The necessity of using a primer or sealer – and the type of product to use – varies from job to job. Here are some general guidelines for common applications.
Use either a quality acrylic latex or an oil-based primer. Oil-based stain-resistant primers are the best type to use on severely staining boards.
Previously Painted Wood
If bare wood is exposed, sand thoroughly, dust off, and apply a quality acrylic latex primer; if the old paint is very chalky, and all the chalk cannot be removed, use an oil-based primer. Otherwise, if the old paint is still adhering well, a primer may not be needed.
Use either a quality latex or oil-based primer. Apply immediately after surface preparation (thorough sanding and scraping).
Stucco, Concrete and Other Masonry
On new masonry, or older surfaces that are porous, apply a latex masonry sealer. Consider using a “block filler” if the surface is very rough, as with cinder block. These heavily pigmented products expand upon drying to fill the pores and provide a smooth, uniform finish. In a repaint situation, use sealer only where the old paint has been removed during surface preparation or through weathering.
To help prevent rust, apply two coats of a corrosion-resistant primer (acrylic latex or oil-based) when painting any metal that contains iron.
Aluminum or Galvanized Iron
When using a 100% acrylic latex paint, no primer is needed when painting aluminum or galvanized steel, as long as there are no signs of rust or oxidation; however, a primer should be applied if you plan to use an oil-based or vinyl water-based paint. When rust or oxidation is present, use an acrylic latex or oil-based corrosion-resistant primer after removing the rust or oxidation.
The core content for Painting Tips is provided by the courtesy of Dow Chemical as found on CaliforniaPaints.com.