Cleaning and Sealing Your Deck
Wood left exposed to sun and moisture will quickly begin to degrade. Leave your deck untreated and you can expect it to
turn grey with age. In addition, the decking boards are likely to cup, warp and split. Ignore the problem for too long and you’ll have to make major repairs — or even replace sections of deck. Deck sealing is a three-part process. Remove any old stains or coatings, clean the wood, and seal it against weather damage. If the deck has never been sealed before you won’t have to strip it, but brand new wood has special pre-stain preparation needs.
If your deck has been sealed before, use the water test to see if it’s time to seal it again. Drizzle some water onto the boards. If the water beads, the wood is still sealed and protected. If the water is absorbed into the wood, it’s time for a treatment. Remember to test several different areas of the deck. High-traffic spots are likely to wear down before corners and rail spindles.
Stripping is essential for creating an even surface on which the new sealant can adhere. If the high-traffic areas of your
deck have worn down, but there is still sealant remaining in other areas, strip the entire deck before you re-stain.
Stripping is most important if you are changing colors. Traces of an old color left underneath will affect the way a new color appears.
Choose a stripper that is formulated for:
- Removing clear and toned finishes and sealers, which requires less stripping power.
- Removing semi-transparent or opaque stains, which requires more stripping power. Consult the manufacturer’s
instructions to determine which stripper is right for your project.
After the deck is free from existing stain or sealant, clean it. (If you didn't have to strip the deck, this will be your first step.)
When looking at deck cleaners, you'll probably find one these active ingredients:
- Chlorine bleach, which appears on the label as sodium hypochlorite, calcium hypochlorite or dichloroisocyanurate.
These chemicals do a good job getting rid of mildew, but they are less effective at removing dirt. They are usually
mixed in with other ingredients.
Chlorine bleach products can be harsh on wood if used improperly, causing fuzzing and uneven coloration. Use a
chlorine bleach product if you have a mildew problem, but be careful not to mix it any stronger than the
Also, rinse well.
- Oxalic acid, which usually will be listed that way in the ingredients list. Oxalic acids are particularly effective at
removing tannin stains and iron stains — a particular consideration with cedar and redwood decks.
Oxalic acid is not as effective against mildew. If you have a mildew problem, try a cleaner made with bleach before
using oxalic acid to attack the tannin and iron stains.
There are four main options for deck sealers: clear, wood-toned, semitransparent and solid/opaque. As a general rule, wood that is older and more weathered requires a more opaque stain to cover imperfections.
Think about these other considerations:
The best sealers penetrate the wood the most to provide the most protection. Look for an oil-based product that is mixed
with latex for easy clean-up.
- Clear treatments allow the wood to fade to a natural weathered, silver grey, while still providing protection from UV and water damage. The other types will retain a constant color.
- It’s tricky to work backwards on the spectrum. For example, if your deck is currently covered in an opaque stain, it will take a great deal of stripping and surface preparation to ready it for a clear or wood-toned stain. It’s usually easiest to continue with solid/opaque coverage.
- The more opaque a stain, the quicker it will show wearing and weathering. A solid stain might need re-application
every year, while a clear or wood-toned treatment probably will last longer.
- Solid/opaque stains are better suited for vertical surfaces (railings, pillars, caps) than for horizontal (decking, stairs). The wearing from foot traffic is particularly noticeable with an opaque stain, and it's possible to track the residue inside the house.
- Solid/opaque stains do not show the grain of the wood. All others do.
- Darker colors, particularly solid/opaque and semitransparent stains, will absorb heat more easily. They could make the deck uncomfortable for barefoot walking.
- Choose a color that matches the siding on your house, or one that contrasts with it nicely. Use the color wheel to
- For a decorative look, select two or more colors that work together for decking and rails, post caps, stencil work,
- If you have ChoiceDek® or some other type of composite decking, not all cleaners will work for you. Consult the
manufacturer for the correct types of products to use.
- If you have a brand new deck made of treated lumber (as opposed to cedar or redwood), you should wait at least a
few weeks before sealing it for the first time. This allows the wood to dry so the stain can be absorbed. To find out if
the wood is dry enough to stain, use a moisture meter that tests the moisture content (MC) of wood. The wood can
feel dry to the touch but still be too wet to absorb the stain properly.
If you don't have a moisture meter, press the head of a flat screwdriver into the decking in an inconspicuous place.
If any moisture appears, the wood is still too wet to stain.
- Be sure to remove grade marks and other markings before staining. They will show through all but solid/opaque
Your deck restoration shopping list will contain more that just cleaner and sealer. Here are some other products that will
make the job easier:
- A pump-action sprayer to apply cleaning solutions. You can buy one labeled "deck sprayer" or "garden sprayer," but
do not use it for spraying your garden once it has had deck cleaning chemicals in it.
- A stiff brush on a long handle for scrubbing. Do not use one with metal bristles, because it might damage the wood.
- A paint roller on a long handle for spreading stain or sealant. Look for a 1/2" or 3/4" nap.
- Paintbrushes made to apply the stain you have chosen.
- Plastic tarps to protect nearby plants from overspray.
- Tape to mask off areas that you don’t want to stain.
If you have ChoiceDek® or some other type of composite decking, not all cleaners will work for you. Consult the
manufacturer for the correct types of products to use.