Posted on November 4th, 2013 No comments
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.
Posted on November 4th, 2013 No commentsInexpensive 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.
Last month we featured an article by extraordinary woodworker, Charles Neil, showing how to create antique finishes. Below is the second part of the article. Before reading the article, take a look at Charles’s latest project, a gorgeous coffee table made from “junk wood.” It looks so far from being “junk” and is really a stunning piece of sculpture. We love the “bird’s nest” below the table.
Charles loves to experiment with finishes, and use his knowledge to play with techniques, wood and coatings. We can all learn from his ideas. Here are some great tips from a great finisher:
This is a piece of 8/4 cherry just to show the technique. I like to take a power carver or carving chisel and “bark” the edges of slabs and so forth. Then give it a light coat of finish and glaze it dark, it gives it that “hewn, barky look,” and it’s really nice if you’re into slabs and so forth as you can sort of free form it the way you want and get a nice complimentary edge treatment.
Here is a piece of tiger maple I jigsawed to a “natural form” and then used the same technique.
This is a piece of tiger maple that I oxidized. The brown was done with a mixture of vinegar and steel wool let soak for a day or so. The more steel wool and the longer you let it soak the more intense the color will be.
The bluish/steel look is done with Ferrous Sulfate, which is an iron supplement you can get at any drug store, just dissolve 5 or 6 tablets in a pint of water and you’re good to go. In both cases it’s a reaction with the tannins in the wood.
However, not all woods have sufficient tannins to react, but we can cure that. Boil some green tea bags, (the real stuff) and make it really strong. I usually use about 3 or 4 bags to the pint, and apply and let dry before applying the vinegar or Ferrous sulfate. The tea adds tannins to the wood; I have also heard that strong black tea will do the same thing.
This is a piece of yellow pine that has been wire brushed with the grain then given the green tea and the vinegar solution).
This is the same yellow pine with the tea and Ferrous Sulfate. You will note in both cases how the strength of the tea, as well as the solutions, affect the color. The nice thing about the techniques here is that they are safe, nonflammable and can be enjoyed and used in either the home shop or at work.
Posted on August 6th, 2013 No comments
The principle differences between nitrocellulose lacquer and shellac are ease of application and their ability to block off problems in the wood. Both finishes are evaporative finishes, meaning that they dry entirely by solvent evaporation; there is no crosslinking as there is with varnish and catalyzed finishes.
As a result, both lacquer and shellac are more vulnerable to being damaged by coarse or sharp objects, heat, solvents, acids and alkalis. Shellac is more vulnerable than lacquer to being damaged by alcohol spills, of course, but keep in mind that beer, wine and mixed drinks are usually very watered down, so the vulnerability is much less than a straight alcohol spill.
Lacquer is much more user friendly than shellac because of the difference between thinners. Lacquer thinner is made up of a number of different solvents (usually about six, except in areas with strict VOC rules) that evaporate at different rates. This allows finishers to control the drying rate of the finish to avoid blushing, and runs and sags. With the right lacquer thinner, lacquer can even be applied successfully in cold temperatures. We have almost no control of the drying rate of shellac with just alcohol as the solvent.
But shellac has the advantage of being able to block off problems in the wood, such as silicone, which causes fish eye, various other oils, resin in oily woods, wax, etc. Shellac, therefore, can be useful as a sealer coat if you have one of these problems. For the most part, shellac is a great tool for refinishers who often encounter silicone problems, but of almost no advantage for finishing new wood.
The greater user friendliness of lacquer was the principle reason lacquer replaced shellac as a finish in the 1920s.
Posted on August 6th, 2013 No comments
Many, probably most, store-bought stains are made with both dye and pigment. If wood stained with these stains is exposed to sunlight or fluorescent light for a while, the dye color will fade away, but the pigment color will remain. The effect is that the stained wood changes color.
In the accompanying picture the red dye in this “cherry” stain has faded on the top half (I covered the bottom half) after only a few days in direct sunlight, leaving the color significantly different. It’s definitely no longer cherry color.
The fading occurs much more rapidly in direct sunlight than indoors with a window providing a partial barrier to UV light. Nevertheless, you need to be aware of the problem when choosing a stain, depending on where the object will be placed.
To my knowledge manufacturers never tell us if there is dye in the stain, so we have to determine this ourselves. The easy way is to open the can after it has sat on a shelf for a week or two to allow the pigment to settle, then insert a light-colored wood stirring stick an inch or so into the stain. If it colors the stirring stick, there is dye in the stain because dye dissolves; it doesn’t settle.
If you insert the stirring stick to the bottom of the can, and the pigment has fully settled, you should be able to bring up a little pigment. Very few stains contain no pigment, but some do.
Posted on July 9th, 2013 No comments
With shellac and lacquer finishes, which are the finishes used on almost all old furniture and woodwork, you can use their solvent for stripping instead of a paint-and-varnish remover. Depending on the object being stripped, I often find this method easier in the sense of spending less total time. It’s also less messy.
Use denatured alcohol for shellac and lacquer thinner for lacquer. You can test the finish to find out which it is by dabbing a little of each solvent onto the finish. The alcohol will soften shellac and make it sticky or remove it. Lacquer thinner will do the same to lacquer.
Spread some paper towels (or cotton rags) over the surface and pour on the appropriate solvent to thoroughly wet the towels. Keep wet for 10 or 20 minutes, or until you can wipe off all the finish quickly and easily. If you have done a good job, a quick wipe with a towel or rag soaked with the solvent will clean up any remaining finish residue.
One advantage of using this method of stripping is that you don’t have to mess with removing the wax that is included in many strippers to slow their evaporation. This wax causes many refinishing problems, because people often don’t get enough of it removed.