What Is This Stuff? And What Should I Do About It?

[TeeG]

I purchased an Edwardian Mid-Terrace several years ago and have finally got round to stripping off the layers of wallpaper and paint in the dining room. Not surprisingly the walls underneath are not great. I have no damp issues in that room at the moment but am concerned that 2 of the walls have seemingly been 'treated ' for damp previously with stuff that is clearly not lime plaster. Does anyone know what this stuff is (pictures attached)? It is rock hard and a kind of grainy sandy colour.

I am is discussions with my builder re what to do about it. I wanted it lime plastered but he says it wont adhere to whatever the render is. He is in favour of plastering over it with BreathAplasta. In an ideal world I am thinking I should remove it but I think this may be beyond my capacity. BTW the walls above the damp treatment are dry and the plaster isn't blown in any way.

Any ideas of what it is and what would be a reasonable solution?

 

[Cubist]

Seems like this might be another of my days for dumb questions.

Any chance the upper edge of this material is consistent and roughly 3 feet /1 metre from ground level around the room?

 

[TeeG]

Seems like this might be another of my days for dumb questions.

Any chance the upper edge of this material is consistent and roughly 3 feet /1 metre from ground level around the room?

That's exactly what it is Its quite a bit higher on the chimney breast (fire place has been covered up) but otherwise spot on. I have been diligently hacking off the modern plaster that was on top of that (it's coming off easily in places) but not sure if I should be doing that.

 

[Cubist]

A couple pf possibilities then in the shape of wainscoting and/or a dado rail. Wainscoting could have been installed using an adhesive to glue the wooden boards/panels to the wall with a dado above. Alternatively a dado rail alone may have been installed with some kind of wallpaper below. In both instances the adhesive used would likely have penetrated the plaster to some depth. When the wainscoting/wallpaper was removed the top-most surface of the plaster skim coat would have been taken with it to expose the grainier coarse structure of the plaster. Currently PVA and water solutions and proprietary products are used as 'stabilisers' for old plaster to re-consititute their structure. If applied many times or repeatedly, if say wallpaper had been re-freshed from time-to-time, this could lead to the plaster becoming surprisingly hard. This may also explain why the exposed material seems to reflect light in places.

 

[TeeG]

A couple pf possibilities then in the shape of wainscoting and/or a dado rail. Wainscoting could have been installed using an adhesive to glue the wooden boards/panels to the wall with a dado above. Alternatively a dado rail alone may have been installed with some kind of wallpaper below. In both instances the adhesive used would likely have penetrated the plaster to some depth. When the wainscoting/wallpaper was removed the top-most surface of the plaster skim coat would have been taken with it to expose the grainier coarse structure of the plaster. Currently PVA and water solutions and proprietary products are used as 'stabilisers' for old plaster to re-consititute their structure. If applied many times or repeatedly, if say wallpaper had been re-freshed from time-to-time, this could lead to the plaster becoming surprisingly hard. This may also explain why the exposed material seems to reflect light in places.

Thank you for that. That wasn't a possibility I was aware of. At first I thought it was concrete but closer inspection revealed that it wasn't.
This raises the next question, could I lime plaster over it (despite what the builder says) and is it a good idea for me to continue to remove the gypsum plaster that sits on top of some of it?
Really appreciating your help as the situaion is causing a LOT of sleepless nights!

 

[Cubist]

Frankly I don't see why not; old failing lime plasters are frequently stabilised using PVA solutions or other stabilisers before final repair and/or addition of a new final skim coat. However, beyond the enhanced quality of the bond between the old and new plasters being better, when both are lime based, there may be little to be gained. There is of course the advantage of enhanced breathability but this is less important with internal walls. For external and party walls on the other hand the advantage can be greater as typically these include old chimneys with the water ingress problems that can result from same. In my opinion if you have large areas of gypsum plaster on an external wall then that would be fair game but if they are just small patches of old repairs then the advantage is probably not worthwhile pursuing.

That all said, you might like to test a a small patch of a lime plaster skim on one of the walls you described earlier to see how well it takes and whether the finish you're looking for can be achieved.

 

[Kearn]

PVA primers do somewhat defeat the benefits of line…

@TeeG if that’s your builders recommendation, then I’d find an actual lime plasterer who will approach it correctly. It’s an expensive bagged NHL 3.5 plus prompt cement mix, designed to dry fast and adhere to things line wouldn’t. Not very traditional or really appropriate, especially indoors.

You might find gypsum comes off easily, either gently prising away with a plastered small tool or I get a lot of use out of a cake icing stainless spatula - flexible and round ended so it doesn’t dig in and damage the lime. A bit of steam from a wallpaper remover helps break the bond between gypsum and lime.

 

[TeeG]

Frankly I don't see why not; old failing lime plasters are frequently stabilised using PVA solutions or other stabilisers before final repair and/or addition of a new final skim coat. However, beyond the enhanced quality of the bond between the old and new plasters being better, when both are lime based, there may be little to be gained. There is of course the advantage of enhanced breathability but this is less important with internal walls. For external and party walls on the other hand the advantage can be greater as typically these include old chimneys with the water ingress problems that can result from same. In my opinion if you have large areas of gypsum plaster on an external wall then that would be fair game but if they are just small patches of old repairs then the advantage is probably not worthwhile pursuing.

That all said, you might like to test a a small patch of a lime plaster skim on one of the walls you described earlier to see how well it takes and whether the finish you're looking for can be achieved.

Thanks again. Am learning all the time.

 

[TeeG]

Frankly I don't see why not; old failing lime plasters are frequently stabilised using PVA solutions or other stabilisers before final repair and/or addition of a new final skim coat. However, beyond the enhanced quality of the bond between the old and new plasters being better, when both are lime based, there may be little to be gained. There is of course the advantage of enhanced breathability but this is less important with internal walls. For external and party walls on the other hand the advantage can be greater as typically these include old chimneys with the water ingress problems that can result from same. In my opinion if you have large areas of gypsum plaster on an external wall then that would be fair game but if they are just small patches of old repairs then the advantage is probably not worthwhile pursuing.

That all said, you might like to test a a small patch of a lime plaster skim on one of the walls you described earlier to see how well it takes and whether the finish you're looking for can be achieved.

Thanks again. Am learning all the time.

PVA primers do somewhat defeat the benefits of line…

@TeeG if that’s your builders recommendation, then I’d find an actual lime plasterer who will approach it correctly. It’s an expensive bagged NHL 3.5 plus prompt cement mix, designed to dry fast and adhere to things line wouldn’t. Not very traditional or really appropriate, especially indoors.

You might find gypsum comes off easily, either gently prising away with a plastered small tool or I get a lot of use out of a cake icing stainless spatula - flexible and round ended so it doesn’t dig in and damage the lime. A bit of steam from a wallpaper remover helps break the bond between gypsum and lime.

Thanks for your answer. Much appreciated. The gypsum is coming off easily where it's thin. Bit harder where it's really thick but the wallpaper steamer is slowly winning the battle. .

I am afraid I didn't understand the NHL comment. Are you talking about the BreathAPlasta? Ironically my builder was very happy to lime plaster my previous, listed (this one isn't) house but is very resistant re this one.

 

[Kearn]

I wouldn’t immediately say that lower level finish is bad, could be a rougher lime finish - looks aggregate heavy, but it’s tone is very sandy. What’s it feel like? Theres def patches of gypsum on it and below.

The stuff above looks like a nice chalky plaster over daub. Finished with a pinky/red distemper

Yes - Breathaplaster is recent attempt to make ‘lime plastering’ more accessible. It’s not the most appropriate materials and it’s overpriced. It’s basically a medium strength NHL plus pozi additives for a quick set. NHL does not really belong indoors, it’s way too hard. Especially 3.5. Only place I use it on our project is In a weak mix for rebuilding the limestone plinth wall.

 

[TeeG]

I wouldn’t immediately say that lower level finish is bad, could be a rougher lime finish - looks aggregate heavy, but it’s tone is very sandy. What’s it feel like? Theres def patches of gypsum on it and below.

The stuff above looks like a nice chalky plaster over daub. Finished with a pinky/red distemper

Yes - Breathaplaster is recent attempt to make ‘lime plastering’ more accessible. It’s not the most appropriate materials and it’s overpriced. It’s basically a medium strength NHL plus pozi additives for a quick set. NHL does not really belong indoors, it’s way too hard. Especially 3.5. Only place I use it on our project is In a weak mix for rebuilding the limestone plinth wall.

Totally correct re gypsum. I am slowly hacking this off. The other stuff is hard and a feels a bit like medium grade sandpaper.

I wondered where the pink on the lime plaster came from. Now I know. .

The BreathAPlasta doesn't sound so good now. Is it any better than any multi finish plaster? I am on a deadline with the wall and having to make compromises I wouldn't otherwise make.

 

[Kearn]

Totally correct re gypsum. I am slowly hacking this off. The other stuff is hard and a feels a bit like medium grade sandpaper.

I wondered where the pink on the lime plaster came from. Now I know. .

The BreathAPlasta doesn't sound so good now. Is it any better than any multi finish plaster? I am on a deadline with the wall and having to make compromises I wouldn't otherwise make.

Unfortunately lime is not something you can rush. Cutting corners doesn’t really pay in the long term…

Hack it off below, if it is a hard sand/cement mix, redi in two coat to save time (no third visit). But you’ll need a competent lime plasterer who knows what they’re doing and can happily cut into existing old nice chalky plaster.

 

[larry]

The BreathAPlasta doesn't sound so good now. Is it any better than any multi finish plaster? I am on a deadline with the wall and having to make compromises I wouldn't otherwise make

It's only an anecdote, but I used breathaplasta (fine) as a finish and am very happy, and certainly a lot better than multi finish.

 

[TeeG]

Thanks, Larry. Did you use it on an internal or external wall? And how long has it lasted so far?

Good to know that, if I have to make a short term compromise, BreathAplasta is still a better choice than multi finish.