No primer needed. If there's a lot of them, touch up the patches 1st with the masonry paint. Check the existing painted area for big blistered areas which look ok at 1st glance. Heavy coat for 1st coat which will make the second coat just a skite. Check for any staining burning through after 1st coat & seal up with any oil based paint then 2nd coat. Bucket trough style tray, not the flat diy things, big roller sleeve which you may have to change after 1st coating. Hope this helps