Primers and Sealers Defined
Also see:Primers are special paints intended for bare surfaces. They are designed to bond to bare surfaces creating a sound foundation for a finish coat. Different kinds of materials require different kinds of primers. In addition, exterior and interior surfaces will require a primer appropriate to those conditions.
A sealer is a special primer intended to be absorbed by porous materials such as wood or masonry. Sealers can be clear or they may have a white pigment added. For a natural finish, wood and masonry sealers are usually clear, while sealers intended to go under a paint coat, will be pigmented.
A primer should be used on any bare surface as a foundation for finish paint. A sealer should be applied to guard against water penetration or to prevent stains from bleeding from a surface thru the paint top coat. For example, any painted surface that has been damaged by water should be sealed with a primer–sealer to block the stain before any repair and painting is done. Below is a list of the most common primers and sealers for household use.
Alkyd primer is used mainly for bare wood and metal. Alkyd has replaced linseed oil–based paints and primers because of its lower odor and comparable durability and finish.
Drywall primer is specifically made to prime new drywall. It is thinner and usually a little cheaper than standard latex primers and paints. Flat latex paint will also serve fine as a drywall primer and will make application easier when using the same paint to finish coat.
Enamel undercoat used mainly on trim molding for a good foundation for an enamel finish. Usually alkyd–based although latex is also available. Alkyd–based should always be used under an oil or alky–based enamel top coat.
Galvanized metal primer is used on bare galvanized metal. Because galvanized metal is a specially treated material, it requires a specially formulated primer. Priming galvanized metal with anything else will create a peeling paint problem. Galvanized metal primer may be hard to find in home stores but will be available at a paint store. Be sure to remove the oil coating on new galvanized metal before applying any paint. See Choosing Paint for more.
Latex primer interior primer used mainly on drywall, plaster and wood trim molding. It is also suitable for priming interior masonry. Use an exterior latex primer for exterior wood siding, trim and masonry.
Masonry sealer is clear and made especially for bare masonry. If the surface is to be painted, a latex primer will also work but for a natural finish use the clear sealer. Allow at least 6 months for new masonry to cure before priming or sealing.
Rust inhibiting primers are for rusted metal surfaces. These are usually red in color and contain red iron oxide pigment. Stopping rust formation after it has started is hard to do, it will sometimes be impossible. Before apply a rust inhibiting primer, first remove all loose rusted material. Treat the area with naval jelly and then apply a coat of rust inhibiting primer. See Stopping Rust for more.
Shellac–Based Primer–Sealer is used to block stains and to prime and seal surfaces before painting. This product dries very quickly and can be top coated in about an hour. It cleans–up with mineral spirits. Because the solids settle out quickly make sure to shake the can or stir the primer well before using it. Avoid breathing the harsh fumes from this primer. Provide plenty of ventilation and wear a painter's respirator when using this product inside on large surfaces.
Water–Based Sealer Water–based sealers are generally a poor choice for most sealing requirements. However, they are better for sealing the tannin in redwood. These stains bleed thru alkyd and shellac–based primer–sealers.
