How Cleaners Work.

Cleaners are formulated to clean away the top layers of dead wood cells, the main cause of graying decks. Cleaning any surface, (whether it be fabric, porcelain, glass, concrete, vinyl, plastic or wood) is a function of contact time, temperature, type and concentration of chemicals, mechanical action and composition of the surface to be cleaned.

Time & Temperature

Time and temperature are fairly easy to cover. The oxidizing cleaners used on wood decks all work in 10 to 20 minutes and all are used at ambient temperatures. However, the hotter the water the faster they work.

The types of chemicals, strengths, mechanical action and the various species of woods used for cleaning, is more complicated and it is the most important part of this paper on cleaning chemicals.

Chemical Cleaners

Chemical cleaners fall into four basic types:

  1. Chlorine Bleach
  2. Oxalic Acid (Timber Brite)
  3. Oxygen Bleach (Timber Wash, CPR, House Prep)
  4. Trisodium Phosphate

Historically, the most common substance used to clean wood has been household bleach. It may be labeled as sodium hypochlorite in its liquid form or as calcium hypochlorite or di and tri sodium salts of chlorinated cyanuric acid in dry forms. Chlorine Bleach should not be used on wood decks or any wood surface for a host of reasons. Chlorine is a toxic chemical and if misused it can be very dangerous, even fatal. Never mix household ammonia or detergents containing ammonia with chlorinated products. When mixed you get immediate release of chlorine gas, which is very irritating to the lungs. If mixed in a poorly ventilated room, breathing the fumes can be fatal. (In North Carolina alone there were 12 deaths related to inhaling household cleaners in 1992 and 6 more in 1993). Chlorine will kill plants, especially new growth and delicate flowers. Of course, it will discolor clothing. Chlorinated products have warnings to keep pets away. Chlorine is such a strong oxidizer that it leaves behind degraded cellulose cells. Over bleaching generally occurs and gives the wood a "washed out" whitened appearance. It destroys the natural lignin in the wood that give it its natural color and luster. "In fact, the difference between a sodium percarbonate (oxygen bleach) and sodium hypochlorine-based cleaner (chlorine bleach) can be likened to the difference between all-fabric bleach and chlorine bleach: one enhances color while the other bleaches color out. Chlorine is very corrosive to metal and will corrode the very nails that hold your deck together. Common iron nails and hardware can be a source of additional iron staining.

Only the uninformed would use chlorine on wood

Oxalic Acid

Oxalic Acid can be purchased in liquid or crystalline form. Crystalline material is applied by dissolving 4 ounces of oxalic acid crystals in warm water in a non-metal container. Liquid material is usually diluter with water prior to application. Oxalic Acid is particularly good at removing tanning stains. It is the product of choice on redwood only. It is also the best product for removing rust stains. It is not particularly effective on mildew and dirt. CAUTION: Oxalic Acid is a poison. It carries the warning "Harmful or Fatal if swallowed" The California Redwood Association endorses the use of oxalic acid to clean redwood but issues the following: C.R.A. "Recommends that you hire a professional painter to work with this chemical. If you do the work yourself, wear rubber gloves and be careful not to let acid or solution touch your skin or eyes. Wear old clothes and try not to spill on plants. When you have finished, wash containers, clothes, and brushes thoroughly."

Sodium Percarbonate (oxygen bleach)

Sodium Percarbonate is the active oxidizer in a number of wood bleaches. Percarbonate is sold in beaded or granular form. It fully dissolves in water in two minutes and the recommended usage rate is typically 6 ounces per gallon. Follow manufacturer's recommendations. Sodium Percarbonate is totally environmentally sound. In water it disassociates into hydrogen peroxide, soda ash and water. (However, do not use Sodium Percarbonate on unaged redwood. New redwood has a pH of about 4. Basic products like Percarbonate, pH 10.5, will darken redwood. As redwood ages the pH becomes more neutral.) Of all the bleaches, it is the only environmentally friendly choice. Percarbonate is ideal for bleaching and cleaning wood surfaces. CAUTION: Be careful not to get Sodium Percarbonate bleaches in your eyes. Sodium Percarbonate is a severe eye irritant.

Sodium Percarbonate bleaches is the product of choice of the informed buyer.

Trisodium Phosphate

Trisodium Phosphate may be purchased at your local hardware store. California Redwood Association recommends cleaning redwood decks with TSP. Mix one cup of TSP granules to one-gallon water. Scrub surface with a bristle brush and rinse with cold water. Remove stains from redwood with oxalic acid. Remove stains or discoloration from all other woods with sodium percarbonate products. If you are concerned about the use of phosphates, most laundry detergents (without chlorine bleach) will help to clean debris and airborne particulate off your wood.


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