Almost every property in Augusta sits on red clay, and clay is the reason most slabs here fail early. This explains what the clay does and what has to go between it and your concrete.
Augusta sits on the Georgia Piedmont, and the subgrade under nearly every lot in Richmond County is red clay. Clay is not inert ground. It takes on water and swells, then dries out and shrinks, and it does that every season for as long as the house stands.
The movement is not small. Expansive clay can change volume by several percent between a saturated spring and a dry August. A slab sitting directly on it has to follow that movement, and concrete does not bend. It cracks.
This is the single most common shortcut in Augusta, and it is easy to sell because the finished slab looks identical on day one. Nobody can see what is underneath.
What happens next is predictable. The clay swells unevenly, because it holds water unevenly — wetter near the downspout, drier under the middle of the slab where rain never reaches. The slab is now supported at some points and unsupported at others, and it breaks across the unsupported span. Usually within two to four years, usually diagonally from a corner.
Four to six inches of compacted crushed stone over a compacted clay subgrade. The stone does two things. It spreads the load so no single point of clay carries the slab, and it drains, so water moves through rather than sitting against the clay and swelling it.
Compacted is the word that matters. Stone dumped and raked is not a base. It has to be run over with a plate compactor in lifts, and the clay underneath has to be compacted before the stone goes down. That step is invisible in the finished job, which is exactly why it gets skipped.
Ask how thick the stone base is and whether the subgrade gets compacted. If the answer is vague, or if the quote does not mention a base at all, that is the whole ballgame. Two quotes for the same patio can differ by a third purely on what is under it, and the cheaper one will crack first.
Also ask where the water goes. Downspouts discharging next to a new slab keep the clay there permanently wet while the rest dries out, and that differential is what breaks slabs. Extending a downspout costs almost nothing and prevents a crack nobody can repair properly.
Concrete shrinks as it cures, and every slab develops fine cracks. That is why control joints exist — they decide where the crack goes. A hairline crack following a joint is the slab working as designed.
A crack that wanders diagonally across a slab, or one where the two sides sit at different heights, is a base problem, not a curing problem. The difference matters because one is cosmetic and the other means the ground moved.
A poured slab sized to the furniture and the door it serves.
Georgia red clay swells when wet and shrinks when dry, moving several percent by volume between seasons. A slab poured directly on clay has to follow that movement and breaks. A compacted stone base prevents it.
Four to six inches of compacted crushed stone over compacted clay subgrade. Stone that has been dumped and raked rather than compacted in lifts does not count.
Fine cracks following the control joints are normal and expected as concrete cures. Cracks wandering diagonally across a slab, or with a height difference between the two sides, indicate the base moved.
A cosmetic crack can be filled or the surface resurfaced. A crack from base movement will reopen, because the cause is under the slab, and repairing the surface does not address it.
Pouring Concrete in Augusta Summer Heat · Control Joints: Where Cracks Are Supposed to Go ·