OK to lime plaster over these bricks?

[reejoc]

Hi,

I'd be grateful for advice on this situation. The photo below shows the back of an inglenook fireplace which now has a woodburner. The exterior side of the wall is rendered with sand and cement. Someone has done some inappropriate pointing and rendering inside as well which is now all coming away. Several of the bricks are blown at the face. The wall feels dry.

I want to lime plaster the wall to a) hide this mess and b) allow it to still breathe. I'll scrap off any cement mortar and plaster beforehand.

The question is whether this is sensible or whether there is any other remedial work to do first

Many thanks

 

[Lacan07]

That sounds like a plan. I would probably dub out any really deep holes, ridges, etc, with some lime mortar first. There appears to be a sizeable ridge in the middle of that wall in the photo, or is it a trick of the light?

The other thing to consider here is the soot (if indeed it is soot in the photo), it will almost always seep through the plaster so you might consider a barrier. For lime the only breathable option is cow sh*t fresh of the floor, you mix it in with your initial scratch coat.

And then at some point you'll need to tackle the exterior cement render as the wall won't really be breathable until it breathes both sides.

 

[reejoc]

That sounds like a plan. I would probably dub out any really deep holes, ridges, etc, with some lime mortar first. There appears to be a sizeable ridge in the middle of that wall in the photo, or is it a trick of the light?

The other thing to consider here is the soot (if indeed it is soot in the photo), it will almost always seep through the plaster so you might consider a barrier. For lime the only breathable option is cow sh*t fresh of the floor, you mix it in with your initial scratch coat.

And then at some point you'll need to tackle the exterior cement render as the wall won't really be breathable until it breathes both sides.

Thanks for your thoughts. It's not particularly clear in the photo but that 'ridge' is actually where the central section of the inglenook is set back by one brick course.

Yes I think the blackened brick is soot staining from when it would have been an open fireplace. I hadn't realised it can migrate through plaster. Is there a permeable membrane as an alternative to cow sh*t!?

You're right of course about the exterior wall but this is a major undertaking and will have to wait!

 

[erikwoolf]

Thanks for your thoughts. It's not particularly clear in the photo but that 'ridge' is actually where the central section of the inglenook is set back by one brick course.

Yes I think the blackened brick is soot staining from when it would have been an open fireplace. I hadn't realised it can migrate through plaster. Is there a permeable membrane as an alternative to cow sh*t!?

You're right of course about the exterior wall but this is a major undertaking and will have to wait!

Not 100% the same but we had a coal hole that the bricks had similar stains. We washed everything with sugar soap first, then very lightly scratched the surface with a wire brush and finally plastered over with Diathonite Deumix. There have been no stains coming through.

 

[Lacan07]

Not 100% the same but we had a coal hole that the bricks had similar stains. We washed everything with sugar soap first, then very lightly scratched the surface with a wire brush and finally plastered over with Diathonite Deumix. There have been no stains coming through.

Yes, thats a good shout actually, I forgot to mention above you should always clean as much of the soot off as possible anyway before plastering.

The problem with old soot is it often interacts with the lime mortar and creates salts that attracts moisture.

 

[Lacan07]

Yes I think the blackened brick is soot staining from when it would have been an open fireplace. I hadn't realised it can migrate through plaster. Is there a permeable membrane as an alternative to cow sh*t!?

Unfortunately not

 

[tobydog]

Hi. We did exactly the same with our 1640's inglenook. We're Grade II listed so the CO was involved and even he said that the back wall "isn't exactly pretty". It was a mish mash of bodged repairs and spalling bricks.

We had a considerable amount of very old soot and tar but didn't want to consider traditional cow**** parging for obvious reasons. We actually got a very good conservation builder in (hence the CO involvement) and he wasn't concerned with the soot and tar. He did say that it would start coming through the lime but it could eventually give up. We originally lime washed the wall but found that chalk paint was better at covering up any stains that did came through. We do get the occasional patch and we re-paint the bottom with chalk paint part every couple of years. If you look at the top right of the back wall you might see where we conserved a small patch of the original parging.

If you're wondering why the brick shaping on the back wall isn't in the middle, it's my belief that this inglenook previously belonged to a larger house that my have been lost. The right hand side of the inglenook is thinner than the left and there is a bricked up space on the right for what was probably a large bread oven. Clearly there had to be something on the right for the oven to go into but that's no longer there. The inglenook is way too big for the house as it is now but it is impressive.

 

[Zebra]

Wait what? Cow shit stops soot bleeding through lime plaster? This is amazing. How have I been on this forum for ten years and not learned that before? Wish I'd known before I redid my chimney. How fresh does it have to be? (Trying to think where the nearest cows are... can't think of any!) What is the ratio of poo to plaster?!

 

[Lacan07]

Wait what? Cow shit stops soot bleeding through lime plaster? This is amazing. How have I been on this forum for ten years and not learned that before? Wish I'd known before I redid my chimney. How fresh does it have to be? (Trying to think where the nearest cows are... can't think of any!) What is the ratio of poo to plaster?!

Something to do with the mucus in the stomach, I think it has to be pretty fresh. Ratio at your discretion really, 30% to 40% poo perhaps.

 

[lizziecupcakes]

Not 100% the same but we had a coal hole that the bricks had similar stains. We washed everything with sugar soap first, then very lightly scratched the surface with a wire brush and finally plastered over with Diathonite Deumix. There have been no stains coming through.

Hi there.

I’ve found a spot of damp on the top of my bedroom chimney breast. It looks to be longstanding (there was a water stain on the dark wallpaper that i missed. Surveyor missed it too). It looked damp suddenly after heavy rain back in September. I peeled off the wallpaper and looked like there was mould in the lime plaster beneath it. But when i presses it with my fingers, it felt like maybe soot because it smudged quite a bit.

I’ve added before and after photos. I used a paper scraper to remove the wallpaper bits and what looked like white paint.

It’s been nearly 8 weeks since I “cleared” it up. I wanted to help it dry out.

Now, I’m thinking about just spraying the area of lime plaster with mould spray just in case, but before that, cleaning it.

In your comment you used sugar soap… what is this? Is it effective on lime plaster?

I’m not sure if mould spray is a good idea to use. It’s been effective enough when i used it on gypsum plaster when i rented a flat before and there was mould on a part of the wall. Thank you.

Just tagging @Lacan07 too since you are in this thread

 

[housegolem]

for the OP

If the soot area is visible, it's definitely worth some preventative measures in my experience. Here's what i tried

Removed surface soot with grinder

I then used a baumit plaster(mc55), as i had it spare from covering plastic trunking on wiring

I then i followed with baumit premium primer which i had kicking about - this was all used to reduce the leaching

Picture 1/2 show the layer of mc55 over the sooted brick, the area to the left of the chimney breast is the path of an old old central heating system, picture 2 from the open fire. You can see some leaching from the open fire, this i think was mainly from me using a thinner layer.

Picture 3 shows the wall after a few coats of baumit premium primer this kills suction and also left the wall pretty clean and in my opinion i think it will lock in the soot pretty well, the only thing i could see causing leaching in the future would be the wall becoming wet for a prolonged period

Picture 4 is the wall as is, no leaching, been that way for a couple of months, its just waiting for me to skim it properly

 

[Cubist]

In your comment you used sugar soap… what is this? Is it effective on lime plaster?

Sugar soap is available from every DIY outlet and is used to clean all painted surfaces to remove accumulated grime and oils ahead of re-painting. It will help to remove some of the black mould/staining you're seeing but it may be wise to follow up with a little bleach/water in solution ahead of making the plaster good.

 

[lizziecupcakes]

Thanks @Cubist !!

Off to b&q on my lunch break now. I’ll use the sugar soap for my kitchen cabinets too (which I’m painting this week!! FINALLY ).

They are a very orange 90s colour, and veneer. I need to clean them, fill tiny cracks with food filler (only a couple really), sand very lightly, prime, sand again and paint. Please wish me luck!

Thanks, OP for a very helpful thread !

 

[Cubist]

Thanks @Cubist !!

Off to b&q on my lunch break now. I’ll use the sugar soap for my kitchen cabinets too (which I’m painting this week!! FINALLY ).

They are a very orange 90s colour, and veneer. I need to clean them, fill tiny cracks with food filler (only a couple really), sand very lightly, prime, sand again and paint. Please wish me luck!

Thanks, OP for a very helpful thread !

BTW - Marigolds or similar are vital and safety glasses are good too.

 

[lizziecupcakes]

What are marigolds @Cubist ? I tried to google this but only flowers came up

 

[David Williams]

What are marigolds @Cubist ? I tried to google this but only flowers came up

Washing up gloves

 

[lizziecupcakes]

Oooooh, I have those already!! Thank you

 

[Cubist]

What are marigolds @Cubist ? I tried to google this but only flowers came up

As the First Lady would happily tell you - Marigolds are an essential equipment for any man in the kitchen.