Yes............ carefully remove the loose/blown areas (don't go mad as you don't want to disturb solid areas to much) treat bricks and edges of existing plaster with some PVA/water mix then re-plaster with Thistle Hardwall.

What does it mean when plaster is blown?

by thedoctor » Mon Apr 23, 2007 7:33 am. Plaster blows because it either has no, or has lost its, adhesion with the surface it has been applied to. This can be for a variety of reasons the most common of which are 1. The surface its being applied to is very porous.

Is blown plaster a problem?

It can be that hollow sounding plaster is absolutely nothing to worry about, as patches can lose their bond and be hollow very soon after application. If these areas are not that great an area, and anchored every now and again by adhered plaster, then there is often no problem.