Concrete walks, slabs and drives in Mobile

Mobile is one of the rainiest cities in the country, and a lot of that rain comes down hard in a short time. Every walk, patio and driveway around a house has to send that water somewhere. A walk that dips toward the foundation, a patio that holds a puddle against the back wall, a driveway that runs water into the garage: that is where most concrete trouble around a Mobile house starts.

So the first thing set on a new slab is the slope. It is slight, hard to see when you stand on it, and it runs away from the house toward the yard, a drain or the street.

Concrete sits on whatever is under it, and around Mobile that is often clay that swells when wet and shrinks when dry, or sand that washes out from under an edge after enough storms. A slab poured over soft fill, old roots or topsoil settles unevenly and cracks.

Good prep means digging out the soft material, putting down a base and packing it firm, and setting steel or wire in the slab where it needs it.

Anyone who has walked an older Mobile street has seen what live oak roots do to a sidewalk. A root grows under a panel, lifts one edge, and leaves a lip that catches your toe. Near a house the same roots can heave a driveway or crack a patio.

No slab is strong enough to stop a big oak root. What helps is keeping new concrete back from the trunk where you can, and breaking long walks into panels so a lift happens at a joint instead of across the middle. Before cutting roots on a tree you want to keep, call an arborist.

All concrete cracks some. The joints cut or tooled into a slab give it a place to crack in a straight line instead of wandering across the surface. A hairline crack in a slab that is still flat is usually only cosmetic.

The cracks that matter usually mean the ground underneath has moved. That section comes out and is poured again on a firmer base. These are the ones to watch for.

• A lip where one side has dropped or lifted
• A panel that rocks or sounds hollow when you step on it
• A slab tipped back toward the house
• Water still standing on the surface a day after rain
• Soil washing out from under an edge

Most of the year it is hot and humid here. Summer sun dries the top of fresh concrete faster than the inside, and that can leave a weak surface that dusts and shows fine cracks. Keeping new concrete damp and shaded while it cures lets it gain its strength. Afternoon storms are the other worry. Hard rain on concrete that has not set can pit the finish, which is why pour day depends on the forecast.

On most Mobile houses, concrete and brick touch somewhere. A patio poured up against the brick ledge of a slab house. A walk that runs to brick steps. A porch slab with brick on its sides. Where they meet, the concrete should fall away from the house and stay below the weep holes in the bottom course of brick, since those small openings are how water behind the brick gets out. A patio poured up over the weep holes traps that water in the wall.

A new driveway or a replaced apron at the street usually touches the city right of way. Ask the City of Mobile what that needs before the old concrete comes out. If you are outside the city limits, ask Mobile County.

Text Donald one photo from far back so he can see how the ground falls, a few closer ones of the cracks or low spots, and a note on what you want: new concrete, a section replaced or a set of steps. Call or text (251) 305-5966. He is based in Mobile.