Stucco PH effect on coatings

[Unregistered-Greg-Fine]

I, a former Paint camtractor, have had a very similar experience with Elastomeric over stucco. Though I applied Elastomeric over stucco already coated with a reliable Elastomeric, that upon inspection appeared to have no “faults or defects”, the coating that I applied dicolored and eventually blistered and emitted effloresence(a powdery substance). I assumed it was the Elastomeric that I had applied so I peeled some it off and sent it ti KTA testing lab which determined that the Elastomeric was OK. I have since tested the stucco immediately after exposing it tothe elements and found it to be “hot”, which means that it has high alkilinity. Further research with the PDCA has led me to discovery that paint coating exposed to high PH “will: discolor, lose adhesion, become brittle, blister or a combination of these.”
Most likely the stucco over which the DE Elasomeric was applied was not cured(hadn’t reached a neutral PH and the non breathable coating locked in the high PH causing the blistering that you are experiencing. I do believe that removal of the Elastomeric so that the stucco can complete the curing process is the best solution. Bead blasting would seem the most effective way to accomlish removal.
I’m Greg Fine @ gregfine@cableone.net