mp75 needs ruling two or three times, initial ruling soon as sprayed on to flatten , let pick up rule again wif rule at nearly 90 degrees to open face, leave to pick up more and spatula to tidy up, this is where you need to leave it as long as possible before spaying wif water and sponge floating laying in the fat as u would laying a wall down when skimming, second trowell should be left as long as posiible to ,as face tears if u go over to early, 30 mins later polish, as for prices i ve heard as little as 4m2 but 5m2 is average, if ur good at ruling u should be ok, just dont get on it to quick