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Dealing with Mold and Mildew Before you Paint

Deal with mildew

A fresh coat of paint will certainly make the home look new and clean, but it will not help overcome the most common cause of discoloration: mildew.

Mildew is parasite fungus that often appears as a dark color, such as black, green or brown and is rather fuzzy as well. Its body can digest right through painted surfaces and destroys the integrity of the paint itself. Mildew can also cause the underlying wood to rot and even cause masonry to crumble. Continue Reading →

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Wax Bleed

Painted hardboard can sometimes be discolored by “wax bleed,” named for the wax that is used during manufacturing to make hardboard more water-resistant. The wax can migrate to the surface, where it can change the wood’s appearance.
What Causes It?Wax bleeding is most often caused by:
Dark paints, which show discoloration more readily than lighter paints due to their tendency to absorb heat.
Areas without adequate coats, which are more likely to show staining.
Paints with low levels of binder, which are more likely to allow wax to migrate from hardboard.
Direct sunlight and heat.
How to Solve ItTo correct discoloration caused by wax bleeding, it is first necessary to figure out whether wax bleeding is indeed occurring. Do this by:
Placing a few drops of household bleach on the discolored area. If no whitening or bleaching occurs, the stain is probably wax.
Placing water droplets on both normal and discolored areas. If the water beads up and runs off, it is likely due to wax bleeding.
If the surface wax is light, use a detergent solution to clean any discolored areas. With severe cases of wax bleeding, clean the surface completely by wiping it with a solvent such as mineral spirits. Change your rags frequently as you clean, and allow the surface to dry thoroughly before painting.
Note: Images provided by The Rohm & Hass Paint Quality Institute

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Vinyl Siding Warps

Vinyl siding panels that have been repainted sometimes warp or buckle.
What Causes It?The most likely cause is that the vinyl siding was repainted with a darker color paint than the original color. Dark paint tends to absorb the heat of the sun, transferring it to the substrate. When vinyl siding expands dramatically, it is not able to contract to its original dimensions.
How to Solve ItPaint vinyl siding in a shade no darker than the original. Whites, off-whites, pastels, and other very light colors are good choices. Top-quality acrylic latex paint is the best type of paint to use on vinyl siding, because the superior flexibility of the paint film enables it to withstand the stress of expansion and contraction cycles caused by outdoor temperature changes.
Siding that has warped or buckled should be assessed by a siding or home repair contractor to determine the best remedy. The siding may have to be replaced.

Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Tannin Staining



Painting over red cedar, cypress, and redwood can lead to tannin staining.
What Causes It?Stains from the tannins in these woods are caused by a combination of moisture and insufficient sealing. Moisture can carry tannins contained in the wood through paint on the surface, and are likely to be visible especially with light or medium colors.
How to Solve It – Unpainted WoodIf your wood becomes stained when you are applying paint, use two coats of primer before you apply your topcoat. Be sure to wait 24 hours between coats after applying the first primer coat.
If stains occur, prime the stained spot again and allow it to dry. Then apply the finish coat. In some cases, it is best to allow new wood to weather for several weeks before painting.
How to Solve It – Painted WoodWash stained areas with a mixture of denatured alcohol and water. You can also use wood bleach (oxalic acid).Rinse all treated areas well and let them dry thoroughly, and then apply one coat of your selected primer and topcoat.
Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Poor Gloss Retention

Poor gloss retention is the deterioration of the paint film, resulting in excessive or rapid loss of luster of the topcoat.
What Causes It?The paint film may deteriorate if an interior paint has been used outdoors or a lower-quality paint has been replied.
Using a gloss alkyd or oil-based paint in areas of direct sunlight may also cause poor gloss retention.
How to Solve ItDirect sunshine can degrade the binder and pigment of paint, causing it to chalk and lose its gloss. While all types of paint will lose some degree of luster over time, lower- quality paints will generally lose gloss much earlier than better grades.
The binder in top-quality acrylic latex paint is especially resistant 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 in chalking surfaces (see Chalking).

Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Poor Galvanized Metal Adhesion

Paint can lose its adhesion to a galvanized metal substrate. 
What Causes It?
Poor galvanized metal adhesion can occur:
When a surface has not been properly prepared.
When a primer has not been applied before an oil-based paint is used.
When baked-on enamel finishes or glossy surfaces have not been sanded before painting.
How to Solve ItFirst, use a wire brush to remove any rust on your metal surface. Then, apply a corrosion-resistant acrylic latex primer—one coat is usually sufficient.
With galvanized metal that is new or has been painted before and is rust-free, clean the surface to remove all fabricating oils.
Then, paint it with a top-quality acrylic latex paint without applying a primer.
With unpainted galvanized metal, however, always use a metal primer before you apply an oil-based or vinyl latex topcoat.
Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Alkali Resistance

Poor alkali resistance can cause color loss and overall deterioration of paint film on fresh masonry.
What Causes It?Applying oil-based paint or vinyl acrylic latex paint to new masonry that has not cured for a full year may lead to poor alkali resistance.
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 that it can attack the integrity of the paint film.
How to Solve ItAllow masonry surfaces to cure for at least 30 days, and ideally for a full year, before painting. If this is not possible, you should apply a quality, alkali-resistant sealer, or latex primer, followed by a top-quality 100% acrylic latex exterior paint.
The acrylic binder in these paints resists alkali attack.

Note: Images provided by The Rohm & Hass Paint Quality Institute

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Paint Incompatibility



Paint incompatibility can cause loss of adhesion where many old coats of alkyd or oil-based paint receive a latex topcoat. 
What Causes It?When water-based latex is painted over more than three or four coats of old alkyd or oil-based paint, the old paint may “lift off” the substrate.
How to Solve ItRepaint the surface using another coat of alkyd or oil-based paint. Alternatively, you can 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.

Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Nailhead Rusting



Nailhead rusting appears as reddish-brown stains on the paint surface.
What Causes It?This problem occurs when non-galvanized iron nails that have not been countersunk and filled over begin to rust, and the rust bleeds through to the topcoat.
Sometimes this condition is caused by galvanized nailheads that have been sanded or have weathered excessively, and they then begin to rust.
How to Solve ItWhen painting new exterior construction where non-galvanized nails have been used, you should first countersink the nailheads, then caulk over them with a top-quality, water-based all-acrylic or a siliconized acrylic caulk. Each nailhead area should be spot primed, then painted with a quality latex coating.
When repainting exteriors where nailhead rusting has occurred, wash off the rust stains, sand the nailheads, then follow the same surface preparation procedures as for new construction.
Note: Images provided by The Rohm & Hass Paint Quality Institute.

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Mildew



Mildew forms most often on damp areas that receive little or no direct sunlight. It can also form on walls with a northerly exposure, and on the undersides of eaves.
What Causes It?Mildew is most often caused by:
Using lower quality paints, which may have insufficient amounts of mildewcide.
Failing to prime bare wood before painting.
Painting over a substrate or coating from which mildew has not been removed.
How to Solve ItYou can test for mildew by applying a few drops of household bleach to the area you suspect contains mildew. If it disappears, mildew is likely present.
To remove mildew from a surface, scrub it with a mixture of household bleach and water—one part bleach, three parts water. Be sure to wear rubber gloves and eye protection when you do so.
You can also use power washing to remove surface mildew, though you must still use a bleach solution to completely kill the mildew spores.
After cleaning a surface, rinse it thoroughly and apply primer to any bare wood. Then, apply one or two coats of a Benjamin Moore exterior paint, which contains the proper amount of mildewcide.
Note: images provided by The Rohm & Hass Paint Quality Institute