Craftsman, Woodworker, Antiques Refinisher, Columnist, Author and Television Host
"How do I prepare my wood?"
Just as you always need to prepare the food you bring home for cooking, we also need to prepare the wood we bring home for staining and finishing.
Why? Because wood is unpredictable.
Wood is a product of nature, and nature, whether it be the weather, the grass in our back yard, or a piece of wood, doesn't always act in a consistent manner. Even two boards from the same tree or two boards side-by-side in the same piece of furniture can take a stain or a finish differently from each other.
Fortunately, since we know this, we can take two steps to reduce the unpredictability of wood: sanding and conditioning. To explain, let me share with you some questions I have received from other readers.
And, as always, if you don't find the answer to your question here, just send me an email -- and pictures -- to firstname.lastname@example.org.
Q. - Why is it necessary to sand wood before staining or finishing it?
A. -- Wood is a relatively soft, porous material, which is why we are able to change its color by applying a penetrating stain or a dye to it. But since it is soft, it can be scratched and dented between the time it leaves the sawmill and reaches our garage or basement workshop. These dents and scratches actually absorb more stain than does unblemished wood, so unless we sand them out, these dents and scratches will appear even worse after staining.
In addition, the final milling process often crushes the top layer of pores in the board, making it more difficult for our stain to penetrate the wood. A light sanding will open the pores so that we can achieve the color we want.
Q. - What grit of sandpaper should I use?
A. -- The grit number appears on the back of each sheet of sandpaper, along with several indecipherable letters and symbols. Grits below #100 are considered "Coarse" and are used when you need to quickly remove a good deal of wood or thick finish, such as when you are refinishing a floor or a painted door. Grits between #100 and #200 are considered "Medium" and are used most often to remove shallow scratches and to open the pores of the raw wood. Grits between #200 and #400 are considered "Fine" and are used between coats of dried new finish. Grits above #400 are "Very Fine" and are used for final buffing of the last coat of finish (more on that in Finishes).
Q. - Why do instructions always call for us to sand "with the grain of the wood" ?
A. -- If you examine any board you will see that the pores of the wood align themselves in one direction, called the "grain" of the wood. Many of these pores look like tiny scratches. When we sand the wood, the abrasive in the sandpaper often leaves similar scratches in the wood. When these sanding scratches align themselves with the pores of the wood, headed in the same direction as the grain of the wood, we don't notice them. But when these sanding scratches go "against the grain," they stand out like a sore thumb. You may not see them while sanding, but as soon as you apply your stain - watch out!!!!
Q. - A friend says I should never over-sand an antique I am refinishing. Is she correct?
A. -- Absolutely!While we want our new furniture to be blemish-free, we expect an antique to show signs of age. We call it "character." Some people refer to the mellowness which old wood and an old finish acquire after decades of sunlight, dusting and daily use as "patina," which is what distinguishes an antique from a nearly identical, but new reproduction. Naturally we don't want dangerous splinters or broken rungs on our antiques, but we do want those shallow scratches, dents, dings and worn spots to remain. Before staining or finishing, sand very lightly with #180-grit or finer sandpaper just to remove any remnants of the previous finish and to open the pores for the stain or finish.
Q. - What is the best way to remove sanding dust?
A. -- I use a soft bristle attachment on the end of a vacuum. Second best is a tack rag, which is generally cheesecloth moistened with just enough varnish to make it "tacky." Do not use a tack rag if you are going to apply a water-based stain, for any oil left on the wood by the tack rag will prevent the water-based stain from penetrating the pores of the wood (more on water-based products in Staining and Finishing). Instead, use a rag moistened with water before applying a water-based stain or finish.
The three worst ways to remove dust are (1.) using a dry rag which only pushes the dust around, (2.) using a dry paint brush which only flips the dust temporarily into the air, and (3.) blasting it with compressed air, which sends the dust swirling around the room before it settles back onto your fresh stain or sticky finish after you leave.
Q. - In the past when I have applied a stain, my wood turned blotchy. How can I avoid this next time?
A. -- Stains and dyes both rely on the open pores in the wood to absorb them. Oftentimes, however, those pores don't always present themselves in an organized and unified manner. Most softwoods, such as pine and fir, have an irregular pore structure, especially around knots and natural blemishes. Many hardwoods, including cherry and maple, present a similar problem. In nearly every case the board looks perfectly fine before the stain has been applied, but afterwards turns blotchy as the irregular pores absorb the stain unevenly.
The most well-known exception, one which generally looks great when stained any color, is oak, for oak has a more predictable grain pattern and pore structure. Even so, knots in oak are going to turn blotchy and even the grain in oak can benefit from the following technique, called "conditioning."
The best way I have discovered to reduce the blotchiness is to apply a coat of Minwax Pre-Stain Wood Conditioner to the wood after sanding but just prior to staining. The thin-bodied conditioner prevents the larger pores from absorbing too much stain but won't completely seal the smaller pores. It is available in both oil-based and water-based formulas, so read the instructions carefully as they vary from each other in the amount of time needed to be absorbed into the wood.
If you insist on staining any extremely porous softwood, such as pine, with a dark walnut stain, however, no amount of Pre-Stain Wood Conditioner is going to eliminate all blotchiness, so don't expect miracles. Stains can vary the natural color of wood somewhat, but can't be expected to turn a knot-riddled pine board into premium walnut.
Three Important Rules: Always follow the manufacturer's directions, take all safety precautions and first test every product in an inconspicuous spot.