Growth on wall after bubbling
- Thread starter mark1a
- Start date
Will take months or longer for this to subside.
Would 50/50 white vinegar help temporarily or even take the wall around the area back to brick plaster then skim? With a baby on the way and other rooms to decorate, this is not what I wanted.
External and I wouldn't have a clue on the brown colour plaster
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- 1 May 2018
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Seen it in my house. My theory is wall is salt poisoned due to coal fires in the past and combustion products reacting with lime etc. to form salts in the wall. When you apply a new wet trade, the water absorbs the very soluble salts, and then as the water evaporates from the surface as the plaster dries (or dab), it leaves a salt deposit on the surface. The salts are hygroscopic and draw water vapour out of the air to grow crystals.
In my case I see this effect (to a far less and controllable degree) coming out where the dabs are on a PB overboard of a wall where I know a coal fire burned every day for over 100 years.
In the worst areas around the fire places, I have SBR slurried the bare brick wall in the affected area and then fixed PB over with foam adhesive. Seems to have cracked this nut 100%.
If it's a small area only, I would cut a square back to brick (diamond wheel in a grinder - dusty but neat, or if the plaster is soft, maybe a multitool which is less dusty. Not hammer and chisel - you'll likely drop the whole wall if it's old plaster), fix in a piece of PB with foam, chamfer the edge of the original plaster around the cutaway, scrim the joint and skim over.
In my case I see this effect (to a far less and controllable degree) coming out where the dabs are on a PB overboard of a wall where I know a coal fire burned every day for over 100 years.
In the worst areas around the fire places, I have SBR slurried the bare brick wall in the affected area and then fixed PB over with foam adhesive. Seems to have cracked this nut 100%.
If it's a small area only, I would cut a square back to brick (diamond wheel in a grinder - dusty but neat, or if the plaster is soft, maybe a multitool which is less dusty. Not hammer and chisel - you'll likely drop the whole wall if it's old plaster), fix in a piece of PB with foam, chamfer the edge of the original plaster around the cutaway, scrim the joint and skim over.