Selected Answers

From Bill Slama of International Paint/Ceilcote Products on January 25, 2018:
Most readers probably noted the typo for surface s ...read more Most readers probably noted the typo for surface strength in  my earlier answer to the question on when concrete is sound enough to receive a thick-film coating. "3000 psi" should be "300 psi"

From Bill Slama of International Paint/Ceilcote Products on January 23, 2018:
First, it is important to know why the surface str ...read more First, it is important to know why the surface strength of the concrete substrate is important. The thick film coating or lining needs to be bonded to the concrete surface to function. And the coating will transfer stress to the surface of the concrete due to shrinkage, thermal stress because of the different coefficients of thermal expansion and potential localized loads to the surface of the coating/lining. All of those potential stresses transfer from the coating/lining to the surface of the concrete. If any of these exceed the surface strength of the concrete, the concrete can break (shear) underneath the coating/lining, and in nearly all cases, the lining will crack and not be able to protect the substrate. There is a convenient way to measure the strength of the surface after it is prepared. That is the "pull-off" test per ASTM D 7234. The concrete should be prepared first so that any weak surface laitance or contamination is removed. Manufacturers' minimum surface strength may vary, but most thicck film coatings or linings typically require a minimum surface strength of 3000 psi (2 MPa). Some thin film coatings are stated to require 150 or 200 psi surface strength.