Photos by Lakeside Lumber Contact Lakeside Lumber, (866) 635-3695 or mail@lakesidelumber.com, for details about cleaning, brightening and restaining your deck.
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Typically, reddish brown extractive (aka tannin) stains can appear in several forms. Diffused discoloration can result from rain or dew penetration through the finish whereas rundown discoloration typically results when water collects on an unfinished surface, such as the back of siding or unprimed ends of boards. Water-based finishes can dissolve extractives and cause discoloration as a result. Several factors will affect the amount and type of extractive discoloration. The heartwood of certain wood species, such as Western Red Cedar and Redwood, may have high concentrations of water soluble extractives, whereas other species, like some pines and firs, may have higher concentrations of pitches and resins. The moisture content of the wood substrate also affects extractive staining. Generally, the drier the wood prior to application of the finish, the less chance for initial extractive discoloration. Dried lumber not only has fewer water soluble extractive problems than unseasoned lumber, but kiln drying tends to harden pitches and resins making them much less likely to bleed. However, introduction of moisture into the siding at any time during the service life can cause extractive staining. The type of finish also plays an important role in preventing extractive bleeding. Non film forming finishes like water repellents and semitransparent stains are not effective at preventing extractive discolorations. For water soluble extractives in redwood or cedar solid wood sidings, the most effective finishes are solvent borne oil or alkyd based film forming finishes. Water based stain blocking primers have also been developed that are moderately successful over cedar or redwood solid wood sidings and are preferred over veneered sidings such as plywood. For non water soluble extractives, knot sealers and varnishes are currently used. To remove extractive bleeding stains when they first appear, wash them in a mild solution of trisodium phosphate or other detergent and water. If they are not removed and are permitted to oxidize, they become increasingly dark in color. In that condition it may be necessary to remove them by scrubbing them with a soft brush (do not use wire brushes) in a solution of 50% alcohol and water. WARNING: Never mix bleach with detergent containing ammonia, as fumes can be harmful or fatal. Source: Western Red Cedar Lumber Association
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Mildew is a generic term for a variety of parasitic growths that appear as discoloration of a surface and ultimately degrade or destroy the material upon which they grow. The growth of these organisms is supported by moisture, temperature and organic material for food. Thick shrubbery planted in front of a painted surface can hinder air circulation and block out sunlight, making a perfect environment for mildew to grow. Their appearance varies from the green slime found on wet, shaded sidewalks and walls behind bushes and plants, to the microscopic black dots that from a distance look like a dulling of color or deposit of soot. Mildew is inhibited by direct sunlight, so that it is most often found in shady areas, particularly on north-facing walls. Mildew food includes all organic building materials such as wood, man-made wood products and may even include resins used in fiberglass or vinyl products. Food is also the dirt and fertilizer products that are deposited on a surface by the wind, or the organic binder used in paints. Mold and mildew spores are microscopic and are found universally in the air, transported by the wind. These spores can remain dormant on a surface indefinitely. When conditions are favorable for their growth, such as lengthy periods of warm moist conditions, growth can start on what appears to be a perfectly clean surface. Mildew-contaminated homes in any neighborhood can supply the spores for contamination of other homes in the area. It is most important to realize that the appearance of mildew is a sign of surface degradation that will lead to the loss of paint on the surface and ultimately, the rotting of wood, or rusting of steel substrates. Most exterior paints contain fungicides designed to protect the paint from mildew growth. Paints cannot be claimed to protect a surface from mildew growth unless they are registered with the Federal Government as a mildewcide. However, it is reasonable to expect that a paint which protects itself against mildew attack might minimize such problems on surfaces to which it is applied. Government restrictions on the use of some fungicides together with the tendency of the parasites to develop immunity to previously successful products has resulted in new, localized, outbreaks of mildew problems. Many of the problems are intensified by construction practices which use wood or wood products in which mildew spores may already predominately present. These appear as black areas that may appear dead and dry, but in fact only require moisture for reactivation. When these areas are not treated before painting, they can be a never-ending source of mildew problems. To determine if mildew is present, apply a small amount of household bleach on the discolored surface. If mildew is present, bleach will destroy the fungus and its discoloration. If the discoloration is simply dirt, the bleach will have no effect. Mildew MUST be removed before the painting process begins. Painting over a mildew-laden surface guarantees return of the mildew. Mildew will grow through any paint film very rapidly and correction may well then require complete removal of the coatings! All mildew-stained surfaces should be washed in a solution of household bleach and water shortly before painting. Commercial mixtures for washing the surface are also available. Repaint as soon as the surface is dry with a mildew-resistant paint. The addition of an additional mildewcide to the finish coat may add protection. Apply generous amounts of topcoats, since thin coats allow mildew fungi to penetrate more easily. Painting should always be performed in dry conditions. Mildew-Killing Wash50% Bleach and 50% Water Solution left on siding for 15 minutes followed by a good rinse. Use of a window-washing brush and some washing detergent compatible with the bleach is recommended to remove surface dirt and help the bleach wet the surface being treated.
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The Pacific Northwest's dew, fog and rain can present a peculiar problem to exterior surfaces freshly painted with latex paint. All latex contain detergent-like materials called surfactants. Surfactants are necessary to:
Surfactants are not necessary to the dried paint film, and sometimes come out of the film over a period of time. When they are removed slowly by the washing action of rain, there is no problem. However, under certain environmental conditions present during and shortly after paint application, this process can occur rapidly, causing a building at the surface. This buildup can appear as light colored crystalline deposits or soft white, brown or clear spots. The usual cause is the occurrence of high humidity and low temperatures in the first few days after painting, particularly if condensation (or dew) occurs on the painted surface. It may also be caused by sprinkler water wetting the surface. The appearance of this phenomenon is most noticeable on medium to dark colors often because it is simply more visible and these colors usually have more surfactant in them. The problem may often be corrected by simple rinsing with a hose, if caught before the sun bakes the deposit. It if becomes sun-baked, it may be necessary to wash with a household detergent solution and a soft brush. However, except in protected areas, rain will eventually remove the deposit. WARNING: Never mix bleach with detergent containing ammonia, as fumes can be harmful or fatal. Source: Miller Paint Product Information and Specifications Revised 2/93 |
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