. A better terminology would be “film-building” for all finishes that harden and can be built up, and “non-film-building” for all finishes that don’t harden and have to be wiped off.
Pigment is finely ground earth or colored synthetic particles made to resemble earth. Pigment is used to add the color to stain, glaze, toner, paste wood filler and, of course, paint. Pigment is opaque and hides the wood if built up thick. But if the excess is wiped off, the pigment remaining in the wood’s pores highlights them, which adds depth and grain definition to the wood. The pigment settles in cans and must be stirred into suspension before each use.
Rubbing and polishing is the procedure used to level the surface of the final coat of finish and raise or lower the sheen. Various types of abrasives are used to do this, including sandpaper, steel wool, abrasive pads and rubbing compounds in liquid, paste or powder form.
Sealer is the first coat of finish applied to the wood. This first coat seals the pores of the wood so that any liquid applied on top, including the next coat of finish, will remain on top; it won’t penetrate into the wood. A sealer can be the first coat of the same finish you’re using for the topcoats, a special varnish or lacquer “sanding” sealer made to sand easily, a water resistant vinyl sealer commonly used under catalyzed finishes, or shellac, which forms an effective barrier over oil, resin and odors (from smoke or animal urine) in the wood.
Shading stain is a toner used to change or adjust the color of part of the wood without affecting other parts. Examples of situations where shading stain (toner) is used include highlighting (darkening the areas around the area to be highlighted) and matching sapwood to heartwood. Shading stains are always sprayed.
Sheen is the degree of gloss in a cured finish. All film finishes cure to a gloss sheen unless they have flatting paste (gloss-reducing solid particles) added. Semi-gloss, satin, matte and flat finishes have flatting paste added. These finishes must be stirred before use to put the flatting particles into suspension.
Solids content is the ratio of finish (the part that hardens) to thinner (the part that evaporates) in a finish. Most finishes are supplied with a solids content ranging from 20 to 40 percent.
Solvent is any evaporating liquid that will dissolve a dried finish. The solvent for a finish can also be used to thin the finish. Examples of common solvents are lacquer thinner for lacquer, denatured alcohol for shellac and mineral spirits for wax.
Stain is any liquid that colors wood. Two colorants are used in stains: pigment and dye. Pigment requires a binder (finish) to glue it to the wood. Dye can be used with or without a binder.
Thinner is any evaporating liquid that can be added to a finish, stain, glaze, toner or paste wood filler to thin it and make it easier to apply with a brush, cloth or spray gun. Examples include mineral spirits for oil-based products, water for water-based products, lacquer thinner for lacquer products and denatured alcohol for shellac products.
Toner is finish, usually lacquer, thinned with up to six parts thinner and a pigment and/or dye colorant added. Toner is always sprayed and can be used to add color in very thin layers between coats of finish. Toner is most often used to adjust the wood’s color after it has been stained and sealed, or used as a shading stain.
Topcoat refers to all coats applied over a sealer coat.
Washcoat is any finish thinned to 10 percent, or less, solids content. A washcoat can be applied directly to the wood to partially block the penetration of a stain and prevent blotching, or to harden end grain so it becomes easier to sand smooth. A washcoat can also be applied between coloring, filling and glazing steps to keep them separated and make them stand out better.
Wood Conditioner (also called stain controller and pre-stain) is a commercial washcoat product made by thinning varnish with two parts mineral spirits, or thinning water-based finish an equivalent amount. Wood conditioner is used to prevent blotching in pine, cherry and other blotch-prone woods. To be effective, the product should be allowed to cure thoroughly before applying a stain.
In the photo above we definitely see a very severe case. This is a pour on epoxy finish over copper. While finishing over copper is a separate challenge unto itself, the extreme cracking of the finish was due to being subjected to freezing temperatures and can happen with any finish. In this case the table was transported from Florida to Maryland in January and the table sat on a truck for several days.I would be the first to agree the copper (metal) was a contributing factor as the copper contracting due to the cold didn’t help things out at all.
I have however seen this several times before.A finish, if left in extreme cold, can and will crack. I have also observed that heavier film finishes are more subject to cracking. In all the cases I have seen , it occurred via a move from a warm climate to a cold one and the finishes were subjected to a rapid temperature change due to transport.
In the case of the copper table, the owners assumed it had been dropped, but there is no evidence of that, it simply froze and cracked, again the copper had a lot to do with it because the epoxy is simply lifting off which means that the adhesion was totally lost.
Be aware that it can happen. I have also see furniture stored in very cold conditions with no effect, thus it really seems to be the rapid change in temperature is a major contributor. If you are moving, be aware.
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When sanding wood in preparation for a stain or finish, you need to remove all the problems in the wood – mill marks, tear outs, gouges, etc. – with the coarsest grit sandpaper you’re using before moving on to finer grits (to remove the coarse-grit scratches). This means that the coarse-grit sandpaper you begin with should be able to remove the problems quickly and efficiently to reduce the amount of work required.
As an example, 100- or 120-grit sandpaper is usually coarse enough to begin with. Beginning with 150-grit sandpaper is usually inefficient because you have to sand too long to remove the problems.
On the other hand, with factory pre-sanded veneered plywood or mdf, beginning with 150-grit sandpaper is usually adequate.
These are general observations. We all sand differently, so you may want to adjust the beginning grit you sand with depending on the problems you want to remove. But the basic rule still applies: It’s most efficient to remove all the problems with the coarsest grit you’re using before moving to finer grits.
Testing Finishes for Heat Resistance
Resistance to damage from hot objects is an important finish quality for tabletops and counter surfaces in kitchen and dining areas. The type of finish you’re using will be a strong clue to its resistance. For example, oil-based polyurethane and catalyzed lacquer are very resistant to heat damage, while shellac, lacquer and water-based finishes are less so.
There are two tests for heat resistance that are easy to do.
To test for dry heat resistance, place a metal cup or pot containing water heated to just below boiling on a fully cured finish, as shown in the accompanying picture. Remove the cooled container after an hour and look for splits, indentations or discoloration in the finish.
To test for wet heat resistance, do the same as for dry heat resistance, but place a cotton cloth or cheesecloth wetted with the same hot water under the cup or pot. After an hour check the surface for splits in the finish or discoloration.
Testing Finishes for Scratch Resistance
Finishes vary in hardness and scratch resistance. To a large extent the relative hardness of various finishes are known. For example, oil-based polyurethane is more scratch resistant than lacquer or shellac. So are catalyzed finishes and water-based finishes. But what if you want to be more exact about the differences, or want to compare brands within any single type of finish?
The easy way to do this is with architect’s pencils because these vary in hardness themselves.
Begin by buying a set of architect’s drawing pencils ranging in hardness from about 2B (soft) to 5H (hard). Sharpen each pencil using a knife so you leave the sharp cylindrical edge of the lead intact. If you damage this edge, or if it becomes worn, sand it flat, holding the pencil 90 degrees to the sandpaper.
Beginning with one of the softer pencils, hold it as you would for writing and push it forward across the fully cured finish as shown in the accompanying picture. Maintaining equal pressure, follow with pencils of increasing hardness until you find one that cuts into the finish.
The hardness rating for that finish is the number of the previous pencil – the hardest lead that doesn’t cut.
One of the most difficult aspects of wood preparation is knowing how much to sand to remove all the machine marks and other flaws. Here’s a trick that may make it easier.
Draw some pencil marks on the wood. Then sand the wood until you have removed them entirely.
Sanding is very personal. We all sand differently. We use different grits, more or less pressure, more or fewer passes and with more or less wear on the sandpaper. So you may determine that, for you, sanding off the pencil marks once is enough. Or you may determine that drawing a second set of marks after the first has been removed and then sanding off these marks works better. In other words, doing it twice.
You should never have runs or sags in your dried finish. The trick to avoiding them is to spot them before the finish dries and remove them with a brush. The way to see runs and sags developing is to look at the surface in a reflected light, as shown in the accompanying picture. You may need to move your head, walk around, or even arrange some special lights other than the overhead lights or the light coming in through a window.
Once you have spotted the problem, use a brush to brush out the excess finish even if you’re spraying. If there is too much finish to brush out successfully, lift some off the surface with the brush and deposit it onto another part of the object, wipe the brush dry with a cloth, or drag the brush over the lip of a jar or can to remove the excess.
In most cases when repairing a finish (for example, removing a water ring, touching up a scratch or ding, or doing a burn-in or epoxy fill to a gouge) it’s most important to get the sheen the same as the surrounding surface and make the surface feel smooth. Even if the color of the repair doesn’t match exactly, the repair will be successful because people will think the mismatch is a flaw in the wood.
If you don’t get the sheen right, however, people will notice the repair immediately when they see it in a reflected light. Even if the do get the sheen right but not the color exact, most people will run their fingers over the repair, so it’s also important to make it feel smooth.
The two widely available pigment colorants for oils and varnishes are oil colors and Japan colors. The difference is that oil colors are pigment ground in linseed oil while Japan colors are pigment ground in varnish.
So the difference in practice is that Japan colors dry faster and harder than oil colors, though if you were to mix an oil color with varnish, it should dry well.
The name “Japan” comes from the attempt in the West to imitate Japanned furniture (also called Japanese or Oriental Lacquer) that was imported in the 17th and 18th century. So the harder drying and glossier varnish base worked better than an oil base.
In my experience you can also use widely available universal colorants (normally meant for tinting latex paint) in oils and varnishes successfully if you let these colorants sit in the binder overnight while stirring occasionally.
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