Popular Woodworking 2009-12 № 180, страница 58

tive. You are quite familiar with products that have been made thixotropic. They include ketchup, mayonnaise, many facial creams and salves, and latex wall paint.

All these substances appear thick in their containers. Once on the bread, face or wall, however, they spread easily. This is because thixotropic substances have the added characteristic of responding easily to a shearing force, such as brushing, wiping or spreading. When the shearing stops, the substance returns quickly to its thickened state.

A good example is latex wall paint. The paint appears thick in the can but stirs and pours easily. It also spreads easily under a roller. But as soon as the roller is past any given point on the wall, the paint thickens so that the protruding nibs created by the nap hold their shape and don't run down the wall.

Gel varnish is the same. It appears thick in the can, but it spreads easily. It also retains the ridges left by a brush or cloth, so almost all the excess has to be wiped off after each application.

The thixotropic additive in gel varnishes gives them a satin sheen.

Just as with all varnishes, gel varnishes can be applied over any stain as long as the stain is dry.

Applying Gel Varnish

Gel varnish applies almost exactly like oil/ varnish blend. Wipe or brush the finish on the wood and wipe off the excess before the finish dries.

There are two minor exceptions. Because gel varnish doesn't soak into the wood like oil/varnish blend, there's no reason to continue wetting the surface until the soaking-in stops. In other words, there's no benefit to leaving the finish wet on the surface for any length of time. You can wipe off immediately.

Also, gel varnish dries much faster than oil/varnish blend. So on large surfaces you have to move rapidly. You may even have to divide the object into sections and finish each before moving on, or get a second person to wipe offwhile you apply. (Bartley's brand dries noticeably faster than the others I've tried.)

You'll learn the drying characteristics of the gel varnish you're using very quickly. But if some dries too hard to wipe off while you're learning, simply remove it within a

Flexner on Finishing

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Sheen. In contrast to the gloss sheen of wiping varnish (applied on the left half of this panel), gel varnish (right half) produces a satin sheen. This is due to the thixotropic additive, which also gives the varnish its thickness and easy spreadability.

short time by wiping with a rag soaked with mineral spirits, then adjust your application method when reapplying the finish.

Just as with any finish, it's important to sand the surface smooth after the first coat (the sealer coat) and after each additional coat unless the surface feels perfectly smooth - that is, no dust nibs. Unless you have an unusually rough surface, use #320-or #400-grit stearated sandpaper. The most widely available brands are Norton 3X and 3M Sandblaster.

Gel varnish is almost the perfect compromise between oil/varnish blend and wiping varnish, but not quite. Though a pleasing satin sheen can be achieved in three or four coats, it takes a great many coats to produce a completely water-resistant film. Even though you can usually apply two, and maybe even

Wiping on. To apply a gel varnish, simply wipe it on the wood like you would an oil/varnish blend. You can use a brush to help get the thickened varnish into recesses and inside corners, but wiping is much faster on level surfaces. You can wipe in any direction.

three, coats in a day because of the rapid drying (more rapid in warmer temperatures), getting this degree of protection can still take many days and be a lot of work.

So to speed the goal of good water resistance on a critical surface such as a tabletop, apply several coats of wiping varnish and leave most or all of the excess of each to build a thickness. (See "Applying Wiping Varnish" at popularwoodworking.com/finishing.) Then follow with one or two coats of gel varnish to get a satin sheen.

Be sure to sand between coats of wiping varnish to remove dust nibs, and rub the last coat before applying the gel varnish with #000 or #0000 steel wool to dull the finish in the pores and other recesses. You can also sand this coat. But the sandpaper won't get in the pores to dull them, so some gloss may show through.

The most difficult surfaces to coat with gel varnish are those with three-dimensional recesses such as inside corners, carvings, turnings and mouldings because of the difficulty getting the finish into, and the excess out of, the hollows. Ifyou are struggling with a cloth, switch to a brush. To remove excess, use the brush dry. A cheap throwaway "chip" brush works well.

Just as with oil/varnish blend, gel varnish is very easy to repair if it gets scratched or damaged. Simply clean the surface, sand out any roughness, then apply another coat. You can use any brand. PW

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

Removing. Use a cloth to remove the excess gel varnish before it begins to harden, which it does much faster than liquid varnish. To aid in getting the varnish out of recesses and inside corners, use a dry brush as I'm doing here.

14 ■ Popular Woodworking December 2009