How to Inspect and Clean Your Deck
Your deck takes a beating from winter ice, spring rain, and UV exposure. Before you fire up the grill and start hosting, take the time to inspect every board and structural connection for damage, then give the entire surface a proper cleaning. Catching a rotted joist or a loose ledger board now is far cheaper than rebuilding a collapsed section later—and a clean deck is safer underfoot and ready for stain or sealant.
Quick Summary
Time Required
3–5 hours
Difficulty
Moderate — DIY friendly
Cost
$30–$80 DIY / $200–$500 professional
Structural Inspection: Boards, Nails, and Fasteners
Start with the surface you walk on. Every loose board and popped nail is both a safety hazard and a sign that moisture or age is taking its toll on the structure beneath.
Walk every board and listen for movement
Step on each deck board near the ends and in the center. Boards that flex, bounce, or creak have likely pulled free from the joists below. Mark them with painter's tape for refastening. Look for nails that have popped above the surface—these are trip hazards and indicate the wood has expanded and contracted repeatedly.
Probe for rot with a screwdriver
Press a flathead screwdriver into any dark, discolored, or soft-looking areas on boards, railing posts, and stair treads. Healthy wood resists the probe. If the screwdriver sinks more than a quarter inch with little effort, that section is decayed and needs replacement. Pay extra attention to end grain and areas where water pools or boards meet metal connectors.
Check for insect damage
Look for small round exit holes, sawdust piles near post bases, or hollow-sounding wood when tapped. Carpenter ants and termites target moisture-damaged wood first. If you find active insect damage, address the moisture source that attracted them and consult a pest professional before making structural repairs.
Inspecting Posts, Joists, and the Ledger Board
The framing underneath your deck is what keeps everything standing. Ledger board failure is the single most common cause of deck collapse, making this the most critical part of your inspection.
Key Structural Checkpoints
- Ledger board connection: The ledger is the board bolted to your house that supports one side of the deck. Check for any gap between the ledger and the house wall. Verify that flashing is installed above the ledger to divert water. Look for rust stains below the connection, which indicate water is penetrating behind the ledger and rotting the rim joist of your house.
- Joist hangers and hardware: Inspect every joist hanger for rust, missing nails, or separation from the ledger or beam. Each hanger should have nails in every hole—missing nails reduce load capacity significantly. Replace any hangers that show heavy corrosion or bending.
- Support posts: Posts should be plumb and firmly connected to both the beam above and the footing below. Wiggle each post at the base—any movement means the connection has loosened. Check where posts meet concrete footings or the ground for rot, especially in the first 6 inches above grade where splashing water concentrates decay.
- Beams and rim joists: Sight down each beam to check for sagging or bowing. A beam that dips in the center is either undersized or has developed internal rot. Tap along the length with a hammer and listen for dull, hollow sounds that indicate hidden decay inside otherwise solid-looking wood.
Power Washing Your Deck the Right Way
A pressure washer makes quick work of embedded dirt and mildew, but too much pressure damages wood fibers and creates a fuzzy surface that makes staining difficult. The key is matching your PSI and technique to the deck material.
Choose the right pressure and nozzle
For softwood decks like pine or cedar, stay between 1,200 and 1,500 PSI with a 25-degree or 40-degree fan tip. Hardwoods like ipe can handle up to 2,000 PSI. Composite decking should be washed at 1,300 PSI or less. Never use a zero-degree nozzle on any deck surface—the concentrated stream gouges wood instantly.
Work with the grain in overlapping passes
Hold the nozzle 8 to 12 inches from the deck surface and spray along the length of each board, never across the grain. Overlap each pass by about one-third to avoid striping. Keep the wand moving at a steady pace—pausing even briefly in one spot will etch the wood. Start at the house side and work outward so dirty water drains off the edge.
Apply deck cleaner for stubborn stains
For mildew, algae, or deep grime that pressure alone does not remove, pre-treat with a deck cleaning solution. Oxygen bleach-based cleaners are effective and safe for plants. Spray the solution on, let it sit for 10 to 15 minutes without drying, then scrub with a stiff-bristle brush before rinsing with the pressure washer. Avoid chlorine bleach, which strips wood color and damages surrounding vegetation.
Choosing the Right Cleaning Solution
Not all deck cleaners are created equal, and using the wrong product can damage the wood or void your composite warranty. Match the cleaner to your deck material and the type of stain you are tackling.
- Oxygen bleach (sodium percarbonate): The best general-purpose choice for wood decks. It kills mildew, removes grime, and brightens grayed wood without harming plants or changing the wood's natural color. Mix the powder with warm water according to the label, apply with a pump sprayer, and let it work for 10 to 15 minutes before scrubbing.
- Composite-specific cleaners: Composite manufacturers often recommend or sell their own cleaning formulas. These are pH-balanced to avoid damaging the plastic-wood blend. Using unauthorized chemicals can void your warranty, so check your documentation before choosing a product.
- Brighteners for gray wood: If your wood deck has turned silver-gray from UV exposure, an oxalic acid-based brightener restores the original color after cleaning. Apply it as a second step after the deck has been washed and rinsed. This step is especially important before staining, as stain adheres poorly to weathered gray fibers.
- What to avoid: Never use chlorine bleach on wood decks—it breaks down lignin in the wood and can cause premature deterioration. Avoid oil-based solvents on composite materials. Steer clear of wire brushes, which gouge soft wood and scratch composite surfaces.
Pro Tips
- •Test pressure on a hidden area first: Before washing the entire deck, test your pressure setting on an inconspicuous board underneath or at the far edge. If the spray raises wood fibers or leaves marks, reduce the pressure or increase your distance from the surface.
- •Protect nearby plants: Wet down shrubs and flower beds adjacent to the deck before applying any cleaning solution, and rinse them again when you are finished. Even plant-safe cleaners can stress vegetation if left to sit in concentrated form.
- •Replace nails with screws: If you find many popped nails during your inspection, consider replacing them with deck screws. Screws hold significantly better than nails in wood that expands and contracts with seasonal moisture changes, and they are less likely to pop over time.
- •Let the deck dry completely before sealing: After power washing, wait at least 48 hours of dry weather before applying stain or sealant. Wood that looks dry on the surface may still hold moisture inside, and trapping that moisture under a finish leads to peeling and bubbling.
Frequently Asked Questions
How do I know if my deck boards need replacing?
Push a flathead screwdriver into any discolored or soft areas. If the screwdriver sinks more than a quarter inch with little resistance, the wood is rotted and needs replacing. Also check for boards that flex excessively underfoot, deep cracks that run the full length of the board, and splintering that cannot be sanded smooth. Composite boards should be replaced if they show significant delamination, permanent staining, or structural warping.
Can I pressure wash a composite deck?
Yes, but use a lower pressure setting of no more than 1,300 PSI and a fan tip nozzle to avoid damaging the surface. Keep the nozzle at least 8 inches from the deck and work in the direction of the board grain pattern. Some composite manufacturers recommend using only a garden hose with a deck cleaner designed for composite materials. Always check your warranty documentation, as improper cleaning can void the warranty on some composite products.
How often should I inspect my deck?
Perform a thorough structural inspection at least once a year, ideally in late spring or early summer before heavy outdoor use begins. A quick visual check after winter storms or heavy rain is also wise. Pay special attention to the ledger board connection, which is the most common point of deck failure, and to any posts that sit in direct contact with soil or concrete. Decks older than 15 years should be inspected more frequently as fasteners, wood, and structural connections degrade with age.
Related Guides
Seal or Stain Your Deck
Protect your deck with the right finish after cleaning
Service Your Grill for Summer
Deep clean and safety check your grill before the cookout season
Maintain Outdoor Lighting
Replace bulbs, clean fixtures, and test timers and sensors
Power Wash Siding
Remove dirt, mildew, and pollen buildup from exterior walls