learnig to use bonders when you use masonary over masonary is a really tricky biz.. the bonders have ideals i`ll not go into because the lhe time i redid the gunite(sp?) on my swimming pool, i screwed up about $2000 worth of work. turned out fine in the end. i did learn that the bonder i had used had to be coated before it became dry to the touch(w/masonary). there are lots of other considerations: including temp. humidity; set up time; amount of tempering,# of bags per mix, oxygen-alitude-and so on really research the techinique you plan on using when you tear ever thing out and starting out new.