The best way to address moisture-related issues is through testing and using a moisture mitigation system.
Moisture testing is typically completed when project specifications require it. The ASTM D4263 Concrete Moisture Test using a plastic sheet is one of the oldest methods for testing moisture in concrete. Typically conducted on unprepared concrete, this test is highly flawed by today’s standards and provides only qualitative results which are subjected to inspector interpretation. ASTM F1869, Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride, is a better option if protocols are followed. Contractors must prepare about 0.09 m² (1 sf) of the surface, exactly how the floor will be prepped for the coating application. Then, they will adhere a dome-covered petri dish of calcium chloride onto the floor, leaving it there for up to three days undisturbed to determine the rate of moisture vapor emitted from the concrete. Finally, relative humidity (RH) testing is the preferred method, as it measures the amount of RH remaining in the concrete. It is generally accurate, but it is important to remember all concrete contains moisture, and RH testing does not address how much moisture is actually coming to the concrete’s surface. More importantly, it does not reveal the concentrations of hygroscopic elements such as calcium hydroxide and sodium hydroxide. These concentrations are not identified by either RH or ASTM F1869.
For many jobs, moisture testing is not performed. Therefore, what should installers do if they suspect moisture, or if they encounter a problem through moisture testing? They need to mitigate the moisture, and this must take place before the concrete is coated. Otherwise, it is too late to stop the moisture from affecting the flooring.
The three most common types of moisture mitigation systems are barrier, breathable, and reservoir systems.
A barrier system blocks the rate of moisture transmission by providing a low-permeation, high-density base for either penetrating or topping. These systems feature very dense resins and will help to tie up the free salts that form as moisture moves from the concrete to the flooring bond line. A non-breathable floor coating can then be applied on top of the barrier system with confidence.
Both breathable and reservoir systems allow moisture in vapor form to pass through their films at a controlled rate and then dissipate, rather than condensing into a liquid. They are appropriate for use with a thin-mil coating which does not require non-breathable properties and will be applied over concrete which has a low CSP. With a reservoir system, however, a contractor can have a greater CSP and apply thicker, non-breathable flooring systems on top, as one might do when trying to achieve elevated chemical resistance for the floor.
Potential floor failures
There is a wide array of causes for flooring failures, several of which are described below.
One of the most important functions of resinous flooring is to withstand a certain amount of abuse, particularly from chemicals breaking down an insufficiently chemical-resistant coating. Building a coating system to resist chemical abuse can be challenging. Some questions to consider include:
- What is the highest concentration of each chemical likely to spill onto the floor surface?
- At what temperature will the chemical be applied to the floor?
- How long will the chemical remain on the floor before it is cleaned off (its “dwell time”), or will it be washed off at all?
These questions are important to address, since the longer a concentrated chemical remains on a floor, the more any added water evaporates, leaving a higher concentration level of the solution behind. This higher concentration may exceed the chemical resistance capabilities of the coating, making it critical for specifiers to understand every potential chemical exposure and duration before deciding on the floor coating.
