How do I deal with efflorescence

sounds like cold spots on your walls, check your external wall that aline to your internal walls in question,one remedy you can try,bleech or honestly vinegar.but this is a short time remedy but it could work,long term if treaded right,also salts coming through off the bricks behind the new plaster.because of moisture still in the walls.could also be salt that is in the sand that has been used in your plastering. try also a salt neutraliser called permagaured ! Apply directly to brick or stone when it froths you know then that salts are in the stone or brick spray it on or with a brush dilute with water 3 parts permagaured 1 part water it will work allow 24 hrs then plaster your wall ! Regards Martin MJ PLASTERING.