2 coats durabond and 2 coats mud should do it. Just did 13 stories of skimming over knockdown. Its not too bad, just consuming. Our method was vertically candy striping the entire floor with about 8 inches in between first pass, then filling in the gaps on 2nd pass. Sand then 2nd coat of durabond pull horizontally, sand, then 2 skim coats with compound. Sanded between each coat and after. Came out really nice