Popular Woodworking 2007-12 № 166, страница 63

Popular Woodworking 2007-12 № 166, страница 63

Actually, these solvents seem to have similar characteristics to turpentine in that they have the solvent strength of naphtha but an evaporation rate closer to mineral spirits. So they are useful to fine artists but provide no special benefit to wood finishers.

These are all of the petroleum distillates used in wood finishing. Now for the other solvents.

Alcohol

Alcohol is the solvent for shellac. The solvent dissolves solid shellac flakes and thins the liquid shellac after dissolving. There are two alcohol types available at paint stores: metha-nol and denatured.

Methanol evaporates a little faster than denatured, but it is toxic and could blind or even kill you ifyou breath too high a vapor concentration for too long. You shouldn't use it unless you have good ventilation in your shop.

Denatured alcohol is ethyl alcohol (the alcohol in beer, wine and liquor) that has been made poisonous so we don't have to pay liquor taxes to buy it. This is the alcohol you should use with shellac.

In situations where shellac is not the finish, alcohol has the further use as a felt-pen-ink remover. Dampen a cloth and wipe over the mark and you will remove it in most cases. You won't damage any finish except shellac as long as you don't soak the surface.

Lacquer Thinner

Lacquer thinner is the solvent and thinner for all the types of lacquer, including nitrocellulose, CAB-acrylic and catalyzed. It's the most interesting of the solvents because it's composed of half-a-dozen or so different individual solvents. Manufacturers vary these to control solvent strength and evaporation rate.

Solvents from five different families are used in lacquer thinners, including toluene, xylene and "high-flash" (meaning fast evaporating) naphtha from the petroleum-distillate family. The other four families are ketones, esters, glycol ethers and alcohols.

All the individual solvents from the ketone, ester and glycol-ether families dissolve lacquer on their own, but they evaporate at different rates. So manufacturers choose among them to make a thinner that evaporates in steps at the speeds they want. Alcohol doesn't dissolve lacquer on its own, but it does when in combination with these other solvents. So one or more of the alcohols is usually added

Flexner on Finishing

Felt-tip removal. Denatured alcohol is especially useful for removing felt-tip-pen marks. The solvent won't damage any finish except shellac as long as you don't soak the surface.

to the mix to reduce cost.

The nature of lacquer is that is can be fully dissolved and still be too thick to spray efficiently. So to further thin the lacquer without adding expensive dissolving solvents, manufacturers add up to 50 percent toluene, xylene or high-flash naphtha to, in effect, "thin" the lacquer thinner.

By varying the solvents used, manufacturers can control the strength of lacquer thinner (automotive lacquers need a higher percentage of dissolving solvent) and the speed of evaporation. For example, lacquer retarders are made to evaporate slower so the lacquer stays "open" on the surface of the wood longer in order to eliminate blushing (turning white) in humid weather and dry spray (a sandy surface) in hot weather.

The purpose of using multiple individual solvents evaporating at intervals is to control the thickening of the lacquer on a vertical surface to reduce runs. The lacquer thickens quickly after being sprayed but enough of the slower evaporating solvents remain so the finish has time to flatten out. Lacquer thinner is unique among solvents for having this characteristic.

A cheaper "clean-up" lacquer thinner is often available. It's made with a higher percentage of "thinning" petroleum-distillate solvents and doesn't dissolve lacquer well. You will have problems if you use this thinner for thinning lacquer.

Acetone and MEK

Only one of the families of active solvents in lacquer thinner (ketones, esters and glycol ethers) is commonly available in paint stores. This is the ketone family. The two fastest evaporating ketones, acetone and methyl ethyl ketone (MEK), are usually available.

Both make excellent cleaners, but keep

Thinning lacquer. Lacquer thinner is a blend of half-a-dozen or so solvents specially formulated for thinning lacquer. The blend allows for differing evaporation rates and for evaporation in steps to reduce runs on vertical surfaces.

in mind that they will damage and remove all but the most solvent-resistant paints and finishes.

Brush Cleaners and Deglossers

Brands of brush cleaner and deglosser (liquid sandpaper) vary greatly in their composition. Some are even water-based, but these work more slowly and are less effective than solvent-based.

You can usually substitute a brush cleaner for the mineral spirits or lacquer thinner you may otherwise use to clean your varnish, lacquer or water-based finish brushes. (It's easiest to clean shellac with household ammonia and water.) Brush cleaners are usually more expensive, however.

What is left unsaid about deglossers is that it matters greatly what paint or finish you're trying to clean and dull. Cleaning grease or wax is no problem, but high-performance paints and finishes such as powder and UV-cured coatings, catalyzed lacquer, conversion varnish and even oil-based polyurethane are very solvent resistant. So it's rarely possible to dull them short of abrading with real sandpaper or steel wool.

Conclusion

Manufacturers are very creative in their labeling, so you could easily come across solvents with different names than the ones I'm using. But if you read the intended uses listed on the containers, you should be able to place them in one of the above categories. PW

Bob is the author of "Understanding Wood Finishing" and a contributing editor to Popular Woodworking.

92 ■ Popular Woodworking December 2007

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