Chimney plaster and green substance on bricks

[Cheshirecat44]

Hi everyone!

We have recently moved house. Our new house is real mix of ages due to several extensions, but the oldest part (part of the lounge and room above) is pre 1840 ish.
We have some damp in the chimney in the lounge, which we are getting sorted. Part of the chimney is plastered with modern plaster and part is brick painted with modern paint. As the damp had damaged both finishes, and assuming it was the original brick beneath it all, we started to pull off some of the plaster with the aim of replacing it with lime plaster.
However, we found a couple of unexpected things:

First, only part of the brick is original. It seems an additional course has been added with lots of cement - see pic. So now I'm not sure if there is any point in replacing the plaster with lime plaster...



Secondly, beneath the plaster that is covering the original brick, there is also a fairly thick layer of a hard black material. Not sure what this is. My husband thought it looked like some kind of cement? Beneath this, we discovered that the original bricks have a patchy green substance on them, you can see this on the pic above and a close-up shown on the pic below, also showing the black layer.
At first we thought the green was a mould, but as we uncovered a bit more it looked more like a patchy paint. Am I right in thinking that this may be an arsenic-based paint based on the age of this section of the house? If, so what is the best way to get this off safely?



Thank you for any input!

 

[Zebra]

That looks like essentially an extra skin of brickwork over the top of the original wall (a "course" of brickwork refers to a horizontal layer, with apologies for my pedantry). Is this over the whole room? There may be little breathability in the wall in that case. I'd be wanting to see how far that extends. Why do you think they did that?
The stuff in your second picture is indeed cement. I'm not sure what the green stuff is, but I doubt that there's any risk if you were to remove it with a dust mask on, bag it all up and take it to the tip.

 

[Cheshirecat44]

Thanks for your input and sorry about the terminology!
So far, it looks like it's just been done to this bit and also the same bit on the other side of the log burning stove, but we've not taken the plaster/paint off all the walls so not 100% sure. We were just going to replaster the chimney for now and leave the other walls until a later point (as there is an awkward staircase next to the chimney which we may move at a later point so we thought we'd leave the rest of the plastering until that goes). If I stick my head in the gap under the stairs I can see bare brick which I think is original bricks in the corner where the plastering ends, but I need to get a better light and have a proper look.
I'm not sure why it's been done, perhaps for support or to make the opening narrower? My dad is coming over this week to help with another task so I will ask him to take a look too as he is a retired bricklayer. If it's not supporting I suppose we could re-do it.

 

[88v8]

Bit hard to see from the pic, it's me eyes you know, but is that the fire opening to the right? If so, I reckon that vertical row of brick has been added to shrink the opening, either because it was smoking or simply to fit some smaller fire surround.

Unless a narrower lintel has been fitted at the same time, those bricks are not doing anything structural and could be removed.

Damp... above the fire opening? Could be because there is no liner and the fire has been burned too cool, or because the flashing around the chimney is/was leaking. That old cement skim could represent some past attempt to deal with it.

Ivor

 

[bennoa1]

The green looks like a residue of a skim of cement - why, who knows. To get it off without damaging the brick you'll need to get some decent small chisels. Got mine from here, not cheap but absolutely fantastic tools:
http://www.harbrosupplies.co.uk/product-category/tungsten-tooling-kits/masonry-chisels/

 

[Zebra]

Yes, it is hard removing cement from old bricks. Results may vary.
Those tools look very good. The cheaper alternative is an old flat screwdriver!

 

[bennoa1]

Yes, it is hard removing cement from old bricks. Results may vary.
Those tools look very good. The cheaper alternative is an old flat screwdriver!

Been using them to remove cement pointing and also to break and trim old bricks to rebuild some areas (loose or non existent lime mortar behind gypsum board or plaster but that's another story) and they are fab. Wouldn't be without them now. Recommended to me by my window guy who makes traditional frames but specialises in traditional glass work and has worked on lots of historic buildings but doesn't entertain all the publicity lark. Luckily he is only a few miles away.

 

[Lime]

Why worry about the green paint if you are going to plaster over it?