Under most of the Las Vegas Valley there is a cemented layer the desert spent thousands of years building. Whether it sits six inches down or six feet decides what your job costs, and no quote is honest until someone has looked.
Caliche is calcium carbonate that has precipitated out of the soil and cemented the material around it into a hard layer. In parts of the valley it is a thin crust. In others it is effectively rock, thick enough that ordinary excavation equipment stops working and something with a hammer has to come in.
It is not distributed evenly. Two houses on the same street can have completely different profiles, which is why a quote based on a neighbour's job or on a phone call is a guess.
Anything that has to go below grade meets it. Footings, post holes, drainage, a pool deck that needs excavation. Hitting caliche at eight inches turns a morning of digging into a day with a jackhammer or a breaker attachment, and that difference is real money.
This is the single most common reason a Las Vegas concrete quote gets revised upward after work starts, and it is avoidable. A test hole before the number is written tells everybody what they are dealing with.
Caliche is a strong bearing material. Unlike the expansive clays that plague slabs in Texas or Georgia, caliche does not swell and shrink with moisture. A slab bearing on properly prepared caliche sits on something very stable.
So it is a cost problem, not a durability problem. The trouble comes from working around it badly — for example backfilling a trench through caliche with loose material and pouring over the top, which leaves a soft strip under an otherwise well supported slab.
Four to six inches of compacted aggregate base over native material, with the caliche located by test hole before the quote is written. That last clause is the local part. Elsewhere you assume you can dig; in the valley you find out first.
If a trench or a footing has been cut through caliche, the backfill has to be compacted in lifts to match the surrounding bearing capacity. Otherwise you have built a soft lane under the slab and the crack will find it.
Ask whether they dug a test hole, and at what depth they hit caliche. Ask what happens to the price if it turns out shallower than expected — a contractor who has already thought about it will have an answer, and one who has not will find out on your job at your expense.
A poured slab sized to the furniture and the door it serves.
A layer of calcium carbonate that has cemented the surrounding soil into a hard mass. It occurs across most of the Las Vegas Valley at depths from a few inches to several feet, and varies house to house.
Not by itself — unlike expansive clay it does not swell or shrink, so it is a stable bearing material. Problems come from uncompacted backfill in trenches cut through it, which leaves soft spots under the slab.
Most often caliche found shallower than assumed. A test hole before the quote is written prevents it, which is why it is worth asking whether one was dug.
Frequently yes. Thick caliche stops ordinary excavation and needs a jackhammer or a hydraulic breaker, which is the cost difference people are surprised by.
Sulfate Soil: Why a Perfect Slab Fails in Year Five · Why Las Vegas Concrete Pours Start Before Dawn ·
Photos of recent pours, before and after shots, and the jobs we are on this week.