Different exterior surfaces require different types of paint and sometimes primer. Generally, use primer whenever paints layered over one another may be incompatible (acrylic- over oil-based paint, for example), when the underlying surface may be porous (such as with bare wood), or when there is already a layer of existing paint that has fallen into disrepair (be sure to prepare the painted surface following the directions in Preparing Exterior Siding for Painting).

If painting over a wood surface, always consider the effects of mold and mildew over time. Mold and mildew can thrive on the minerals and oil in paint, resulting in a dirty appearance and even making their way beneath the paint to the wood below. For this reason, it is prudent to consider the mildew-resistance of the paint you choose. Exterior paints available at hardware stores now include fungicides; ask your local retailer about which varieties offer the most protection.

Below are paint recommendations for the various types of exterior surfaces:

Bare wood
Apply either oil- or latex-based primer, depending on the paint you decide to use. Use oil-base or stain-blocking latex primer on wood with lots of knots or with cedar or redwood, which have oils that can bleed through your paint job. Acrylic latex paint will resist mildew and cracks and retain color better than alkyd varieties, although both types can be used.

Painted wood
Prime surface if existing paint job is unsound or you are applying latex paint over an alkyd-based paint, using a latex- or oil-based primer suitable for pre-painted wood surfaces. Use acrylic latex paint in a finish of your choice—eggshell finishes are easier to maintain then flat finishes. (You may choose an oil-base paint if the existing paint is also alkyd.)

Chalky or poor wood
With this type of wood, it may be difficult for a new layer of latex paint to adhere—consider oil-based paint for this application.

Rough wood siding
Semitransparent alkyd stains or water-based stains with alkyd resins will saturate rough wood fibers and are less apt to peel than other paint options.

Hardboard siding
Prime the surface with an exterior latex primer (even if your hardboard comes pre-primed, this is recommended). Use two coats of acrylic latex paint. Any finish may be used, but satin finishes work best because they are not as susceptible to wax bleed as flat paints. Take care to prime and paint all cut edges.

Stucco and concrete
Prime the surface, using an acrylic latex paint suitable for masonry or stucco. Use two coats of acrylic latex paint, latex masonry paint, or acrylic elastomeric wall covering.

Vinyl siding
Primer is unnecessary, although be sure to remove all mold, mildew, and dirt when preparing the surface. Apply two coats of acrylic latex paint in a flat or satin finish; it is best to spray paint onto vinyl. Never paint on a shade darker than the vinyl siding’s original color; the darker under-layer may absorb heat from the sun, causing your siding to warp.

Metal siding
No primer is needed for aluminum. For steel, use two coats of a latex- or oil-based primer suitable for metal to prevent corrosion. Apply two coats of acrylic latex paint in your desired finish.