Wood deck needs restoration to retain natural finished look
Q: We have an outdoor wood deck that has become gray and stained over the years. The previous owners said it was treated with a wood preservative when it was new, some six years ago. My neighbor suggested cleaning it and using an opaque stain for better wear. However, I prefer the natural look of wood. Do you have any suggestions for do-it-yourself refurbishing and maintenance of a wood deck, including product recommendations?
A: Even the best protective finish will succumb to the ravages of weathering in a few years and the wood will need to be refinished. Proper cleaning and restoration is an essential step in the refinishing process.
Clear the deck of all furniture and plants. Cover any surrounding vegetation and begin by sweeping the surface thoroughly. Remove general dirt and loose debris with a hard spray from a garden hose. A power washer, often used by professionals, will do a more thorough job of cleaning. However, if you use too much pressure it can raise the grain of the wood and damage the surface.
It is essential to do this with caution. If there is dirt and grime between the decking boards, use a putty knife to dislodge it. If the spacing between boards is too narrow, use an old saw to run along the cracks to open a space. Your deck needs good air circulation between boards and adequate water drainage.
In recent years a number of commercial wood-cleaning products have been introduced to the market that are specifically designed to clean and restore weathered wood surfaces such as decks and siding. These commercial cleaners are a great improvement over previously recommended household bleaches and cleaners. They address specific problems of stain removal on wood decks, including both chemical and biological discoloration.
The major sources of discoloration of wood decks include:
1. Dirt and other foreign materials such as tree sap, bird droppings, grease.
2. Fungal discoloration from mildew, mold and decay.
3. Algae, moss and lichen growth.
4. Nail and other iron or metal stains.
5. Tannins and other elements from the wood.
6. Graying of the wood due to surface decomposition by sunlight and moisture.
7. Fading/decomposition of protective coatings.
Most deck cleaners and restorers fall into three categories — chlorine bleaches, oxygen bleaches, or oxalic acid-based formulas.
Formulas based on chlorine bleaches are effective against mildew but have limited efficacy against other sources of discoloration. When used on wood decks, chlorine-based bleach products can do more harm than good. They can leave the wood with a white unnatural tone due to the bleaching out of natural components or fuzziness on the wood’s surface due to the loosening of small fibers during the cleaning process. Moreover, if not rinsed properly, the chlorine salt can gray the wood.
Oxygen-type bleaches are usually based on disodium peroxycarbonate, commonly known as sodium percarbonate, an ingredient present in some color-safe fabric bleaches. Sodium percarbonate is a powder that, when mixed with water, forms hydrogen peroxide. This type of bleaching agent is effective in removing dirt, mildew and weathered gray residues. It leaves the wood with a natural appearance. Certain woods, such as cedar and redwood, contain natural resins known as tannins. These are water-soluble materials that are reddish brown in color. Water can extract these from resins from within the wood and deposit them on the surface, leaving brown or black discolorations.
Tannins can also react with iron, present in fasteners or nails, resulting in blue-black stains. Neither chlorine bleaches nor oxygen bleaches are effective against tannin stains or iron stains. Oxalic acid, on the other hand, chemically works on tannin and iron staining, rendering them colorless. However, oxalic acid is not as effective against mildew. For this reason it is sometimes necessary to treat redwood and cedar with a sodium percarbonate or chlorine-based cleaner and follow it up with an oxalic acid-based product. Concentrated oxalic acid is toxic and should be handled with care.
Sometimes, in order to restore a wood deck and prepare it for refinishing, the previous finish, or what’s left of it, must be removed.
Most deck cleaners and restorers are ineffective in removing paints or protective stains. This can be accomplished by mechanical removal or chemical means.
The mechanical method of choice for cleaning and restoring wood decks is a power washer. This is sometimes used in conjunction with chemical cleaners, i.e. commercial deck cleaning products.
Power washers are employed more by contractors than do-it-yourselfers because they are somewhat tricky to use and can damage wood if not used properly. However, with proper instruction and care, the use of a power washer is not beyond the skill of the average homeowner.
Power washers are available at rental equipment outlets.
Sanding is an effective method of removing old finish. However, sanding can damage the surface of the wood. Paint strippers are heavy duty products designed to chemically remove unwanted coats of paint or stain from wood surfaces. They are effective but need to be used properly — with drop cloths and protective clothing — because they might contain hazardous ingredients.
A commercial cleaner, such as Wolman’s DeckStrip Stain & Finish Remover, is easier to use than most paint and varnish strippers. It is designed specifically for wood surfaces such as your deck. It is a ready-to-use exterior wood stripper that removes solid and semi-transparent stains and clear finishes — either oil-based or latex coatings. Other stripping products are often designed for one or the other. It is also easy to use on vertical surfaces. It is biodegradable and relatively safe around grass and plants, requiring only that the surrounding area be hosed down before and after use.
Care should be taken to thoroughly rinse all cleaner/restorer products from wood surfaces. Failure to remove dirt, mildew and cleaning agents is an open invitation for early failure of future coatings.
Once the wood surface has been cleaned — this would apply to all vertical components as well as the deck flooring, railings, spindles, vertical planks, risers on staircases, etc. — the wood should be allowed to dry thoroughly prior to application of a wood preservative.
Inspect your deck and replace any broken, warped or rotting boards, treating joists or beams with wood preservative before nailing and wherever new wood will contact supports. Refasten railings and stairs as needed. Sink any protruding nails.
Once your deck is clean and looks great, you will need to apply a water repellent, preservative or stain to keep it that way and protect the wood from absorbing water and damaging ultraviolet rays. You can use either a clear penetrating finish or an ultraviolet resistant stain in a solid color or semitransparent finish. Today, there are semitransparent stains on the market that are just as durable for the rugged wear a decking surface takes as solid stains.