Efflorescence? on plaster from removed chimney breast in first floor bed room

3 Sep 2016
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United Kingdom
Hi guys,

First time posting here, been on here quite frequently over the last few years for info and advice, the forums here are really good knowledge base for the DIY noobs like me, so thanks! :D

Any how, we bought a Edwardian Mid terrace about 2 years ago and we've had a few issues with damp in the back bedroom where the chimney breast was removed, when we bought the property the room had been freshly plastered and painted so it looked fine.. however over the last two years a monstrous damp patch has appeared and the paint is constantly flaking off..


We've had several roofers out to look at the remaining chimney stack above the room in this corner, its been re-pointed, re-leaded and re-capped - as far as the roofers are concerned their cant be a leak. (I've checked on a wet day and it is dry in the loft above the room).

The wall to the right is the adjoining wall to next door and is 2 skin solid brick, with what looks like a gypsum based plaster, the window wall is cavity, with bonded bead insulation, the external pointing is in good condition.

The only remaining thing I can think of is that the plaster is contaminated with salts causing efflorescence, the salts could potentially left behind from a previous leak or through the process of burning fossil fuels over the last 100 years the property has stood.

We're expecting another baby, so I've been tasked with 'sorting out' the room on a shoe string budget! So i'm not allowed to call in the pros!

I'm thinking of removing the plaster and either re-plastering with renovating plaster with salt inhibitor additives, or alternatively battening and plaster boarding. I may call in a pro to do the final skin (I have found in hindsight, I'm not the best for finishing plaster lol)

Any suggestions? Anyone have any similar experiences? Any Advice would be appreciated, thanks
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Why would a seller plaster and paint just before a sale?

When a c/breast is removed the soot impregnated flue brickwork remaining needs to be wire brushed clean of all surface soot, and two coat SBR'ed - with the second coat tacky its necessary to render with a 4:1 or 3:1 sand & lime mix.
A remedial skim (non-gypsum) is used as a finish.

You should hack-off left to the window reveal corner bead, and right 300mm past all signs on the party wall.
Work from floor to ceiling.

Does your neighbour complain of damp or staining?

Why not post pics of the loft area. and externally, the outside wall and chimney stack?
Did any of the roofers supply you with a video of your roof/stack?
Thanks for the swift response vinn, really appreciate your advice!

Sorry for all the questions to follow!

The whole house was re-plastered as part of a renovation, to be honest we didn't really think it through as to 'Why' being a first time buyer! Obviously we made a mistake there! This is causing a bit of headache down stairs too as they have removed the original lime plaster and re plastered with gypsum, this seems to be trapping a little moisture at the foot of the walls causing salts; given the lack of a proper damp course, it doesn't help either that the previous owner thought it would be a good idea to install concrete floors throughout removing the suspended floors - but that's a whole other story!

I know i'm gonna have to hack the whole lot back to the brick - thanks for confirming, I intend to start this tomorrow. I've got a decent SDS drill with the chisel pieces - i'm guessing this will be the easiest way to remove the plaster? Little paranoid that the chimney stack might fall thorough while i'm hacking away; so if you dont hear from me again, i'm most likely already burried!

I've got a mostly full tub of Cemoentone SBR left from another job -can i use this stuff? (pic attached) Also do i literally just paint the stuff on as it is? Do i need to PVA the wall aswell?

For the finishing skim, whats the best plaster to use? Hydraulic or non Hydraulic lime? Is Lime plaster more difficult to work with than gypsum?

The neighbour still has the chimney breast on their side, however its no longer used and is capped. They dont have any damp/staining on their side, however its worth noting that the neighbours ajoining room is their bathroom and that wall is fully tiled - the damp on our side is only present at the top of the wall, not the bottom which leads me to believe that it cant be caused by a leak on their side?

I've attached a picture of the external wall; I cant get into the loft at the minute to take a picture (ladders at my parents and the loft hatch is above the stair well, so i'm looking at a 20 foot drop if i try climb it!) The roofers didn't provide any pictures or videos - i'll bare this in mind in future, never thought of asking for it before!


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Thanks for the photos.

You would be as well to, in agreement with your neighbour, remove that stub of a shared stack, & any remaining c/breast below. Roof over the ridge space remaining.
Its fairly common now for roofers to supply a before and after video.

The gable looks as though it could do with a complete pointing.

The Cementone is fine. Dont use any PVA.

Use NH Lime from any builder's supplies. The render is exactly like, and as workable, as sand and cement. Dont confuse it with lime putty.

Forget about loft phots. Later you should remove the loft hatch to a safer location.

If you want to discuss the GF damp issues post photos of inside and outside at ground level.
I notice you that have render on the GF to FF height. Render is often applied to hopefully prevent damp penetration - your neighbour has a fully rendered gable half.

You could inform your neighbour about your soot residue & they might get their blocked off flue(s) swept.

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