A section of the wall in our house developed flakiness due to dampness, prompting us to undertake repairs. Specifically, the affected area was located behind an air conditioner. It appeared that poor initial plastering, combined with water leakage from the old AC indoor unit, caused the concrete to become flaky. Consequently, the old plaster was removed, exposing the brickwork, and a new layer of plaster was applied by a professional mason. Once this was completed, I proceeded to apply a layer of waterproof putty, specifically, this product.
After allowing the putty to dry, I noticed certain areas that appeared thin, so I decided to apply an additional layer without sanding the surface. My intention was to maintain the layer's thickness. Although the resulting surface was not perfectly smooth, it wasn't of great concern since it was a wall hidden behind an air conditioner. The main objective was to protect it from dampness for as long as possible.
Once the second layer of putty dried, I proceeded to apply a waterproof primer. I used this particular primer, which, according to the technical data sheet, could be thinned with water. However, it did not explicitly state whether dilution was necessary. To clarify, I consulted with the shop owner from whom I purchased the primer, and he confirmed that thinning the primer was not strictly required.
Consequently, I applied the primer as is, without diluting it. As it began to dry, the wall started to exhibit flakiness:
Before long, the entire wall peeled off. I believe the primer removed a layer of putty as well. All labour lost.
In order to rectify the situation, I will need to apply another layer of primer. However, before proceeding, I need to understand why the primer peeled off. Do you have any insights into the possible reasons behind this issue? I believe I have to thin the primer, right?