Decks, fences, pergolas, even composite structures attract mold and mildew like any other non-porous surface. The problem here however is wood is not a non-porous surface and therefore should be treated as such. Lets break this down in Layman’s terms and keep it very simple. Porous surfaces are areas covered with highly porous material that allow water from precipitation to pass through, yet are strong and durable enough to support vehicular or pedestrian traffic (i.e. wood). Non-porous surfaces are mainly smooth surfaces which the latent print resides on the surface. Examples of non-porous surfaces include glass, plastics, metals, and varnished wood. When we think of these types of surfaces we automatically use a bleach cleaner to clean and disinfect these surfaces so we would automatically think to use it on anything where mold or mildew is present. That is simply not the case and for very good reason.
The use of bleach as a mold disinfectant is best left to kitchen and bathroom countertops, tubs and shower glass, etc. The properties of chlorine bleach prevent it from “soaking into” wood-based building materials to get at the deeply embedded mycelia (roots) of mold. The object to killing mold is to kill its “roots”. Reputable mold remediation contractors use appropriate products that effectively disinfect properly scrubbed and cleaned salvageable mold infected wood products. Beware of any mold inspector, mold remediation contractor or other individual that recommends or uses chlorine bleach for mold clean up on wood-based building materials. OSHA is the first federal agency to announce a departure from the use of chlorine bleach in mold remediation. In time, other federal, state and other public safety agencies are expected to follow OSHA’s lead. The public should be aware, however, that a chlorine bleach solution is an effective sanitizing product that kills mold on hard non-porous surfaces and neutralizes indoor mold allergens that trigger allergies. Mold and mildew is a vegetative growth, and NOT a type of dirt to be cleaned. It is produced by a tiny plant of the fungus family. It can sprout on most surfaces especially if a food source is present for the minifungus to thrive on, especially on paper and wood. Additionally, mildew can grow on the dirt and soil on them, especially in dampness. Mold spores (seeds) exist everywhere and will grow when the conditions are right. Like a weed growing on your front lawn, mold and mildew must be killed by an effective, acknowledged, E.P.A. registered disinfectant cleaner making mold and mildew claims.
The affects of bleach on decks/fences
Bleach is the old standard used for years. The chlorine kills algae, moss and mildew. BUT – chlorine breaks down the lignin that holds the wood together, causing excessive damage to otherwise healthy wood. Chlorine is dangerous, environmentally unsound, and likely to cause damage to surrounding greenery. The corrosive effects of chlorine bleach on wood decks are cumulative and are more numerous than you might imagine. Not only does chlorine bleach break down wood fibers and alter the color of wood, it also corrodes metal fasteners – including the screws and nails holding your deck together. Bleach literally bleaches the wood, resulting in a lightening of wood’s natural coloration. This bleaching effect may provide initially pleasing results, but over a period of several months the wood begins to take on a lighter appearance. The natural pH of wood is just slightly acidic, and bleach is a basic solution. As a result, use of bleach on wood shifts the pH from wood’s natural, near neutral, pH to a basic pH which will damage the cellular structure. As a cleaner, bleach provides minimal results. The natural bleaching action creates the impression of a cleaner surface which, in reality, is only bleached but still needs cleaning. Cleaning with bleach does kill mold and mildew which may be on the deck, but does not eliminate the spores from which mold and mildew grow.
Safer more effective alternative to using bleach
Sodium Percarbonate (Oxygen Bleach) is an excellent detergent and bleaching agent based on hydrogen peroxide. It is a good cleaning and bleaching agent at normal temperature, and has strong fungicide effect. (Fruits and vegetables treated with sodium percarbonate can be kept fresh, and be stored for a long time. In medicine, it can kill staphy lococcus, and colon bacillus). This product is a white particle powder, non-toxic no contamination, non-flammable, non-explosive, easy to get damp, and soluble in water. It is efficient, safe and economical. It is environmentally safe, biodegradable, leaves no harmful by-products or residues which can harm the environment. Except for industrial-strength cleaning or stripping jobs, sodium percarbonate is, hands-down, the choice for most average wood preparation jobs. Your first line of attack is undiluted hydrogen peroxide which is an oxidizing agent (JUST LIKE CHLORINE BLEACH) and should kill the mildew on contact within several minutes. However, hydrogen peroxide is a far safer substitute. Its chemical formulation is H2O2. As the excess molecule of oxygen is released during the oxidizing process, H2O (water) remains as its residue. Oxalic or citralic acid (deck brightener) must be applied after the Sodium Percarbonate has been used in the cleaning process. The deck brightener will restore the wood to its natural pH and neutralize the Sodium Percarbonate cleaner. This will provide for a beautiful finish when applying the final stain.
You paid a lot of money for that deck, why not keep it looking healthy and new for as long as you own your home!