I got excellent advice here a month ago, to use Peel Away I to strip paint off 70-year-old plaster walls where it was cracking and peeling. I did that, only to find that there were several serious areas of cracked plaster beneath the 20+ layers of paint. Should I tape or otherwise mend the more serious cracks before I apply the skim coat of joint compound? Also, I've found some strange (to me) repair stuff in some cracks; it's bluish white, smooth and non-porous. Should I leave it alone and just skim JC over it, or should I dig it out?