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Exterior paint problems and how to fix them


Author: NJR Steel
Article Views:7045
Categories: Construction, Renovation, Paint, DIY

Alligatoring

The problem: Patterned cracking in the surface of the paint film resembling the regular scales of an alligator.

Possible causes:

  • Application of an extremely hard, rigid coating, like an alkyd enamel, over a more flexible coating, like a latex primer.
  • Application of a top coat before the undercoat is dry.
  • Natural aging of oil-based paints as temperatures fluctuate. The constant expansion and contraction results in a loss of paint film elasticity.

The solution:

  • Old paint should be completely removed by scraping and sanding the surface; a heat gun can be used to speed work on large surfaces, but take care to avoid igniting paint or substrate.
  • The surface should be primed with high quality latex or oil-based primer, then painted with a top quality exterior latex paint.

Blistering

The problem: Bubbles resulting from localised loss of adhesion, and lifting of the paint film from the underlying surface.

Possible causes:

  • Painting a warm surface in direct sunlight.
  • Application of oil-based or alkyd paint over a damp or wet surface.
  • Moisture escaping through the exterior walls (less likely with latex paint than with oil-based or alkyd paint).
  • Exposure of latex paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.

The solution:

  • If blisters go down to the substrate: try to remove the source of moisture. Repair loose caulking; consider installing vents or exhaust fans. Remove blisters (see below).
  • If blisters do not go all the way down to the substrate: remove them by scraping, then sanding, prime bare wood and repaint with a quality latex exterior paint.

Chalking

The problem: Formation of fine powder on the surface of the paint film during weathering which can cause color fading. Although some degree
of chalking is a normal, desirable way for a paint film to wear, excessive film erosion can result from heavy chalking.

Possible causes:

  • Use of a low-grade, highly pigmented paint.
  • Use of an interior paint for an outdoor application.

The solution:

  • First, remove as much of the chalk residue as possible, scrubbing with a stiff bristle brush (or wire brush on masonry) and then rinse thoroughly; or use power washing equipment.
  • Check for any remaining chalk by running a hand over the surface after it dries. If noticeable chalk is still present, apply a quality oil-based or acrylic latex primer (or comparable sealer for masonry), then repaint with a quality exterior coating; if little or no chalk remains and the old paint is sound, no priming is necessary.

Cracking / flaking

The problem: The splitting of a dry paint film through at least one coat, which will lead to complete failure of the paint. Early on, the problem appears as hairline cracks; later, flaking of paint chips occurs.

Possible causes:

  • Use of a lower quality that has inadequate adhesion and flexibility.
  • Over-thinning the paint or spreading it too thin.Poor surface preparation, especially when the paint is applied to bare wood without priming.
  • Painting under cool or windy conditions that make latex paint dry too fast.

The solution:

  • It may be possible to correct cracking that does not go down to the substrate by removing the loose or flaking paint with a scraper or wire brush, sanding to feather the edges, priming any bare spots and repainting.
  • If the cracking goes down to the substrate remove all of the paint by scraping, sanding and/or use of a heat gun; then prime and repaint with a quality exterior latex paint.

Efflorescence / mottling

The problem: Crusty, white salt deposits, leached from mortar or masonry as water passes through it.

Possible causes:

  • Failure to adequately prepare surface by removing all previous efflorescence.
  • Excess moisture escaping through the exterior masonry walls from behind.

The solution:

  • If excess moisture is the cause, eliminate the source by repairing the roof, cleaning out gutters and downspouts, and sealing any cracks in the masonry with a high quality, water-based all-acrylic or siliconised acrylic caulk. If moist air is originating inside the building, consider installing vents or exhaust fans, especially in kitchen, bathroom and laundry areas.
  • Remove the efflorescence and all other loose material with a wire brush, power brush or power washer; then thoroughly rinse the surface.
  • Apply a quality water-based or solvent-based masonry sealer or primer, and allow it to dry completely; then apply a coat of top quality exterior house paint, masonry paint or elastomeric wall coating.

Fading / poor colour retention

The problem: Premature and/or excessive lightening of the paint color, which often occurs on surfaces with sunny southern exposure. Fading/poor color retention can also be a result of chalking of the coating.

Possible causes:

  • Use of an interior grade of paint for an outdoor application.
  • Use of a lower quality paint, leading to rapid degradation (chalking) of the paint film.
  • Use of a paint color that is particularly vulnerable to UV radiation (most notably certain bright reds, blues, and yellows).
  • Tinting a white paint not intended for tinting, or over-tinting a light or medium paint base.

The solution:

  • When fading/poor color retention is a result of chalking, it is necessary to remove as much of the chalk as possible (see Chalking).
  • In repainting, be sure to use a quality exterior house paint in colours recommended for exterior use.

Paint incompatibility

The problem: Loss of adhesion where many old coats of alkyd or oil-based paint receive a latex top coat.

Possible causes:

  • Use of water-based latex paint over more than three or four coats of old alkyd or oil-based paint may cause the old paint to “lift off” the substrate.

The solution:

  • Repaint using another coat of alkyd or oil-based paint.
  • Or, completely remove the existing paint and prepare the surface - cleaning, sanding and spot-priming where necessary - before repainting with a
  • top quality latex exterior paint.

Peeling

The problem: Loss of paint due to poor adhesion. Where there is a primer and top coat, or multiple coats of paint, peeling may involve some or all coats.

Possible causes:

  • Seepage of moisture through uncaulked joints.
  • Worn caulk or leaks in roof or walls.
  • Excess moisture escaping through the exterior walls (more likely if paint is oil-based).
  • Inadequate surface preparation.
  • Use of lower quality paint.
  • Applying an oil-based paint over a wet surface.
  • Earlier blistering of paint (see Blistering).

The solution:

  • Try to identify and eliminate source of moisture.
  • Prepare surface by removing all loose paint with scraper or stiff wire brush, sand rough edges, and apply appropriate primer.
  • Repaint with a top quality acrylic latex exterior paint for best adhesion and water resistance.

Poor alkali resistance

The problem: Color loss and overall deterioration of paint film on fresh masonry.

Possible causes:

  • Oil-based paint or vinyl acrylic latex paint was applied to new masonry that has not cured for a full year. Fresh masonry is likely to contain lime which is very alkaline. Until the lime has a chance to react with carbon dioxide from the air, the alkalinity of the masonry remains so high that it can attack the integrity of the paint film.

The solution:

  • Allow masonry surfaces to cure for at least 30 days, and ideally for a full year, before painting.
  • If this is not possible, the painter should apply a quality, alkali-resistance sealer or latex primer, followed by a top quality 100 percent acrylic latex exterior paint. The acrylic binder in these paints resists alkali attack.

Poor galvanised metal adhesion

The problem: Paint that has lost its adhesion to a galvanized metal substrate.

Possible causes:

  • Improper surface preparation, such as inadequate rust removal.
  • Failure to apply a primer before application of an oil-based or vinyl latex paint.
  • Failure to sand baked-on enamel finishes or glossy surfaces before painting.

The solution:

  • Any rust on the metal should be removed with a wire brush. Then, an acrylic latex corrosion-inhibitive primer should be applied (one coat is usually sufficient).
  • Previously painted galvanized metal that is completely rust-free can be painted without applying a primer.
  • A latex metal primer should be applied to unpainted galvanized metal, followed by a top quality exterior acrylic latex paint.

Sufactant leaching

The problem: Concentration of water-soluble ingredients on latex paint, creating a blotchy, sometimes glossy appearance, often with a tan or brownish cast. More likely with tinted paints than with white or factory-colored paints.

Possible causes:

Painting in cool, humid conditions or just before they occur. The longer drying time allows the paint’s water-soluble ingredients - which would normally evaporate, or be leached out by rain or dew - to rise to the surface before paint thoroughly dries. Mist, dew or other moisture drying on the painted surface shortly after it has dried.

The solution:

  • Avoid painting in the late afternoon if cool, damp conditions are expected in the evening or overnight. If the problem occurs in the first day or so after the paint is applied, the water-soluble material can sometimes be rinsed off rather easily.
  • Fortunately, even more stubborn cases will generally weather off in a month or so.
  • Sufactant leaching should not affect the ultimate durability of the coating.

Wrinkling

The problem: A rough, crinkled paint surface occurring when paint forms a “skin.”

Possible causes:

  • Paint applied too thickly (more likely when using alkyd or oil-based paints).
  • Painting a hot surface or in very hot weather.
  • Exposure of uncured paint to rain, dew, fog or high humidity levels.
  • Applying top coat of paint to insufficiently dried first coat. ¥ Painting over contaminated surface (e.g., dirt or wax).

The solution:

  • Scrape or sand substrate to remove wrinkled coating.
  • Repaint, applying an even coat of top quality exterior paint. Make sure the first coat or primer is dry before applying the top coat.
  • Apply paints at the manufacturer’s recommended spread rate (two coats at the recommended spread rate are better than one thick coat).
  • When painting during extremely hot, cool or damp weather, allow extra time for the paint to dry completely.

Source: Paint Quality Institute


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