MRCB paints & papers: Problem Solver

• Painting a warm surface in direct sunlight.
• Application of solvent-based paint over a damp or wet surface.
• Moisture escaping through the exterior walls (less likely with water-based paint than with solvent-based.
• Exposure of water-based paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.
• Multi coat blistering usually occurs when acrylic paints are applied over many layers of alkyd and acrylic paints; often when darker colours are used causing heat build up.

Solution:

• If blisters go down to the substrate: try to remove the source of moisture. Repair loose sealants; 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 water-based exterior paint.

Crocodiling:

Patterned cracking in the surface of the paint film resembling the regular scales of a crocodile.

Possible Causes:

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

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 substrates. The surface should be primed with high quality water-based or solvent-based primer, then painted with two coats of a top quality exterior water-based paint.

Chalking:

Formation of fine powder on the surface of the paint film during weathering which can cause colour 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.

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 solvent-based or acrylic water-based 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.

Chalk run-down:

The washing down of chalk from an excessively eroding paint onto another area below (a brick foundation, for example), ruining its appearance (see Chalking).

Possible Causes:

• Use of a lower quality, highly pigmented paint.
• Use of an interior paint for an outdoor application.

Solution:

• Remove as much of the chalk residue as possible(see Chalking). Scrub any stained areas with a stiff brush, using a detergent solution; rinse thoroughly. In cases of severe staining, an acid wash may be necessary. Either way, if the affected area dries to a different colour, consider painting it with a quality water-based paint.

Cracking / flaking:

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 paint that has inadequate adhesion and flexibility.
• Overthinning the paint or spreading it too thin.
• Poor surface preparation, especially when the paint is applied to bare wood without priming.
• Painting under excessively cool or windy conditions that make water-based paint dry too fast.

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 water-based paint.

Dirt pickup:

Accumulation of dirt, dust particles and/or other debris on the paint film; may resemble fungus or algae.

Possible Causes:

• Use of a low quality paint, especially lower grades of satin types.
• Air pollution, car exhaust fumes and flying dust collecting on houses.

Solution:

• Wash off all surface dirt before priming and painting, using a scrub brush and detergent solution, followed by a thorough rinse. Heavier dirt accumulations may require the use of a power washer. While dirt pickup can’t be eliminated entirely, top quality exterior water-based paints typically offer superior dirt pickup resistance and washability. Also, higher gloss paints are more resistant to dirt pickup than matt paints, which are more porous and can more easily entrap dirt.
• Regular wash down will give longevity to the paint film.

Efflorescence / mottling:

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.

Solution:

• If excess moisture is the cause, eliminate the source by repairing the roof, cleaning out gutters and drainpipes, and sealing any cracks in the masonry with a high quality, water-based all-acrylic or siliconised acrylic sealant. 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:

Premature and/or excessive lightening of the paint colour, which often occurs on surfaces with sunny south facing exposure. Fading/poor colour 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 colour that is particularly vulnerable to UV radiation (most notably certain bright reds, blues, and yellows).
• Tinting a white paint not intended for tinting, or overtinting a light or medium paint base.

Solution:

• When fading/poor colour 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.

Frosting:

A white, salt-like substance on the paint surface. Frosting can occur on any paint colour, but it is less noticeable on white paint or lighter tints. On masonry, it can be mistaken for efflorescence (see Efflorescence and Mottling).

Possible Causes:

• Forms mostly in protected areas (such as under eaves and on porch ceilings) that do not receive the cleansing action of rain, dew and other moisture.
• Use of dark-coloured paints that have been formulated with calcium carbonate extender.
• Application of a dark-coloured paint over a paint or primer containing calcium carbonate extender.

Solution:

• Frosting, though not common, can be a stubborn problem. It often cannot be washed off readily. Moreover, the condition can recur even as a bleed-through when a new top coat is applied. In extreme cases, it can interfere with adhesion. The best remedy is to remove the frosting by wire brushing masonry or sanding wood surfaces; rinse, then apply a solvent-based primer before adding a coat of high quality exterior paint.

Fungal / algal contamination:

Black, grey or brown areas of fungal or algal growth on the surface of paint or sealant.

Possible Causes:

• Fungus forms most often on areas that tend to be damp, and receive little or no direct sunlight (north facing walls and the underside of eaves are particularly vulnerable). Algae forms in the presence of light and moist environments.
• Use of a lower quality paint, which may have an insufficient amount of fungicide or algicide.
• Failure to prime bare wood before painting.
• Painting over a substrate or coating on which fungus or algae has not been removed.

Solution:

• Test to distinguish fungus or algae from dirt by applying a few drops of household bleach to the discoloured area; if it disappears, it is probably fungus or algae. Treat the contamination with either a fungicidal wash or by applying a mixture of water and bleach, 3:1, and leave on for 20 minutes, applying more as it dries. Wear goggles and rubber gloves. Then scrub and rinse the area. Apply an exterior water-based primer, then a premium exterior water-based paint in matt, silk, satin or gloss finish, depending on the desired appearance.

Lapping:

Appearance of a denser colour or higher gloss where wet and dry layers overlap during paint application.

Possible Causes:

• Failure to maintain a “wet edge” when applying paint.

Solution:

• Maintain a wet edge when painting by applying paint toward the unpainted area and then back into the just painted surface. This technique (brushing from “wet to dry” rather than vice versa) will produce a smooth uniform appearance. It is also wise to minimise the area being painted, and plan for interruptions at a natural break, such as a window, door or corner (especially important when applying stain to bare wood). Solvent-based paints generally have superior wet edge properties.

Paint incompatibility:

Loss of adhesion where many old coats of solvent-based paint receive a water-based top coat.

Possible Causes:

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

Solution:

• Repaint using another coat of solvent-based paint; although it is preferable to remove the existing paint and prepare the surface - cleaning, sanding and spot-priming where necessary - before repainting with a top quality water-based exterior paint.

Peeling:

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 unsealed joints, worn sealant or leaks in roof or walls.
• Excess moisture escaping through the exterior walls (more likely if paint is solvent-based).
• Inadequate surface preparation.
• Use of lower quality paint.
• Applying a solvent-based paint over a wet surface.
• Earlier blistering of paint (see Blistering).

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 water-based exterior paint for best adhesion and water resistance.

Poor alkali resistance:

Colour loss and overall deterioration of paint film on fresh masonry.

Possible Causes:

• Solvent-based paint or water-based paint (vinyl acetate copolymers type) 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.

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 water-based primer, followed by a top quality pure acrylic exterior water-based paint. The acrylic binder in these paints resists alkali attack.

Poor galvanised metal adhesion:

Paint that has lost its adhesion to a galvanised metal substrate.

Possible Causes:

• Improper surface preparation, such as inadequate rust removal.
• Failure to apply a primer before application of a solvent-based or water-based paint (vinyl acetate copolymer type).
• Failure to sand baked-on enamel finishes or glossy surfaces before painting.

Solution:

• Any rust on the metal should be removed with a wire brush; then, an acrylic water-based corrosion-inhibitive primer should be applied (one coat is usually sufficient). Previously painted galvanised metal that is completely rust-free can be painted without applying a primer. New galvanised iron should be allowed to weather for at least 6 months or washed down with turpentine to remove any oil. A water-based metal primer should be applied to unpainted galvanised metal, followed by a top quality exterior acrylic water-based paint.

Poor gloss retention:

Deterioration of the paint film, resulting in excessive or rapid loss of lustre of the top coat.

Possible Causes:

• Use of an interior paint outdoors.
• Use of a lower quality paint.
• Use of a gloss solvent-based paint in areas of direct sunlight.

Solution:

• Direct sunshine can degrade the binder and pigment of a paint, causing it to chalk and lose its gloss. While all types of paint will lose some degree of lustre over time, lower quality paints will generally lose gloss much earlier than better grades. The binder in top quality acrylic water-based paints is especially resistance to UV radiation, while solvent-based paints actually absorb the radiation, causing the binders to break down. Surface preparation for a coating showing poor gloss retention should be similar to that used for chalking surfaces (see Chalking).

Surfactant leaching:

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

Solution:

• If possible, 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. Surfactant leaching should not affect the ultimate durability of the coating.

Tannin staining:

Brownish or tan discoloration on the paint surface due to migration of tannins from the substrate through the paint film. Typically occurs on “staining woods,” such as redwood, cedar and mahogany, or over painted knots in certain other wood species, such as pine.

Possible Causes:

• Failure to adequately prime and seal the surface before applying the paint.
• Use of a primer that is not sufficiently stain-resistant.
• Excess moisture escaping through the exterior walls, which can carry the stain to the paint surface.

Solution:

• Correct any possible sources of excess moisture (see Efflorescence and Mottling). After thoroughly cleaning the surface, apply a high quality stain-resistant solvent-based or acrylic water-based primer. Solvent-based stain-resistant primers are the best type to use on severely staining boards. In extreme cases, a second coat of primer can be applied after the first has died thoroughly. Finish with a top quality water-based paint.

Wax bleed:

Stains that come from waxy substance in the reconstituted wood products such as chipboard or MDF. When the substrate is painted, these staining substances bleed through the paint; they can even bleed through some ordinary primers, possibly causing dirt pickup, fungal/algal contamination and/or poor paint adhesion (see Dirt Pickup and Fungal/Algal Contamination.

Possible Causes:

• Failure to apply a proper primer to hardboard before applying the top coat.

Solution:

• We recommend a quality water-based acrylic primer followed by two coats of quality acrylic paint.

Wrinkling:

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

Possible Causes:

• Paint applied too thickly (more likely when using solvent-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).

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.