Deck Power Washing
The Key To a Good Finish

No finish will last long if applied to a dirty surface. Deck power washing is an important beginning step, and in some cases the only preparation you'll need to undertake before staining.

Pressure washing is the single best way to clean your deck or porch.

This method:

Safely removes dirt and dust.
Opens wood pores allowing deep penetration of the deck stain or finish.
Is better than a garden hose for rinsing away chemicals, including bleaches and brighteners.
Removes many types of staining and discoloration using plain water.
Safely strips old finishes, including stains and peeling paint.

Proper Deck Power Washing Technique
Form Counts

The last thing you want is to damage your deck; improper form can produce ridges and gouges in the surface of the wood. The key to avoiding this is to use a sweeping motion and keep the nozzle moving at all times.

Pull the trigger at the beginning of your first pass, directing the water at a low angle to the surface. Working on a swath of wood two boards wide, walk the spray from one end of the deck to the other without stopping. Your second pass will overlap the first; walk back the entire length of the deck. If you need to stop before the entire deck is clean, sweep the nozzle up and away from the deck before releasing the trigger.

Deck Power Washing After Sanding

If your deck has just been constructed, it may seem that the wood is clean enough to skip pressure washing. Unfortunately, that's not the case. Sanding dust clogs the pores of the wood and prevents stain from penetrating effectively. This causes uneven color and a less protective finish. In severe cases, the stain will not penetrate at all, but will instead sit on top of the wood like paint. And just like paint, unabsorbed stain can flake and peel.

If your deck has been freshly sanded, low pressure and plain water are all you need to do the job right. Use a 40 degree spray nozzle (this is the widest one available) and low pressure; 1000 to 1200 psi is more than enough. Hold the nozzle 12 inches from the deck's surface.

While you're at it, go ahead and wash off the siding as well. Sanding dust gets everywhere, and some will have inevitably stuck to the side of your house.

Power Washing an Existing Deck

Often, water alone will be sufficient to remove grime, sanding dust, and old finish and restore the wood to like-new condition. In some cases, though, chemicals can produce a cleaner, more uniformly colored surface.

If you're pressure washing an old deck, consider using a wood restorer or brightener. These formulas can remove mildew, rust and tannin streaks, and even most commercial deck stains, leaving you with a raw surface.

Safely Using Wood Restoring Chemicals

Pre-moisten the deck using the pressure washer and water only to remove the worst of the surface grime and help the cleaner soak into the wood.

Mix the wood cleaner according to the manufacturer's instructions. Use a clean 5 gallon bucket and mix half a bucket at a time. It's a good idea to wear eye protection and gloves when doing this, because many chemicals can cause irritation.

Apply the solution to the deck with a stiff brush; a broom or specially designed deck cleaning brush should do the trick. Scrub in the direction of the wood grain. Allow the solution to remain on the deck for 5-10 minutes, depending on the manufacturer's recommendations.

Use a 25 degree spray nozzle and 1500-1800 psi to rinse the deck clean using plain water. Hold the nozzle 12 inches from the deck surface. Remember to use a sweeping motion and keep the nozzle in motion at all times to avoid creating grooves.

Use the lowest pressure setting to rinse surrounding landscaping and plants. Most pressure washing formulas are designed to be safe for vegetation, but that doesn't mean you want them sitting on the foliage undiluted.

Chemical Free Deck Restoration

If, for safety or other reasons you prefer to wash your deck without the use of chemical cleaners and brighteners, you can do it with a pressure washer. This is a good way to remove peeling finishes before sanding- unless you suspect that your deck has been painted with lead-based paint.

Higher pressures and smaller nozzles create the best result; use 2000 or 2500 psi and a 25 or 15 degree nozzle. Hold the wand close to the surface- just eight to ten inches away. Unfortunately, the same conditions that contribute to a perfectly smooth surface also increase the chance of damaging your deck, especially if the wood is old or soft, or if you're inexperienced with a pressure washer. Moving the wand slowly allows better control. If you're hesitant, use lower pressure or a wider nozzle for now; any staining or uneven color that remains can be removed with a light sanding.

The Next Step

If your deck is in good condition and you've recently applied a solid color deck stain, you're done; solid color stains aren't removed by pressure washing. In most cases, however, you'll want to apply a fresh coat of stain to protect and color the wood. Don't be penny wise and pound foolish; choose the best deck stain you can afford, because a high quality product will help your deck last longer. Allow the deck 24 hours to dry (avoid walking on it, if you can), sand lightly to knock down any raised grain, and then apply the deck stain according to the manufacturer's recommendations.