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Cleaning the Floors Outdoors

Martha Stewart Living, March 2008

A gleaming deck or patio is a delight. But it's not surprising if, after years of constant exposure, it begins to look a bit worn and stained. Whether yours is made of wood, brick, stone, concrete, or composite, routine maintenance and an occasional cleaning will ensure it always looks as good as new.

Basic Care Tips
1. Use a broom made for outdoor surfaces, and sweep as often as needed to eliminate dust and debris.

2. Hose occasionally to remove substances that stain.

3. Start with the gentlest cleaning methods. If these don't work, then try products with strong chemicals.

4. Before you work with cleaning products or apply stains or sealants, read all directions carefully.

5. Use only natural-bristle or plastic scrub brushes. Metal brushes can scratch surfaces easily and cause staining.

6. Saturate surfaces with water before using cleaning solutions to avoid staining. Never let cleaning solutions dry on surfaces. cool, overcast days are best for this task.

7. Be certain to rinse all cleaning solutions thoroughly from surfaces with plain water.

8. Avoid power washing, except on concrete. It can save time, but it can also etch some types of brick and soft stone, damage mortar joints, and splinter wood.


Although brick is durable and can last for generations, gentle cleaning is still the best way to keep it looking fresh.

Deep Cleaning
Use a masonry cleaner: Mix according to directions, and scrub with a stiff-bristle broom or brush.

To keep efflorescence, a salt residue that creates a white, powdery haze, at bay, avoid deicers with calcium chloride. Experts don't recommend sealing brick, as sealers can trap moisture in the pores, causing damage. Be vigilant in cutting away plant growth with garden shears. Plants direct moisture into mortar joints, loosening the bricks. A plant's roots will die shortly after it is cut and can be gently pulled out.


Use a masonry poultice, a solvent mixed with an absorbent material, such as kaolin clay. The solvent dissolves the stain, and the absorbent material pulls it from the brick's pores. Read labels to ensure that you're buying a poultice appropriate for the stain. Those with naphtha or trichloroethylene are most effective on oil stains. Efflorescence can be removed with water and a stiff-bristle brush or a masonry efflorescence remover. To remove moss or other organic growth, scrub brick with a solution of one part chlorine bleach to 10 parts hot water.


This a durable, forgiving material, but strong acids may damage concrete. Even a weak acid solution can roughen the surface if it is left on for any length of time.

To remove oil that has leaked from a car's engine, blot with paper towels. Then cover the spot with cat litter, and leave overnight. Remove the litter, and repeat until oil is no longer being absorbed. If needed, follow with a poultice: Mix one part trisodium phosphate with six parts water. Apply, and leave on for 24 hours. Scrub and rinse with plain water. To remove grease caused by food, scrub with a household scouring powder. To remove moss and organic matter, apply a solution of one part chlorine bleach to 10 parts water.

Sealing concrete will make it stain resistant (but not stain proof) and easier to clean. If you opt to seal, choose a penetrating concrete sealer. A clear, silicone-based water-repellent sealer is a good choice if you want to maintain the appearance of the concrete. If you want to do more than preserve the surface -- for example, enhance the color (often desirable with exposed aggregates) or add gloss -- choose an acrylic-based sealer. Don't use deicers that contain ammonium nitrate or ammonium sulfate, which can destroy concrete. Never let fertilizer sit on concrete; if it gets wet, it can leave stains.

Deep Cleaning
In a bucket, mix together hot water and an all-purpose household cleaner or a concrete cleaner. Use a stiff-bristle broom or brush to scrub the surface thoroughly.

Wooden Decking

All wooden surfaces eventually turn gray from sun exposure. North American woods, including Southern pine (which is often pressure treated), cedar, and redwood, benefit from regular sealing; this can help prolong the rich look of the wood. Tropical woods, such as ipe, Bangkiria, and mahogany, are dense and oily and usually don't need sealing.

North American woods need to be sealed yearly to protect them from the elements. Clean surfaces, and remove any stains. Sand off any existing finishes. Apply either a clear water-repellent preservative or a penetrating semitransparent stain. Semitransparent stains protect better than clear water-repellent preservatives. Neither coating will need to be sanded during your next annual cleaning. Products with an ultraviolet protectant may slow the graying caused by the sun, but they won't prevent it. Be sure to follow the directions: Never apply more coats than recommended; doing so can lead to serious mildew infestations and rot.

To remove mold and rust stains, bird droppings, and tannins, mix oxalic-acid crystals (often labeled wood bleach or wood brightener) with hot water, according to directions. Apply with a soft-bristle brush or broom. After stains have faded, rinse well.

Deep Cleaning
In a bucket, mix a gallon of hot water with powdered oxygen bleach, according to directions. Scrub well using a soft-bristle brush or broom. Rinse and repeat. The first scrubbing gets rid of visible mold; the second destroys the mold spores. Don't use chlorine bleach, which destroys wood's ligninthe "glue" that binds wood fibers.

Composite Decking

Composite decking materials are made of wood and plastic (sometimes recycled grocery bags or milk jugs). Manufacturers typically do not recommend painting, staining, or sealing composite surfaces.

The best way to combat mildew and other stains is to keep the deck clean with regular use of a broom and a hose.

Like regular wood, composites can become moldy and develop tannin stains. A deck cleaner that contains sodium hypochlorite should remove mold; one that contains oxalic or phosphoric acid will remove tannin stains and get rid of dirt and rust.

Deep Cleaning
Most composites can be washed with deck cleaner containing phosphoric, oxalic, or hydrochloric acid, or sodium hypochlorite, and a stiff-bristle brush or broom. Consult the composite manufacturer.


Patio stone can be divided into two categories. Siliceous stone (granite, slate, sandstone, brownstone, and bluestone) is hard and durable. Calcareous stone (marble, travertine, and limestone) is more delicate and porous, so it is susceptible to stains. To tell which kind you have, put a drop of white vinegar in an inconspicuous spot. If it fizzes, the stone is calcareous.

Deep Cleaning
Use a pH-neutral stone cleaner, and scrub with a soft-bristle brush or broom. Avoid household detergents, which tend to be too acidic or too alkaline. Repeated use of them can erode calcareous stone and dull the polish on siliceous stone.

Use a stone poultice. Read the label to be certain you're choosing the right stain remover for your needs. When cleaning siliceous stone, you can boost the power of a stone poultice by adding a little all-purpose household cleaner, as long as it doesn't contain chlorine bleach. To remove moss and organic matter from siliceous stone, use a stone cleaner that has phosphoric acid. For calcareous stone, choose a nonacidic algae remover.

Weathering and the sun will fade most stains over time, but they fade the luster of surfaces, too. A stone enhancer will bring a more saturated look to the stone, particularly to slate and tumbled marble. If you opt for an enhancer, choose one with a built-in sealer to add stain resistance.

Calcareous stone surfaces in high-traffic areas will benefit from sealing to aid stain resistance. Remember that the sealer won't make surfaces stain proof. Choose a penetrating stone sealer, which allows vapor transmission to prevent damage from freezing and thawing. As always, read labels to be sure the sealer is designed to protect against the stains you're likely to encounter. Reapply it every three to five years.

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