Exterior Surface Prep by Substrate


Contrary to common belief, all exterior wood should be coated as soon as possible after installation. Ultraviolet rays from the sun will degrade the wood and produce loose surface wood fibers in as little as two weeks. Pressure treated wood should be coated immediately before it splits, cracks or exhibits separation of the graining. It should be assumed that even “new” wood will have some contamination from mold, mildew or fungus spores. All bare exterior wood must be primed with a specific wood primer.

• Pressure wash at a minimum of 2200 PSI or hand scrub with a mildew killing product or a 50%-50% mix of household bleach and water using appropriate safety measures. This will kill any living organism contamination and remove loose surface wood fibers.
• Rinse thoroughly with clean water and allow to completely dry. Wood moisture content should be below 15%.
• Sink all non-aluminum or stainless stell nails and fill the voids with an appropriate exterior wood filler.
• Caulk all butts, joints and voids with acrylic sealant, butyl rubber or moisture cured urethane caulk.

Pressed Fiberboard

Pressed fiberboard is re-manufactured wood. Special treatment is required to maintain the integrity of this material. Read the following information thoroughly.

The extremely high cost of cedar clapboards, shakes and shingles over the last several years has forced many building contractors to find alternative, less expensive, siding material. Hardboard siding, which is also known in the construction industry as compressed fiberboard or wood based fiberboard siding, has become a major factor in the siding market for new home construction.

Hardboard, which was originally developed by the Masonite® Corporation is now manufactured by several companies. This wood based fiberboard siding is offered in a fairly extensive variety of grades, textures and densities which vary with the manufacturer, and on occasion, within the regional plants of the same manufacturer.

Most hardboard producers have a lap siding (flatboard), embossed siding (wood grained or special texture) and a prefinished siding (flatboard or wood grained).

Hardboard siding composition varies slightly among the manufacturers, but is basically composed of wood cellulose fiber, mixed with phenolic resins and reactivated lignin (the natural glue that holds wood fibers together). A small amount of was (1%), usually paraffin, is added to increase resistance to water penetration. This material is then formed into panels under high heat and allowed to cure. The density (hardness) of the hardboard siding is determined by the resin mixture and manufacturing process.

Smooth lapboard siding, which is the largest selling type of hardboard, is usually primed in large four foot wide sheets by roller coater at the factory with a fast-dry solvent primer. After the sheets are cut into standard lapboard widths, the raw edges are sprayed with the primer. The paint primer is applied at about 1.2 mils dry. Federal Housing Administration (FHA) specifications call for a totally dry paint film thickness of 4.0 mils. Two additional coats of paint are required after the hardboard is erected to meet FHA paint finish specifications.

Lapboard siding can be marred, bruised and abraded during erection. Butt ends of hardboard are always wide open and unprimed. Nails rupture the siding, producing natural pockets for wicking moisture. The fast dry low end primer does little or nothing to block water soluble extractive bleeding. These deficiencies in the lap siding are usually accentuated in the lower density hardboard products, which account for most painting problems.

Concrete/Masonry Block

Concrete is strongly alkaline in its natural state because of it’s high calcium content. 100% acrylic latex, because of it’s alkali resistance, flexibility and color retention qualities, is the most successful product for use over all forms of concrete.

• No finish EXCEPT acrylic latex should be applied to new concrete until it has aged 28 – 30 days.
• Paraffin or oil type form oils must be removed by solvent washing before paint is applied. New types form oils are coatable without being removed, 30 to 60 days after removal of the forms. All • residue from oil should be removed from new concrete by solvent cleaning before finishing.
• Voids should be filled with an appropriate concrete patch before application of primer. All dirt or foreign material should be brushed off.
• New concrete floors may require mechanical abrasion to create the proper profile for adhesion.


Stucco is designed as an integral finish and is seldom painted until it has weathered for many years and has begun to blotch, stain or streak. Stucco that has aged for long periods of time will gradually “sand” as its top surface loses its film integrity. Brush or wash as necessary to remove surface contamination. Major cracks should be cut out and repaired with a Portland Cement stucco mix. The entire old and “sanding” stucco surface should be rejuvenated with a waterborne acrylic sealer before any finish painting is attempted . This process will insure excellent adhesion, without suction spots or unevenness of sheen of the top coats of acrylic latex.


Porosity and density of these kiln baked products varies greatly, so that the preparation is normally dependent upon the type of brick involved. All varieties of brick and clay products require some standard surface preparation before finishing. Efflorescence should be removed by wire brushing. Nibs and mortar should be eliminated by “bricking” down protrusions. 100% Acrylic latex because of its excellent adhesion, alkali resistance and longevity, is by far the most successful coating for brick products. Mortar or brick surfaces on which 100% acrylic latex is to be utilized, should not be acid washed.

Cement/Asbestos Shingles

Glazed shingles should not be finished until glaze has weathered from the surface, usually in about two years.

Weathered and unglazed shingles that have started to erode or “sand”, should be primed with an acrylic masonry primer before finishing to insure adhesion of the top coats.

• Wash with a garden hose to remove surface contamination. Power washing or scrubbing are not recommended as they disturb asbestos fibers.


Grease, oil and weld flux must be removed by solvent cleaning. Use mineral spirits and a clean cloth that is changed frequently to avoid spreading surface contamination rather than removing it. Power or hand tools should be used to remove all mill scale and rust. All bare ferrous metal must be primed with a rust inhibiting metal primer.

Bare Metal

• Solvent clean to remove dirt, oil, grease, soil, salts and other contaminants (SSPC-SP1).
• If corroded or pitted, bare metal should be wire brushed or power tooled to remove oxidation (SSPC-SP2, SP3).

Previously Painted Metal

• If the old paint film is loose, it must be removed by scraping, wire brushing, power tooling or sandblasting (SSPC-SP2,SP3,SP6).
• Solvent or detergent clean to remove oil, grease and dirt.
• When applied over old paiint films, a test patch of any new coating should be tried to be sure it does not lift or wrinkle the old film.


As with ferrous metals, aluminum and light alloys will be attacked by atmospheric conditions causing oxidation unless protected by a coating. Galvanized metal is ferrous metal that is covered with a zinc rich coating to prevent corrosion. This is usually done by a “hot – dip” process.

Bare Metal

• Solvent clean to remove dirt, oil, grease, soil and other contaminants. Use mineral spirits and a clean cloth that is changed frequently.
• If corroded or pitted, bare aluminum should be wire brushed or power tooled to remove oxidation.

Previously Painted Metal

• If the old paint film is loose, it must be removed by scraping, wire brushing or by power tool.
• Solvent or detergent clean to remove oil, grease and dirt.
• Sand glossy surfaces and remove the dust.

Galvanized Metal

• Galvanized metal is usually treated with an oil, silicone or silicate to protect it and prevent it from sticking together during shipment. This must be removed before painting by solvent washing or by weathering at least six months.

Aluminum/Vinyl Siding

Vinyl or aluminum siding fades and oxidizes with time. These surfaces are excellent materials to paint, because unlike finished wood, there is no moisture transmission or splitting, checking and cracking. 100% acrylics directly applied to properly prepared surfaces make excellent coatings because of their flexibility, oxidation resistance and color retention. Always paint vinyl siding with a similar or lighter color since dark colors absorb heat and can cause warping or buckling. Satin Gloss acrylics provide the longest lasting finish and approximates the original sheen of the siding.

• Pressure wash at a minimum 2200 PSI or hand scrub to remove surface contamination and oxidation.
• Rinse thoroughly with water and allow to dry.

Cement/Composition Siding & Panels

This exterior siding material is a cement based product or a mixture of cement with wood fibers that is formed into either horizontal siding or vertical paneling.

• Pressure wash or hand scrub to remove any surface contamination. If surface is chalky, apply appropriate masonry conditioner.

PVC Plastic Columns, Trim, & Deck Board

100% acrylics applied directly to these surfaces are the best recommendation. Proper preparation greatly increases the probability of the best adhesion.

• New unweathered surfaces should be cleaned with solvent alcohol to remove any surface plasticizers that have leached from the plastic. The surface should be thoroughly roughed up with fine sand paper or steel woold and wiped clean.

WARNING! If you scrape, sand or remove old paint from any surface you may release lead dust. LEAD IS TOXIC. EXPOSURE TO LEAD DUST CAN CAUSE SERIOUS ILLNESS SUCH AS BRAIN DAMAGE, ESPECIALLY IN CHILDREN. PREGNANT WOMEN SHOULD ALSO AVOID EXPOSURE. Wear a NIOSH-approved respirator to control lead exposure. Clean up carefully with a HEPA vacuum and wet mop. Before you start, find out how to protect yourself and your family by contacting the National Lead Information Hotline at 1-800-424-LEAD or log on to www.epa.gov/lead.

The core content for Painting Tips is provided by the courtesy of Dow Chemical as found on CaliforniaPaints.com.