Here is what I did

Moderator Post: > Popcorn removal Answer by Handyman on 01/30/2008

Greetings, I scoured the web trying to find this answer but could not find it so after successfully doing it I'm posting my method.

I simply did it the same way as if it wasn't painted. I really had to soak it though and the water did penetrade to the drywall. It doesn't turn pasty but it will come off in sheets.

As far as technique, after soaking I put a trash lid in my left hand and an 8" scraper in my right and ran the blade from one wall to another catching it as I went along. Then I ran the blade corner down every seam where the wall met the ceiling, then I took a block sander and hit the same seams. Make sure it is level and it is read to paint. Oh yeah, make sure the ceiling is completely dry before sanding. Good luck.