Paint Problems

Listed below are examples of common paint problems and their characteristics with a full description and recommended solutions.  Courtesy of Sherwinn-Williams Company.

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Cause: Plywood cracks from its expansion and contraction with changing moisture content. Plywood is prone to cracking because of its original method of manufacture involving peeling thin sheets of wood from logs. Stresses are induced which later show up as cracking. Many small fissures are produced in films of paints and stains that have been applied to insufficiently dry plywood. The edges of these cracks protrude upward and can be felt as sharp burrs. Subsequently, this coating may become detached from the edges of the cracks and lead to flaking.

Solution: New wood: To prevent cracking of newly installed plywood, sand and prime with Sherwin-Williams Latex Exterior Wood Primer.

Repaint: If cracking is severe, replace the wood, for this is an unpaintable surface.

If the cracking is not extensive, sand surface smooth. The plywood must be thoroughly dry. Apply latex primer.

Caution: Wear a face mask to avoid inhalation of dust particles during the sanding procedure.

Recommendations: New Wood

One coat A-100 Latex Exterior Wood Primer

Two coats Exterior Latex House and Trim Paint

Repaint

Spot prime with A-100 Latex Exterior Wood Primer

Two coats Exterior Latex House and Trim Paint

Note: Tint primer to compliment topcoat color. Do not use white primer under dark colors since future cracking of the topcoat will disclose a white pattern.

Cause: Steel nails that are in contact with moisture will rust. Depending on conditions, this rust can either be red or black. Nail heads exposed to air will always be red rust-colored. If the nail is extracted and the nail shank is red, then the wood is saturated with moisture. Damp wood that possesses a high amount of tannic acid may develop black discoloration if it comes in contact with steel. Nail heads that are a black color are usually under the coating surface and will ultimately cause adhesion failure of the topcoat. Once exposed, the nail head will develop red rust.

Solution: Locate and eliminate the source of moisture. Replace nails with galvanized or other non-rusting nails. Rusty nails that cannot be removed must be sanded to shiny metal, countersunk, coated with a rust-preventive primer and then caulked. Repair moisture damage by sanding weathered wood to a fresh surface.

Recommendations: One coat A-100 Alkyd Exterior Wood Primer

(Spot-prime exposed wood and caulked nail heads.)

Two coats Exterior Latex House and Trim Paint

Cause: Many different water-soluble materials are used in the manufacture of latex emulsion paints. When these paints are applied during hot and humid periods and expected to dry during cool evenings, the painted surface will cool, allowing dew to form. This accumulated moisture on a paint surface whose curing is temporarily delayed will extract and concentrate different water-soluble materials from within the paint at the paint surface. As the water evaporates, a concentrated residue is left behind, causing staining, unsightly runs and gloss patterns.

Aluminum siding will react to temperature changes faster than solid wood siding because of the smaller amount of material involved. Consequently, aluminum siding will develop surfactant leaching quicker and more easily; however, all siding is prone to this problem under identical conditions.

Solution: Apply paint to all surfaces during climatic conditions that allow proper curing of the paint film. When "surfactant leaching" happens, flush with clean water immediately before the stains have sufficient time to set up or harden. Light scrubbing with a soft brush is acceptable. If stains cannot be removed in this manner, then repainting will be necessary during more favorable weather conditions.

Recommendations: One coat Exterior Latex House and Trim Paint

Cause: Red-colored woods contain a water soluble dye called tannin. Tannin is not soluble in most solvents. Application of latex topcoats directly to these red-colored woods may develop a red-colored stain on the finish coat. If the dry film is intact and discoloration occurs at a later date, then staining is being caused by water moisture within the board wall. This moisture will migrate and eventually carry staining substances from within the wood to the surface of the paint film.

Some cedar woods contain colored dyes such as tannin which is water soluble, and other colored extracts which are soluble in mineral spirits. In these instances, a primer that has discolored should be spot tested with a second coat of primer or a latex topcoat to determine which will successfully block future discoloration.

Solution: If dry film is intact and discoloration is occurring at a later date, then internal moisture is the culprit. The moisture source must be located and corrected. Remove stains by washing with a solution of equal parts alcohol and water. Allow to dry thoroughly.

New red-colored woods must be sealed with an undercoater that will function as a barrier coat, preventing staining of the topcoat. This undercoater can be either a solvent or latex primer, depending on severity of available tannin dyes in the wood.

Although the latex primer contains water, the product chemistry is designed to minimize surface discoloration by tannin bleed. Extreme cases of tannin bleed may require one or two coats of alkyd primer to prevent discoloration.

Recommendations: light-colored woods:

One coat A-100 Latex or Alkyd Exterior Wood Primer

Two coats Exterior Latex House and Trim Paint (Flat, Satin, or Gloss)

dark-colored woods:

One coat A-100 Alkyd or Latex Exterior Wood Primer followed by

Two coats Exterior Latex House and Trim Paint (Flat, Satin, or Gloss)

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