Interior Surface Prep By Substrate

Plaster / Veneer Plaster

Plaster or veneer plaster (skim coat) is a cementitious substrate highly subject to alkalinity and efflorescence, a white powdery salt usually brought to the surface by water.

All new plaster should cure a minimum of 30 days (10 days for skim coats) and should have a moisture content below 15%. 100% acrylic latex primers or finish coats provide the best adhesion and maximum alkali and moisture resistance on plaster. Alkyd products can react to free alkali and lose adhesion.

• Brush off or vacuum all efflorescence and loose surface material.
• “Knife down” the surface to remove nibs and other protrusions.
• Voids, holes or cracks should be cut out and filled with prepared patching compound.
• Wipe the entire surface with a wet sponge to redissolve any free alkali and minimize “hot spots”.
• Allow plaster to dry thoroughly.
• DO NOT SAND PLASTER BEFORE IT IS PRIMED.

Sheetrock/Wallboard

Wallboard, sheetrock, gypsum board (sheet plaster with a paper surface) is the most prevalent substrate in construction today. The use of re-manufactured surfacing paper which may incorporate waxes or be coated with silicones to prevent the sheets from sticking together requires the use of an acrylic primer for maximum adhesion. In some instances, the tannins or high alkalinity from these papers can discolor finish coats unless a stain blocking primer is applied first.

Since solvent primers can severely raise the grain of the paper surface, acrylic primers or two coats of 100% acrylic latex are used to combat this and possible high alkalinity.

• Fill all holes and voids with prepared patching compound or joint compound
• Sand all joints and patches even with the surrounding surface taking care not to abrade the adjacent paper surface.
• Brush or vacuum off all sanding dust and loose material.

Wood/Plywood

Interior finish wood products should be properly kiln dried with a moisture content of less than 10% when installed.

• Fill all holes and voids with prepared patching compound or joint compound
• Sand to obtain smooth surface.
• Brush to remove dirt and sanding residue.

Ferrous Metal (Iron and Steel)

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.

Galvanized Metal

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.

• 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.

Bare Galvanized

• Remove all oil, grease, weld flux and contaminants with a solvent cleaning (SSPC-SP1).

Previously Painted Galvanized

• If the old paint film is loose, it must be removed by scraping, wire brushing, or sandblasting (SSPC-SP2, SP3, SP6).
• Solvent or detergent clean to remove oil, grease and dirt (SSPC-SP1).
• When applied over old paint film, a test patch of any new coating should be tried to be sure it does not lift or wrinkle the old film.

Aluminum/Light Alloys

• As with ferrous metals, aluminum and light alloys will be attacked by atmospheric conditions causing oxidation unless protected by a coating.

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 Surfaces

• 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.

Copper/Brass/Bronze

• As with ferrous metals, copper, brass and bronze will be attacked by atmospheric condition causing oxidation unless protected by a coating.

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 Surfaces

• 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.

Ceramic Tile

Although these surfaces can be successfully coated as detailed below, it is a complicated process using sophisticated products. Most homeowners would do well to replace these surfaces rather than coat them.

• Scrub thoroughly with TSP and water
• Rinse with clean water
• Etch with 20% Muriatic Acid
• Rinse with clean water
• Dry thoroughly before applying primer

Brick/Clay Products

The surface should be brushed to remove loose dirt and particles. Oil and grease should be removed by solvent cleaning. All mortar nibs and splatter should be “bricked down” until all protrusions are removed. Mortar joints should be raked clean of loose mortar and “pointed up” with new mortar where necessary. Small structural cracks should be filled with acrylic, urethane or silicone caulk for maximum flexibility. Efflorescence should be removed and alkali neutralized with appropriate concrete etching solution.

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.

PVC Plastic Columns, Trim, & Deck Boards

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 plstic. The surface should be thoroughly roughed up with fine sand paper or steel wool 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.