The general term for smoothing wood prior to applying a finish is ‘abrading’. This is simply the wearing away of wood fibres by the sharp teeth of abrasive material.
Abrasive papers have abrasive particles bonded to their surface: glass paper (or sandpaper) is the cheapest abrasive paper; garnet paper is harder and better quality and used for fine finishing of furniture; silicon-carbide paper is often called wet-and-dry paper, because it can be used either way. Use it wet for removing the glaze from paint before repainting: the water acts as a lubricant and also keeps down paint dust, which may contain lead. The particles are called ‘grit’ and these are numbered. Generally, you work through the grades, starting with the coarsest and working through to the finer ones until the wood is smooth and there are no sanding marks.
Other methods of abrading wood include rasps and files (bars of variously shaped steel with patterns of teeth cut onto their surface), or surform tools (a combination of files and planes). Steel wool, graded by ‘0’s – the more ‘0’s, the finer the wool – is used with white spirit for taking the gloss off sealers and varnishes before recoating.
Sanding by Hand
Always sand in the direction of the grain of the wood. Before the final sanding, dampen the wood with water to raise the grain. When it has dried, sand with very fine abrasive paper for a perfect, smooth finish.
Using a Power Sander
Power sanding is done with an attachment to a power drill or with a specially designed sanding tool. The most popular sanding attachment for a power drill is the disc sander. This has a flexible backing pad that holds a removable abrasive with a screw and washer. Because the disc always cuts across the grain of the wood, leaving marks that are difficult to remove, you should reserve this tool for ‘rough’ work.
Orbital sanders use 1/2 or 1/3 size abrasive sheets, which are cramped to a padded baseplate. These are available as attachments for power drills or as separate power tools. The sanding action is elliptical and is ideal for sanding large panels flat. Let the weight of the tool itself do the work, but keep it moving up and down and across the work piece in a gentle sweeping action.
A belt sander is a semi-professional power tool that has a continuous 75mm or 100mm (3in or 4in) wide belt, which passes over a flat bed via two rollers. It can also be inverted for flat and curved sanding once the tool has been securely cramped to a workbench. A belt sander is ideal for final smoothing after planing, for levelling floorboards and for getting into corners where a large, hired floor-sanding machine cannot reach. Hold onto it firmly as you work so that it doesn’t snatch at the wood or take off across the surface.
Planing prepares wood for accurate marking and cutting of joints, and also smooths the wood ready for the finishing steps. Plane blades should be razor-sharp and carefully adjusted to shave off just the right amount of wood required. Planing is a skill that takes practice, so be prepared to spend some time getting used to the tool and the techniques needed to sharpen, adjust and use it accurately.
There is a wide range of wood-working planes to cope with all kinds of work, but a long bench plane gives an accurate result. While a small plane follows the contours of the surface of the wood, a long plane rides over high spots in the wood, gradually removing them until the wood is even and a single, long shaving can be removed.
Bench planes are 350-380mm (14-15in) long and are used for levelling and smoothing long lengths of timber. A block plane is useful for small work and for end-grain trimming: these are available in sizes from 90-200mm (3 1/2-8in) long.
You will need to make sure the wood you are smoothing is held completely flat and that you are working with the grain. Set the plane’s cutter and blade depth for the merest skimming cut and test that the shavings are paper thin. Working with a skewed, drifting stroke, start planing at the furthest end of the wood, skimming off any high spots, and back up along the length of the wood.
If this sounds too complicated, a power planer is a great way to achieve a quick finish. The blades, however, soon become nicked and can result in thin ridges on the wood running in the direction of the grain, which you have to remove with a smoothing plane in the end.
A good alternative is a surform, a sort of combination tool of file and plane. The open-toothed structure of the surform allows you to cut and shape wood like a hot knife through butter and work without the teeth becoming clogged up.