8. Measuring the Pull-Off Adhesion of Coatings on Concrete
Testing coating adhesion on concrete substrates using a pull-off adhesion gauge is similar to testing coatings on metal substrates. However, there are a number of differences in the test procedures and equipment used.
Firstly, as the coating adhesion values on a concrete substrate tend to be considerably lower than those on metal substrates, a 50mm diameter dolly is most commonly used. This allows for consistent and more reliable results at low pull-off values.
Secondly, as the dolly diameter is two-and-a-half times larger than a standard 20mm dolly (or pull stub) used for other substrates, either the gauge used or the actuator skirt will be different.
Gauges such as the Elcometer 106 Scale 6 are designed specifically for testing coatings on concrete, as are the Elcometer 506 and Elcometer 510, which have specially designed dolly skirts for use with 50mm dollies.
Thirdly, as coatings on concrete have a lateral bond strength that can produce misleadingly high values, if the coating is thicker than 500 microns (or 20 mils), the coating must be cut down to the substrate, and it must be cut before adhering the dolly to the substrate.
It is also worth noting that coatings less than 500 microns (or 20 mils) thick may also require cutting, but this would be at the request of the client or contractor.
Either way, whether you cut or don’t cut, it is important to report what you have done, and then ensure all adhesion tests are carried out in the same way.
This video is part of a series on Pull-Off Adhesion Testing, to view the series playlist please click here.