Coatings on Tips and Tricks:

NOTE: The following comments are the opinion of the author based on experience using the following equipment in both a laboratory and field environments. Any comments are welcome and can be forwarded to me at tswan@cci-inspection.com

Doe to interest in coatings on concrete, below are some tips and tricks for measuring and checking coatings on concrete. Unfortunately, due to the nature of concrete, there are some inherent limitations on measuring and testing coatings on concrete.

How can I measure the thickness of coatings on concrete?

Electronic “non-destructive” gauges

One of the questions I get most often is can I use a “nondestructive” Dry Film Thickness (DFT) gauge to measure coating thickness on concrete. There are several manufacturers that make instruments for this purpose.  These instruments work by sending ultrasonic pulses into the coating. But they do not “assume the wave will travel through the substrate at the same rate”. In fact, the principle of operation entails reflecting the pulse from a material different than the coating, i.e. the substrate. Therefore the make-up of the substrate does not effect the accuracy of the meter.

We are a Distributor for Dakota Ultrasonics and we are currently working with a DAKOTA CMX Meter to measure coatings over concrete.  After our current evaluation period I will update this article with the results of our testing.  The problems discussed below will still continue to be a problem but within those restrictions, we believe we can get an accurate measurement.

The main problem is unlike metals, even freshly prepared concrete has a profile. When preparing concrete to accept coatings, several methods may be used to roughen up the surface to improve adhesion of the coatings to the concrete. This profile can be a few mils to 20-30 mils or greater. When measuring thin film coatings on concrete, between the difficulty in the meter establishing the surface as well as the profile being close to the thickness of the coating, getting any accuracy in the measurement is unlikely.

On thicker coatings, generally you have a greater profile and if you have a 20-30 mill profile on the substrate, again it will effect the accuracy of the reading.

If there is any aggregate in the coating material, such as in non-slip coatings, a UT type DFT meter will not work at all.

Since I have no field experience with these new meters I can neither vouch for their accuracy or inaccuracy.  Bottom line, if you try a “concrete” DFT meter, make sure you can return it if it does not work.

Destructive Gauges.

Some good news. You can use a Paint Inspection Gauge (PIG) or Tooke gauge to measure coatings on concrete up to about 60 mils. This is a destructive test and does have some limitations. It can be difficult to make a good cut in concrete due to the unevenness of the surface. It may take several cuts to get a good straight cut and you are only measuring the thickness where you make the cut. It can give you a general idea of the coating thickness.

I generally find the Elcometer 141 works well because of the solid base on the cutter. While I have not used it, I understand that the Elcometer 195 (Saberg Drill) works well.

How can I Measuring the surface Profile of concrete?

The only good current standard to measure coatings on concrete are the ICRI Technical Guideline No. 03732 - Selecting and Specifying Concrete Surface Preparation for Coatings, Sealers, and Polymer Overlays

This document and comparator set provides a useful written and visual guide to selecting an appropriate method of concrete surface preparation prior to the installation of a coating, lining, or other protective system. Discusses the unique aspects of 12 different surface preparation and cleaning methods: detergent scrubbing, low-pressure water cleaning, acid etching, grinding, abrasive blasting, shotblasting, scarifying, needle scaling, high- and ultrahigh-pressure waterjetting, scabbling, flame blasting, and milling/rotomilling. Appendices discuss selection processes, sealers and coatings, safety, and additional reference standards. Published by the International Concrete Repair Institute (ICRI)

What is the best way to measure Adhesion on Concrete surfaces?

The key to getting Adhesion good measurements on Coatings on concrete is to use a large surface area on the dollies. The Elcometer 106/6 is made specifically to test adhesion on concrete. It uses 50 mm (2”) dollies and measures to 500 psi.. The reason for using larger dollies is to compensate for any imperfections in the concrete. By using a larger surface area, it minimizes the effect of a “weak” area in the concrete. The other meters that work well on concrete are the DFD series of adhesion testers. These are the Elcometer 1940 and 1941. There are a number of dolly sizes available up to 70 mm or 2.76 inches.

The main limitation of using larger dolly sizes it reduces the strength that the dolly will pull at since the PSI needs to be divided by the increase of surface area of the dollies. In general, if a coating pulls at 250 to 300 psi on concrete, that is generally sufficient to meet the specifications of most of the coating manufacturers. Uncoated concrete will generally pull at 150 to 250 psi.

Note that some of today’s high strength concretes can now pull in excess of 1000 psi.

Finding and measuring rebar in concrete

The Elcometer Protoval 331 cover meters can be used to locate rebar in concrete, determine its depth and even determine it’s diameter to within one size. For additional information check out these meters in our web store under the Protovale category.

Corrosion potential of the rebar:

The new Protoval covermeters now have half-cell capabilities. This helps determine if the rebar is stable or corroding.

If you need to determine the hardness of the concrete, we now sell Concrete test Hammers