How to Prepare Wood for a Finish Part 1 | Apollo Sprayers HVLP

How to Prepare Wood for a Finish Part 1

The main reason you sand wood before applying a finish is to remove machine marks. All machine tools leave cuts or impressions in wood that are highlighted by stains and finishes, especially by stains. Before machine tools appeared in the mid-nineteenth century no sanding was needed. Indeed, there was no sandpaper. Wood was smoothed with hand planes and scrapers.

You can still use hand planes and scrapers so you don’t have to use sandpaper. You can hand plane or scrape the wood straight from the saw, or you can begin the smoothing with a planer and then finish off with a hand plane or scraper. You can also use molding planes and scratch stocks to shape wood rather than routers and shapers.

Few woodworkers choose this route because machine tools are much faster and easier to learn to use than hand tools.

This is an important mental point. It makes sanding less burdensome when you remind yourself that you don’t have to do it. It’s just the price you pay for the increased efficiency of substituting machine tools for hand tools.

How to Sand

The trick to efficient sanding is to begin with a sandpaper grit that cuts through machine marks and other problems in the wood with the least amount of effort and without creating larger-than-necessary scratches that then must be sanded out. This holds true whether you are sanding by hand or using a sanding machine.

When you have removed all the machine marks with the coarsest grit you choose, sand out the scratches left by this sandpaper using increasingly finer-grit sandpapers until you reach the sanding grit that produces the size scratches you want.

As an aid to determining when you have sanded out all the machine marks, draw some marks on the wood using a no. 2 pencil and sand until no evidence of these marks remain. To be extra sure you have sanded enough, do it again.

In practice, the best grit to start with is usually #80 or #100 grit. But, if the problems in the wood are so severe that #80 grit doesn’t remove them quickly, drop back to a grit that does.

If the problems can be removed with a finer-grit sandpaper, such as #120 grit or #150 grit, you are wasting time and energy if you begin sanding with a coarser-grit sandpaper. Rarely do you need to begin sanding with coarser than #120 grit. If you’re refinishing, you can usually sand with just #180 grit to be sure you’ve removed all the previous finish.

The best grit to end with is usually #180 or #220 grit, though it can be helpful to sand to #320 or #400 grit to reduce grain raising when using water-based finishes. Woodworkers disagree about which grit to sand to. We rarely sand beyond #180 grit.

The primary goal of sanding is to produce a surface that doesn’t show either machine marks or sanding scratches after you apply a stain or finish. If the scratch pattern can be made even, you may achieve satisfactory results sanding only to #150 grit. Stationary sanding machines are best for doing this, though hand sanding will also work, especially if you aren’t applying a stain.

If you could sand just the right amount with each sandpaper grit, it would be most efficient to go through each consecutive grit—#80, #100, #120, #150, #180—and so on. But most of us sand more than necessary with each grit, so you may spend less effort skipping grits. This is especially true when using machine sanding tools.

Sanding is very personal. We apply different pressures, use sandpapers to different degrees of wear, and sand for varying lengths of time. The only way to know for sure that you have sanded enough is to apply a stain and see if any machine marks or sanding scratches show. It is therefore wise to practice on some scrap wood until you get a feel for what works best for you.

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