How To Sand A Wood Deck Before Staining and Painting

Cleaning or stripping a deck can lift wood fibers and leave the wood feeling furry. As the deck dries, those fibers often stay lifted and can harden and cause splinters. To smooth out the wood and prevent slivers, lightly sand the deck before staining, sealing, or painting it. Many homeowners recognize this but wonder how to sand a deck for the best results.

To open the wood grain so it absorbs stain or paint, sand the deck using 20 to 50 grit sandpaper on the first pass and 60 to 80 grit on the second pass on a belt sander or orbital floor sander. Use the same grits to sand railings, posts, and stairs using palm or orbit sanders.

In this guide, we’ll discuss when to sand a deck, how to sand it, and what grit to use. We’ll discuss rental sanding machines and recommend several that can be purchased instead. By the end of the guide, you’ll have a better understanding of how to sand a deck, what tools to use, how often it should be sanded, and how long it can take.

 

Should You Sand A Deck Before Staining

Old and newly built decks should be sanded before staining so they are better able to absorb the stain. Plus, it will remove or smooth raised grain that could cause slivers.

Sanding a New Deck

A new deck should season for 30 days or more to allow it to dry to the outdoor climate. Some pressure-treated lumber can take up to half a year to dry enough to absorb sealant or stain. Use the water test and sprinkle some water on the boards. If the water beads up, you need to wait longer. If it absorbs into the wood, then you’re good to go.

Make sure the decking boards are clean; which means sweeping, vacuuming, or spraying it down. If hosing it clean, let it dry afterward for at least 24 hours. The drying or short weathering period can cause wood fibers to rise up and harden into potential splinters. Sanding takes a lot of elbow grease but will smooth the surface and allow the wood to absorb stain or sealant better.

Sanding a Painted or Stained Deck

A previously painted deck should be scuffed with sandpaper to remove and smooth chips, edges, and flaking. It will also provide a roughened surface for the paint to adhere to. When preparing to stain a previously stained deck it will be observed that some sections are still moisture protected. Sanding will smooth any raised wood fibers and open those areas still protected to the new stain.

Pros and Cons of Sanding

Pros:

• More consistent and better absorption of the stain
• Smoother and longer-lasting finish
• Fewer slivers

Cons:

• It is labor-intensive
• Takes time
• Is hard on the body

Over sanding can thin boards and expose deck screws or nail heads, while using too fine a paper can make pore openings smaller and inhibit the absorption of stain, paint, or sealer.

How To Sand A Wood Deck

Decks, no matter the size, are costly investments and require periodic maintenance to keep them sound and looking great. Paying a premium dollar for cedar or redwood and letting it go gray is a waste of money when pressure-treated lumber weathers better and is less expensive. All wooden decks, except composite decking, will need to be sanded and stained or sealed especially after cleaning.

Before staining, sealing, or painting a deck, it should be cleaned and pass the water test – a few scattered droplets of water to see if the water beads or absorbs. If it absorbs water, it will take a stain. New decks should wait for 30 or more days to acclimatize before staining, and like old decks, should pass the water test.

When cleaning or sanding it’s good to remember that cedar, redwood, pine, and most pressure-treated decking is a softwood. They can be easily damaged by pressure washers and heavy sanding pressure, so test the pressure in hidden locations. If the washer lifts the wood fibers, move the nozzle further away.

What is the Best Time to Sand?

The quick answer, you want at least 3 warm dry days in a row with NO chance of precipitation for your deck project. Stains, sealers, and paints all have temperature ranges for application and recommended drying times. Prior to applying any of those products, the deck should be cleaned and sanded. Once the deck has been washed, it needs to dry for 24 to 48 hours depending on the products used before sanding. If it rains during the drying period, give it extra time to dry.

After the wood is dry, it’s ready to sand. Sanding may take an hour or several days depending on the size of the task. The best time to sand a deck is when the forecast predicts 3 or more consecutive dry days. Once sanded, the wood needs to be stained, painted, or sealed before it rains. Otherwise, you’ll end up sanding it again if it gets wet before it can be sealed.

Prepare the Deck Surface

Existing and new decks should be inspected before sanding or sealing. Make sure decking screws are set properly, wood shrinks as it dries and can leave screw or nail heads raised. Repair or replace damaged boards, especially if cupped, rotted, split, cracked, or broken. Remember to check and tighten bolts for railings and other locations too.

Clean the Deck

Clean the deck with a deck cleaner or mild detergent. Use a bucket, hose, or power washer depending on the size of the job and the power tools available. Older decks may also require a stain or paint remover and anti-mildew treatment.

Clean the exposed ends of the deck boards and joist surfaces visible between gaps too. To restore wood luster and the pH levels, apply wood brightener after cleaning. Once the deck is clean, let it dry for the recommended time – between 24 and 48 hours is common – before sanding.

Remember, follow the directions on the cleaners and wear recommended protective gear.

Sand the Deck Rails

The railings are a visible part of the deck, and one many people see and touch. Once it’s clean and dry, fill any cracks, holes, or scratches. Use an epoxy wood filler and a putty knife to apply and scrape off any excess.

Once it’s cured, sand the railings before sanding the deck. Use 20 to 80 grit for the vertical pieces and up to 100 grit where hands commonly touch. Don’t over sand or the stain won’t very well penetrate into the wood. Blow, wipe, or vacuum the dust off before staining.

Sand the Deck Floor

Make sure the boards are dry before sanding and that the forecast for the next 3 or more days is for warm and dry weather. Once you start sanding, you’re not done until the deck is stained, sealed, or painted. A big drum or disc floor sander may look ideal for the task; however, it’s made for flat, smooth surfaces. It’s too big and heavy for sanding the uneven boards on a deck.

Sanding deck boards is often hands down, on your knees, arm, and back tiring task, so if you’re not up to it, hire a professional. You’ll want a belt sander, palm or oscillating sander, several sanding sponges, and sandpaper or belts of different grits for edges, ends, and hard to reach places. The deck size and condition impact the grit size and how much sanding is necessary.

Rent an orbital floor sander to do large flat deck surfaces. The rectangular 12”x18” sanding pad will do 3 boards at once and is easier on your knees – still hard work on arms, back, and shoulders, though. The orbital floor sander doesn’t leave scratch patterns like the rotary or rip off a ¼” of deck board surface as a drum sander can.

The first pass commonly is with a belt or floor sander using a 20 to 50 grit belt, working against the grain. Use the palm or orbital hand sander for hard to reach places or where the belt or floor sander misses. Don’t forget to sand the exposed ends of the boards. Sweep or vacuum up the dust, and sand the deck again with a 60 to 80 grit to smooth the surface and still leave the pores open to suck up the stain.

Remember, softwoods like cedar and most pressure-treated lumber don’t require much pressure applied to the sander. You don’t want to thin the decking, just smooth it. Additional thought should go to knee pads, dust masks, safety goggles, and ear protection. Wood dust is known to irritate the eyes and respiratory system.

Should You Wash The Deck After Sanding?

Once the deck has been sanded, it needs to be cleaned to remove the wood dust from the pores and wood surface. One reason for sanding is to remove the raised wood fibers left from pressure washing the deck. So power washing will just raise more fibers and require another sanding, plus more time for it to dry before re-sanding.

Sweep, vacuum, or blow (with a leaf blower) the sanding dust off the deck and use a tack cloth to wipe hard to reach surfaces. Once the dust is removed from the whole deck, apply the paint or stain immediately. Keep a tack cloth handy for if you find any sanding dust.

Let the Deck Dry Before Sanding

The wood needs to dry fully after washing and brightening before it is sanded. Some cleaners require longer drying, so check the directions. The wood needs to be dry to absorb the paint, stain, or sealer. Use the water test on the opposite end of the deck that you plan to stain first. If the sprinkled drops absorb into the wood, it’s dry.

How to Sand Between Deck Boards

Sanding between deck boards isn’t an easy task. Gaps may be uniform or irregular depending on wood shrinkage. A small detail power sander with 60 to 80 grit may work, or a thin sanding block wrapped in sandpaper. The sanding block may even do both sides of the gap in one pass. Sand the wood as evenly as possible for the best staining results.

If the deck boards have rounded edges, sand them by rotating the sander on each pass. For gaps that are tight, wrap a paint stir stick or other appropriate thickness of wood with 60 to 80 grit paper and work your way along. A sawing motion often works well, although joists can frustrate the motion. Additionally, if the joists are exposed wood and visible between boards, attempt to sand them too so they will absorb the protective stain or paint better.

What Grit Sandpaper to Use for Deck Sanding?

The condition of the wood determines the sanding grit required for the task. The pros often do the first pass on deck boards with 60 grit. If the wood is in poor condition, 20 grit may be used first. The second pass is commonly done using 80 grit sandpaper. Finer grit will make pore openings smaller and interfere with the stain or paint being absorbed into the wood.

Railings have vertical and horizontal components which often weather differently. The sanding process for railings is done with the same grits as the deck, with the occasional exception of the top rail. Top rails that commonly have more hand contact frequently have a final pass with 100 grit sandpaper to provide a smoother finish.

Best Way to Sand a Deck: Deck Sanding Machine Rental

Sand the perimeter of the deck, hard to reach places, stairs, railings, edges, gaps, and board ends with a belt and orbital hand sanders, and sponge blocks. For large flat deck surfaces with little or no cupping or warping, rent an orbital floor sander. It will sand 3 or 4 deck boards at a time – 18-inches wide – and saves a lot of time. Although hard on the back, shoulders, and arms, it’s a knee saver.

Don’t use a disc or drum sander on softwood decking. A disc floor sander will leave scratch marks that will require more work to remove. A drum sander can too easily sand off more in one pass than desired and can expose or cause damage to decking screws and nails.

An orbital floor sander weighs between 60 and 150 pounds (or more), so it adds more sustained pressure to the job. The handles and built-in vacuum system make it easy to control and reduce dust and clean-up. Do the first pass with 20 to 40 grit sandpaper depending on the condition of the boards. For the second pass, use 50 to 60 grit, and finish off with a pass with 80 grit paper.

Rental of an orbital floor sander is approximately $45 for 4-hours, $65 for a day, and $260 for a week, while purchase can set you back upwards of $5,000. Rental locations also carry a good selection of sandpaper grits sized for the machine, and commonly accept unused sheets with a full refund. Sandpaper costs will vary based on job size and deck condition, often between $20 and $30.

Recommended Sanders for Deck Sanding

Selecting the best sander for sanding a deck is important. The larger the tasks the more work the sander must stand up to, and in turn the operator. A poor quality sander can overheat or burn out, or vibrate your hand and arm numb, so you can’t control the machine.

Palm sanders work well on horizontal and vertical surfaces like railings, tight areas, board ends, and stairs.

Belt sanders are better for larger horizontal surfaces like top railings or deck boards.

Orbital power sanders are good for both railings and wood decks. Even drywall sanders with sandpaper work well on deck sanding. Here are some recommendations:

Best Cordless Orbital Sander

The 20V Max DEWALT DCW210B orbital sander is low profile and cordless, making it ideal for sanding deck edges and ends, railings, stairs, and hard to reach places. The palm-size molded rubber grip makes it easy to control the 2.5 pounds (without battery) sander, and the collector bag decreases clean-up. Plus, the hook-and-loop pad makes changing the 5” diameter 8-hole sanding discs easy too.

The brushless motor won’t overheat and has a dust-sealed switch for longer life. The little powerhouse offers speeds of 8,000 to 12,000 orbits per minute (OPM) and has a variable speed dial for better control. Run-time will vary between 20 and 50-minutes with grit coarseness and wood condition, so multiple batteries are needed.

Corded Random Orbit Sander

DEWALT’s 3.0 Amp, 5” random orbit sander DWE6421K provides 12,000 OPM. The compact, 4-pound palm controlled sander has a molded rubber grip, one-hand locking dust collector, and dust sealed on-off switch.

The hook-and-loop sanding pad takes commonly available, easy to change, 8-hole, 5”-diameter sanding discs. The sand is easy to control and is well suited for sanding stairs, railings, deck edges, board ends, and hard to reach spots.

Belt Sander

Makita 9403 11 Amp belt sander weigh a hefty 13-pounds and have a speed of 1,640ft/min, making them ideal for sanding decks and other surfaces. The cloth dust bag swivels 360° and catches most of the dust for small tasks or connects to a hose for larger jobs.

Its sealed labyrinth constructed motor keeps dust out for longer life and produces a comparative quiet 84dB.

The innovative design allows for sanding closer to walls and posts, and efficiently removes stock. The 9403 is well balanced and has a large rear handle and front grip which improves control and comfort.

Economical Option

Black & Decker’s 2 Amp 3.2-pound 5-inch diameter random orbit sander BDER0100 is an economic yet powerful little sander. The sander has a sealed on-off switch to keep dust out which improves its life span, and an easy to remove and empty dust collector. The rubber ergonomic grip improves control and comfort and minimizes slippage.

Plug the 6.5’ cord in and the 12,000 OPM speed quickly smooths out nicks and rough spots. It is compact for use on railings, board ends, and hard to reach spots. The hook-and-loop system makes changing sanding discs quick and easy too.

How Often Should You Sand a Deck?

The quality of stain or paint is an important factor in how often a deck will need to be sanded, as is the climate where the deck is located. The more transparent the stain or paint, the more often you’ll be doing a deck refinishing project. Dampness and snow are as damaging as blistering sunlight to exposed wood, so UV and mildew inhibitors in stains and paint are helpful.

The deck should be sanded after it is stripped and before a coat of stain or paint is applied. A solid stain or paint commonly lasts for five years and a transparent stain for one to two. If water doesn’t bead on the deck, then it is being absorbed. A sure sign it is time to sand and protect it again.

How Long Does It Take to Sand a Deck?

The size of the deck, the condition of the surface, and the type of sander are variables in determining how long sanding will take. The smaller the surface to be sanded, the less time it will take. A new deck may only require a single pass, while an older deck may need three passes. Additionally, an orbital floor sander will do the task much quicker than a palm sander.

It commonly takes 2-hours to sand 100sqft once, using a belt sander. Expect to add another 30 minutes for edges, ends, gaps, and around posts. A second pass with a finer grit will usually take the same amount of time. So, expect to take 5 hours to fully sand 100sqft of decking.

Conclusion

Sanding a deck before staining provides a clean, smooth, and absorbent surface for stain and paint to adhere to. It is a key part of cleaning and preparing a deck for finishing. Most decks take two passes with a power sander; the first with 20 to 50 grit and the second with 60 to 80. Expect to take 5-hours for the two passes on 100sqft of decking.

I hope you have a better understanding of how to sand a deck, the tool to use, and how long it can take. If you found this guide helpful, please share it with others. As always, your comments and suggestions are appreciated.