Understanding Stains

Go to any home center and you will probably be offered a choice of four types of stain: oil, varnish, water-based and gel (though the shelf arrangement and labeling of these stains rarely makes this clear).

Go instead to a paint store that caters to the professional painting and finishing trades and you will likely find lacquer stains and NGR (non-grain-raising) dye stains in addition to all or at least some of the stains available at home centers.

Shop at a woodworkers’ store or from a catalog that caters to woodworkers, and to many of the stains already mentioned you can add water-soluble dyes and sometimes alcohol- and oil-soluble dyes.

Instead of buying any of these products to color wood, you could use “natural” stains such as the juice from walnut husks (boiled in water) or berries, or even coffee or tea. Or you could use a chemical such as lye, ammonia or potassium dichromate. (Natural stains fade rapidly; chemicals offer limited colors and are dangerous to use and difficult to control.)

You could also use a shading stain, toner or glaze to stain wood, though each of these is designed to be applied in between coats of finish. (I’m not going to discuss these products, or natural or chemical stains here.)

There are many types of stain. In this regard stains are like saws. (There are also many saws: table, band, jig, scroll, radial-arm, miter, sabre, hand, etc.) Each cuts wood just as all stains color wood.

But it is not likely you would use a table saw to cut a curve or a scroll saw to crosscut 8/4 oak. Each saw performs some cuts better than others; likewise, each type of stain handles and colors in its own unique way. To have full control of the coloring process, you need to understand how stains differ and what each does best.

Oil Stain
Oil stains are the most widely available and are the type most people think of when they think of stain. These are the easiest to use because the linseed oil base or “binder” (sometimes a mixture of linseed oil and varnish) allows plenty of time to remove the excess before the stain dries – even on large projects.

You can identify oil stains by their thinning and clean-up solvent: mineral spirits (paint thinner). Most manufacturers list it as “petroleum distillate.” Minwax uses the more technical (and user unfriendly) name: “aliphatic hydrocarbon.”

Unfortunately, oil stains are often referred to as “pigment stain” or “wiping stain” and this introduces confusion.

Though some oil stains contain only pigment, most contain pigment and dye, and many contain only dye. Moreover, many varnish, water-based, gel and lacquer stains contain only pigment, and these are rarely referred to as pigment stains.

Oil stains can be wiped, of course, but so can all stains – especially if the project is small. So technically, all stains can be wiping stains and the term loses its usefulness.

Choose an oil stain to apply under any finish except water based, and in all cases where you don’t need any of the special characteristics offered by other stains.

Varnish Stain
Varnish stains resemble oil stains in every way but one. Varnish stains use only varnish (sometimes polyurethane varnish) as the binder, so varnish stains dry hard while oil stains don’t. Therefore, a varnish stain can be brushed on wood and left to dry without wiping whereas excess oil stain has to be wiped off or the finish applied on top may chip or peel.

Think of a varnish stain as alkyd paint with less colorant added.

Fortunately, most manufacturers label their varnish stains to distinguish them from oil stains because varnish stains use the same thinner as oil stains: mineral spirits. If you aren’t sure whether a stain is varnish or oil, put a puddle of stain on top of the can or on another non-porous surface and see if it dries hard after several days in a warm room. Thick oil stains never harden.

Varnish stains are more difficult to use than oil stains because there is less time to wipe off the excess. Brushing and leaving the excess usually leaves prominent colored brush marks.

Traditionally, varnish stains were used most often to overcoat already stained and finished furniture, and woodwork that had become dull or scuffed. Because the stain hardens well, it didn’t require a topcoat of finish in these situations and the brush marks were disguised by the already existing color.

Choose a varnish stain to overcoat an already stained and finished surface that is dull or scuffed, or if you’re wiping off excess on a small project.

Water-based Stain
Water-based stains use water-based finish as the binder and replace most of the organic thinner with water. So these stains pollute less, are less irritating to be around and are easier to clean up than oil or varnish stains.

You can identify water-based stains by their thinning and clean-up solvent: water.

Water-based stains are usually best under water-based finishes because these finishes don’t bond well over oil or varnish stains unless you give them a week or longer to thoroughly dry. Unfortunately, water-based stains are more difficult to use because they raise the grain of the wood and they dry fast.

Sanding off raised grain inevitably leads to sanding through color in places. To avoid this, raise the grain and sand it off before applying the stain, or “bury” the raised grain.

To raise the grain first, wet the wood with a wet cloth. Let the wood dry overnight. Then sand off the roughness and apply the stain. To bury raised grain, simply apply the first coat of finish over the stain and raised grain, and then sand smooth.

Overcoming the quick drying time is more difficult. You can add a slow evaporating solvent (usually propylene glycol) provided by some manufacturers or you can add lacquer retarder. But adding either reduces the color intensity of the stain and defeats the purpose of using water-based products – to reduce exposure to solvents.

A better method is to divide your project into smaller parts and apply and wipe off the stain on each before going to the next. You can also have a second person follow you, quickly wiping off the excess.

Choose a water-based stain for use under a water-based finish.

Gel Stain
Most gel stains are oil- or varnish-based, so they thin and clean up with mineral spirits. They are identifiable by their thickness, which is similar to mayonnaise. This makes them rather messy to apply, but gel stains solve the single biggest problem in wood finishing – blotching on pine.

Blotching is uneven coloring caused by varying densities in the wood and is the only problem that can’t be fixed by stripping and starting over. The only way to remove blotching is to sand it out, which is very time consuming, or paint the wood, which is seldom a desired solution.

So gel stains serve a very important role in wood finishing. And they are much more predictable and easy to use (only one product to apply) than applying a wood conditioner before staining. (See “Wood Conditioner Confusion,”  October 2005, issue #150, to understand why the directions on most brands don’t produce good results.)

Choose a gel stain when staining pine or similar soft woods.

COMMENT