Taking bottom half wall back to brick to lime plaster... but now stuck

[CheshireCat]

Hello,

We live in a late Victorian terrace in London and are finally tackling damp issues that exist on the internal walls on one side of our house - in the living room and back room. And its the back room we're currently a bit stuck with!

We have a lime plasterer lined up, and in the back room agreed with him to take the bottom of the wall back to brick up to 1m. We are doing the hacking off ourselves to save a little money.

We expected the back room wall to be similar to our living room chimney breast and alcove walls that we've already taken back to brick... where the bottom third was cement render, middle third was plasterboard dot and dabbed on brick, and the top third the original lime plaster with a gypsum skim over the top (yes a really weird mixed bag!)

However, it looks like the back wall has been rendered with cement bottom to top (possibly over old plaster?) and then had plasterboard dot and dabbed over it. I sent a picture to our plasterer, who eventually replied saying wait a few days to see if the cement dries out - but we'd already started taking it back to brick by the time we got his reply, thinking we need to help the bottom of the wall breathe.

I guess my question is - what now?

• Do we have to take all the wall back to brick and lime plaster it all?
• Could we take the dot and dabbed plasterboard off rest of wall, but leave top half as cement render? And plaster over it with something else?
  • The top half of the cement render appears to be in sound condition (no darker patches or efflorescence from the test patch we removed further up)
  • But would it cause issues having part of the wall lime plastered and part as cement render skimmed with something else?

Lime plastering half of the back room wall was already an unplanned expense. Originally we were just getting the chimney breast and alcoves in the living room done. So ideally wanting to avoid the cost of doing the full wall if at all possible.

I'm also thinking we'll also need to clean the exposed brick and try to neutralise the salts? As there used to be a chimney breast in the back room that was taken out a long time ago?

 

[paulc]

Personally, once started, I'd try to finish removing all of the cement.
A couple of observations: Pop those cables running up to the sockets in conduit. It will make life so much easier if you ever need to rewire. And on the subject of wiring, get rid of that single cable running off at an angle on the right. Mains cables should only ever run horizontally or vertically from a switch or socket or within 150mm of a corner. Going off at a random angle takes the cable out of the "Safe Zones" and will pose a hazard should anyone drill a hole for say a shelf bracket.
Once you've stripped the wall back to brick, have you considered adding some cork or woodfibre boards to insulate the walls ?

 

[CheshireCat]

Thanks for your reply @paulc!

Regarding the cables, we've got our electrician coming round to add additional sockets and lights in our living room, and will be getting him to sort out the cables in here too as the back boxes for the sockets need replacing anyway, they're corroding away. That random wire will definitely be sorted - we think it used to lead to a socket high up of the wall that has since been removed.

We hadn't considered insulating the wall, mostly because its an internal party wall, so wasn't sure how much impact it would have re: heat loss and we haven't had much problems sound-wise?

 

[paulc]

We hadn't considered insulating the wall, mostly because its an internal party wall, so wasn't sure how much impact it would have re: heat loss and we haven't had much problems sound-wise?

ah, missed the point that it is an internal wall. Absolutely no need to insulate as the other side should be at a similar temperature, so no heat loss. On the other hand, if or when you strip the exterior walls, it is well worth adding insulation. I'm doing my walls upstairs, and it is paying dividends in terms of keeping the heat in and reducing condensation. Whether I'll save enough on my energy bills to cover the cost is debatable, but the improvement in quality of life makes up for it.

 

[CheshireCat]

So we've hacked the full wall back (just a few patches left to hand chisel off in this photo) and our electrician has been and sorted out the sockets with plastic surface mounted boxes to avoid repeat of previous corrosion problems.

My challenge now is the soot on the bricks where the chimney breast previous was (NB: all structurally supported in the loft space). I know that the soot can come through plaster and stain the walls, so trying to figure out how to prevent this? Although not sure if over time it becomes less of a problem if historic soot?

From my research so far:

• Fresh cow manure slurry based on posts in this forum - maybe not the easiest to get hold of in London (or appealing to work with)
• Someone offline suggested scutch(?) chiselling the surface of the bricks to remove the soot layer - but not keen on the idea of damaging bricks
• Saw an old post on here the suggested klingstrip to clean them - could do a test as I have a sample pot somewhere, but would the staining issue still occur even if the bricks looked cleaner?

Are there any other options I could investigate that I haven't managed to discover via Google?

I'm starting to think this might be why there was cement render from floor to ceiling... questionable how well it worked as there were previously some brown stains on bottom of wall before we hacked it all off. Maybe it wasn't soot causing it though.

Don't want to pay £££ to lime plaster the wall and then have issues persist - or new ones crop up - so anything we can do to head off the problem would be great.

 

[a twig]

The approach I took for soot was:

1) Brush off as much as possible, then lime plaster.
2) Wait to see if any staining appears, limewash where it does using a limewash with casein in (I bought mine pre-made, from Mike Wye I think)
3) If staining appears through that, apply a less watery limewash over the areas (I home brew mixed mine from putty to the consistency of double cream)
4) Hopefully no more visible stains but probably some cracking so apply normal consistency limewash with casein again.

Hopefully job done at that point, if not, repeat the last two steps until stains no longer visible or apply a clay paint over the top of the lime wash.

Having said all that, silicate paints didn’t really exist then, so nowadays I’d be tempted to just paint the lime plaster with a silicate interior paint from Keim which would probably solve the problem.

 

[housegolem]

I have a small amount of soot to cover, and like yourself I've found past post on here by "Gervase" who mentions parging chimney soot with manure. similar post - http://greenbuilding.co.uk/GBF_Forum/discussion/288/soot-tar-coming-through-lime-plaster

I think it's probably the best option but not the easiest, my backup was going to be grinding off the top surface of the brick with an angle grinder and then seal with baumit premium primer. Mainly because i have a tub of the primer kicking about. It seems to form a decent layer/crust that should still allow the wall to breathe but stop the black seeping through.

 

[CheshireCat]

Thanks for your reply @a twig - I've just ordered some stiff haired brushes to help with getting as much soot off possible. But hadn't heard about using lime wash on interior walls - is it the same as distemper paint?

And @housegolem I'd seen that post about manure too, but definitely doesn't feel like the easiest option in our area. Someone suggested taking the top surface off the brick too, I'm just nervous of damaging the brick. Though to be fair, there are a few that have a damaged surface already and our plasterer doesn't seem concerned. Maybe I'll ask him about using something like the primer you suggested.

In the mean time, I have tested applying klingstrip to one brick and covering with cling film for a couple of days. Thought it couldn't hurt to see what happens.

 

[Zebra]

I was going to suggest as it's only a small area, it might not be so bad to sacrifice breathability and seal with PVA before you plaster, to prevent staining, but I'm not sure, I suppose you could get a soggy patch where it can't breathe. But if it was only the bricks that were sealed and not the mortar (which you could scrape the soot off with good conscience) then the wall would still be able to breathe...but would you still get staining?... hmm.
I think you have the right approach with scrubbing, cleaning and seeing what happens.
To answer a couple of your questions above: yes, historic soot can still stain; no, I don't think, if you scrub them so they look clean, soot will still leach out.
I'm not surprised you're not getting answers out of your plasterer. Most trades, I'm afraid, just do what they do best and don't really consider the bigger picture, which is why we have to do all the thinking and preparation ourselves. So I think you're on the right track.

 

[paulc]

But hadn't heard about using lime wash on interior walls - is it the same as distemper paint?

Distemper is (usually) made from a finely ground chalk or marble mixed with an animal or plant based glue. It is a horrible surface to redecorate over the top as little will stick to it.
Limewash is just lime putty watered down to the consistency of cream. Painted on to a wall, the lime carbonates, and you end up with a very thin tough layer. As the limewash dries, you could burnish it with a stainless steel trowel for a (slightly) polished finish.

 

[CheshireCat]

Thanks @Zebra and @paulc.

I'm gonna keep going with trying to clean as much off as possible. The plasterer said the bricks would need to be free of any previous dot and dab adhesive / cement haze as well, so might need to look into an actual cleaner for that.

And then I might look at using some kind of sealer as suggested for just the affected bricks - maybe the primer that @housegolem suggested. Most of the soot seems to be on the top half of the wall and dampness was at the bottom of the wall, so hoping the rest wall will still generally be able to breath. And look into the lime wash suggestion - I think we can get a match for the paint colour we want to use.

Gosh, hope it doesn't take too much longer though to get to plaster ready. My husband and I are reaching the point where it already feels like its taken forever to get to even this stage and so fed up of the dust

 

[Zebra]

...already feels like its taken forever to get to even this stage and so fed up of the dust

Well that's a familiar scenario....

 

[Toby Newell]

You cannot remove the 'soot' some of it is wood and coal tar and the rest carbon and deep into the brick. Just remove what you can and as suggested, paint and see, if stains come through, use a stain blocker.

Poo or anything else are old wives tails. Coal tar persists for thousands of years and carbon black is the strongest pigment.