Plastering after flu removal?

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Lacan07
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Joined: Thu 15th Apr, 2021 5:11 pm

Plastering after flu removal?

Post by Lacan07 » Tue 25th May, 2021 8:46 am

Hi all

I've recently removed a flu which spanned from my kitchen up to my bathroom. I'm about to plaster the bathroom section and I'm guessing i'm going to have to seal / PVA the wall due to soot and salts. This is on the upper floor and isn't an external facing wall so I don't mind using gypsum plaster but I was wondering if there is any way of lime plastering a wall in this situation. I read they used to use fresh cow dung mixed with turps in the past.

Thanks

a twig
Posts: 745
Joined: Sun 6th Oct, 2013 10:18 pm

Re: Plastering after flu removal?

Post by a twig » Tue 25th May, 2021 11:14 am

In one chimney I didn’t have too much soot so a quick brush back and a coat of NHL was fine

The other which was a bit more of a state I attached wood wool boards to first then skimmed then with lime plaster, no issues with staining etc

Monty
Posts: 21
Joined: Mon 16th Sep, 2019 7:14 am

Re: Plastering after flu removal?

Post by Monty » Tue 25th May, 2021 12:46 pm

Our neighbour re-plastered the back of his firepalce last year. First he used pva and then he used gypsum plaster and now it is really badly stained and he is going to replace. I fear he will be doing this annually...

I have heard the cow muck and lime solution works so I'm going to roll my sleeves up and have a go in a few years when I do the inside of our inglenooks, as I would rather have the undulations of the wall rather than dry-lining. Ty Mawr have a good factsheet if you haven't seen it. It has a great title :lol:

https://www.lime.org.uk/community/limew ... F2AMVpyoRs

Lacan07
Posts: 16
Joined: Thu 15th Apr, 2021 5:11 pm

Re: Plastering after flu removal?

Post by Lacan07 » Wed 26th May, 2021 8:23 am

Thanks for the reply lads, and thanks for the link Monty.

There's not a great deal of soot on the bathroom wall but clearly there's salts. I've heard mixed reports about sealing the wall with PVA, professionals seem to have differing approaches, a bits worrying to hear about your neighbour experience.

Feltwell
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Joined: Sun 18th May, 2008 7:28 pm
Location: Shropshire, England

Re: Plastering after flu removal?

Post by Feltwell » Wed 26th May, 2021 11:51 am

My neighbour, with a damp end wall and damp staining showing through, has decided to built a timber frame about an inch away from the damp wall and dryline with plasterboard, leaving an unventilated cavity. I suspect he will be growing mushrooms in the not too distant future!

His plasterer told him that was the best solution. :roll: Why is it that the modern attitude to damp seems to be "Don't fix it, just hide it"? It's like all the "damp proofing" companies that hack plaster off to 1m high on internal walls before replastering with an impervious cement render - no "damp proofing" has happened, just "damp hiding".

Mind you I'd like to see the reaction of the average home owner to someone suggesting spreading cow muck on their wall before plastering! :lol: That would be a challenge for the average Marketing department....

I am considering in my downstairs loo - where I have a damp wall with crumbly plaster that I'd like to tile - taking the plaster off, putting an impervious tile backing board up - spaced off the wall on battens made from more tile backing board - before tiling, but crucially tiling to half-height only and arranging ventilation top and bottom - I reckon it'll keep the wall drier than tiling direct onto the wall. A bit like wainscotting, but tiled and no timber involved. The outside was repointed in lime last year and ground levels lowered, so hopefully it'll all become nice and dry over time.

Flyfisher
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Location: Norfolk, UK

Re: Plastering after flu removal?

Post by Flyfisher » Wed 26th May, 2021 2:43 pm

Monty wrote:
Tue 25th May, 2021 12:46 pm
Our neighbour re-plastered the back of his firepalce last year. First he used pva and then he used gypsum plaster and now it is really badly stained and he is going to replace. I fear he will be doing this annually...

I have heard the cow muck and lime solution works so I'm going to roll my sleeves up and have a go in a few years when I do the inside of our inglenooks, as I would rather have the undulations of the wall rather than dry-lining. Ty Mawr have a good factsheet if you haven't seen it. It has a great title :lol:

https://www.lime.org.uk/community/limew ... F2AMVpyoRs
I've often wondered about the 'cow muck' thing - mainly trying to imagine who came up with the idea in the first place!

I doubt there was much science involved when first trying it out, it would have been just one of those things that someone did because they loads of the stuff to hand. A bit like our reverence for using breathable lime-based products . . . I'm sure breathability was not the reason for originally using it, it was simply all they had at the time. Similar to things like linseed paint etc.

However, I'd like to think that someone, somewhere, has investigated the science behind such things and perhaps tried to isolate the underlying chemistry with a view to emulating its performance in a modern formulation.

Or perhaps they have and it doesn't really work, or at least not very well? Even that TyMawr info-sheet states "This method is usually very effective in stopping staining, however, if stains do track through or you choose not to do the above method then for internal use there is a primer that will delay the staining tracking through."

Monty
Posts: 21
Joined: Mon 16th Sep, 2019 7:14 am

Re: Plastering after flu removal?

Post by Monty » Wed 26th May, 2021 3:02 pm

I do hope it is not a load of old bull!

a twig
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Re: Plastering after flu removal?

Post by a twig » Thu 27th May, 2021 7:29 am

Marketing would be easy - call it Raging Bull Organic Anti-Stain Plaster and supply it in exorbitantly priced pre-mixed tubs :D

Lacan07
Posts: 16
Joined: Thu 15th Apr, 2021 5:11 pm

Re: Plastering after flu removal?

Post by Lacan07 » Thu 27th May, 2021 7:57 am

Feltwell wrote:
Wed 26th May, 2021 11:51 am
My neighbour, with a damp end wall and damp staining showing through, has decided to built a timber frame about an inch away from the damp wall and dryline with plasterboard, leaving an unventilated cavity. I suspect he will be growing mushrooms in the not too distant future!

His plasterer told him that was the best solution. :roll: Why is it that the modern attitude to damp seems to be "Don't fix it, just hide it"? It's like all the "damp proofing" companies that hack plaster off to 1m high on internal walls before replastering with an impervious cement render - no "damp proofing" has happened, just "damp hiding".
Yeah, this is why I don't want to baton the wall, although standard plasterboard is breathable without ventilation you may experience issues with a service void / cavity

Lacan07
Posts: 16
Joined: Thu 15th Apr, 2021 5:11 pm

Re: Plastering after flu removal?

Post by Lacan07 » Thu 27th May, 2021 8:00 am

Feltwell wrote:
Wed 26th May, 2021 11:51 am


Mind you I'd like to see the reaction of the average home owner to someone suggesting spreading cow muck on their wall before plastering! :lol: That would be a challenge for the average Marketing department....

If you've got soft wood pine flooring like me that you intend to make use of its probably best to keep the floor well covered in case of spillage!!

MatthewC
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Location: Central/South England
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Re: Plastering after flu removal?

Post by MatthewC » Fri 28th May, 2021 3:32 pm

Feltwell wrote:
Wed 26th May, 2021 11:51 am
My neighbour, with a damp end wall and damp staining showing through, has decided to built a timber frame about an inch away from the damp wall and dryline with plasterboard, leaving an unventilated cavity. I suspect he will be growing mushrooms in the not too distant future!

His plasterer told him that was the best solution. :roll: Why is it that the modern attitude to damp seems to be "Don't fix it, just hide it"? It's like all the "damp proofing" companies that hack plaster off to 1m high on internal walls before replastering with an impervious cement render - no "damp proofing" has happened, just "damp hiding".
You missed a word out: "temporary damp hiding". The damp will simply appear at the top of the impervious render, where it will wreck the lime plaster and also spall the bricks (in my experience).

The only question is how long that will take - sadly it's certainly long enough for the builder to have made his escape; this is the issue with many modern builders and owners - it is expected that the job will be re-done in 10 or 20 years, by which time it's probably someone else's problem.

Matthew

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