If the paint on the exterior of the house has developed a dull, faded appearance and a chalky powder coats the house, one may want to know how to paint over the powder coat. To do this, it is necessary to know that powdering, or "chalking" as it is called, is normal as the paint weathers. When the paint grows old and needs to be re-painted, it is necessary to clean off this chalking in order to apply a new coat of paint. Then it can be primed and painted over so that future powdering is kept at a minimum.
What Is That Powder Coat?
If the paint on the house is old, the natural wear and tear from sunlight and weather exposure will normally cause a sound painting job to develop the powder coat that rubs off on your hand or a dark colored cloth. This powder coat is called "chalking" and is caused by the weathering of the resins binding the pigments in the paint wearing it off and releasing the pigments as a fine powder that is lighter in color than the original paint. This gives a dull, faded appearance to the paint. This is much preferable to peeling and cracking that would additionally occur with a lower quality paint job.
Cleaning the Powder Coat Off
To paint over the exterior of the house that has a powder coat, it is first necessary to clean the powder off. Chalking should be considered the same as dirt and dust, and the walls should be pressure washed. An exterior paint cleaner such as trisodium phosphate (TSP) or an environmentally-friendly TSP substitute should be dispensed with the pressure washer and the pressure should be kept at 1500-2000 pounds per square inch. Pressure wash until as much of the dirt and chalk is removed, then rinse with clean water until the cleaner is completely rinsed off, and the wall is allowed to dry. If necessary, the surface can be scrubbed with a brush and exterior paint cleaning solution to remove more of the powder. If the powdering persists, it may be necessary to hire a professional cleaning contractor to do the job. If the powder has run down onto the brick, the problem is more severe and requires the scrubbing and maybe even the professional cleaning.
Keeping Future Powdering at a Minimum
When the surface is completely clean as much as possible of all the chalking, the walls should be primed with a good quality latex primer and painted with a good quality exterior house paint. This will make the weathering process slower. Also, the higher the gloss of the painted surface, the slower the powdering process will occur. Paint with a higher quality binder will chalk slower than lower quality paints or paints with a high amount of pigment. Make sure the paint is not overly thinned or applied in too thin a coat to keep powdering from occurring too soon. Also, apply a primer that seals the surface adequately if it is porous. Also, you might consider a latex, water-based paint instead of an alkyd, oil-based paint as the oil-based paint tends to chalk faster than a good-quality latex paint.