Plastering solid brick walls (1912 house)

[grouchy]

Hi there, I hope the great minds of the forum can help.

I have a red-brick semi built in 1912, solid 9" walls with what I believe is lime mortar pointing. Not rendered.

We've had the usual array of damp / condensation problems, I think largely caused by previous owners using modern materials and methods.

The next room on our hitlist is the lounge. We have damp (condensation?) patches on the external wall and, on one side, tracking into the internal wall too. I think the previous owners used one of those rubber-based paint-on products to about 4' up the wall; the damp patches generally start above that, either side of a chimney breast. I think there's gypsum plaster underneath but would need to disturb it to confirm. The rest of the house has the crumbly old black (lime?) plaster; it may even be that there's that beneath modern plaster.

There seem to be so many opinions on the best course of action here - and recent posts seem to espouse different views (perhaps because there are different products) to those from 5-10 years ago - that I'm not sure which is the best course.

Additional information:

• The room is on the ground floor and has a suspended timber floor with loads of gaps between the boards and no carpet (those gaps are also on my list - but appreciate they do help with ventilation). The space beneath the floorboards is externally vented through air bricks
• PVC windows are in good condition but pretty old - so no trickle vents. They are (like the rest of the house) fitted right on the inside edge of the window reveals and surrounded by a timber trim. That would make the plastering job simpler, but pulling all the trims off and resetting could be painful
• The pointing outside is all sound, and there's no obvious causes for any penetrating damp (leaking gutter etc.)
• There's nice coving around the ceiling which ideally I would not disturb

I'll consider all options - cost is a factor but not the biggest factor, we just want it to look smart.

This photo shows the damp patches mentioned above. The left hand wall is the external wall, but the right hand wall is an internal (brick) wall - I'm assuming the damp is tracking into the internal wall from the external wall, but could be wrong. I don't know what the round 'bump' in the middle of the photo is beyond a small patch of blown plaster.

Thanks in advance!

 

[RichT]

can you post photo of the outside?

 

[grouchy]

can you post photo of the outside?

Sorry for the delay. Here you go. The damp patch is roughly in line with the rainwater downpipe (which is completely sound). There are a couple of minor pointing repairs behind it - I would say where the original cast iron downpipe was secured the old fashioned way (wooden plugs bedded in the mortar, then long nails into those plugs) - you can see one as a bright grey splodge just left of the downpipe.

I have, previously, dug out all of the gravel along that wall and checked all of the pointing both above and below DPC (slate) level, as well as the old ceramic gully that the downpipe drains into - all fine. Appreciate it's hard to tell from the photo, but the gravel does not bridge the DPC level, and it's all clean 20mm stones (ie. it's not trapping moisture in decades of dirt and dust among all the stones).

 

[aockenden]

You’ve obviously done a nice thorough job examining the exterior situation. Sounds like it must be an internal problem.

One thing stood out to me though… you think you’ve got BLACK original lime pointing? I’ve never heard of nor seen a black lime mortar, but maybe this is a niche I’m ignorant of. Are you sure it’s not some nasty semi-modern bitumen tanking crap? That stuff is actually black.

 

[grouchy]

One thing stood out to me though… you think you’ve got BLACK original lime pointing? I’ve never heard of nor seen a black lime mortar, but maybe this is a niche I’m ignorant of. Are you sure it’s not some nasty semi-modern bitumen tanking crap? That stuff is actually black.

Black lime plaster, not pointing. I'm assuming it's lime anyway. I thought it was pretty ubiquitous, but perhaps not!

Here's a photo of what I'm talking about (this is in a different room where work has been underway since about the beginning of time). Really crumbly old plaster. All the rooms are like this, including the lath and plaster internal walls and ceilings.

 

[aockenden]

Wow that is pretty dark indeed, and it's not just the surface layer. Interesting. If it's directly applied to the laths throughout the house, then I guess it would have to be some historical material I'm just not aware of. If it is a Lime plaster I would love to know what the additive is into the plaster mix that is giving it that dark charcoal-grey colour. Ground charcoal or some kind-of ash as a pozzolan or something?

 

[Stevers]

Ash mortar definitely a thing. It is usually ash with lime, and may be with or without other aggregates. We had it in Yeovil where it had eaten the Japanned wall ties of our early cavity walls causing the outer leaf of the rear (west facing) wall to spread up to around an inch.