I'm trying to undercoat plaster a brick wall that is now inside a
conservatory. I'm using browning which I am mixing fairly wet, also
wetting the wall. There is some cracking of the plaster as it cures but
more worrying is small patches that sound "hollow" as if they haven't
bonded to the bricks.

Is this likely and do these areas need to come off and be re-done?

Any idea how I prevent this from happening?

Thanks,
Jon