House Paint Primers
A paint primer has two basic functions: 1) To attain and maintain adhesion to the substrate.
2) To seal or uniform the substrate. Primers are also expected to contribute to the hiding of
a paint system.
By and large, solvent-thinned primer systems are used for solvent-thinned topcoats, and latex
primers for latex topcoats. Although this is the general rule, there are exceptions: Oil/Alkyd Primers
are still the most popular universal choice. They may be topcoated with either a latex or oil
based finish. Latex primers may also be topcoated with either latex or oil based topcoats.
Why two primers? Both have their own distinct advantages. the oil based primers are much better in
checking tannin bleeding on redwood, cedar and other high extractive type woods. Since these tannins
are water soluable, latex products have a hard time stopping this bleed in severe cases. Out latex
primers are specifically formulated with a blend of resins to help check tannin staining.
In areas that are in less than ideal condition (slight chalk, etc.), the oil based primer will
perform better than a latex primer. The same is also true in cool weather conditions.
A latex primer will perform better than an oil primer in areas where an internal moisture problem
exists. As with all latex, they "breathe" moisture vapor mich better than an oil based product.
Also, on woods that are dimensionally unstable, such as pine, latex primers take the wood stress
much better since they retain their flexability. Latex primers offer soap and water clean up.
Latex primers are excellent on pre-primed hardboard siding. They do not solubilize the wax in
hardboard as may be the case with a solvent based primer. This can result in an early peeling
failure with latex topcoats. This happens only on rare occasions.
Oil based and latex primers may be tinted to the approximate shade of topcoat. Not only does this
add to the hide of the primer, it also decreases the contrast of color between the primer and
topcoat. Regardless of primer, it is always a good practice to topcoat the primer with a week's time
for optimum adhesion.
Primer on Primers Surface Recommendations-
New wood prime with either stain-blocking latex or oil primer. Oil-base primers are better for
severe staining woods, such as redwood and red cedar.
Repaint primer is usually not required, unless surface preparation is not of a quality nature (
very slight chalk, bare wood).
Weathered wood or exposed wood should be thoroughly sanded. Dust off the surface and apply
latex or oil primer.
Masonry should only be primed with a latex primer only. Do not use oil based. If using a latex
topcoat, the topcoat can be used as a self-primer. If old, powdery and eroded, a masonry
conditioner should be applied as an initial prep.
Aluminum, Galvanized - When painting with latex, the surface should be weathered, Non-Ferrous Metals then
solvent-cleaned and/or etched. If metal has oxided, apply latex or galvanized metal primer.
Avoid alkyd topcoats on galvanized surfaces.
Ferrous Metals - For best performance, apply corrosion resistant metal iron and steel primer.
In less aggressive areas, a corrosion resistant latex primer would suffice.
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