Sometimes plastered solid walls become “blown”, i.e. the basecoat becomes separated from the bricks behind. This can be detected by tapping the plaster: it will sound hollow where it is blown. It could stay like that for many years without trouble or it could crumble and fall away at the next shock wave from something as simple as an external door being slammed.

A simple fix for small areas is to glue the loose areas back to the masonry with PVA bonding. Using a 6mm Masonary drill bit in a drill set to normal (not masonary) carefully drill a hole sloping 45deg down near the top of the loose area and work a length of 6mm tubing into the hole. Seal around with plastecine.

Attach the other end of the tube to a washing up liquid bottle with the bottom cut off to form a funnel and securely tape it to the wall above. Fill the funnel with PVA watered down to the consistency of full fat milk and leave it to flow slowly into the hollow between the loose plaster and the brick.

Pressing the loose area gently in and out will help the flow and spread the bonding. A second hole at the bottom of the area will tell you when the bonding has got there. Don’t try and hurry things with a squeezy bottle or you could push the plaster off and break it. Remove the tubing before the glue sets or you may pull more plaster off when you remove it. It should be fixed and dry in 24 hours.

If the area is large the above process will most likely not work as even drilling a hole may cause the plaster to fall away. These large areas are best treated by removing the plaster entirely and putting a new basecost and finsh coat on to blend in with the existing plaster.

This method will not work for for Lath and plaster walls as the glue will most likely run behind the laths and hence not stick the two together.