Moisture and Concrete – What is the Correct Moisture Level?

When it comes to concrete substrates and the moisture within, it’s all about the water and pressure. Water is the lifeblood of concrete — without a sustainable amount of water in a concrete pour, the substrate weakens and deteriorates prematurely. However, if there is excess water in a concrete slab, the pressure will force a rise in moisture, developing a condition where the substrate does not adhere coating properly.

Applied coating to substrates that have excess moisture is subject to decontamination, and coating system failure. Understanding solutions for moisture problems are key. Looking at concrete composition assists with determining the moisture content within concrete substrates.

What’s in My Concrete Slab?

Many people interchange terms “concrete” and “cement”, but one is actually a part of the other. Cement powder is created by mixing the materials of water, sand, and aggregate together. A chemical reaction happens when mixing these ingredients, the additives bind, and the result forms a concrete substrate. The curing process can take several weeks as it’s contingent on, the concrete pour thickness, the ambient temperature, and air humidity.

The curing process of the concrete substrate can still contain nearly two-thirds of moisture from the original mixture. This excess amount of water does not allow for the coating system to properly adhere to the surface. The concrete continues to dry overtime through moisture vapor transmission. The porous substrate contains pressure that causes moisture to surface in the slab through capillary action and then evaporates into the atmosphere. Conducting a moisture test is the best way to determine if concrete is dry enough to receive a coating system, or if moisture mitigation is necessary.

Moisture Testing in Concrete

Measuring the moisture vapor emission rate (MVER) is the calcium chloride test that is most commonly used. This examination is typically administered every 1,000 square feet (93 m²), and it consists of sealing a small amount of calcium chloride beneath a plastic dome on a clean section of concrete.

Salt absorbs the moisture under the dome for 72 hours. During that time weight gain is calculated, and used to determine the MVER. This method is the standard test method for measuring moisture vapor emission rate of concrete.

The relative humidity method is another test where “in situ” probes are inserted into the substrate via drilled holes. This method measures the moisture content within the substrate rather than just the surface as described in ASTM F2170 (The Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes).

It may seem that moisture issues only occur with newly poured concrete, but older concrete slabs also require moisture mitigation. A major moisture problem could be hidden within the porous composition of concrete, if the curation process was altered during the original pour, excess water was added to the mix, or the vapor retardant was faulty. For this reason, moisture tests should always be conducted prior to the application of any concrete coating system.

The Concrete Moisture Solution

SealWell inc mechanically prepares concrete and applies a moisture mitigation system as a solution to moisture issues. Sealwell uses a three-component, water-borne, solvent-free, moisture-tolerant epoxy, and high-performance cementitious self-leveling slurry mortar, as an effective moisture mitigation system.

This specialty formulated chemical process takes the standard A and B components (epoxy and emulsion hardener) and mixes them with a C (cement copolymer). This cement copolymer cross-links with the water in the concrete substrate and creates a bond that is stronger than upward moisture pressure. In other words, this system blocks moisture rising to the surface and distributes it laterally throughout the substrate. The expert technicians at Sealwell can perform moisture tests on any concrete substrate. To test the strength of your concrete slab, or for services such as Concrete Polishing give us a call at 1-877-843-9816.