What sandpaper grits should be used when refinishing exterior wood?

Exterior wood is not furniture

People who have refinished a table know to work up to 220 or finer. Outdoor wood is the opposite. Sunlight, moisture and movement mean the finish has to anchor into the wood rather than sit on a polished surface, and an exterior finish that cannot penetrate fails early. A deck sanded to 220 looks beautiful for about a week and then the oil beads on top and wears off in blotches.

The goal outdoors is a surface that is clean, flat and open, with no visible scratches at arm's length. That is a 100 to 120 grit surface on most wood.

The sequence we use

Sanding always comes after cleaning and brightening and after the wood has dried. Sanding dirty or wet wood loads the paper instantly and drives grime into the grain.

• 60 grit: only for removing a failed film finish, heavy weathering or deep raised grain. It leaves visible scratches that every later grit must remove.
• 80 grit: the usual starting point on deck boards, rails, fence boards and pergola members. It cuts mill glaze on new wood, levels fuzz on cleaned gray wood and flattens small cups.
• 100 to 120 grit: the finishing grit for anything receiving a penetrating oil, semi-transparent stain or solid stain. Stop here. The pores stay open and the finish goes in.
• 150 to 180 grit: for wood getting a film finish such as spar varnish or paint, like a front door, and for scuffing between coats. Finer than this and even varnish can struggle to bond.
• Between coats of varnish: 220 or a fine sanding sponge, very lightly, just to knock down dust nibs and give the next coat a tooth.

Why you cannot skip grits

Each grit's job is to remove the scratches left by the one before. Jumping from 60 to 150 leaves the deep 60 grit scratches in place, hidden under finer scratches, and stain or oil darkens them so they show as lines across the grain. On a deck in afternoon sun those lines are obvious. The rule is to go no more than one step at a time, roughly 60 to 80 to 100 to 120, and to sand with the grain on the last pass.

Random orbit sanders are forgiving about direction, but they still leave swirl marks if you press hard or move too fast. Let the sander's weight do the work and keep it moving. Belt sanders remove material quickly and are useful on a badly cupped deck, but they dig if you hesitate and should be followed by an orbital pass.

Species and situation change the numbers

Soft woods like redwood and cedar fuzz easily and are usually finished at 80 to 100 so the finish can penetrate the softer earlywood. Dense tropical woods like ipe and teak are so hard and oily that 120 is fine and some finishers go a little higher, then wipe with solvent to clear the oil just before finishing. Pressure-treated lumber is sanded as little as possible, mainly to remove splinters, since the treatment is concentrated near the surface.

Weathered gray wood that has been cleaned and brightened often needs only a light 80 grit pass to remove raised fibers. Fully stripping an old film finish is the exception, and we prefer a chemical stripper or a careful scrape first so the sander is cleaning up rather than grinding through paint. On homes built before 1978 that old paint may contain lead, and power sanding it without containment is not allowed.

Dust, edges and the last pass

Sanding dust left in the grain turns muddy under oil and pale under stain, so we vacuum and then wipe with a damp cloth or blow the surface off and let it settle. On tannin-rich woods we never use steel wool, which leaves particles that turn black in the first dew; synthetic pads do the same job. Ease every sharp edge slightly with a hand pass, because finish pulls thin on a sharp corner and that is where it fails first. Then the wood is ready for finish, and ideally the finish goes on within a day or two, before the fresh surface has time to oxidize and close up again.

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