In article ,
Cordless Crazy writes:

Did a bit of plastering the other day. Put undercoat on to normal depth,
but it cracked/crazed and went off very quickly. Am I right in thinking
it was because to backing wall was too dry and sucked the moisture
out?very

Possibly. Another reason could be you did it too thick in one
coat. Plaster shrinks anyway as it goes off which you normally
don't notice as the layer just gets thinner, but if the layer
is too think, it can crack across too.

This doesn't necessarily matter as long as it's not loose. The
cracks will provide more key for the finish coat.

Going off too quickly can be due to high temperature or old plaster.

--
Andrew Gabriel