The essential element in all good communications is that the parties involved must understand the vocabulary of the language used by one another in expressing their ideas and thoughts. In an attempt to prevent this miscommunication, the National Plasterers Council will address the often-misused terms of hydration and curing.

In the NPC Technical Manual, hydration is defined as “… the chemical reaction between hydraulic cement and water forming new compounds, most of which have strength-producing properties.”  The American Concrete Institute defines hydration as “formation of a compound by the combining of water with some other substance: in concrete, the chemical reaction between hydraulic cement and water.”

The Portland Cement Association, in its engineering bulletin (book) titled Design and Control of Concrete Mixtures, describes how “Hydraulic cements set and harden by reacting with water. During this reaction, called hydration, cement combines with water to form a stone-like mass.”

Many people in our industry erroneously describe abnormal or staining discoloration issues in
cementitious based interior finishes as “hydration.”  The NPC Technical Manual describes the difference between normal, abnormal, and staining discoloration.

Another common misconception is the erroneous use of the term “curing” in our industry’s language.  Curing often is applied to cementitious interiors to describe the maturation process or hydration process.  Curing (of plaster) in the NPC Technical Manual is defined as “the act or process by which the cementitious surface coating continues hydration. Curing is typically done by immersing the cementitious coating in water as soon as possible after final set. The hydration of the cementitious compounds will continue underwater.”

Summary: Simply put, hydration is the chemical reaction of hydraulic cement with water that forms new cement compounds, ultimately producing a stone-like mass. Curing is the process of providing the proper environment for the hydration or maturation process to proceed until the pool’s cementitious interior finish achieves its desired properties. Interior cementitious finishes begin to hydrate during the mixing process. The new finish is cured by filling the pool with water.