FINISHING SECRETS . . .|
A spectacular grain "picture" calls for a spectacular finish, and a polished lacquer is the ideal choice for such a piece of wood. Lacquer has the unique ability among finishes to build a durable crystal clear film that gives depth and clarity to the wood surface.
Lacquer is the easiest of all finishes to apply, but it is also the most difficult to do well because it is the least forgiving of anything that we can put on a piece of wood. It will add some new words to our finishing vocabulary, "blush," "fish-eye," "blister," "sag," and "run"; and you will learn to invoke the wrath of God in several languages. Don't let this scare you away because they are problems that we can easily work around once we know what causes them.
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Lacquer can be applied with either spray or brush. The results from brushing can be equal to spraying, but it will take a lot more time and handwork to get there. I prefer to use air because it is faster. Brushing is discussed after we have explored the spray application.
This discussion is a "what works for me" approach to using lacquers. It should help the novice finisher get past the trial-and-error part of learning a new finishing technique. The missing ingredient is the experience with using lacquer and developing the motion and rhythm for using the spray gun or brush. That takes the practice, and that I can't give you.
Equipment For Spraying
Don't write-off a sprayed lacquer finish because you have been led to believe that large and expensive equipment is required. Nothing can be farther from the truth. A good brush costs more than a good spray gun. A "best buy" is the siphon-type detail gun that is available from Harbor Freight retail stores for something like $15.00. The same thing will cost twice that from Home Depot or Lowe's.
A compressor rated at 4CFM at 100PSI can support spraying our turned wood. That is not a large compressor.
I do use an in-line air filter, but use neither a water-separator nor an air-dryer. My approach to spraying lacquer is that if water condensation is a problem, the atmospheric conditions are wrong, and I shouldn't be doing it anyway.
Moisture and "Blushing"
"Blush" is a white cloudy appearance of the finish that is caused by water vapor that condenses on or under the finish as is applied or dries. In either case the water is absorbed into the finish and forms the characteristic cloudy appearance. Understanding the problem can keep us away from the situations that have an effect on our finish.
All air contains water vapor. The amount is defined by the "Relative Humidity" (RH), and the temperature where it will condense is called the "Dew Point" (DP). The secret to spraying lacquer is to prevent either the finish film or the air that carries it to the surface from cooling to below the dew point.
Rapid evaporation of the thinners in the lacquer also cools the surface film. If the surface temperature cools to below the dew-point temperature, the water vapor in the surrounding ambient air will condense on the surface as it dries. This evaporative cooling is enhanced when the finished has already been cooled by the air system that carries it to the surface.
To some degree, "blushing" can be controlled through the use of "retarding thinners" that evaporate more slowly than the normal lacquer thinners.
Water vapor can be a problem in the air stream that passes through the compressor and spray equipment. This air is heated as it is compressed, and then it cools again as it expands. If there were no intermediate cooling between the compression and the expansion, it would return to its ambient temperature. However, if it is allowed to cool, such as in an air-tank, after it has been heated by compression, it will then expand to a temperature that is lower than what was ambient before it was compressed. When this new lower temperature is below the dew point of the air, the water vapor will condense.
In the worst condition, the condensation will form water droplets in the air stream, making craters, called "cat eyes," in the surface film. Even when the air does not cool sufficiently to form water droplets, it can cool the lacquer that it is carrying to the surface, adding to the cooling of the film that takes place from the evaporating thinners.
Water droplets that condense in the air stream can be removed with mechanical separators that are installed in the air lines, but the cooling effect on the finish product that it carries remains. HVLP (high volume - low pressure) spraying equipment eliminates both the water and cooling effect of the air stream because the air pressures are low. The cheaper solution is to obey a few rules that keep us away from the conditions that will cause problems.
Lacquer is not as forgiving of our working environment as other wood finishes. Because of inadequate ventilation in our shop/studio, most of us have to spray lacquer outside, or in an open doorway, where we have no control over the surrounding ambient air. We can all but eliminate many of our problems if we obey a few simple rules.
The amount of water vapor in the air can be measured, as well as the probability for it condensing into droplets or "blush." Knowing the ambient air temperature, its "relative humidity" and the "Dew Point Temperature" we can determine whether any day will be a good one for spraying lacquer. This information is available from the Weather Channel website at www.weather.com or other sources for similar information.
We should recognize that there are places and seasons where we cannot spray lacquer under any conditions. One that I know of Western Washington during the winter rains when the humidity is very high and the DP very close to the ambient temperature.
While there is no single set of values that will insure successful spraying, I have learned that the following guidelines can be useful.
Using The Rules
- The "Rule of 65"
I have learned the hard way that lacquer should not be sprayed when the temperature is below 65°F or the Relative Humidity (RH) above 65%. It should be obvious why we should not spray lacquer until after the morning fog has lifted, or while there is dew on the grass. The Weather Channel (www.weather.com) or other weather source with temperature, humidity, and dew point information
Violation of this rule can result in "blushing" (cloudy appearance) of the surface film from trapped water vapor. If we deviate too far, water droplets will be blown on the surface. The range of temperature and RH for brushing lacquer is broader because of its slower drying rate and the fact that we usually try to do it inside the shop.
- The "20°F Rule"
How far above or below, and far apart these two numbers should be is defined by another rule that states - It is safe (usually) to spray lacquer when the dew point temperature (DP) is greater than 20°F lower than the ambient temperature.
This is an additional guide when it might seem impossible to spray lacquer if we were to obey the "Rule of 65." In other words, I might get away with spraying lacquer or other finishes with fast drying thinners at an ambient temperature of 100°F, as long as the dew point was below 80°F, regardless of the RH.
I would improve my chances of successfully spraying the lacquer by using a small capacity tank that would allow very little cooling between compression and expansion of the air. This may permit us to work with a DP that is closer to the ambient temperature than the recommended 20°F.
A typical example of when not to spray lacquer would be the typical winter day in Western Washington where the temperature is 45°F, the humidity is 90%, and the dew point is 43°F
There are several other conditions that will improve the success of our sprayed lacquer finish.
About The Lacquers
- Bugs and dust
Bugs love lacquer. Don't try spraying a finish when there are a lot of them about. And, try to choose a calm day to reduce problems with dust. Contamination by bugs and dust particles is more noticeable in a lacquer than any other finish that we can put on a piece of wood.
Do not expose the work to direct sunlight while the lacquer is still wet. To do so will usually result in "blistering" and bubbles in the surface film as it dries.
- Oils and Silicones
Do not contaminate the wood or film surface with oils of any type. These oils will cause a small circular dimple in the surface film, called a "fisheye." To insure a clean surface, do not use sandpaper that has anything added to its surface for easier sanding.
Do not use a sanding sealer unless you know that it is compatible.
Steel wool must be "oil-free." I recommend either the Libronâ brand that is available from Craft Supplies or purchasing steel-wool from an automotive paint supplier. Don't trust the package label on commercial steel-wool because "oil free" is a relative term. If in doubt, rinse it two times in clean Mineral Spirits and thoroughly dry before using. Then test it by spraying lacquer onto a wood surface that has been vigorously rubbed with the cleaned wool.
Do not use any wax containing silicones anywhere in the shop. Keep your hands washed and dry, and avoid getting any perspiration on the wood surface.
- Shop Dust
When we spray or brush lacquer in the shop, we can control the temperature, RH, sunlight and bugs. But, shop dust is a larger problem. A clean shop is the obvious solution. Spraying the lacquer when first entering the shop, before the dust has become airborne, will help.
There are three (3) new problems to solve when spraying lacquer in the shop - ventilation, ventilation, and ventilation. Spraying indoors is not recommended unless you have a dedicated spray booth, a good supply of fresh air, and a full-face respirator with carbon filter cartridges.
All commercial lacquers contain a few "solids" and a lot of thinner. The solids are what is left behind as the finish after the thinners have evaporated. Not all lacquers are created equal, and lacking any other knowledge, price is a good indicator of quality, and the weight of the can the amount of "solids" it contains.
We will not even consider the water-borne products that are called and sold as "lacquer." They aren't even close to being the same thing. The manufacturers keep trying, but they still have a long way to go. Their film has a cloudy bluish tint, and they weren't crystal clear the last time I looked. And, we will not discuss the use of the catalyzed lacquers. While they are excellent products that will yield a durable gloss finish, they are for "professional use only" because they require ventilation and personnel respiration equipment that is beyond the scope of the normal woodturning shop/studio.
- Commercial Cellulose lacquers (Park, etc.)
These are not recommended for our use because their surface film will turn yellow in color and become brittle with age. These lacquers will turn a very dark brown color with age while they are still in an unopened can, If you want to use one of these products, ALWAYS open the can before making the purchase to see whether it is clear or amber in color. If it is amber in color, then it is either poor quality or stock that has started to age. Expect to pay about $15.00 per gallon for these products.
"Brushing lacquers" have been blended with "retarding" thinners that take longer to evaporate, and this allows allows leveling of the surface film. The Deft® that is familiar to all woodturners is a brushing lacquer. Brushing lacquers can also be used in a spray gun, but their slower drying rate will allow sags and runs to form more easily.
Regardless of the advertising claims, a can label that nowhere uses the word "lacquer," and the many mysterious attributes that it claims to have, I can only judge the product by how it compares to other lacquers. For a price of $32.00 a gallon, it offers the same solids content as the less expensive lacquers. It offers a slight advantage over the other cellulose lacquers because it has been modified to remain more flexible, and not yellow as fast with age. Out of habit more than any logical reason, I still use Deft as a general wood sealer finish where clarity isn't important. It is easy to use, brushable, and readily available. But, I will never use it for the "museum quality" lacquer finish that we are discussing in this article.
Deft, like any other brushing-lacquer, can be used in a spray gun, and usually without using any thinner. Its slower drying rate can useful, but will also contribute to "runs" and "sags" in the surface film if we are not careful. Contrary to what is printed on the can, or in their literature, Deft can be thinned with any commercial lacquer thinner.
- CAB-Acrylic Lacquer
To some degree, all lacquers become brittle with exposure to sunlight, but the CAB-Acrylics will stay more flexible than anything else that I have used. At a price that is only slightly higher than Deft ($36.00 a gallon), the lacquer by Sherwin-Williams is "water white" in the can, and it will not turn yellow in our lifetime. There are similar products available from Kelly-Moore and other sources, but some of them can already be an amber color when the can is opened.
I thin it to no more than 50/50 with a commercial thinner for application with 30 PSI at the spray gun. Any product labeled "Lacquer Thinner" can be used.
- Ditzler (PPG)® Automotive Lacquer
This is the best of the several brands that I have used over the years. It will not turn yellow with age, and its film is flexible enough that it will not show cracks on any but the most flexible of our wood turnings.
We will have to go to the automotive paint supplier to purchase this product. Be prepared for a shock when you see the price because it retailed at $36.00 a quart the last time I bought it. Yes, that is "quart"! This lacquer is sold for use in high-pressure spray equipment, and as such has an extremely high solids content. I thin it to a 3-to-1 or 4-to-1 thinner-to-lacquer ratio for application with my siphon gun at 30 PSI. At that thinning rate, it is actually cheaper than Deft.
- Waterborne Lacquers
These products are not a true lacquer, and have none of the properties of clarity, grain enhancement, or gloss that are found in the nitrocellulose lacquers. As such, they are not appropriate for this discussion.
Wood Selection and Preparation For Finishing
The statement, "The appearance of the finish that you put on the wood can only be as good as the surface under it" has never been more true that when we are applying a high gloss lacquer finish. The wood surface must be the closest to perfection that is possible. The clear high gloss film will magnify every surface flaw, sanding scratch, and tool mark, and many of them will not be visible until after the finish is applied.
Such a wood surface isn't all that difficult to accomplish if we follow the directions for sanding that were discussed in my article, "Sanding Savvy," presented as No. 3 in this series of articles.
All wood species are not suited for a lacquer finish. Avoid those with a coarse open grain (Oak and Ash), those that are very soft (Cedar and Redwood), and those that are very oily Cocobolo), until you have some experience with lacquer. The coarse grain doesn't develop an attractive appearance unless a lot of fillers are used, and fillers can be the cause of other problems. Soft wood doesn't provide a rigid foundation for the surface film. And, some oily woods can cause adhesion problems. Maple, Walnut, Cherry, and Mahogany are a few of the common woods that are ideal for a high gloss lacquer finish.
A heavy lacquer finish is not suitable for a piece that is flexible, or one that has sharp "inside" corners where a heavy fillet can build. In either case, we would be asking for cracks or separation from the wood. Although they can be easily repaired with a coat of very thin lacquer, it is best to avoid their happening at all.
Wood Moisture Content
The moisture content of the wood must be at its equilibrium with the relative humidity of the environment. Some deviation can be tolerated, but not much. Excess moisture in the wood can condense on the underside of the surface film as it cools. This can cause either a blushing under the surface film, or cracking of the surface film from movement of the wood as it continues to dry. Depending on the amount of moisture, it may be absorbed back into the wood, but normally that doesn't happen, and it will require removing the lacquer film from the wood. Fortunately, this is often made easier because the moisture will also cause adhesion problems, and that can make it easier to remove.
Application of the "Finish"
I hope that all of the above hasn't frightened anyone away from a high gloss lacquer finish. It isn't more difficult than other finishes, it is just less forgiving. When the piece is sanded to perfection, we are ready to proceed.
- Brush on a heavy sealer coat of either Deft or the same lacquer and thinner that you will be using for spraying. Let it sit for no more than a few seconds, and then wipe it all off with clean paper towels, changing them often, until the wood surface is smooth and dry. Make a final wipe with a towel that has been dampened with thinner.
- Wait about 30 minutes for the lacquer that has been absorbed by the wood to dry. Then buff with 0000-grade steel wool, and proceed with the first coat.
If you want to accent the grain of a wood like Maple, apply a liberal coat of any oil/varnish finish and immediately wipe the surface dry. Wait until the following day, and buff with 0000-steelwool. To avoid any potential for adhesion problems, brush on a coat of a 2-pound cut dewaxed shellac. It is best to mix your own shellac because any wax in the shellac could cause problems with the lacquer.
Commercial pre-mixed shellac can be dewaxed by pouring it into a quart Mason jar, letting it sit for several days until the heavier waxes have settled to the bottom, and then decanting the clear shellac into another container, leaving the waxes behind. Sand the shellac lightly with 600-grit or the same grit that used last for finishing the wood. Buff lightly with steel wool and proceed.
- Adjust the air-regulator to 30PSI. Fill up the spray gun with lacquer that has been thinned to no more than about 30% thinner, and practice on a smooth piece of scrap wood to find the correct balance of finish viscosity and air pressure. Add thinner if you cannot get good atomization and coverage, but no more than a 50/50 mixture. Use a retarding-thinner if there is a problem with "blushing." If the surface develops a mottled appearance (called "orange peel"), reduce the air pressure. "Orange peel" is caused by the impact of partially atomized droplets of finish impinging the wet surface film.
- Apply a wet coat to the entire surface, but not so much that the lacquer runs. If you get a run, or a "fisheye," leave it alone for now. Try to avoid over-spray, but don't be concerned because there will always be some present. It is impossible to totally eliminate it. Some degree of "blush" can also be tolerated, and it may disappear with the addition of more lacquer or after it is buffed.
Wait three minutes and shoot another wet coat. Then wait three more minutes, and shoot a third. If the "blushing" doesn't disappear, or gets worse, the weather conditions are wrong, and you didn't read our previous discussion on that subject.
- Then wait at least 2-hours, and buff the surface with 0000-steelwool until it is smooth and all surface blemishes have been removed. If the lacquer balls up in the steelwool and it is difficult to get a smooth surface, wait another couple hours, or until the next day.
- Repeat Steps 4 and 5, and apply another three wet coats followed by buffing with steelwool. Then repeat a third time. You will now have a total of nine coats of lacquer; three successive coats applied three times.
- Thin the lacquer to 2/1 ratio of thinner to lacquer, and apply two successive wet coats no more than five minutes apart. Set the piece aside for at least two days.
- Buff lightly with the steel wool to remove dust, bugs, over-spray, runs, etc.
- Wet sand with 1000-grit, followed with 1500 and 2000-grit, both lubricated with water. For a rough or brushed on surface, you may have to start at 400 or 600-grit, and work your way up to the finer grits. A couple drops (only) of liquid dishwashing detergent in lukewarm water makes a better lubricant for sanding than water alone.
- Polish with 4F Pumice that is lubricated with water. Use a piece of felt or a ball of cotton tee-shirt material for polishing pads. Then buff clean with a cotton cloth.
- Polish the surface with Rottenstone, lubricated with water.
- Polish one more time with Rottenstone, only this time it is lubricated with mineral oil.
- Buff with a clean cotton cloth. It may be necessary to wipe with soap and water or mineral spirits to remove all of the oil from the surface. Lacquer will not dissolve in mineral spirits.
- Admire your creation. Now, was that as difficult as it appeared when you first read this article?
Trouble…..what to do with blushing
Sometimes we will get blushing, regardless of our efforts to control it. All is not lost, and there are two things that we can do……
The first thing to do is nothing.
Take the piece inside where the temperature is at least 65°F and wait until the next day. The change in environment will often allow the moisture that is causing the blush to evaporate through the surface film or be absorbed back into the wood.
If that didn't work, add 10-25% retarding thinner to the same thinner that you were using, spray the surface with the mixed thinners, and allow it to dry. The thinner softens the surface film, and the retarding agents slow the drying time, allowing the trapped moisture to escape. I would recommend that 10% retarding thinner be used, and the quantity increased to a maximum of 25% only if that didn't work.
In the rare occasion where the thinner doesn't remove the blush, you will have to wait for more favorable weather conditions, remove the surface film with 0000-steelwool until the cloudy area is removed, and then recoat with fresh lacquer.
Doing It With A Brush
We can get the same quality finish with a brush, it just takes longer and more work. Follow the same steps as described for spraying, except apply the lacquer with a brush, and only one coat at a time rather than three. Apply a smooth and heavy coat, blending as many of the brush marks and over-laps as possible before the surface film starts to form. Stop brushing when the film starts to dry and drag on the brush.
The quality of the brushed finish is directly proportional to the cost and quality of the brush. There are better brushes, but you can get acceptable results with the 1" diameter pony-hair mop brush available from Craft Supplies for about $15.00, and the 1" wide badger-hair brush from Woodcraft is another good brush for about the same price. I would not expect anyone to be satisfied with the finish that results from using anything less than either of these brushes. A high quality lacquer brush is a good investment because it will last for many years. The current cost of a similar sized sable-hair brush is about $95.00, but still a good investment if you will be using brushing lacquer finishes on turned wood.
Clean the brush with thinner after using, and wrap it in a piece of grocery-bag paper to keep the dust away. Soak it in thinner again before using.
Use adequate ventilation, and be careful of dust. We have a tendency to ignore both when we are brushing lacquer in the shop/studio. The slower drying rate of the "brushing lacquer" allows more dust into the surface film. Lacquer should be brushed in the morning as soon as we enter the shop, and before any equipment is started to raise a dust cloud.
If you are using the Sherwin Williams CAB Acrylic or similar lacquer, thin it with 25% "retarding thinner." This slows the drying time and allows the brush marks to flow out. Add more thinner as desired, but no more than an additional 25% (50/50 thinner total). Or, use clear Deft® straight from the can. It may not be the best, but it sure is easy to use.
The sanding and buffing will be more difficult because it is necessary to remove the imperfections from brushing. Be careful not to go through the film into the wood. It may be necessary to apply additional brushed coats to get the desired uniform film thickness.
A lacquer finish is neither quick nor easy, but the spectacular results are worth the effort. Always remember that a high gloss lacquer finish will not have the appearance of "plastic." If it does, we have done something wrong.
© 2002 - 2009 by Russ Fairfield. All rights reserved.
No parts of this publication may be reproduced in any form
or by any means without the written permission of the author.