Had a very similar problem to this last year grade 2 listed thatched cottage burnt down on the rebuild building regs wanted insulated plasterboard conservation officer was having none of it ended up using a pre bagged nhl lime with insulation in it
not sure why it happens! Could it be that yesterday was very hot? 26 degrees? I properly pva’ed it and waited until it went tacky, by the time I plasteted that section of the wall the pva would have dried, could that be it?
edit: they little crack marks feel completely smooth, they arent actual cracks they just look like it..
i think it was over watering after applying. I pvaed the walls three or so times the days before and just before plastering. I noticed that ifI wasnt fast enough on big walls the plaster would go off too quick so when I was doing my first and second dry trowel to polish it up, i needed to add water.
the areas where I added more water almost always ended up crazing.
did another wall and decided to test so very little water to dry trowel and had no issues.
eitherway, my job is now done and im ready for the little one. Its definitely got me interested in doing more plastering (maybe for mates and not as a job though!). You guys work hard and I honestly think its the biggest craft skill going. Super hard to get right, I had lots of respect for plasterers, having done my upstairs ive got even more now.
At least on site I can sound like I know a bit more about your craft.