Live oaks, wet clay and cracks in Mobile brick

Brick does not bend. When the ground under a wall shifts even a little, the brick and mortar crack to let go of the strain. So most cracks in brick are a record of something that happened in the soil below.

Around Mobile the soil is a mix. Some lots sit on clay, some on sand, and a lot of them have both in layers. Clay swells when it soaks up water and shrinks when it dries. Sand does not swell much, but water running through it carries it away, and loose sand can settle after a long soaking.

With heavy rain most of the year, the ground near a house is wet more often than not. Trouble starts when one part of the ground under a house gets much drier or much wetter than the rest. A dry spell, a downspout that dumps in one corner, a leaking pipe, or a big tree drinking from one side can all do that. One corner moves and the rest of the house stays put, and the brick cracks where the two meet.

Live oaks are everywhere in Mobile, and some of them are older than the houses they shade. Their roots spread wide and stay fairly shallow, often reaching well past the ends of the branches. A big oak pulls a lot of water out of the ground, and more of it in dry weeks.

Near a house, that does two things. Roots can lift and crack anything light that sits over them, like walks, driveways, brick steps and low garden walls. And on clay ground, a big oak can dry out the soil under the nearest corner of a house so it shrinks and settles while the far side stays where it was.

Roots growing into a foundation and pushing it over is less common than people think. The usual damage comes from the water the tree takes and from roots lifting the lighter things close by.

Cutting a big tree down is not a simple fix either. On clay, the ground where the tree stood can take on water and swell for a good while after it is gone, and that can move the house the other way. Before cutting a big oak or its roots, talk to an arborist, and ask the City of Mobile whether any permission is needed.

Different houses crack in different places. On the older houses downtown and in the historic districts, look at the brick piers and skirting under raised cottages, the chimneys, and the brick over windows and doors. On brick veneer houses on slabs in Spring Hill and West Mobile, look at the corners, the brick ledge where the veneer sits on the slab, and the brick over garage doors and wide windows.

These are the kinds of cracks people find:

• Thin cracks in the mortar joints only, short and scattered
• Step cracks that climb the mortar joints like a staircase, usually from a corner or the edge of a window
• Straight cracks that run up through the brick and the joints
• Cracks that are wider at the top than the bottom, or the other way around
• A gap opening between the brick and a window or door frame
• Cracks along the brick ledge at the bottom of a veneer wall

Thin cracks in the mortar that have not changed in a long time usually come from early settling or the mortar shrinking as it dried. They are cosmetic. They can still let water into the wall, so they are worth repointing, but they do not mean the house is moving.

Step cracks are the most common kind on brick houses here. A thin one that has stopped growing is often old settling. A step crack that keeps getting wider, or one where the brick on one side sits out past the brick on the other, is one to watch.

Cracks through the brick itself, cracks wider at one end, and cracks that come along with doors that stick, windows that will not close, floors that slope or new cracks in the drywall inside all point to movement that is still going on.

Cracks over windows and doors can also come from a rusted steel lintel, the angle iron that holds the brick up over an opening. Rust swells as it builds up, lifts the brick and cracks the joints. That has nothing to do with the ground, and it has a different fix.

The surest way to know if a crack is moving is to watch it. Put a small pencil tick just past both tips of the crack and jot the day it was marked beside each tick. Snap a picture with a coin pressed to the brick beside it so you have something to measure against later.

Check it every month or two, and again after a long dry spell and after a very wet stretch. If the crack runs past your pencil marks or gets wider, it is moving. Small plastic crack monitors that stick across a crack are sold for this, and they make a change easy to read.

Keep the photos and dates together in one place. They help anyone who looks at the house later, from a mason to an engineer.

Since water is what moves the ground, keeping it even around the house is the most useful thing you can do yourself. Keep the gutters clear and carry the downspouts away from the foundation so roof water does not pool at one corner. Build the dirt up so rain runs away from the walls instead of toward them. Fix leaking hose bibs and pipes. Set sprinklers so they do not soak one side of the house and leave the other dry.

Watch where the air conditioner drain line empties, too. A line dripping into the same spot by the foundation all summer keeps that corner wetter than the rest.

Flowerbeds with edging built up against the brick hold water at the base of the wall. On veneer houses, mulch piled over the weep holes at the bottom row of brick keeps the wall from draining.

Some cracks are a masonry repair and some are a sign of a foundation problem. A crack that keeps growing, brick that is leaning or bulging, a block foundation wall with a long sideways crack, piers that are leaning, or cracks that come with sticking doors and sloping floors all mean someone should look at the structure.

Some jobs call for a structural engineer or a foundation company. An engineer works out why the house is moving and what it needs, and gives you a plan that is not tied to selling the repair. A foundation company does the work under the house.

The brick gets repaired once the movement is dealt with or known to have stopped. Brick patched while the ground is still shifting tends to crack again along the same line.

Donald W Carpenter does the masonry side of this around Mobile: cracked block, brick that has come loose, and joints in brick or block foundations where the mortar has washed away. The foundation repair page covers that work, and the brick repair page covers cracked and loose brick higher up the wall. Brick piers under raised houses are a separate question, so ask Donald about those.

Send him photos of the crack, with your pencil marks and dates if you have them, and tell him where in Mobile the house is. Call or text (251) 305-5966.