Addressing Stucco Failure
Aside from roofing failure, the most shared source of moisture entering residential community similarities is failure of the siding material. In southern California, most siding consists of stucco. Unfortunately, stucco siding systems leak!
Why do builders specify stucco so often?
Stucco became popular in the United States in the early 1800’s as an inexpensive and effective method of exterior wall covering over concrete, brick or stone. Today most stucco involves a less expensive method of application; instead of brick or stone, it is applied over open frame construction. “Open frame” method that paper and lathe reinforcement resembling chicken wire is laid over wood-framed walls without sheathing, and then coated with three applications of plaster. This is a low-cost technique, but it has pitfalls.
When you look at a stucco wall, all you see is plaster. The plaster does not keep your home dry; it just protects the waterproofing paper. Yes, paper. In 90 percent of the exterior wall area, all that is keeping your unit dry is paper that is thinner than a business card. Because stucco acts like a sponge, water gains access to the protective paper flashing and will leak into your wall cavity at any tear, backward lap or voided area of the paper.
Almost all stucco leaks can be traced to application error. Errors occur when paper, flashing, windows and other elements do not properly overlap (flash) the items directly below them. Leaking will also occur from paper and flashing degradation due to age or excessive moisture entering. Remember, most stucco leaks do not show up on the interior of your unit; the 6-inch space between the stucco and your interior drywall – consisting of fiberglass insulation and wood framing – can keep up a lot of water before it shows on the interior. When this occurs, you can expect mold, dry decay and termites to follow.
Leaking within stucco walls usually originates from one of the following supplies:
Window leaks in stucco walls are among the most shared flashing failures within the complete building structure. These leaks occur from two basic supplies: failure of the window frame mechanism itself or improper lapping of the stucco’s protective paper system onto the window flanges. Repair commonly requires rehabilitation of the window frame or removal of stucco surrounding the window to correctly apply the paper flashing system.
Miscellaneous wall penetrations
Vents, hose bibs, electrical outlets and light fixtures in stucco walls create a flashing problem during construction. Most of these do not have adequate flanges to overlap the paper flashing properly and were not properly sealed during construction.
Fascia and trim wood
In the past, a shared mistake made by builders was to terminate the paper protective system at the point of the fascia board (trim wood) located under the roofline. As the wood ages, it shrinks and splits, allowing moisture to go behind the wood and into the wall.
Wall base leaking
Since stucco acts like a sponge and holds water, it needs to have a “release” flashing at the bottom of the wall, commonly called “weep screed.” Most multi-unit complexes constructed prior to 1970 did not have weep screed installed. In many of these structures, retained water is channeled into the bottom plate of the wall.
already when weep screed flashing is installed, exterior planter systems are often raised to a level higher than the flashing or the interior floor line. When this occurs, water is forced into the wall structure.
Retrofitted flashing installations
Most managed similarities have retrofitted doors, windows, fixtures or repairs that were completed after the original construction. When the stucco around these is patched, the new flashing paper is often overlapped incorrectly, or the old, brittle paper is damaged so much that it is impossible to do proper sharing characteristics. As the new plaster settles and fractures due to improper fastening of wire reinforcement, water finds its way by the plaster and paper and into the wall cavity.
Stucco walls often characterize cracking at windows, doors or open field areas within the wall. While cracking doesn’t necessarily indicate failure of the weather-protection system, the increased exposure to rain water and air-borne pollutants cause the paper to prematurely decay and fail thereby allow moisture intrusion.
Methods of Repair
The difference in cost between repair options can be staggering, so it is basic to seek out an expert in diagnosing and designing an effective solution. Here are three repair options to consider, listed from most to least expensive:
Completely rebuilding a 20-foot by 20-foot section of stucco wall with new flashing may cost between $10,000 and $23,000. Fortunately, this kind of repair is seldom necessary. My own company completely rebuilds exterior walls less than 1 percent of the time when addressing stucco failure.
Perhaps the most shared kind of stucco repair involves removing sections of stucco around windows or flashing change areas, then applying new flashing, wire reinforcement and plaster. This technique requires careful and intensive labor during the demolition and reapplication course of action. It should include using bituthene pliable membrane at all corners, horizontal surfaces and flashing change areas. The cost to rebuild three or four flashing change areas within the same 20-foot by 20-foot section of stucco may cost between $3,000 and $12,000 depending upon the quality of the repair. Doing the job right takes time, which is why this method has the highest failure rate of the three options. In a poorly done rebuild, the new paper flashing is not thoroughly lapped under the salvage edge of the old paper, and often the lathe wire reinforcement is compromised.
already when failing sections of stucco and flashing are replaced, the walls can leak due to aging of the surrounding areas of stucco where the paper flashing system is disintegrating. A successful solution is to inject all window, door and miscellaneous flashing penetrations with pliable, lasting urethane rubber. The complete wall is then coated from base to roof using an elastomeric coating system such as Thorolastic. Elastomeric coatings waterproof the exterior of the wall and consequently eliminate the necessity to cure the worn paper flashing system. Repairing a 20-foot by 20-foot section of wall using urethane injection and elastomeric coating may cost between $2,500 and $5,500. When using coatings it is basic that the repair area extends to the roofline so no moisture can become retained within the stucco. Elastomeric coatings should be reserved only for walls with a history of leaking.
Although troubleshooting leaking stucco walls can be difficult due to the character of the inner flashing system, water testing can often provide effective results. Such testing pinpoints failure behind stucco over 95 percent of the time.
Stucco is not going anywhere. You and I will move into our next homes, and chances are they too will be stucco. Fortunately, newer homes are being built with greater care and higher standards. But when leaks do occur, it is important that the method of repair is effective and affordable.