mp-75 is indeed used in an out.its a german material that u never wana use by hand.awful.it was designed 2 run thru a plaster machine g4-g5 etc.there are2types 1gypsum 1silocne.i have used it thru a machine in both holland and germany
yes score the wall for key then use bond it or if u are on a budget give it a coat of neat pva with a roller,let it dry overnight then give it a second coat jus before skimming
id say the walls most certainly werent prepeard properly.when over skimming espescially on painted backgrounds you must b careful 2apply a near pure coat of pva and score the surface first 4 extra key.i would av given it a coat of pva let it dry and seal,then applied a second.as the second coat...
mp-75 is a god awful material when use by hand.its a german material designed 4 use thru a plastering machine,with diff types 4external work .its not2bad then.who can ever say ant thing about sand an cement 4 the money.if u want insulation go 4 silocone based scratch back colour system.