DIY Know How
Exterior Problem Solver
Most exterior paint problems and painting mistakes can be solved. Here you will find solutions for the most common exterior paint problems.
Bubbles resulting from localized loss of adhesion, and lifting of the paint film from the underlying surface.
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 acrylic paint than with oil-based or alkyd paint).
Exposure of acrylic paint film to dew, high humidity or rain shortly after paint has dried, especially if there was inadequate surface preparation.
If blisters go down to the substrate: try to remove the source of moisture. Repair loose sealant; 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 acrylic exterior paint.
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.
Use of a low-grade, highly pigmented paint. Use of an interior paint for an outdoor application.
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 acrylic 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 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.
Poor surface preparation, especially when the paint is applied to bare wood without priming. Painting under cool or windy conditions that make acrylic paint dry too fast.Use of a lower quality paint that has inadequate adhesion and flexibility. Overthinning the paint or spreading it too thin.
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 acrylic paint.
Patterned cracking in the surface of the paint film resembling the regular scales of a crocodile.
Application of an extremely hard, rigid coating, like an alkyd enamel, over a more flexible coating, like an acrylic 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.
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 acrylic or oil-based primer, then painted with a top quality exterior acrylic paint.
FADING / POOR COLOUR RETENTION
Premature and/or excessive lightening of the paint colour, which often occurs on surfaces with sunny southern exposure. Fading/poor colour retention can also be a result of chalking of the coating.
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.
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.
EFFLORESCENCE / MOTTLING
Crusty, white salt deposits, leached from mortar or masonry as water passes through it.
Failure to adequately prepare surface by removing all previous efflorescence.
Excess moisture escaping through the exterior masonry walls from behind.
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 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.
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).
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.
Frosting 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 wirebrushing masonry or sanding wood surfaces; rinse, then apply an alkyd-based primer before adding a coat of high quality exterior paint.
Appearance of a denser colour or ligher gloss where wet and dry layers overlap during paint application.
Failure to maintain a "wet edge" when applying paint.
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). Alkyd paints generally have superior wet edge properties.
Black, grey or brown areas of fungus growth on the surface of paint or sealant.
Forms most often on areas that tend to be damp, and receive little or no direct sunlight (walls facing south (if located in the southern hemisphere), and the underside of eaves are particularly vulnerable).
Use of a lower quality paint, which may have an insufficient amount of mildewcide.
Failure to prime bare wood before painting.
Painting over a substrate or coating on which mildew has not been removed.
Test to distinguish mildew from dirt by applying a few drops of household bleach to the discoloured area; if it disappears, it is probably mildew. Treat the mildew 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 acrylic primer, then a top-of- the-line exterior top coat acrylic paint, of a premium self-priming acrylic top coat in low sheen or gloss finish, depending on the desired appearance.
Reddish-brown stains and spots on the paint surface.
Non-galvanised iron nails have begun to rust, causing bleed-through to the top coat.
Non-galvanised iron nails have not been countersunk and filled over.
Galvanised nailheads have begun to rust after sanding or excessive weathering.
When painting new exterior construction where non-galvanised nails have been used, it is advisable to first countersink the nailheads, then sealant them with a top quality, waterbased all-acrylic or siliconized acrylic sealant. Each nailhead area should be spot primed, then painted with a quality acrylic coating. When repainting exteriors where nailhead rusting has occurred, wash off rust stains, sand the nailheads, then follow the same surface preparation procedures as for new construction.
Loss of adhesion where many old coats of alkyd or oil-based paint receive an acrylic top coat.
Use of water-based acrylic 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.
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 acrylic exterior paint.
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.
Excess moisture escaping through the exterior walls (more likely if paint is oil-based). Moist or damp walls due to unsealanted joints, worn sealant or leaks in roof or walls. Inadequate surface preparation. Use of lower quality paint. Applying an oil-based paint over a wet surface. Earlier blistering of paint (see Blistering).
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 exterior paint for best adhesion and water resistance.
POOR ALKALI RESISTANCE
Colour loss and overall deterioration of paint film on fresh masonry.
Oil-based paint or vinyl acrylic acrylic 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.
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 acrylic primer, followed by a top quality 100 percent acrylic exterior 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.
Improper surface preparation, such as inadequate rust removal.
Failure to apply a primer before application of an oil-based or vinyl acrylic paint.
Failure to sand baked-on enamel finishes or glossy surfaces before painting.
Any rust on the metal should be removed with a wire brush; then, an acrylic 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. An acrylic metal primer should be applied to unpainted galvanised metal, followed by a top quality exterior acrylic paint.
POOR GLOSS RETENTION
Deterioration of the paint film, resulting in execessive or rapid loss of luster of the top coat.
Use of an interior paint outdoors.
Use of a lower quality paint.
Use of a gloss alkyd or oil-based paint in areas of direct sunlight.
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 paints is especially resistance to UV radiation, while oil and alkyd binders 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).
Concentration of water-soluble ingredients on acrylic 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.
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.
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.
Brownish or tan discolouration 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.
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.
Correct any possible sources of excess moisture (see Efflorescence and Mottling). After thoroughly cleaning the surface, apply a high quality stain- resistant oil-based or acrylic primer. Oil-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 dried thoroughly. Finish with a top quality acrylic paint.
Warping or buckling of vinyl cladding panels that have been repainted.
Most likely cause is that vinyl cladding was painted with a darker colour paint than the original colour. Dark paint tends to absorb the heat of the sun, transferring it to the substrate. When vinyl cladding expands dramatically, it is not able to contract to its original dimensions.
Paint vinyl cladding in a shade no darker than the original. Whites, off-whites, pastels and other very light colours are good choices. Top quality acrylic paint is the best type of paint to use on vinyl cladding, because the superior flexibility of the paint film enables it to withstand the stress of expansion and contraction cycles cause by outdoor temperature changes.
Cladding that has warped or buckled should be assessed by a cladding or home repaint contractor to determine the best remedy. The cladding may have to be replaced.
Stains that come from waxy substance in the reconstituted wood products used to make hardboard cladding. When the substrate is painted, these staining substances bleed through the paint; they can even bleed through some ordinary primers, possibly causing dirt pickup, mildew and/or poor paint adhesion (see Dirt Pickup and Mildew).
Failure to apply a proper primer to hardboard before applying the top coat. Allowing hardboard cladding to weather before being painted.
To treat or prevent, apply a quality exterior acrylic primer; follow with a coat of high quality exterior acrylic paint. The American Hardboard Association recommends two coats of top quality acrylic exterior house paint for best results. Some hardboard grades have adequate factory primer and need only a quality paint applied. Low quality, highly pigmented flat paints are more prone to wax bleed than are higher quality paints.
A rough, crinkled paint surface occurring when paint forms a "skin."
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).
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.
Kindly supplied by Rohm and Haas - Paint Quality Institute