As an Arizona local, you likely know that the most predictable thing about monsoon season is its unpredictability.
In fact, with half of the state’s annual rainfall coming during the summer months, brief thunderstorms can dump large amounts of water in just minutes, according to the Climate Assessment for the Southwest.
While that’s good news for vegetation, reservoirs, and wildlife, it can be hard to deal with when you own a home on Arizona’s expansive soil. That’s because expansive soils contain clays with minerals that change significantly when they absorb or release moisture.
“Add a little water — say during a monsoon storm — to expansive smectite clay and it swells to many times its original volume,” the Arizona Geological Survey says. “Remove that water during the hot, dry summer and the clay component of the soil shrinks. The resulting changes in soil volume can cause considerable damages to homes, sidewalks, pipelines, and streets.”
You can recognize whether your home was built on expansive soil by watching for mud cracks when the soil dries and a popcorn appearance or sticky texture when the soil is wet. The USDA Natural Resources Conservation Service of Arizona has maps that will help you identify what the shrink and swell potential is for the soil in your area.
If you have expansive soil, here’s what to watch for when monsoon rains arrive.
Uneven floors or slab edges that appear to be pushed down are signs of foundation heave, a problem that is often misdiagnosed.
“These drying forces aren’t in play underneath a slab,” Arizona Foundation Solutions says. “Over time, moisture can easily accumulate under the slab from rain, roof runoff, leaks in nearby storm drains and other sources. So the expanding clay pushes up, causing central sections of the slab to move upward as well.”
That expansion can exert pressure of up to 5,000 pounds per square foot, more than enough to lift your foundation.
Cracks and gaps
You may also notice diagonal cracks in your walls, inside or outside. When a concrete slab is forced to move because of expansive soil, your walls can crack or bow under the pressure. That leads to cracks in internal walls and between bricks.
It can also cause gaps under your walls.
Moisture and mold
When your slab is saturated, it can lead to further problems: wet floors and mold or mildew.
“If you have moisture coming up through the slab, that’s a fairly common problem, delaminating your tile and creating mold and lots of other problems,” Arizona Foundation Solutions founder Bob Brown says. “This has before been a very difficult problem to solve, but with our sub slab moisture drying process — our moisture management process — it’s a very simple, easy process.”
That process is the MoistureLevel Smart Foundation System, which involves installing a fan and plastic pipe to introduce dry outside air to the soil under your home. This encourages evaporation that reduces expansion and, consequently, prevents damage to your foundation.