Posted on December 2nd, 2013 No comments
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.
Posted on December 2nd, 2013 No comments
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.
It seems that one of the topics I get a tremendous amount of emails about is when folks are having issues due to the heat and humidity. A huge number of woodworkers spray their finishes outside and in doing so, are at the mercy of uncontrolled temperatures. Spraying in these conditions can be risky business.
Most finishes simply do not like to be force dried. When spraying in direct
sunlight the surface of the finish will skim over leaving the underlying finish still soft. The finish can then blister; this is most predominant in solvent base finishes. The surface dries and the air that is trapped in the pores of the wood cannot readily escape.
As the air rises it must now break through the dried film and forms a blister. It is a situation where the direct sunlight is the culprit and being able to shade the surface makes a huge difference.
Another issue as a result of the surface drying rapidly is called “blushing”, particularly in hot humid areas. Again, the moisture is trapped within the finish as with blistering. The solution once again is to shade the surface from direct sunlight. If using compressed air, make sure your air is dry and filtered. Turbine systems are the best solution to ensuring clean dryer air.
Lately, the biggest issue is being able to wipe on any non-oil dye or stain in hot/humid weather. Oil-based stains, because they dry so slowly, are usually not an issue. Gel stains, because of their heavier viscosity, dry quite rapidly. Water base stains and dyes can be very problematic. Alcohol/Lacquer dyes and stains can be all but impossible.
Here are a few tips to help when you find your dye/stain drying too rapidly and not allowing you to wipe evenly.
For oil base gel stains, have a cloth damp with mineral spirits ready. Work in as small an area as possible. The objective here is to be able to wipe the stain on and off before it sets. The mineral spirits will help to prevent the stain from drying as fast, but it can also produce a lighter color so often two coats are required. Just be sure to let the first coat dry thoroughly or you run the risk of the second coat softening and pulling off the first coat.
Waterbase dyes and stains can be controlled to some degree the same as the gel stain. Use a dampened applicator which can help, as well as working in as small a section as possible.
In the case of dyes, premixed dyes are not as good as powdered dyes that you mix yourself. Pre-mixed dyes have chemicals that speed the drying process and they are not typically just mixed with water. Powdered dyes that you mix yourself, because it’s simply water, seem to dry slower giving more work time.
We have experimented with utilizing “Floetrol” which is a paint additive used for slowing the drying process in order to improve leveling of water base paints in water base dyes and stains. Floetrol is available at most hardware and box stores where latex paint is sold. We have found it to be very helpful. Our normal mix is approximately 1 ounce to 1 quart of dye or stain. We have used as much as 2 ounces without issue. We have tested this under numerous water base finishes with no issue. But as always, it is a good idea to test any formula on a piece of scrap to ensure total compatibility.
Without question one of the best ways to apply a dye or stain in hot weather is to spray it liberally, again in as small sections as possible, then immediately wipe it back. The spraying allows for a rapid application of the colorant, thus giving more wiping time before it starts to set.
If spraying is not afforded then you want a good stain pad; it will hold more liquid and allow you to cover more area faster. Trying to take a brush or foam brush and apply a colorant in hot weather is all but impossible. The brushes simply do not hold enough material to allow you to evenly wet any sizable area. Just the short time of having to reload the brush is allowing the dye or stain to start to set.
You will also find that using paper towels to wipe off the excess is very
beneficial. They absorb rapidly and allow you to wipe the surface quicker.
To cut to the chase, the bottom line is you have to move quickly before any of the colorants begin to set. It’s not a bad idea to have someone helping you wipe off almost as fast as you wipe on. The general rule of thumb of allowing the dye or stain to set for a few minutes simply put doesn’t work in hot weather.
As stated above, my preferred method is to spray it really wet and start wiping as fast as possible, and in all cases avoid direct sunlight.
Wood panels set in frames tend to shrink over time, exposing an unfinished stripe at one or both sides. Even paint won’t keep this from happening, as demonstrated in the accompanying picture.
The only effective way to keep panels from showing the stripe is to stain or paint them before assembly. Gluing them in won’t solve the problem because this will cause the panels to split, which is worse.
With the panel already colored, it can shrink as much as it wants without leaving unsightly stripes.
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.
A common situation in furniture restoration is matching a newly made part to the color of the rest of the object. Water-soluble dyes are much more effective for doing this than commercial store-bought stains.
The water-soluble dyes I’m referring to are those made by WD Lockwood. They are also sold by Woodworker’s Supply under the name Moser.
Metalized dyes like those sold as NGR stains or Transtint aren’t nearly as effective because they are difficult to lighten. Trying to tweak the color usually results in it getting darker as the two colors blend and there’s no easy way to lighten it.
The water-soluble dyes from Lockwood, which are sold as powders for you to dissolve yourself, are easy to lighten simply by wiping with a wet cloth after the dye has dried. They are also easy to tweak or even change the color entirely, as shown in the accompanying picture.
On this panel I stained the entire surface with the red dye shown in the middle section. Then I wiped the left section with a yellow dye and changed the color to orange. I wiped the right section with a black dye and changed the color to brown. This sample shows an extreme example of how much control you have of the color.
The usual way to match the color of a new part is to practice on scrap wood of the same species until you get it right. Then apply the color to the part. But if you’ve tried this you know that it rarely works to your satisfaction. Somehow, the color that seemed good on the scrap often looks wrong on the new part.
With water-soluble dyes you can practice right on the part. Go ahead and glue it into the furniture, then apply a dye color you think is close to a match. Because the color you’re going to get with the finish applied is the same as the color of the part with the dye still damp, you can see right away what adjustment you need to make. It’s usually adding a little red to warm the color, a little green to cool the color, or a very little black to dull the color.
A big advantage of using a water-soluble dye is that you don’t have to worry about damaging an adjoining finish if you get some of the dye on it. Just wipe it off.