What is this wall made from?

[Cluemore]

Finally (and just in time, given the squeezing rental market) bought myself a 1920s semi in a former pit town near Doncaster. I've been going round the place finding the various things that need looking at, old bodges, etc etc; it's like a used car, but bigger and with fewer rusty bits. At any rate, I've a room upstairs that's surplus to requirements for the moment, and clearly has a fair number of problems, so I've decided to set that room aside as a project room. The aim is to get it at least basically habitable for guests by Christmas.

Among other issues, the plaster on the stud wall connecting the two small rooms upstairs is badly blown on the Project Room's side of the wall; when I moved in, I gave it a tap and it moved quite visibly in relation to the wall. I've set to removing the upper layers of plaster, and in the meantime, decided I'd support some shelves the former owners left behind (which were held up just by a couple of battens and a couple of table legs). First problem: Couldn't find the uprights. Some reading suggested the wall should be lath-and-plaster, but try as I might, finding the uprights was impossible. This was not helped by the fact that there's a layer of grey-black plaster, which turns out to be magnetic, on the wall; my guess is it was bulked out using slag from nearby ironworks. In any event, I decided I'd chance just drilling in where the wall sounded most solid. The wall didn't fall down and the shelves are now much better supported. Hurrah.

Today, I decided it was time to chop away a section of the blown black plaster and see what I found underneath. What I've found is below, and distinctly confusing! (Sorry if the pics are too large, please let me know and I'll resize.) It should be added that, so far as I can tell, this is all original and hasn't been altered since construction; indeed, the adjoining room still has what I suspect is its original plaster, complete with rather nice decorative rosettes and swirls.

Now as I understand it, the usual material for stud walls in the 1920s (which is, I'm told, when this place was built) is lath-and-plaster. I can't, so far, find any laths at all in this wall. I've measured the thickness of the white-grey stuff in the pics, and it's about 3/4" thick and rock-hard. (The water marks are from my splashing it to test absorbency, not a damp ingress issue.) The plant material embedded in the grey substance appears to be reeds, not wooden laths; the wall seems to have been built (judging by this section) out of some sort of blocks of the stuff; and the lines horizontal and vertical seem too neat, to me, to be the result of cracking, which makes me think it might be machine-cut. (Again, the thin gouges in the material on the left are from me taking the loose plaster off with a bolster chisel.) I still haven't seen anything to show there are any uprights in this section, and am a bit baffled as to what this material is and what to expect of it. It's certainly stout enough to withstand multiple hits with a cold chisel and a three-pound club hammer with little more than gouges in it (the two crude, square-shaped holes at the bottom of pic #1).

So, what am I up against?

 

[Gothichome]

I can’t say for sure but it looks like plaster panels reinforced with waddle. Interesting. the panels look to be factory made, all the scarifications are perfectly uniform and meant to give bight for the finish coat of plaster?
Ron

 

[Cluemore]

I can’t say for sure but it looks like plaster panels reinforced with waddle. Interesting. the panels look to be factory made, all the scarifications are perfectly uniform and meant to give bight for the finish coat of plaster?
Ron

Interesting point; I hadn't noticed until I nipped in to check the absorption progress, but the two vertical gaps are aligned damn near perfectly. It's as if the stuff was supplied in blocks ready to fit together; I'm quite impressed by how modern the arrangement looks.

 

[Drayton]

Clinker blocks or breeze blocks (an early version)?

From https://www.greenspec.co.uk/building-design/blocks/

'In the early twentieth century block manufacturing became an established industry. The earliest blocks manufactured in the UK were made using cement mixed with locally available aggregates – often waste products of industrial processes such as breeze (cinders retrieved from gasworks and coke ovens – from the French ‘braise’ meaning ‘hot coals’) and clinker (blast furnace slag).

These early lightweight blocks were popular as internal partition walls because of their ease-of-use and cheapness, but it was only as a result of the development of cavity walls and the advent of mass housing programmes of the post-war years that the industry dramatically expanded.'

 

[Cluemore]

Clinker blocks or breeze blocks (an early version)?

From https://www.greenspec.co.uk/building-design/blocks/

'In the early twentieth century block manufacturing became an established industry. The earliest blocks manufactured in the UK were made using cement mixed with locally available aggregates – often waste products of industrial processes such as breeze (cinders retrieved from gasworks and coke ovens – from the French ‘braise’ meaning ‘hot coals’) and clinker (blast furnace slag).

These early lightweight blocks were popular as internal partition walls because of their ease-of-use and cheapness, but it was only as a result of the development of cavity walls and the advent of mass housing programmes of the post-war years that the industry dramatically expanded.'

Interesting possibility. They seem quite lightly built for such blocks; I'd estimate the dimensions of each section as roughly 36x12x2in, or a yard by a foot by two inches; quite convenient to remember. There's no load-bearing wall beneath them, so whatever they are, they must be very light. I suppose the door frame on one side, and the exterior wall on the other, would have acted as anchors, although I'm not sure how far I trust whatever mortar is holding them together in the centre.

 

[Zebra]

I have seen wall panels made of unusual stuff. It reminds me a little of a wall I had to run some wiring in once, that seemed to be made of hollow terracotta blocks.

 

[stuart45]

You do get partition walls built with 2 inch blocks on the upper floors to keep the weight down, although the standard size was smaller than those.
Quite an unusual type of block.

 

[Cluemore]

You do get partition walls built with 2 inch blocks on the upper floors to keep the weight down, although the standard size was smaller than those.
Quite an unusual type of block.

What sort of stuff are these blocks made from? Sorry, completely new to this - so far I'm gathering it could be clinker/breeze, or possibly gypsum, mixed with straw or similar?

 

[Cluemore]

I have seen wall panels made of unusual stuff. It reminds me a little of a wall I had to run some wiring in once, that seemed to be made of hollow terracotta blocks.

I did wonder if it might be hollow; however, experimental drilling leads me to believe the blocks are solid (no change in resistance to the bit until I reached thin air on t'other side). A terracotta-block wall sounds... well, odd!

 

[stuart45]

What sort of stuff are these blocks made from? Sorry, completely new to this - so far I'm gathering it could be clinker/breeze, or possibly gypsum, mixed with straw or similar?

The 2 inch blocks I've laid were mainly AAC, but were smaller than yours(18in x 9in). I'm not familiar with your type, they may be more common to your area. 2 inch wide blocks are not the easiest things to lay.

 

[Cubist]

Dumb question; are you planning to remove any part of that wall or any section of it? If not, then why are you puzzling over this block-work? So long as its sound and you can drill whatever holes you need for any purpose then surely all you need to do is make the plaster good. Or am I missing something.

The block-work itself could be a much later addition to the house or you may even find that all the internal walls of the house are constructed with the same. At this stage all you need to be careful of is to ensure it's not a supporting wall.

This was not helped by the fact that there's a layer of grey-black plaster, which turns out to be magnetic,

Magnetic - seriously? I wouldn't bank on getting a good wi-fi signal in that room! Sounds like a crude 'Faraday Cage' to me.

 

[Cluemore]

Dumb question; are you planning to remove any part of that wall or any section of it? If not, then why are you puzzling over this block-work? So long as its sound and you can drill whatever holes you need for any purpose then surely all you need to do is make the plaster good. Or am I missing something.

The block-work itself could be a much later addition to the house or you may even find that all the internal walls of the house are constructed with the same. At this stage all you need to be careful of is to ensure it's not a supporting wall.



Magnetic - seriously? I wouldn't bank on getting a good wi-fi signal in that room! Sounds like a crude 'Faraday Cage' to me.

Yep, magnetic. You need a good neodymium magnet, mind, but it's possible to pick up broken-away sections of the black plaster with a magnet. As I say, I suspect they used slag from nearby ironworks as a bulking or binding material; there must have been plenty of it at the time.

The reasons I'm puzzling are twofold: Pure curiosity (I'm a nosy bugger) and so that I know what I can and can't do with the material. For instance, I'm now confident it can't support the shelves next door if I choose to fill them entirely with books, at least not without ripping the existing rawlplugs out, so I'll tread carefully when it comes to loading them. (Naturally, the shelves are one big unit - oh well, at least they came for free). There's also some repair work necessary, so I'd like to know what material I'm going to be plastering over as I fix the wall up, how to repair the cracked block at the bottom, etc etc. But, mainly, sheer intrigue. I've never had a house before, and I enjoy learning about how things are made.

 

[Cluemore]

The 2 inch blocks I've laid were mainly AAC, but were smaller than yours(18in x 9in). I'm not familiar with your type, they may be more common to your area. 2 inch wide blocks are not the easiest things to lay.

Hmm. I am, in fairness, speculating as to their length, but the height is definitely a foot. I'd have thought even aerated concrete would be quite heavy, to be supported only by a floor joist (there's definitely no wall directly below this one). Then again, what I know about concrete wouldn't fill a stamp!

 

[stuart45]

It used to be quite common to build the upper floor partitions with masonry units on top of a timber sole plate fixed to the floor. 3 inch blocks were probably the favourite.

 

[Cubist]

And the other reason this thread piqued my curiosity - now that I've discounted the lath and plaster wild goose chase that diverted me - is that the blocks themselves contain what may be straw or reed. I've never seen them but I vaguely recall hearing that one enterprising company had used cut straw or reed to make very light weight building blocks. These would be manufactured in moulds that were laid flat and the cut straw/reed and a cement slurry fed/poured into it in parallel. The process was clearly inspired by cob wall construction and would have been very light and capable of sustaining quite large vertical loads. However, nails or screws could easily disrupt these materials, making such blocks nigh on useless for anything other than hanging the odd picture. You may do well to consider using a resin based fixings approach for your bookcase and/or fix floor length vertical mounting battens to the wall first.

 

[Cluemore]

Today's job has been getting the remaining dud plaster off (which in turn has resulted in more plaster coming away - oh joy). While doing so, I've exposed much more of the wall, and the results are below.

The manufacturer's mark seems to read "CAFF" - for some reason, the name Caffrey/Caffery springs to mind. Nothing much comes up on web searches; the closest match is a McCaffrey and sons in NI, who make concrete blocks. Any light anyone can shed from that would be pretty neat

In lieu of chopping the plaster out (and to avoid having to redo the entire bloody wall), I've decided it's better to cut the blown sections free. This has, so far, cost me three Dremel bits, but it's also not resulting in any more plaster lurching free of the blocks. Overall, a positive. Hats off to Dremel for their cutting kit's useful depth-stop feature.

Current plan is to clean everything thoroughly, repair any knackered pointing, and then plaster. Or rather, try to; having never done any of this before, I'm expecting a steep learning curve! I have some Blue Circle ready-to-use mortar to hand, so I intend to try that out between them and see if it sticks.

 

[Cubist]

looks like a cement mortar was used to lay those blocks. Best to make sure if you can but I would be tempted, if the plaster depth is deep enough, to consider a a primary rendering coat of a cement mortar to be sure of getting a grip on those blocks before finishing with a float coat of gypsum plaster assuming ithe old stuff is not lime.

 

[Stevers]

If it's a modern house with cavities and damp proof courses, or an internal wall, then you could just use Thistle One Coat. Most places including Wickes do smaller bags and although the professionals hate it, it seems to stick to just about anything and has a more open surface than pink finishing plaster. I buy a 25kg bag (much better value) and put into a couple of Rooster Poo tubs and it keeps forever like that, even in my shed. That way I've always got some to hand when I need it.

 

[ThornhillMike]

If it's a modern house with cavities and damp proof courses, or an internal wall, then you could just use Thistle One Coat. Most places including Wickes do smaller bags and although the professionals hate it, it seems to stick to just about anything and has a more open surface than pink finishing plaster. I buy a 25kg bag (much better value) and put into a couple of Rooster Poo tubs and it keeps forever like that, even in my shed. That way I've always got some to hand when I need it.

Okay, I'll take the bait... what on earth is a Rooster Poo tub...?

 

[stuart45]

Maybe an empty one of these.

https://www.amazon.co.uk/Westland-Organic-Chicken-Manure-Pellets/dp/B006KS5HHW/ref=asc_df_B006KS5HHW?tag=bingshoppinga-21&linkCode=df0&hvadid=79989527879996&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583589102955215&th=1