"It seems we can just keep scraping and scraping, and the paint keeps peeling off the wall" was the comment from our painter.
At a recent commercial warehouse repainting job, we encountered some paint that was peeling off the concrete wall. Not too unusual a situation, so we scraped and cleaned the area, and (after spot priming) painted the wall as usual. But within a couple of months what we thought had been corrected was continuing to peel, and peel, and peel. The areas we had scraped to bare concrete were fine, but other areas were now causing further problems. What was going on?
A bit of research, some deeper investigation, and consultation with a representative from the Master Painters Institute (MPDA) revealed something was hiding "under the covers." Under the paint coating was a textured finish, and that finish was poorly bonded to the concrete wall. In places the texture and paint had been previously removed, and similar to our earlier work, this was now holding on tight. But under the covers, beneath the texture, we found a powdery substance that easily dissolved in water. This was acting as a "bond-breaker" between the texture and the concrete, and literally breaking the hold of the paint and texture to the wall behind.
In this case, there was a second complication -the color. The recently darkened bottom band was causing the area to get much hotter as the sun shone on it, and this was aggravating the problem. The opposite wall (facing North) showed no similar peeling concerns. It's likely that the extra shock of heating & cooling caused by the sun beating down on this section of the wall was just too much for the already weak bond the texture had to the wall.
The proper solution was to fully remove all the texture and paint on the area affected, and then clean, prime and repaint. Unfortunately that was an expensive solution for the customer. Our final process included fully hand scraping over all the lower painted area, and removing any evidently loose or bubbling areas. We then cleaned the powdery residue, and primed with a unique primer from Sherwin Williams called Loxon. It can handle uncertain substrates like this poor concrete, and also the higher Ph (alkalinity) that goes along with it.
The finished product was good, and a recent review showed the areas we'd addressed were now holding tight to the concrete wall. A reminder, to always look under the covers!