How to Clean a Deck to Remove Tough Stains and Grimy Buildup

Outdoor living spaces collect a lot of dirt and grime throughout the year. Learn how to remove stains on decks, including greasy spills, mildew, rust, and other grimy buildup, for a spotless outdoor space.

Decks play host to a wide range of outdoor activities during the warmer months. A season's worth of alfresco cooking, dining, and entertaining can easily dirty the surface with spots from grill grease, food or drink spills, soot from the firepit, and more. And because these spaces are exposed to the elements, they can naturally gather stains from dirt, leaves, tree sap, rusty furniture, and other grime throughout the year.

Deck stains can be difficult to remove, but with the right cleaning method and supplies, you can get your outdoor space looking good as new. Keep in mind that the best deck stain remover will depend on the type of stain. Use the instructions below to learn how to clean a deck to restore your space for outdoor living.

multi-level back deck with outdoor dining, kitchen and lounge areas
Aniko Levai

How to Clean a Deck

Plan to clean stains on decks as soon as possible to prevent the mark from setting into the wood permanently. In general, it's best to avoid using harsh chemicals to clean your wood deck. Chlorine bleach, for example, breaks down the wood fibers and can result in permanent damage to your deck or harm to the surrounding environment.

To maintain your wood deck's good looks, reapply sealer or stain about every one to two years. Use these cleaning methods to tackle some of the most common deck stains.

Barbecue Stains (Including Grease and Sauce)

If your last backyard barbecue got messy, remove grease spots or saucy spills using a household dish detergent.

What You Need

  • Grease-cutting dish soap
  • Stiff-bristled brush
  • Hot water
  • Damp sponge or mop
  • Garden hose

Step 1: Scrub the Stain

Mix dish detergent designed to cut through grease, such as Dawn Ultra Liquid Dish Soap ($3, Target) with hot water. Using a stiff-bristled brush ($8, The Home Depot), scrub the area.

Step 2: Rinse the Area

Use a dampened sponge to mop up the loosened grease. Rinse the area with a garden hose before it dries.

Candle Wax

Clean up candle wax following these steps.

What You Need

  • Credit card or putty knife
  • Brown paper bag or similar paper
  • Iron
  • Wet rag

Step 1: Scrape Away Wax

To clear away wax drips from outdoor candles, first carefully scrape away as much residue as possible using a credit card, putty knife, or similar tool that will not gouge the wood.

Step 2: Warm the Wax

Cover the area with plain paper (such as a brown paper bag) and use an iron set on low to gently warm the wax. The residue should lift away on the paper. Repeat until the wax is gone, replacing the paper as needed.

Alternatively, you can clean candle wax off a wood deck using mineral spirits ($7, The Home Depot). Saturate a rag and set it on the dried wax until it absorbs the residue, rubbing lightly if necessary.

Green Algae or Moss

Spurred on by damp, dark conditions, algae and moss growth creates a slippery deck surface and can lead to wood rot or other permanent damage. These stains are difficult to remove and usually reappear once the roots are formed in the wood, so it's important to treat them right away.

What You Need

  • Oxygen bleach
  • Borax
  • Dish detergent
  • One gallon water
  • Scrub brush

Step 1: Mix Bleach Solution

Remove green algae or moss stains on wood decks using an oxygen bleach solution. Mix together one cup oxygen bleach, 1/2 cup borax, and 2 tablespoons dish detergent in one gallon water.

Step 2: Scrub and Rinse

Scrub the stained areas with a brush dipped into the solution, then wait about 15 minutes before rinsing with a hose.

Leaf Stains

When leaves accumulate on decks or porches, they can start to decompose and leave behind dark marks or silhouettes. You can avoid these stains by regularly clearing away leaves from your deck as they begin to fall.

What You Need

  • Dish detergent
  • Warm water
  • Oxygen bleach (optional)

Step 1: Scrub the Area

To remove leaf stains on wood decks, scrub the area with a solution of dish detergent and warm water.

Step 2: Let Sit, Scrub and Rinse

Let the cleaning solution soak in for about 15 minutes before scrubbing again and rinsing with a hose.

For stubborn stains, try scrubbing with a solution of one cup oxygen bleach ($9, Target) to one gallon of water, repeating as necessary until the stains disappear.

Mildew or Mold

Mildew or mold is a common problem for decks in shady or damp areas, but regular cleaning can help keep it at bay.

Some deck cleaners contain acids or chlorine, which can harm plants; check the label before using the product.

What You Need

  • Commercial deck cleaner/brightener
  • Water
  • Garden sprayer, brush, or roller
  • Stiff brush or broom
  • Garden Hose

Step 1: Clean the Surface and Let Sit

Clean the surface with a commercial deck cleaner/brightener ($16, The Home Depot). If it is not in liquid form, mix the powder concentrate with the recommended amount of water and apply with a garden sprayer, brush, or roller. Let sit for a few minutes.

Step 2: Brush and Rinse

Brush briskly with a stiff brush or broom. Rinse with a garden hose.

Rust

Rusty outdoor furniture can leave red-brown rings or marks on your deck.

What You Need

  • Water
  • Distilled vinegar
  • Cloth
  • Oxalic acid cleaner (optional)

Step 1: Spray Deck and Wipe

To remove rust stains, spray a 50-50 solution of water and distilled white vinegar on the stain and let sit for about 10 minutes before wiping clean with a cloth.

For stubborn stains, try using an oxalic acid cleaner ($10, The Home Depot) following the manufacturer's instructions.

Tannin Stains

Tannins are naturally occurring compounds found in many trees and plants. They can sometimes cause dark stains to appear on wood decks after rain draws tannins to the surface.

What You Need

  • Deck cleaner for tannin stains

Step 1: Use Deck Cleaner

Remove the black streaks of tannin-rich woods with a specially formulated deck cleaner for tannin stains ($10, The Home Depot), following the manufacturer's instructions.

Tree Sap

Tree sap can harden on the surface of your deck, creating stains that are difficult to remove.

What You Need

  • Murphy Oil Soap
  • Scrub brush
  • Water

Step 1: Soften the Sap

To soften the sticky residue, apply Murphy Oil Soap ($3, Walmart) directly on the stain.

Step 2: Scrub and Rinse

Let sit for about 15 minutes, then scrub with a brush and rinse.

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