Water Curing

Technical Bulletin: Cold Weather Water Curing

March 24, 2015

Rapid Set EISENWALL® provides the highest strength, greatest durability, and most crack-resistant base coat of nearly all wall-coating systems. To achieve the highest quality installation as we approach the winter season, it is even more important to follow water curing guidelines carefully. ICC ESR-2671 specifies water curing and neglecting this important step is a violation of the Building Code.

WaterCuringB_1How is EISENWALL® different?

The primary internal force affecting exterior plaster is drying shrinkage. As the cement in the plaster hydrates (chemically combines with water to form a rigid structure), excess water leaves the plaster due to evaporation or absorption. The result is drying shrinkage, or an overall reduction in bulk volume of the plaster. In normal Portland cement based plaster products, only about half of the water required for mixing is actually used in the hydration process. This leaves a tremendous amount of unused water for the evaporation and shrinkage process to occur, and results in drying shrinkage cracks in the plaster. Unlike Portland cement based plaster products, EISENWALL® uses virtually all the mixing water in the plaster for this hydration process. The result is far less drying shrinkage (less than one third), and greater resistance to cracking due to drying shrinkage.

Cracking due to drying shrinkage should not be confused with plastic shrinkage cracking. Plastic shrinkage occurs when excessive water is lost from the plaster while it is still in the plastic state (before hydration, when the plaster is still workable). Common causes include dry, cold, or windy weather, and lack of sufficient water curing. In these types of conditions, it is even more important that proper water curing be performed. The plaster base coat should be kept moist until it has achieved sufficient tensile strength to resist cracking. A good test to determine if the plaster is sufficiently rigid is the nail test: If the surface can be easily scratched with a nail it is not sufficiently hydrated. In normal warm weather conditions this is approximately 90 minutes after application. Cold weather will slow this process down. Regardless, a slight sheen needs to be maintained on the surface until sufficient strength is gained.

Wind causes evaporation, and increases the demand for water curing. Dry weather (such as Santa Ana conditions) will also speed the evaporation process. During windy or dry conditions, the surface will require more frequent misting with water. Cold weather will slow the rate of strength gain in the plaster, and the wall will require water curing for a longer period of time, although evaporation will be slower. Hot weather will require water curing for a shorter period of time, but more frequent misting due to the higher evaporation rate.