Curing is the process of maintaining adequate moisture and temperature in fresh concrete so that hydration — the chemical reaction between cement and water — can continue. Hydration is what gives concrete its strength. Without proper curing, the surface dries out, hydration stalls, and the slab never reaches its design strength.
Think of curing as protecting the investment you just made in placing and finishing the concrete. The mix design, the placement, and the finishing all matter — but if the concrete dries out too quickly, none of that work pays off.
Concrete strength development follows a predictable curve under normal conditions (70°F, adequate moisture):
The concrete stiffens enough that it can no longer be worked. Finishing must be complete before initial set. Hot weather and accelerators shorten this window; cold weather and retarders extend it.
Foot traffic is typically acceptable. The slab is still gaining strength rapidly and must be kept moist.
Most specifications allow form removal and light loading at this point. This is the minimum curing period recommended by ACI for most applications.
The industry standard benchmark. Structural loading, post-tensioning stressing, and other full-load activities are typically permitted at 28-day strength.
Hydration continues beyond 28 days — concrete can gain 10–20% additional strength over the following months — but 28 days is the design target and the number on your cylinder breaks.
Wet curing: The gold standard. Keeping the surface continuously moist with water, wet burlap, or soaker hoses provides the best strength development. It is also the most labor-intensive and is typically reserved for structural elements and critical slabs.
Curing compounds: Spray-applied liquid membranes that seal the surface after finishing. These are the most practical option for flatwork — one application right after final finishing, and the compound retains moisture during the critical early curing period.
Curing blankets: Insulated blankets used primarily in cold weather to retain both heat and moisture. They prevent the concrete from freezing during early hydration and maintain temperatures above the minimum needed for strength gain.
Plastic sheeting: Polyethylene sheets placed over the surface to trap moisture. Effective and inexpensive, but can cause discoloration on exposed surfaces if not applied evenly. Best suited for slabs that will be covered or coated.
Here is the connection most contractors learn the hard way: curing cannot fix what evaporation breaks during placement. If the evaporation rate is high enough to cause plastic shrinkage cracking in the first few hours, those cracks are permanent. No amount of curing compound, wet burlap, or ponding will close a plastic shrinkage crack once it forms.
This is why monitoring evaporation rate before and during placement is just as important as your curing plan. Curing protects the concrete after finishing. Evaporation rate management protects it during placement and finishing — the window where the concrete is most vulnerable.
Hot weather creates a double problem. First, it accelerates initial set, which shortens your finishing window and forces your crew to work faster. Second, it increases evaporation rate, pulling moisture from the surface right when you need it most.
ACI 305R recommends beginning curing as soon as possible after finishing in hot weather conditions. Apply curing compound immediately after the final finishing pass — do not wait. If you are wet curing, start before the surface shows any signs of drying. In extreme conditions, apply evaporation retarders during finishing and curing compound immediately after.
The best strategy is to check your evaporation rate before the pour, plan your mitigation measures, and have curing materials staged and ready. Use our free evaporation rate calculator to run the numbers, or let PourDay do it automatically with live weather data for your exact job site — so you know what you are walking into before the first truck arrives.
Know your evaporation rate before the first truck arrives. PourDay is free on iOS and Android.
The formula, the threshold, and what drives evaporation — the variable that determines whether curing even gets a chance to work.
Read articleWhat happens when evaporation wins — causes, the 0.15 rule, and how to prevent cracks before they form.
Read articleThe standard that governs hot weather placement and curing — and why Type 1L makes it more critical.
Read articleReal-time evaporation rate. 16-day forecast. Pour logging. Free for contractors.