Q: I’ve seen a few concrete porches with stucco exteriors being rebuilt where I live in the San Francisco Bay Area. Can you discuss their construction and what goes bad requiring their repair? I have a concrete porch that is going to need a makeover soon. Are they built with a wooden frame with concrete poured over the wood? Also, the paint is blistering on my steps. How can I redo this so it won’t happen again?
A: There are tens of thousands of stucco bungalows in the Bay Area. Most of them were built in the 1930s and early 1940s. Virtually all of the porches were constructed with concrete decks.
“Concrete porch” is a misnomer. Instead of solid concrete, the typical concrete porch deck is a poured concrete slab on a wooden substrate. The steps aren’t solid concrete either. They’re poured concrete, formed into steps over a wooden ramp. Stucco on the sides of the porch is applied over a standard 2-foot-by-4-foot wood-framed wall.
The bulk of the structure is wood, not concrete. Water is almost always the culprit when “concrete porches” need repair. Wood and water just don’t mix.
The need for costly repairs occurs over the course of many years as water finds it way through cracks in and around the slab and penetrates to the underlying wood frame, rotting it.
Without the support of the frame, the heavy concrete settles, causing more cracks. More water penetrates and causes more rot. Eventually, the porch needs to be replaced.
Framing a porch is virtually identical to framing a floor in a house. Floor joists resting on a cripple wall are covered by a subfloor of plywood or 1-inch-thick boards 8 to 12 inches wide. Most often, but not always, a membrane of building paper was spread over the 1-inch boards in attempt to create a vapor barrier.
Three to four inches of concrete is poured over the subfloor and voila — you have your porch deck.
Steps are created by building a ramp out of wood, then building wooden forms for the steps. Once the concrete in the forms dries, the forms are removed, leaving concrete steps. The wooden ramp remains in place.
A homeowner can slow the decaying process substantially by doing regular maintenance directed at keeping water out of the framing.
Inspect the porch regularly. Seal all cracks. Concrete caulking/sealer is available for this purpose. Pay particular attention to the sides of the slab where it meets the wall of the house. These areas are particularly susceptible to leaks. Finally, keep the porch painted.
The blistering paint may be the result of poor preparation. But more likely it’s also the result of water infiltration. Concrete is porous and conducts water easily. The damp concrete is warmed by the sun, and the water expands and blisters the paint.
Scrape and wire brush all loose concrete and paint from the surface. Patch any holes in steps. A number of quick-drying concrete patching compounds are available. Once you’ve removed the chipped paint and patched, hold off on painting for at least a week. Any residual moisture in the concrete will evaporate.
Apply two coats of a quality porch and deck coating. We’ve always been partial to water-based epoxies.