Rendering/plastering over black mortar??

[two5ey]

Hi all, we have had problems with water penetration in an upstairs bedroom.

The plaster has blown off the wall in big-ish patches revealing a crumbling black salty mortar. We believe we have found and fixed the source of the dampness and now need to repair the internal walls.

Does the whole wall need hacking away, the whole room, or just the cracked/crumbling patches?

What would I need to to do prepare the walls ready for replastering?

Would the underlying black mortar cause a problem in replastering at all?

Any help with this much appreciated.

 

[trowelmonkey1]

i'd suggest removing everything that has blown only, this will make the job easier than removing all of it, for both you and the plasterer, he can then fill out the areas you've removed flush to the existing level using the existing plaster to rule off, then skim the entire wall.

give the brickwork a good brush and let your plasterer look at it before you do anything to it and ask him if there's anything you can do to prep it for him, he'll have a method for the material he plans to use, he may even insist on doing his own prep though, with all due respect a customer never preps thoroughly/well enough in my experience and can lead to trouble later on.

if he's done the prep and there are any problems then it's his responsibility to sort it and he can't blame you for not prepping correctly.