Sulfate, Alkali, and a Water Table Near the Surface
The Lahontan Valley is the floor of an ancient lake bed, and it has been irrigated for more than a century. Both of those facts concentrate salts near the surface: water arrives, it evaporates in the desert air, and it leaves behind what it was carrying. The result is soil that is alkaline and in many places high in sulfate, which is the single most important thing to know about pouring concrete here. Sulfate in solution reacts with the products of ordinary portland cement hydration, forms expansive compounds inside the hardened paste, and progressively destroys it from within. The damage starts where the concrete meets the ground, it is invisible for years, and it eventually shows up as softening, cracking and disintegration at the bottom of the slab and along the edges.
The defense is real and it is a matter of specification rather than luck. A sulfate-resisting cement — Type II for moderate exposure and Type V where it is severe — is the first half. The second half, and the half more often skipped, is a low water-to-cement ratio: sulfate attack requires the solution to get into the concrete, and dense, low-permeability concrete keeps it out. That means the mix is not watered down at the truck to make it easier to place, ever, which is a discipline question as much as a design question. We also keep the base free-draining so the slab is not sitting in salty moisture, and on interior slabs we use a vapor barrier without exception.
The high water table is the second condition, and it compounds the first. Across much of the irrigated valley, groundwater sits within a few feet of the surface for much of the year and rises during the irrigation season. That keeps the soil beneath a slab wet, keeps sulfate mobile and available, and makes moisture transmission through an interior slab a certainty rather than a risk. So a shop floor in Fallon gets a free-draining granular section, a properly lapped and sealed vapor retarder, and enough thickness and reinforcement to handle both the load and a subgrade that is not going to be uniformly stiff. It is also why we look hard at where irrigation water runs on a property before choosing a slab elevation.
Then the ordinary Nevada conditions, which still apply. Fallon summers are hot and the air is dry, so hot-weather concreting practice is standard: first-light starts, chilled mix water where warranted, retarders on big pours, immediate and sustained curing. Winter brings frost and freeze-thaw, so air entrainment goes in every mix. Wind across open valley ground makes evaporation control a working requirement rather than a nicety. And agricultural loading — tractors, loaded trailers, implements, and grain or hay stacked in one place — means slabs get designed for the heaviest thing that will ever sit on them, which around here is heavier than most people initially say.
What we pour in Fallon
- Driveways, replacements, and widening strips
- Patios, walkways, and outdoor living slabs
- Front steps, stoops, and porch slabs on proper footings
- Garage, shop, and outbuilding floors
- RV, boat, shed, and equipment pads
- Repair, resurfacing, slab lifting, and removal
