Oil and water. Most people wouldn't paint over a sandy surface. Rub your finger in any mortar joint and you will see sand on your finger. If the mortar doesn't bound well to itself, than how can we expect a paint to bond to the mortar joint. Mortar joints and convential stucco have similar characteristics in that they are primarily made up or consist of sand. For example:
The Ratios for a covential general building stucco system are as follows:
sand : cement sand : lime : cement
5:1 5:1:1
That's alot of sand. Don't get me wrong, it can be done. But it has to be done professionally. Pointing for brick or block, sealing, parging, wrapping, priming and finally finishing is the way to properly apply either elastomeric or acrylic paint or finish over masonry walls. If it is done any other way, then the system will fail eventually and then everybody and the next guy will blame the EIFS finish for the delamination. It never fails.
RFS