A deep power washing or scrubbing with a brightener/cleaner is an essential step when preparing an aged wood deck for refinishing, but this action causes the wood fibers of the decking, steps, and railings to swell and lift away from the wood as they expand with water. Once dry, these wood fibers can remain raised and may cause splinters. For this reason, light but thoroughly sanding your wood deck is a necessary step before staining or sealing. This crucial step will ensure that your refinishing job gives great results.
Before You Begin
Follow whatever preparation steps are recommended by the finishing product you plan to use. In some cases, this may involve first using some kind of chemical brightener/cleaner on wood that has grayed with age or wood that is stained with dark tannins. This treatment with a brightener/cleaner is usually followed by rinsing with clear water; after the deck dries, the fuzzy wood fibers need to be removed by sanding.
This treatment is most often recommended for aged cedar or redwood, and it may not be called for on pressure-treated pine lumber or with new cedar or redwood. On new wood, the manufacturer sometimes recommends a simple sanding, followed by immediate application of the stain or sealer.
The power sanders used to sand a deck comes in many forms, from standard household orbital sanders operated by hand to commercial upright rental sanders you can lease from home improvement centers and rental outlets. Any of these will adequately sand your deck if used properly. Most homeowners find it entirely possible to sand using an ordinary hand power sander, though patience is required, especially with a large deck that may need several days of work.
Remember that woods used on decks are typically soft-wood species. Belt sanders, whether hand-held models or large uprights, tend to gouge softwoods, so an oscillating or random orbit sander is usually the better choice.
Make sure your deck is thoroughly dry before you sand. If there has been recent rainfall or if you have power washed, wait several days before sanding. Treat the deck surface, the railings, and the edges of boards as different tasks, varying the sanding techniques for each.
Make sure to wear a particle mask and safety glasses while sanding, as wood dust poses health risks if you breathe it. Knee pads and hearing protectors will also make your job safer and more comfortable. Short-term exposure to wood dust probably does not create the risk of cancer faced by industry workers, but even short-term exposure can cause an allergic response or respiratory reaction, such as an asthma attack. The risk of reaction is especially pronounced with dust from red cedar.
Watch Now: Watch Now: Easy Tips for Sanding a Wood Deck Before Refinishing
Equipment / Tools
- Putty knife (if needed)
- Power washer (if needed)
- Scrub brush
- Screwgun (if needed)
- Breathing protection
- Eye protection
- Knee pads (optional)
- Oscillating or random-orbit sander
- Detail sander (if needed)
- Shop vacuum
- Deck brightener (if needed)
- Wood filler (if neeed)
- Deck screws (if needed)
- Sandpaper (60- or 80-grit)
- Clean cloths
- Tack cloths
Wash the Wood
Wash the entire deck, as directed by the stain or sealer manufacturer. If power washing, take care to use a sprayer setting that doesn't damage the wood. If scrubbing with brightener/cleaner, make sure to rinse the deck thoroughly to remove all traces of the oxalic acid or other chemicals in the cleaner.
Inspect and Repair the Surfaces
Start by carefully inspecting all the surfaces you will sand—surface decking, edges, stairs, and railings. Make sure all fasteners are driven down below the surface of the wood. Some very old screws may need to be removed and replaced. Tighten screws that, over time, can raise slightly above the deck and get caught on the sander and cause you to replace the sandpaper. If there are any loose boards, now is the time to drive new fasteners to secure them.
If there are splinters or deep gouges in the wood, make sure these are filled or repaired before you begin sanding. If using wood fillers, make sure they are fully dry and hardened before you move on to sanding.
Sand the Decking Surface
Attach 60- to 80-grit sandpaper in your power sander. Your goal will not be to create the smoothest possible surface, so avoid finer-grit sandpapers, which will clog the pores and prevent stains and sealers from penetrating the wood.
Sand all areas of the surface decking, using medium pressure on the sander. Check for evenness of appearance as you go. Avoid the temptation to sand to a glass-smooth surface; cedar and redwood and pressure-treated pine are relatively soft woods that can be gouged and damaged if you press too hard with the sander.
Use this same technique to sand the top surface of the stair treads.
When finished, thoroughly vacuum the surface of the deck and stair treads with a shop vacuum.
Sand the Board Edges
Sanding the outer edges of the deck board may be a little difficult, especially if the railings have a very low bottom baluster rail that makes access difficult. Here, a smaller detail sander may prove useful if your standard orbital sander won't fit. Again, use a sandpaper grit of 60 to 80 for the end grain of decking boards, and make sure to sand as evenly as possible, since stains can be absorbed unevenly if the end grains are not sanded to the same smoothness.
Vacuum the edges of the boards, then wipe them free of dust.
Sand the Railings
Sanding the railing of your deck is very important since it is the most visible element and the one where people focus their attention. Additionally, the handrail is particularly important to get smooth to avoid splinters that might injure hands.
On railings, use 80- to 100-grit sandpaper, and take pains to sand all surfaces and crevices. Here, a detail sander or even sanding by hand may be necessary to get to all areas, but again, do not sand to a smoothness that will prevent the stain from penetrating.
Vacuum the railings thoroughly.
Vacuum the Entire Deck
Use a shop vac to vacuum the entire deck once more, then use tack cloths to wipe the surfaces free of any remaining clinging dust. Pay special attention to crevices and corners.
Your deck is now ready for staining/sealing. Do this work immediately after sanding, before the deck wood can weather or get dirty. If you must wait before finishing, make sure to vacuum and wipe the deck down with tack cloths once more before applying stain or sealer.