Broken out to solid ground, then poured back

Why the slab moved before it cracked

Concrete does not fail down here the way it fails up north. There is no freeze, nothing lifting the slab from underneath in winter. What we get instead is water. Rain comes hard most afternoons through the summer, the soil is sand over limestone, and sand moves when water runs through it. A slab poured on ground that later washed out is holding itself up on nothing, and it will crack along the line where the support stopped.

So the first thing on a repair call is finding out where the water goes. Usually it is a downspout dumping at the edge of the slab, or ground that grades back toward the house instead of away from it. Other times it is an irrigation line that has been leaking quietly under there for a season. Or a live oak, where the roots have lifted one panel of sidewalk while the panel next to it dropped. Until that part is handled, new concrete in the same spot goes the same way the old one went.

That walk also tells us how much has to come out. A crack you can lay a pencil in, with both sides sitting level, is usually cosmetic and can stay. A crack with a lip you can catch a shoe on means the two halves are on different ground now, and grinding the lip off just hides it for a while. We will tell you which one you have while we are standing on it, because those are two different jobs and you should know which one you are buying.

• Water source found before anything gets poured
• Saw cut to the joint, no ragged edges
• Old concrete broken out and hauled off
• Base recompacted before new concrete goes in
• Site swept and washed down at the end

Taking it out without breaking what stays

Demolition is the part where a repair quietly goes wrong. Anybody can break concrete. The work is breaking only the piece that has to go, and leaving the rest of the slab strong enough to tie into. That starts with a saw cut on a straight line, usually at an existing joint, so the concrete that stays has a clean vertical face instead of a feathered edge that chips off the first time a truck rolls over it.

Around here there is a lot under a slab that you cannot see from the top. Irrigation runs shallow through sandy ground and shifts over the years. Older block houses have plumbing coming up through the slab, and additions were often poured over lines that were already there. On a driveway there may be a water service between the meter and the house. We find out what is down there before the hammer starts, and we break by hand where we have to, because a repair that ends with a cut water line is not a repair.

The broken concrete has to leave, and that part is heavier than people expect. A patio slab four inches thick fills a truck faster than it looks like it should, and dragging it across a lawn tears up more than the concrete did. We plan the path out first, protect what the wheels have to cross, and load as we go instead of leaving a pile sitting in the yard overnight. When the demo is done the ground is graded and clean, ready to pour on, not a crater full of rubble.

Patching a hole so the patch stays

A pothole in concrete is almost never a concrete problem. Something washed the base out from under that spot, the slab lost its support, traffic broke through, and now water goes straight down the hole every time it rains and takes more base with it. Patching the top of that without dealing with the void underneath is filling a bucket with no bottom. It looks right for a season, then the patch drops, and you are looking at the same hole plus a seam.

So we cut the hole square and go past the broken part into concrete that is still sound. Ragged edges and feathered patches break off, every time, because a thin edge of concrete has nothing holding it. Then the base gets opened up, wet sand pulled out, fill brought back in and compacted in lifts until it stops moving under a plate. Only then does anything get poured. The patch is as thick as the slab around it, not a skim over the top of a hole.

A patch is a seam, and a seam is where the next crack wants to start. So the cut edges get cleaned and dampened before the pour, and the new concrete gets worked tight against them instead of poured and left to find its own way. The joint pattern of the original slab carries through the patch. Color is the one thing we will not promise to match. New concrete cures lighter than concrete that has sat in Florida sun for years, and it darkens down over the following months, but it will never be invisible.

Replacing a panel that has sunk

Sidewalk and walkway panels sink one at a time, and that is good news, because the fix can be one at a time too. The joints are already there. We cut on the existing joint lines, lift the bad panel out whole where we can, and the panels on either side stay where they are. What we will not do is pour a new panel back on the same soft ground that swallowed the last one, because the whole thing repeats itself.

Under a sunken panel there is usually a soft pocket, and you can feel it the moment the concrete comes off. Sand that has been washing out for years, or an old trench that was backfilled loose and never got compacted. Sometimes it is a root the size of your arm that grew under there, then died back and left a space. Roots get cut back and the fill goes in clean, compacted in layers until a pass with the plate does not leave a mark. That base is the panel. The concrete is just the top of it.

The new panel has to land at the right height on both ends, and it has to carry water the same way the run around it does. Set it low and water sits in the seam after every rain. Set it high and you have moved the trip hazard instead of removing it. We shoot the grade off the panels that are staying, hold the pitch away from the building, and finish the surface to match what is beside it so the repair does not read as a patch from the street.

What happens after the pour

Heat is hard on fresh concrete, and we pour into it most of the year. Water leaves the surface faster than it can rise from below, the top stiffens while the middle is still soft, and you get shrinkage cracking in the first day on a slab that was mixed and placed perfectly. That is why the truck comes early. Monday to Saturday we start at 6:00 AM, and on a hot week the pour is done before the middle of the day rather than after it.

Then it needs to be left alone. Concrete does not dry, it cures, and the chemistry runs for weeks after the surface is hard enough to walk on. We keep it wet or covered through the early part of that, which matters more here than people think, because an afternoon storm on green concrete can wash the cream off the top and leave a sandy surface that dusts for the life of the slab. If rain is coming, we cover it or we do not pour.

You can walk on a patch the next day in most cases. Vehicles are a different story, and on a drive repair we will tell you how long to keep the car off it before we leave, and we will put something across it so nobody guesses. Pets and kids find fresh concrete the way water finds a low spot, so the barriers stay up until the surface is past being marked. After that, the panel is part of the slab, and it should behave like the rest of it.