Epoxy floor coatings can fail for various reasons, and one significant factor is the presence of water in the concrete slab. Moisture testing should always be performed before installing a flooring system, but sometimes it gets skipped.

Another common cause of epoxy failures is improper surface preparation. However, even if properly prepared, the excessive moisture content in a slab floor would likely lead to problems.

We have created this helpful guide to teach you about epoxy flooring failures, why they happen and how to prevent them.


How Moisture Affects Epoxy Flooring

Moisture has detrimental effects on epoxy coating’s performance and durability. Excess water in concrete creates a barrier that inhibits the flooring from adhering securely, leading to delamination and peeling.

Also, moisture causes concrete to expand and contract, leading to cracks and other concrete substrate movement. These shifts can transfer stress to the epoxy coating, causing it to crack, chip, or develop other structural defects.

Finally, moisture trapped beneath the epoxy can create a humid environment, promoting the growth of mould, mildew, and other microorganisms that can compromise the aesthetics and hygiene of the floor.


Moisture Testing Before Coating Concrete

A reliable method to prevent epoxy floor coating failures is to conduct moisture testing before applying the coating. Two commonly used tests are the calcium chloride test (ASTM F1860-11 Standard) and the in-situ relative humidity test (ASTM F2170-11).

It’s crucial to use the test specified by the floor coating manufacturer and adhere to their moisture content requirements during the application process.


The Calcium Chloride Moisture Test

Calcium chloride moisture testing in the flooring industry dates back to the early 1940s and was developed by the Rubber Manufacturers Association, Inc. This test measures the moisture in the top ½ to ¾ inches of the floor.

Typically, a moisture vapour transmission reading of 3 to 5 lbs. per 1000 square feet is acceptable for coatings. However, it’s essential to consult the manufacturer’s application directions for specific requirements.


The In-Situ Relative Humidity Test

Measuring relative humidity within a concrete slab is a newer technology. This test involves drilling a hole in the concrete and inserting an electronic probe.

The hole is drilled to 40% of the slab’s depth, and the moisture content at that level is measured in relative humidity. Generally, a reading of 75% RH is deemed acceptable for coatings.

Again, it is crucial to follow the manufacturer’s application guidelines.


Painting Over Wet Concrete

If the concrete slab is wet, certain epoxy coatings can be applied as primers over damp concrete, followed by the desired top coat. However, it is vital to strictly adhere to the manufacturer’s recommendations.

When addressing moisture remediation, using coatings from different manufacturers without written consent from both parties can lead to potential issues, including finger-pointing and voided warranties.

Understanding and addressing moisture-related concerns before applying epoxy floor coatings minimize the risk of failures and ensures a successful and long-lasting flooring solution.