adhesion failure

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The paint adhesion is failing in the areas you did not prepare (prime basecoat). The customer did not pay for stripping last time around, and the adhesion failure is apparently a continuation of what was seen 3 years ago. Proper preparation and good paint quality is indicated by the paint adhering to locations that were cleaned to the brick, primed and painted. Also note the paint is not delaminating between the layers you applied and the pre-existing paint, but is comming off the brick substrate. We don't know why the old paint fails, but when it does, it takes your newer application with it.

Moisture problems can be from above (leaks from roof) or below (infiltration from ground). For chimneys the problem may be cracked or missing chimney mortar cap and too small or no rain-shield. Look for evidence of poor drainga or failed gutters. Another source of moisture can be a lack of vapor barrier in the house and no ventilation between the brick veneer and structural wall. Some of these issues are beyond the scope of most painting jobs, but you should be aware of them.

If efflorescence is present, it must be neutralized with 5% muriatic acid and rinsing. Of course all loose paint must be removed. Failures may continue to occur unless the brick is cleaned to the point of failure by sandblasting or other stripping, and the salts removed, and the drainage repairs completed. As far as the wall goes, we assume it is well sealed by paint. If the surface is very porous, apply an alkai-resistant primer or block filler. Cover with latex house paint. Ask your paint dealer for help on this one.

Hope this helps. It covers a lot of ground, but there are lots of reasons for adhesion failure, and lots of places moisture can enter walls without coming through the paint layer. Its going to take some detective work.