Staining Wood Decks Guide: How to stain a deck

More than 80% of all decks in the United States are built entirely or partially with pressure-treated wood. While the market for composite, low maintenance, decking materials continues to grow, the posts, beams, and joists are usually made from pressure-treated wood — known for its structural strength. But how do you stain wood decks?

Why Stain Your Deck?

An unprotected deck absorbs water, softening and swelling the wood fibers. The sun’s heat dries the wood, which makes the wood shrink.

Without protection, even the wood of a pressure-treated deck will cup, warp, and splinter. And if your pressure-treated wood deck was built before 2004 it is probably treated with chromated copper arsenate. Refinishing the deck helps seal in this toxic treatment and protect the environment.

Years ago we purchased cedar and redwood for decks because these species contain natural preservatives and did not need to be protected. However these preservatives are concentrated in the heartwood, or inner core, of the original tree. Decking lumber today is often more knots and less heartwood. This wood is less durable than the inner heart that earned cedar and redwood a reputation for having a high resistance to decay.

Both stains and paint are made of pigments and a carrier and offer protection. Staining a deck is preferable to painting it with exterior porch and floor paint. Semi-transparent stain with sealer is the most popular deck finish, and unlike porch and floor paint, it resists cracking, peeling and blistering. Stain ages by gradually wearing away. The surface does not need priming before it is stained.

Preparing the Deck Surface

Wear gloves and goggles. Clean the deck surface with detergent and water in a garden hose sprayer. Use a non-metal scrub brush if needed. Or to remove grease and dirt use a mix of TSP (Trisodium Phosphate) and water according to product directions. To remove mildew and mold use chlorine bleach — one part bleach to three parts water.

Replace any boards with rot, cracks, splinters, spits, and twists. Once this carpentry is done, sand back the boards to even out the roughness and to remove any traces of the old stain.

Sand across the grain with a belt sander, then sand diagonally, and finally with the grain. Wear eye protection and a mask.

Or remove the stain or paint on the deck with chemical stripper. Stripping is necessary if the stain has worn off unevenly. Stripping is needed if you are changing colors of semi-transparent stains. Read the directions before buying the product. There are strippers for removing transparent, semi-transparent, and opaque stains. Some deck strippers contain sodium hydroxide, better known as lye. Use synthetic bristles and pads here; lye will eat natural bristles.

Water surrounding plants before you get started, then cover them while you are using the stripper. Protect the side of the house where the deck is attached.

Wear neoprene gloves and eye protection. Apply the stripper to a small area about 18”x18” at a time. Do not let it dry. If the stripper dries out apply more. Wash it off the scrubbed area with a garden hose sprayer.

Deck strippers may cause the wood to turn black. Restore the color by using a deck cleaner according to the product directions.

It is best to start cleaning or stripping from the outside of the rails and deck frame, and then work into the deck itself. Don’t work yourself into a corner. Deck stripping agents are slippery; avoid walking on treated areas.

Old stain left on the wood prevents the new stain from penetrating. New wood has natural chemicals called tannins, and mill glaze (compressed wood fibers from planing the lumber) can close the woodgrain to penetrating stains. New pressure-treated wood can actually have paraffin wax on it added to ease stacking at the lumberyard.

For best results, woodgrain needs to be “open.” Some do-it-yourselfers recommend leaving the wood outside for two or three months. The rain and sun will weather the wood — literally open its pores so that it better accepts the stain. In this period, though, the wood can crack and warp. Another option is to sand the wood in the direction of the grain using 80 grit sandpaper. The sandpaper removes the mill glaze, loose wood fibers, and slivers. You can also purchase products that chemically removes the mill glaze. These are available at hardware or home improvement stores.

Selecting the Stain

Select a stain mixed with a sealer. Stains come in varying degrees of clarity (transparency.) This allows either the wood grain to show or be completely covered.

Transparent or semi-transparent stains let the grain and natural color of the wood show through.

Opaque or solid stains come only in matte finish. Like paint, these stains cover the wood and hide the grain. It is a good choice if the surface to be protected has blemishes. While opaque stain has the most pigment and offers wood the most UV protection, it shows its wear quickly in high traffic areas.

Both water- and oil-based stains are on the market. Water-based stains dry faster, have low volatile organic compounds, and clean up with soap and water. Oil-based stains take longer to dry, have higher VOCs, and need a solvent for clean up. Be sure to wear an OSHA-approved mask to protect against inhaling the vapors of solvent based products. And, never leave rags, brushes or containers of solvent containing stains in the sun because they are combustible.

Many do-it-yourselfers find that water-based stains are more difficult to apply evenly, resulting in streaking. Oil-based stain flows more evenly.

If the surface was previously stained with oil it will have to be stained with oil again. Use oil stains on tannin-rich wood like cedar, redwood, and pine. That’s because water-based stains activate the water-soluble tannins, causing the brownish color to bleed through.

Be aware that color cards will give an approximation of the color of a stain in the can, not the color it will appear on your deck. All wood has its own unique natural color. The wood species, coupled with the wood’s degree of weathering, will influence the final color and the absorption rate of the stain.

Factory-mixed, off-the-shelf stains vary in color even with the same production dates. Before application, pour four one-gallon cans into a five-gallon bucket and stir completely with a long stick or mixing paddle. After a gallon is used from the bucket mix in another gallon. This will ensure a deck surface that is uniform in color.

Staining the Deck

Before re-staining the deck check its moisture level. Drop a teaspoon of water on the deck in several places. If it soaks in almost immediately the wood is dry enough — it should have a 10% to 14% moisture content — to stain.

If it lies in a bubble the wood is too wet for staining. Depending on the temperature, wait until the next day or up to several days before checking the moisture level again.

The best way to apply stain is with a special deck brush — a thicker brush with porous bristles holds the low viscosity (thinner than paint) stain.

If the deck is attached to the house or similar structure, cover it at the connection point to prevent it from being spattered.

Stain the rail spindles first working from the side facing outside the deck to the side facing inside. Work a few spindles at a time to maintain the wet edge.

Lay cardboard on the deck beneath the spindles to catch any drips. Dried drips on the deck surface will be very visible beneath transparent or semi-transparent stains.

If you are using a water-based stain use an old paintbrush to wet the horizontal surface of the deck before applying the stain. This will help the stain spread evenly.

If you are using an oil-based stain apply the stain to a dry surface.

Stain three boards at a time along their entire length to prevent lap marks. Apply extra stain to the end boards as the end grain sucks up stain like a sponge.

Apply too much stain and it will skin over before it dries, bubble, pop, and peel. Two thin coats, “wet-on-wet” are better. Use a back and forth sweeping motion to work the stain into the wood.

General Information

To protect your health and the environment always read the label even if you stained the deck last year. The formulations of deck products are always changing.

Buy only what you need because stain degrades and can change color over time.

In our damp climate, mildew and fungus can eat into both the finish and wood itself. It is best to use deck coatings with mildewcide and fungicide. If the product you bought does not have this protection, this additive can be purchased and stirred into one-gallon cans and five-gallon buckets of stain. Adding the protection yourself costs about the same as having bought a more expensive stain that already had mildew and fungus protection.

As your stained deck begins to get dirty, wash it down with a mild detergent and water. As the stain weathers away, its color or tint begins to fade. Check to see if it is time to re-coat the surface. On a day following several dry days, drizzle some water on the deck surface. If it is immediately absorbed into the wood it is time to re-surface the deck. Test several areas because stain in high-traffic areas will wear before corners and rail spindles.

Apply stain in temperatures no lower than 50ºF for water-based products and 40ºF for oil-based products. You need 48 hours of dry weather for the work to cure. If it rains within 24 hours after application, the deck will be marked with lighter discolorations from where the raindrops sat.

Tips to Make Your Deck Stain Last Longer

For new deck construction, be sure to stain all the backsides, sides and supports for the deck before it is built. If the wood is not going to be seen, use an opaque stain because it will outlast transparent and semi-transparent stains.

Build the deck floor with the boards right-side up. All kiln-dried wood will be warped or “crowned.” Place the crown side (slight curve) facing up to prevent the lumber from cupping or holding moisture on the deck surface.

Don’t put a plastic vapor barrier under the deck. The plastic may control weeds but will prevent water from draining away. High humidity will cause the stain to peel and the wood to rot. Landscape fabric is permeable for water run-off and offers some weed control.

Don’t skirt the deck with solid material. This prevents cross-ventilation under the deck, which results in humidity build up. Use open latticework if you need to skirt.

Don’t clean the deck with a power washer. Even at its lowest power, the force will abrade the deck finish.