The largest financial problem in the resinous coatings industry is failure due to moisture.  Some estimate this problem to cost over 1 billion dollars per year in the United States.  This article will hopefully shed some light on not only the problems but how to correctly test a concrete slab for moisture.

Let’s start by looking at ways flooring can be exposed to moisture in the concrete.

1. Water of Convenience:  Simply stated this is the water used by the concrete company to keep the concrete “wet” enough to be able to properly place it.  The typical cement to water ratio should be .45-.50, However, today we are seeing these ratios climb to give the concrete crew more time to “work” with the concrete.  This water typically hydrates the curing process and then excess water evaporates.
2. Improperly Installed Vapor Barrier:  This is material placed before the concrete is poured with the design to block or slow down moisture from the ground finding its way into the slab.  There are design standards for this, with the main goal being to reduce the permeance of water into the concrete.
3. Inadequate Water Drainage:  Water from rain or snow melt that doesn’t properly drain away from the building.
4. Concrete Being Exposed to Rain/Snow:  If the building and concrete are exposed to these weather elements before it becomes enclosed, it will add unexpected water to the concrete.

As a contractor, testing for moisture in concrete is a must.  Yet it is estimated that 90% of all flooring contractors do not possess the proper testing equipment, and those who do own the equipment do not follow ASTM guidelines.  The largest ASTM guideline not being accounted for is NOT TESTING A CONCRETE SLAB THAT HAS HAD AT LEAST 48 HOURS TO ACCLIMATE TO IT’S SERVICE TEMPERATURE.  Improper testing leads to misinformation which leads to bad decisions which leads to flooring failures.

In today’s construction environment everything is about time and money.  Building owners are anxious for their building to be ready to occupy, and the general contractor makes sure that happens.  This “fast-track” method typically does not account for the 72 hours to allow a proper moisture test to be completed.  If the testing is completed and shows high moisture content, there are another few days to properly install a topical moisture mitigation product, such as Thermal-Chem’s #211 VaporGard.

Two tests that provide false negative or false positive tests are the Plastic Sheet Method and the use of a moisture meter with pins that are pushed into the concrete.  If you are going to rely on these tests, it is recommended that you exclude any future problems as a result of moisture damage in the Terms and Conditions of your proposal.

The two tests that are typically accepted by ASTM and architects are the F-1869 Calcium Chloride Test and ASTM F2170 In-situ Relative Humidity.  The calcium chloride test presents its results in lbs. per 1000 square feet, the relative humidity results are given in the percentage of moisture in the concrete.

Our #211 VaporGard has been independently tested lab in 2022, and the 4 samples effectively reduced moisture vapor transmission by 80%.  Thermal-Chem is committed to helping you complete your projects from the beginning through the useful life of the products you have installed.  If you have any questions, please call us at 1-800-635-3773.

Several years ago, the International Concrete Repair Institute (I.C.R.I.) released Technical Guideline No. 310.2R-2013 “Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays, and Concrete Repair”.  This guideline provided ten surface profiles that were considered to be acceptable for various types of systems to be applied to the concrete.  The purpose of this guideline was to provide an industry standard to reduce the large number of coating failures due to insufficient concrete profiles. Surface Prep Profiles as Defined by ICRI No 310.2R-2013 The use of mechanical profiling of concrete that has had curing compounds applied to it is considered the most effective way to remove the curing agents while creating a bond profile for the coatings to adhere to.

Diamond Grinding

This method uses various grit diamonds to grind the curing compound off.  Again, various bond profiles can be achieved with this method. 

Shot-Blasting

This method utilizes small metal beads that are “shot” at the concrete and then reclaimed through a high-powered vacuum system.  By utilizing different size beads, different profiles can be achieved.  Other methods of surface preparation such as acid-etching, light sanding, and power-washing are no longer considered acceptable.  These methods do not remove the curing agents applied to concrete in most cases. To conduct a basic field test to see if your concrete substrate is ready for a coating to be applied, place a few droplets of water on the surface.  If after a few minutes the water remains on the surface, adequate removal of the curing compounds has NOT been achieved.  However, if the water is absorbed into the concrete, the surface tension created by curing agents has been removed.   WHY EPOXY COATINGS FAIL For any questions concerning Surface Prep, contact Thermal-Chem at 1-800-635-3773.