you were taught right mate, if you do pva before dabbing use any strength you like but its a waste of time and money.. just make sure the substrate isnt too dry or dusty... board adhesive isnt like skimming, its designed for medium - high suction backgrounds..
you dont need to pva thermalite blocks for dabbing so you shouldnt need to pva anything alse.. just dampen it down if its old bricks and get straight on it if its new stuff..