Last week we talked about the first of our seven common questions about exterior painting. Our next question is about primers.
Prime or not to Prime? Should I apply a full coat of primer when doing exterior repainting?
An example of Black Mildew on Exterior Surface caused because of oil based primer under the paint.
Appropriate primer should be applied to new/bare surfaces or chalky paint to seal the surface and provide a proper base for the finish coats. Using primer on the problem free paintedsurface is just unnecessary! Especially oil primers for an already painted siding or trim is a BIG NO!
If the entire surface is peeling and must be sanded down to bare wood, then a coat of primer is necessary.
However, It is best to use a proper 100% Acrylic primer if possible with the exception of the certain bleeding type of wood. If not, spot priming the areas sanded to bare wood is sufficient.
Why not oil?
Mildew built-up as a result of oil primer used under the finish coat.
Many homeowners in Westchester County New York tell me the other painters they have met had recommended a full coat of oil primer for the exterior of their houses before applying a 100% Acrylic paint or stain on the top of it. That does not necessarily give you a better exterior paint job.
Oil primers are food for mildew, especially in the humid North East environment and help black mildew thrive!
Organic components of oil based primers such as linseed oil act as food for mildew! Have you noticed black dots of mildew on white exterior trim or siding? I often spot those sections of the trim that was spot primed with an oil based primer by noticing the presence of black mildew. This can be an eye sore on the white fence and white spindles around the deck, not to mention the trim around doors and windows.
Many of the paint manufactures 100% Acrylic solid stains do not require a primer and can be applied directly to the surface. We particularly like those products because of the fact they minimize mildew growth on the exterior of the house or deck.
We hope this answered some of your questions about exterior repainting!
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