Problem Solving Forum
June 24 - June 28, 2019
How do admixtures to concrete (hardeners, anti-dust compounds, etc.) affect coating adhesion? What can be done to eliminate or minimize negative effects?
Pierre Hebert of Mapei Inc on
July 2, 2019:
If I may add to a very well-written answer b ...read more If I may add to a very well-written answer by Mrs. Czora, whenever mechanical preparation is selected to address such a condition, ensure that all fines are properly eliminated from the pores.(This can certainly be considered as good trade practice.) More than often when I ask where is the brush attachment on vacuuming equipment, I generally hear back “I dunno…." This is unfortunate because agitating the surface with the brush attachment fitted on the vacuuming equipment is by far, way more effective in helping to pick up small particles. Applying a coating or an adhesive on a dusty surface (albeit, even as a trace) should be considered a “no-no”. Lastly, I would suggest the applicator considers verifying the absorption rate following the ASTM F3191 field test (including a time-stamped photo with a date) as part of his/her documenting the substrate condition before beginning subsequent work.
Warren Brand of Chicago Corrosion Group on
June 27, 2019:
The short answer is, they don't. As long as the c ...read more The short answer is, they don't. As long as the concrete is hard, porous and has a profile for adhesion (You can use ICRI's CSP standards.) and there's no film on the concrete (Pour some water on it to make sure it doesn't bead. I'm sure there's a standard someplace), you're good to go. Of course, make sure all of the other requirements based on the coating selected are in place. Some coatings can be applied (so they say) over "green" concrete, while others require a 30-day cure.
Zenith Czora of Durotech Industries, Inc. on
June 27, 2019:
The types and uses or functions of concrete admixt ...read more The types and uses or functions of concrete admixtures dictate the chemistry and the chemical reaction within the cement or minerals in the concrete mix. Admixtures most often are based on oils, petroleum products, glass silicates, inert and chemically active fillers, and wax stearates. Admixtures that function as densifiers or hardeners do form a glassy surface when overly applied, which is difficult to be coated over. Damp-proofing admixtures are based on wax stearates and or silicone/siloxane that prevent surface wetting. When those types of admixtures are present in the concrete, there is no way you can minimize negative effects. To be able to apply coatings on a concrete surface with those type of admixtures, the concrete surfaces need to be abraded or grounded to a certain acceptable profile to give key for the coating. Otherwise, a special type of bonding primer designed to prime a very dense and glassy surface can be used. A test patch should be carried out to ensure the compatibility of the coating system.