This isn’t mud clay plaster, is it?

[DampedOut]

I’m just dreaming and it’s gypsum, right? I’ve never removed plaster before. This is dark brown, sandy and crumbly. It’s damp too. It appears to have a scratch coat. Where I dug in deeper, it became drier the deeper I went. It changes colour and is not damp higher up the wall.

The layers above it come off as a unit and are paint, paint, pink (gypsum), grey and solid (cement?) then this layer.

Many thanks for any insights!

 

[Feltwell]

It's very sandy, whatever it is. You've stripped a whole load of impervious finishes off that were over it, I'd be inclined to leave it and see if it dries out and is stuck firmly before you strip it all off. I'd say it's very likely the original plaster that's just been skimmed over later with your cement and then gypsum. You may find the cement stops about 1m up from the floor and is then just gypsum, if it was part of a doomed-to-fail damp proofing attempt.

 

[DampedOut]

Ohhhhh I cannot believe my luck if that's the case. I've been dreading dealing with the plaster because I've been thinking there would be very thick cement that would be hard to remove. This stuff is the thicknesses of paperboard. It comes off as if it wants to. If I'm lucky, most of the house will be like this. More tests probably in spring or summer; this room is the least used.

The material, whatever it is, has dried out overnight and is stuck firmly. I'm hoping this means that in time I can strip off the rest of the inappropriate layers, let it dry out and then skim over the top. I think I'll have to figure out if I can learn how to do clay plastering now, which is very unexpected! I thought it would be lime.

You're right that it must have been part of a doomed-to-fail damp proofing attempt. The ground floor has at least two concrete floors over blue plastic and there seems to be more cement and gypsum behind the facade around the front door. Interestingly, in this particular room that the photos are from, the cement didn't stop even about 1.5m up but it was quite thin. But because the original plaster was dry higher up, in that area, the cement didn't come off so easily.

Insulation will be a fun question from here too but probably 6-12cm of wood fibre, if anything. Will search on the site for any threads about clay plaster. Thanks so much for your input!

 

[Feltwell]

Why "clay" plaster? I would have thought it's likely to be lime plaster.

I'd be tempted to give it a few weeks, then take some small areas back to brick /stone and see if they are still wet or if they have dried out - in other words, is exposing this layer of plaster allowing the wall behind to dry out or not. If it still looks wet you know the lot's got to come off.

I suspect though that someone has taken the "path of least resistance" and just skimmed over what was already there. Their laziness could be your benefit!

 

[RBailey]

Does the brown fizz in vinegar?
Lime will fizz but cement or gypsum will not; However, any lime adhered to the gypsum / cement will still fizz so it's more indicative than absolute.

Here's some I did:
Fizz Test

Cheers,
Richard B.

 

[Kearn]

Hard to tell from the pics and without any details about the age or construction of your house for context?

However, the base coat looks to me much like a daub - which would ideally need to be attached to wattles. Which would mean you have a timber framed house?

Daub historically wasn’t one thing, yes to clay, but also mud, straw, dung… what ever was to hand to make a sticky mix. It’s great thermally, very well structured also very easy to patch fill before skimming or floating then skimming with lime. There are some suppliers who still have daub, but finding it has become trickier. The more common trend is to go for a hemp fibred lime instead for daubing out patch repairs - similar structural properties, but much lighter. The two work together just fine - I’m in the process of doing exactly this on our project. You’d be surprised just how smooth a finish could be achieved with historic daub too…! We have some panels that are almost polished smooth…

Any if the daub that wants to come away, will - there’s no puny fighting this as you need solid substrate and once daub dries and breaks its bond and can turn to dust. Light water misting while you work can help.

 

[DampedOut]

Welllllll time for a long overdue update.

I only visit this house a couple times a year at the moment, so work is always a bit stop and start. Apologies for the silence!

We chipped off a bit of the wall starting today.

At first, it was really encouraging. The material was very sandy and seemed to dry out quickly. The gray sand cement over it and gypsum on top of that were blown in a few places while the material seemed pretty ok. It was just sandy and disintegrated a bit in a few spots. This made me think it was some kind of clay plaster after all.

When a chunk was dropped in vinegar, it fizzed as much as a very flat soda. Not a ton of fizz really, but more bubbles than in the vinegar without it in there.

And then... we kept chipping away at it and discovered there was metal mesh on the corners behind the material at the corners as plastering guides, suggesting the material is modern. What on earth is it then?

There is no sign of hair or straw in it. Here are some photos.

I'm at a bit of a loss now.

Also discovered that the window reveal (and potentially the whole facade?) is the depth of a single course of stone. I could reach my hand out of the window and touch the front of the stones I could see after removing the plasterboard in the reveal. Since the reveal is on an angle, I know that it's not thicker there. ...is that normal?

We're wondering if we remove all this to put on wood fibre boards, the act of drilling to secure them to the stone wall might push the stones out of the facade if it's all one course of stone deep. I joke... sort of. I was looking at insulating plaster with hemp in the mix as well and given the shallowness of the facade around the windows, that's probably a no go because of water ingress leading to rot.

Many questions were answered though. So it was a good exercise. We'd be wondering how water was getting in whenever there was driving rain. And now we know. That water only has to travel about 10"-12" and it's on the material on the inside of the stone facade.

I wanted to post because I figured those who had replied would be curious about what happened next. Anyone with any input or ideas, well, those are very welcome!

The house is quite old, probably 300 years old and it's in Westmorland.

p.s. the photos are of the mesh behind the material, a close-up of what can be seen behind the plasterboard of the window reveal, and then a context photo of where things are. Although the material looks gray in these nighttime photos, it's really brown-red, like in the first photos from this thread.

 

[Kearn]

We're wondering if we remove all this to put on wood fibre boards, the act of drilling to secure them to the stone wall might push the stones out of the facade if it's all one course of stone deep. I joke... sort of. I was looking at insulating plaster with hemp in the mix as well and given the shallowness of the facade around the windows, that's probably a no go because of water ingress leading to rot.

I’m not sure what you mean by the end of that comment, regarding water/rot. If you go with wood fibre boards, then you will have to lime plaster the stone first to affix the boards. You cannot allow any air gaps, to prevent condensation occurring.

For solid stone, the best plan is just hemp lime really in my opinion, you can chuck it on nice and thick, get more of a smoother internal wall and add some extra insulation to the existing stone. Shame it wasn’t a daub, looked hopeful from the army pics, less so from the more recent investigations…

 

[DampedOut]

Thanks for your comment, @Kearn. The lime specialist who sold me the insulating plaster (which contains hemp) said it can't be "wet, wet, wet". And the house is in one of the rainiest villages in England. I've read that hemp rots, so I was thinking it would be an issue. But if it won't... well, that's some relief then!

With the wood fibre boards, do you never drill into the masonry to fix them then? You lay on a layer of lime and fix them to that?

 

[a twig]

This thread might be helpful:

Plastering question

Hello all, After nearly a year of serious unanticipated structural work we've now finished and can get on with fitting windows, plastering and everything else that we thought we'd be finished by now. I have a question regarding use of wood wool boards on an external facing brick wall. This...

www.periodproperty.co.uk

 

[DampedOut]

@a twig I was actually going to DM you and ask for a link to the thread where you gave instructions. I've seen it multiple times and always thought, "gotta copy this down somewhere!". Thanks! You anticipated my question.

I'm afraid the plot thickens a bit on this wall. I got some more material off today and got down to the stone. Around the window, it is 1 course thick, it looks like. But I think it must be two thick in the regular wall area which is a relief. That puts the sandstone external walls at 50cm or higher, though exact measurements haven't been taken yet.
More interestingly, I started dropping bits of it in vinegar. Despite being red-brown, a lot of it fizzed. I'm not sure how much I was expecting things to fizz before, but it doesn't quite fizz like alka seltzer.

Then, after uncovering every layer going down to the stone, I poured a bit of vinegar to hit each layer. Each layer fizzes. Each layer is fairly sandy once you get behind the sand cement. Still not sure what to make of it. I've never heard of someone uncovering a wall and finding a metal mesh with breathable materials around it. Does that mean that someone in the 60s or 70s did the job.... right? I've never heard of that kind of thing. I'm shocked.

Here's some photos of the whole wall trying to give more context and some close-ups of the area with stone showing. Beginning to think it's some kind of local style of lime that has a red-brown colour.

 

[Stevers]

More interestingly, I started dropping bits of it in vinegar. Despite being red-brown, a lot of it fizzed. I'm not sure how much I was expecting things to fizz before, but it doesn't quite fizz like alka seltzer.

Round here they use stone dust in mortar and render mixes. If this dust is a by-product of quarrying limestone (as it generally is here), I'll bet that such a mix would fizz even if it was cement bound. I doubt that the Mendips is unique in doing this, so you might want to consider the local geology and practice.

 

[DampedOut]

I wonder then if it's red sandstone dust in the mix. That could also fizz, depending on the type of stone (according to Google). Most of the buildings around here are sandstone buildings that no longer look red because of moss, ancient lime wash or maybe time.

I'm very confused about what this is now. It feels sandy, porous, coarse and open. I emailed the local lime specialist and will hopefully get a verdict. The gray sand cement and gypsum fly off the wall with the SDS drill. This stuff doesn't budge. It's very hard-going.

 

[Kearn]

Thanks for your comment, @Kearn. The lime specialist who sold me the insulating plaster (which contains hemp) said it can't be "wet, wet, wet". And the house is in one of the rainiest villages in England. I've read that hemp rots, so I was thinking it would be an issue. But if it won't... well, that's some relief then!

With the wood fibre boards, do you never drill into the masonry to fix them then? You lay on a layer of lime and fix them to that?

Ah, I see your point - is the internal face getting wet currently?
if the stone is that thin, I’d probably be looking to thicken it - build up the material if feasible, with more stone or pieces of tile/brick/whatever is to hand as per the approach for filling gaps too large for mortar alone. If you’re worried, then lots of haired line is now artificial fibres as the hair had a tendency to dissolve if not treated correctly.

In terms of the boards, yes they do need mechanical connection, but you won’t want an air gap between them and the solid wall. It needs to be continuous material otherwise you’ll create a nightmare condensation issue. Equally, you’ve also got the balance that you don’t want to over insulate the inside such that the stone structure doesn’t receive internal heat, as then it will never dry out.

 

[DampedOut]

You know, now that you ask and I'm thinking about it, I'm not sure it is still getting wet on the internal face.

18 months ago we had a cement render removed from the exterior on that side, and it's possible the house is mostly dry now. It does get driving rain but it seems better than in the first 12 months after render removal. And it's not against an earth bank or anything. It's a bit hard to tell, and I'm willing to give it a shot with hemp.

The homeowner (the boss) would rather not drill into the masonry, so we probably will end up with a plaster and no boards. @Kearn I'm really curious about this issue of having too much internal insulation. How do you know what's too much?

 

[DampedOut]

Please allow me to ask a stupid question.

The last few days there's been a good amount of wind and rain, but it was particularly strong last night. I went to check on the exposed wall with the red-brown material and it was much darker in areas below the window. The right side of the stone window sill was visibly damp. The right hand corner of the wall around that area was also dark. It felt cool to the touch. This morning, the damp areas are shrinking.

This the stupid question: is this breathability? Rain hit the wall, damp patches showed on the sandy material inside. This morning, with overnight central heating and sun, the damp appears to be shrinking. Is this how a breathable wall behaves?

Last night, with rain:

This morning, after the rain:



p.s. Happy Boxing Day!

 

[a twig]

I mean somewhat extreme but yes, moisture that is getting in is then able to get out again just need to identify and remedy the sources of ingress now based on what I can see on the photos I’d look at the detailing at the bottom of the window

Happy Boxing Day!

 

[DampedOut]

Nice! I wanted to be absolutely sure. And you know, there are surprisingly few photos online that show what a breathable wall looks like when it's damp.

I think the fact that this material, whatever it is, is breathable means we can stick some lime on it as is and see how it goes. I don't want to be too much of a purist about the kind of breathable material on the wall. If it's breathable, that's good enough. I don't want to remove this just because I don't know precisely what it is or because it's not original.

And, luckily, I do know the source of the water ingress! Or I have a really good start on it.

When the cement render came off 2 summers ago, it left the windows sitting flush in the facade and not recessed. Here's some photos. And you can see the damp is really attacking the window sill corners too (the sill photo is from last night, in the rain). You were exactly right in saying the detailing at the bottom of the window.

Think we'll have to find out if it's possible to bring the uPVC windows closer into the building and get them recessed. At least until we can figure out windows and save up for new ones in a few years. And hopefully that will be a good start.

Thank you so much for your reply @a twig and for the great, helpful info!

 

[Lacan07]

Please allow me to ask a stupid question.

The last few days there's been a good amount of wind and rain, but it was particularly strong last night. I went to check on the exposed wall with the red-brown material and it was much darker in areas below the window. The right side of the stone window sill was visibly damp. The right hand corner of the wall around that area was also dark. It felt cool to the touch. This morning, the damp areas are shrinking.

This the stupid question: is this breathability? Rain hit the wall, damp patches showed on the sandy material inside. This morning, with overnight central heating and sun, the damp appears to be shrinking. Is this how a breathable wall behaves?

Last night, with rain:
View attachment 12122
This morning, after the rain:

View attachment 12123

p.s. Happy Boxing Day!

Yes, thats the advantage of a breathable wall but you need to tackle the source of the water ingress

 

[DampedOut]

I'm not really sure how we'll go about that. Any suggestions?

I was thinking some clear silicone paint on the fillets of lime around the window frames as a stopgap. That way it's easy enough to remove if/when the windows are replaced. And at some point in between, try to pull the windows farther back into the building and recess them by a few inches if possible.