Brick and block retaining walls in Mobile

People think of Mobile as flat, and down by the bay it mostly is. But plenty of lots have a change in grade: the higher ground around Spring Hill, yards that fall off toward a creek or a drainage ditch, driveways cut into a slope, and back yards terraced to get a level patch of grass. Wherever the ground steps down, something has to hold the high side back.

Soil behind a wall pushes on it all the time, and wet soil pushes a lot harder. In a place as rainy as Mobile, with clay that holds water and swells, the ground behind a retaining wall can stay soaked for days after a storm. If that water cannot get out, pressure builds behind the wall until something gives.

That is why most retaining wall failures come down to drainage. The wall was built with no way for water to escape, or the drain behind it filled with silt, or the weep holes got buried under mulch and dirt.

A wall that has started to lean does not straighten back up by itself, and the movement is usually slow enough to miss. Pencil a mark and the date at the end of any crack and check it after the next few storms. These are the signs to look for.

• The top of the wall leaning out
• A bulge in the middle of the face
• Stair step cracks running through the joints
• Mortar washing out of the joints
• Soil coming through cracks or out the bottom of the wall
• The ground behind the wall sinking or pulling away from it
• No water from the weep holes after a hard rain, or no weep holes at all

A retaining wall that lasts in this climate sits on a footing that will not settle, with drainage gravel behind it, a perforated drain pipe at the base that carries water out to daylight, and weep holes through the face. Block walls that hold back much ground are usually reinforced, with steel set in the cores and the cores filled solid. Brick is often a face laid over a block or concrete core.

The backfill matters too. Clay packed straight against the back of a wall holds water against it. Clean gravel lets the water drop to the pipe and get out.

A wall that stands straight but has worn joints or a few broken units can often be repaired. The joints are repointed, broken brick or block replaced, weep holes opened back up, and the water problem behind it dealt with.

A wall that leans, bulges or has slid at the base has usually failed behind the face, and patching the front will not hold it. That wall comes down, the ground behind it is dug out, and it goes back up with a proper footing and drainage.

A wall that holds back a lot of ground, carries a driveway, sits on a property line or stands close to the house needs more care than a garden wall. Some jobs call for a structural engineer or a foundation company to design the wall before it is built. Ask the City of Mobile, or Mobile County if you are outside the city, what permits a new or rebuilt wall needs.

A big oak beside a retaining wall works on it two ways. The roots press on the footing and the back of the wall as they grow, and in dry spells they draw water out of the clay so the ground behind the wall shrinks and settles. A crack in a wall near a live oak is one to mark and keep an eye on.

Take one photo of the wall from the end so any lean shows, one straight on, and close ones of the worst cracks. If you know where the water goes behind it, say so. Text them to Donald at (251) 305-5966 with your part of Mobile.