What is Concrete Curing?
Curing Concrete is maintaining a satisfactory temperature and moisture content during the “hydration process”.
Hydration is the chemical reaction of water with cementitious materials as concrete hardens and develops strength.
As long as there is some unhydrated cement present in concrete along with moisture and favorable temperatures, hydration and strength gain continues.
Why Cure Concrete?
- Laboratory tests show that concrete cured in a dry environment can lose as much as 50% of its potential strength compared to concrete that is moist cured.
- Concrete placed under high temperatures will gain early strength, but later strength gains may be reduced.
- Concrete placed in cold weather will take longer to gain early strength.
- Good curing develops better surface hardness and density improving concrete’s durability and resistance to freezing conditions.
- Slabs that are allowed to dry out too early will have a weak surface with poor resistance to wear and abrasion. Proper curing can reduce crazing, dusting and scaling.
How to Cure Concrete
The concrete surface must be kept continuously wet or sealed to prevent evaporation for a period of at least 7 days in 70° temperatures and at least 9 days in 50° temperatures to achieve 50% of the specified strength.
Systems to keep concrete wet during curing:
- Burlap, cotton mats or rugs used with a soaker hose or sprinkler. New synthetic materials (burlene or Armorlon – Transguard 4000) incorporate moisture retention with a vapor barrier.
- Sprinkle on a continuous basis. Concrete should not be allowed to dry out between sprinklings. (Alternate wetting and drying may damage concrete)
- Ponding water on the concrete is an excellent method of curing, but may not be practical in many applications.
Spray on curing compounds:
- Liquid membrane-forming compounds can be applied to the surface after finishing. Do not apply if concrete is still wet and bleeding. Use a dissipating curing compound if you intend to use a penetrating waterproofing/sealer after 30 days.
- White pigmented curing compounds reflect light to keep concrete cooler and assist in applying even coverage.
- If concrete will be painted or covered with carpet, tile, or vinyl, make sure the curing compound is not reactive with the paint or adhesive.
Lay on curing materials:
- Plastic sheeting clear, white or pigmented should be laid directly on the concrete as soon as possible after finishing.
- The white pigmented plastic reflects light and heat. The dark pigment plastic absorbs heat. Pigmented plastic may assist in maintaining temperature.
- Plastic will make dark streaks in concrete whenever a wrinkle touches the concrete. If appearance is important do not cure with plastic.Read more on how to cure concrete for a decorative stain or colored finish