If you transport unfinished wood or an unfinished wooden object through rain or sprinkling, the water drops will raise the grain, and wood stains will show up darker over these spots. The cause is the rough raised grain retaining more of the stain. The accompanying picture shows an example of what can happen.
There are two ways to avoid the spotty staining, both involving sanding (even if the wood has already been sanded). The first is to sand the wood thoroughly to remove the raised grain over the spots. The second is to wipe over all the wood with a wet cloth to wet it everywhere, then sand it smooth.
Because it’s hard to know how much sanding is necessary to cut deep enough to remove all the raised grain over the spots, the second method is actually the safer one because it creates an equal amount of raised grain everywhere. So even if you don’t sand enough to cut through all the water-damaged wood, the staining will still be even, maybe just a little darker.
It’s common to hear the instruction that it’s better to apply several thin coats than one thick one. Why is this so? Or is it?
What’s involved is drying time, nothing more. Thinner coats of all finishes dry faster than thicker coats. The difference is great enough that you can build the same thickness with several thin coats in less time than you can get that thickness with a thick coat. But the thick coat will eventually dry just as hard and perform just as well as many thin coats.
Shellac and lacquer dry entirely by solvent evaporation. The solvent evaporates much quicker from a thinly applied coat than from a thick coat because it takes much more time for the solvent at the bottom of the thick coat to work its way up through the finish and out into the air.
Varnish, including polyurethane varnish, dries by the crosslinking of the molecules in the presence of oxygen. It takes much longer for oxygen to work its way to the bottom of a thickly applied varnish than a thin varnish coat.
Water-based finish dries by both solvent evaporation and some crosslinking, so the result is the same. It takes much more time for a thick coat to dry than several thin coats.
Of course, oil finishes don’t dry hard at all, so coats must always be as thin as possible, accomplished by wiping off all the excess.
Dents and gouges are both flaws in the wood. But they are not the same thing, so they should be repaired differently.
Dents are compressed wood. The wood fibers are still intact, just pressed down or indented. Gouges are also indentations, but the wood fibers have been torn and usually some of the wood has been removed.
Dents can usually be steamed level. Gouges have to be filled with wood putty or some other filling material. Sometimes the indentation is not clearly a dent or gouge, so you can try steaming before resorting to filling.
To steam out a dent, drip some water into the depression using an eyedropper or syringe. If the dent is shallow, the water may swell the wood enough to bring it level with the rest of the surface. If the water doesn’t work, drip some more water into the dent and cover the surface with a dry cloth. Then apply a medium hot iron to the cloth. The hot iron causes the water to turn to steam, which enters the wood and swells it. You can do this several times.
Whether using water or steam, sand the wood well after the moisture has dried out to eliminate any raised grain.
Because water raises the grain of wood, it’s best not to lay a wet cloth on a wide area of the wood, as is often recommended, before heating with the iron, because this will increase the amount of sanding necessary. It’s best to keep the wetted area as small as possible.
Patina is primarily the mellowing and color change that occurs in wood over time due to oxidation from exposure to air and bleaching from exposure to light. Secondarily, patina is the dings, scratches, rubs, etc., that give old furniture character.
The mid-nineteenth-century cylinder roll-top desk in the accompanying picture has patina, primarily the bleaching of the mahogany and also the bleaching of the plaster-of-Paris used to fill the pores. The desk has never been refinished, but the finish has been renewed with French polishing. Adding finish on top doesn’t change the coloring of the wood underneath.
Patina is highly valued by antique dealers and collectors because it helps establish age, and it can also produce a warm, mellow appearance as with this desk.
Paint stripper based on solvent alone rarely removes patina because most of the patina is in the wood, not in the finish. But sanding will remove the top surface of the wood and destroy the patina. This is the reason old furniture shouldn’t be sanded when it is refinished.
The term “penetrating finish” is one of the most misleading in the vocabulary of finishing because all finishes penetrate. The term is generally used to describe just oil finishes, which dry slowly so they may penetrate a little deeper than faster-drying finishes. But depth of penetration doesn’t have anything to do with protection for the wood, and it’s here that the term becomes misleading because many people think it does, and some manufacturers claim it does. The common descriptive phrase is that the finish “protects the wood from the inside.”
But the quality of a finish that creates better protection for the wood—that is, protection from moisture getting into the wood—is that it dries hard so it can be built thicker on the wood. The thicker the finish, within limits, the better it resists moisture penetration, and oil finishes can’t be built up because they don’t dry hard.
The better terms to use are “film-building” to refer to finishes that dry hard so they can be built up, and “non-film-building” to refer to finishes that don’t cure hard enough to be built up. Using these terms, oil finishes, and also wax finishes, are non-film-building finishes. Varnish, lacquer, shellac and water-based finishes are all film-building finishes.
As winter approaches, it’s important to remember that all finishes dry slower in lower temperatures. Runs, sags and pressmarks are all more likely to occur.
To avoid runs and sags, watch the finish in a reflected light as you’re applying it. The reflection allows you to see if either of these problems is developing and you can brush them out to remove them. If you’re spraying you’ll also learn to spray thinner coats. If you’re brushing you’ll learn to brush the finish out thinner.
Pressmarks occur when something is pressed up against a finish that hasn’t fully hardened. The accompanying picture shows an example. The only thing you can do if you get a pressmark is sand out the damage (after the finish has hardened enough to sand) and apply more finish.
To prevent more pressmarking warm your finishing area or give the finish more time to harden, or both.
The general consensus on figured woods is pretty much saturation, or using a trace coat to further intensify the grain. However sometimes a dye can migrate, meaning it just goes way too dark and can create a blotchy mess.
Broad curl woods like Curly Cherry, Flame Birch, etc. can also absorb any colorant unevenly. We’ve looked at many ways to help control this. I want to emphasize how important it is that you do a test on a scrap before you dive in. With that said one of my favorite tricks is to use water to help control the absorption. I have used our blotch control and thinned it, you have to experiment with this as there is no set rule and a particular wood you’re using will determine how much you need to reduce the blotch control.
Take a look at photo 116. Obviously the side with water is lighter, but when dry, I could do water and another coat of dye. Simply thinning the dye, usually does not work because irrespective of how thin the dye is, it’s going to migrate into the softer grain thus causing it to be darker. The water trick, has proved to be pretty successful and is one of my go-to techniques, especially on figured maples.
Remember the rule “Sneak Up on It” !
Charles Neil’s New Book Coming soon!
The wood in old furniture and woodwork often takes on a dry appearance, and people want to know what to do to restore life to the wood.
Because of widespread misinformation from furniture polish manufacturers that wood contains natural oils that need to be replaced by furniture polishes, many people think they need to apply oil to the wood. But the problem is rarely in the wood (and only woods from the tropics contain a natural oily resin anyway). It’s the old finish that has deteriorated and become cracked and crazed that makes the wood appear dry. Light no longer penetrates the deteriorated finish to reveal good depth and color.
There are several ways to restore the depth and color. From least invasive to most, these include:
- Apply paste wax. If the problem is still pretty superficial, the thin wax layer will solve the problem.
- Sand the surface lightly with fine sandpaper to remove the surface roughness, then apply a coat or two of finish. To do this successfully, you’ll need to remove most of the wax, if you tried the wax solution first. You can do this by wiping with mineral spirits or naphtha without damaging the underlying finish. To further avoid bonding problems, use shellac for the finish, because it will bond well over thin wax.
- Worst case, you’ll need to strip the finish and apply a new one. It’s almost always better to use solvent strippers than to sand or abrade off the finish because sanding will cut into the wood and remove the aged color (“patina”) it has developed.
In the example shown in the accompanying picture, paste wax isn’t going to help. It might be possible to smooth the surface with a light sanding, then apply more finish. But the cracking will telegraph through relatively quickly. The best solution in this case, and what I chose to do, was to strip the finish and apply a new one.
If you have ever sprayed the inside of a cabinet with a fast-drying finish such as lacquer or catalyzed lacquer, you have surely experienced dry spray settling on the surface and causing it to feel rough. The bounce back and turbulence created by the force of the spray keeps the finish particles in the air so long that the finish on the surface has already set up before all of the particles land. And when they do land, they stick to the surface, but don’t dissolve in.
The problem is reduced with HVLP and especially with turbine HVLP because there is so much less force creating bounce back. But in the confined space of a cabinet there’s still almost always some dry spray and some roughness.
Minimal dry spray is difficult to show in a picture. But serious dry spray settling on a surface is easy to show, as on the top half of the panel in the accompanying picture.
I’ve often seen instructions to avoid spraying directly into corners in order to avoid the dry spray. Instead, spray the two surfaces that join to form the corner. In other words, make the solution one of spraying technique. But I’ve never found this to work well.
If you think about it, the real cause of the problem is the fast drying of the finish. Slower-drying finishes, such as varnish and water-based finish rarely, if ever, have a dry-spray problem. So the better trick for avoiding dry spray on the insides of cabinets is to slow the drying of the lacquer or catalyzed lacquer by adding a retarder. This keeps the surfaces wet longer, so the dry spray has time to settle and dissolve in, leaving a smooth feel.
You have to be careful, of course, not to retard too much or you’ll have difficulty avoiding runs and sags. So be observant.
Inexpensive tack cloths (tack rags) are available from most suppliers of paints and finishes. They are sticky rags meant for picking up dust, often sanding dust, from a surface just before applying a coat of finish. Here are some tips for using them.
- Limit their use to solvent finishes. They can cause fish-eye and bonding problems with water-based finishes because they leave an oily residue on the surface. Instead of a tack cloth, use a slightly water-dampened cloth to remove the dust when working with water-based finishes.
- Before using a tack cloth on sanded wood, remove the majority of the sanding dust with a vacuum, or blow it off with compressed or turbine air if you have adequate exhaust to remove the dust from the air (so it doesn’t settle back on your work).
- A tack cloth is most effective between coats of finish because there is less dust to remove (so the cloth doesn’t become overloaded too quickly).
- No matter whether you use a tack cloth, vacuum, or compressed or turbine air to remove the dust, wipe over the surface to be finished with the palm of your hand just before beginning to apply the finish. This will remove the last of any remaining dust that might have settled, and it will warn you if there is still excessive dust that should be removed with one of the other means.