The crucial role of water in cement strength and durability

Water affects cement-based products in many ways, which may lead one to ask, “How much water should be used with cement-based products?” That question is not a simple one. To figure out the water-to-cement ratio for cement-based products, we need to look a little further into the chemistry of cement and how water plays such a key role.

Importance of water-to-cement ratio

What many in the industry do not realize is that there is a science behind the curing of cement-based products. When water is added to cement, it starts to crystalize and form “fingers” that interlock one another, creating a strong bond.

When the water-to-cement ratio is off for any reason (such as having excess water used in cement-based mortars, grouts or levelers and patches), large spaces occur between the molecules and the “fingers” are stopped from interlocking tightly, weakening the cement. Weakened cement can lead to shrinkage cracks, along with decreased flexural and tensile strengths.

Tensile strength measures how long a material can withstand being stretched before breaking. We all know that no one is “stretching” a tiled floor; however, when walls and floors move independently of one another, the grout and mortar are “stretched.”

Flexural strength is how much a cement product can “bend,” which is important when considering heavy loads, such as those seen in a warehouse. Flexural strength determines how much weight a system can withstand before “bending” or cracking.

It is important to grasp the type and amount of movement that cement products experience to understand how water plays a part during the mixing and placing stages. When too little water is used, or the water evaporates out too quickly, the cement never reaches a full chemical cure, resulting in a weakened product.

Following guidelines for optimal results

Considering how critical the correct water ratio is to any cement-based product, we always recommend that you follow the manufacturer’s guidelines on water quantity. To answer the question that was at the beginning of this blog, follow instructions carefully! Not all cement-based products are the same.

With MAPEI cement-based products, be sure to consult our Technical Data Sheets for specific mixing and installation guidelines. For any questions that you may have, please contact our Product Support line at (800) 992-6273.