What treated lumber does and does not do
Pressure-treated lumber is infused with preservatives to resist rot and insects. That protection is against decay, not against weathering. Sun and rain still gray the surface, and boards can crack, cup and develop mildew. Regular cleaning, inspection and an occasional water-repellent finish help the deck look better and last longer. Maintenance does not guarantee a particular lifespan, but it removes many of the common causes of early deterioration.
A simple yearly routine
Spring
- Inspect the whole deck, including the structure underneath.
- Clean the surface and between the boards.
- Make repairs.
- Check whether the finish is still repelling water.
Summer and fall
- Sweep regularly and lift planters, mats and furniture occasionally so moisture does not sit trapped.
- Clear leaves and debris, which hold moisture and encourage mildew.
- Before winter, clear snow with a plastic shovel where practical, avoiding metal blades that can gouge the surface.
Every few years or as needed
- Clean and recoat with a water-repellent stain or sealer, based on how the deck is wearing.
Cleaning the deck
- Clear off furniture and planters, and sweep.
- Use a putty knife or thin tool to clear debris from the gaps so water can drain.
- Wet the deck, apply a cleaner suited to wood decks (many are oxygen-based or formulated for mildew), and scrub with a stiff-bristle brush. Follow the label and dilution directions, and protect nearby plants.
- Rinse thoroughly.
- Let the deck dry before staining.
Can you use dish soap? A mild dish soap in water with a brush can remove light dirt. It is not designed to kill mildew or strip graying, and residue should be rinsed well. Heavy mildew, algae or graying usually calls for a purpose-made deck cleaner or brightener.
Pressure washing safety and technique
- Wear eye protection and closed-toe footwear. A pressure washer stream can cause serious injuries, so never point it at yourself, others or pets.
- Use a wide fan tip and moderate pressure, and keep the wand moving at a consistent distance. Concentrated streams can etch and splinter softwood.
- Work with the grain.
- Be careful on ladders or wet, slippery decks.
- Avoid driving water under siding or toward electrical outlets.
If you are unsure about pressure settings, a soft brush and low-pressure rinse is a gentler option.
Inspecting and repairing
Check for:
- Loose, cracked, split or badly cupped boards
- Raised or popped nails and rusted or loose screws
- Soft or spongy spots, which may indicate rot (probe with a screwdriver)
- Wobbly railings and stairs, which are safety issues
- Loose or corroded connections at the ledger board and posts
- Water staining or damage where the deck meets the house
Structural issues, especially at the ledger and railings, affect safety, so consider having a qualified contractor or inspector evaluate anything doubtful. Wear eye protection and hearing protection when cutting or sanding, and use a dust mask. Sawdust from treated wood should not be burned, and you should follow label guidance on handling and disposal of treated offcuts.
When to seal a new treated deck
New pressure-treated lumber often holds a lot of moisture from the treatment process. Finishing too soon can trap moisture or cause poor adhesion. Many manufacturers advise waiting a period of weeks to months, depending on climate and the product, but guidance varies. See pressure treated vs. kiln dried wood for why moisture content differs between boards.
A common test: sprinkle a little water on the boards. If it soaks in quickly, the wood is likely ready for a penetrating finish. If it beads, the wood may need more time. Check the instructions on both the lumber tags and the finish you plan to use, since some products are made specifically for new treated wood.
Choosing a sealer or stain
For treated decks, a penetrating, water-repellent sealer or semi-transparent stain with UV protection is a common recommendation (see wood sealer vs. stain). Penetrating products generally wear gradually rather than peeling. Thicker film-forming coatings can trap moisture and may peel, especially on horizontal surfaces. If you are weighing coating types, see deck paint vs stain.
Check that the product is labeled for the kind of lumber and surface (deck, horizontal) that you have.
Applying it safely
- Choose a dry period with moderate temperatures and no rain in the forecast, as the label directs.
- Ventilate, and wear gloves, eye protection and a respirator if the label advises.
- Apply evenly in manageable sections, working with the grain, and avoid puddles.
- Keep ignition sources away from solvent-based products.
- Rags with oil-based finishes can self-heat and ignite. Spread them flat outdoors to dry, or place them in a sealed metal container filled with water.
- Keep pets and children off until the finish has dried per instructions.
More background on how finishes keep water out is in our guide to how to waterproof wood.
How often to reapply
Intervals depend on the product, sun and rain exposure, and foot traffic. Some guidance suggests every couple of years for semi-transparent stains, while others vary. Use the water test as your cue: if water no longer beads on the surface and soaks in, it is likely time to clean and recoat.
How long does a treated deck last?
Lifespan varies widely with climate, installation quality, design, ground contact and maintenance. Well-built, maintained decks often last many years, but do not rely on one figure. Good drainage, airflow, correct fasteners and regular inspection tend to extend service life.
FAQ
What is the best treatment for treated wood decks? Cleaning followed by a penetrating water-repellent stain or sealer with UV protection is the usual approach.
Can you use Dawn dish soap on a wood deck? Mild soap can clean light dirt, but dedicated deck cleaners handle mildew and graying better. Rinse well.
How long should you wait to seal a treated deck? Until the wood has dried enough to accept the product. Use the water test and follow product directions.