Blown plaster question

[lee666]

Our back dining room has a bit of blown plaster in various places and a couple of bits have come away from the wall.

Underneath these bits, the wall it is joined to is crumbling away as it appears there is a coating over the bricks almost like cement. I have put some pics below so you can see.

At some point I want to chip away all of the blown plaster so it can be patched either by myself or a plasterer.

My question is, is there any work I should do to the wall behind as it is quite unlevel. I will make sure all of the crumbling coating behind has been removed but I don't want the same to happen again.

If anyone knows what the coating behind is then I would be grateful to know for the future.

Thanks

 

[lee666]

forgot to add that it is a victorian house, so don't know if the crumbling mortar underneath is lime mortar.

Is it advisable to get rid of everything to plain brick and then plaster on top, or should another layer of lime mortar be used prior to plastering?

 

[lee666]

I can post more pics if needed but my father in law has said he will help but he was talking about using patching plaster which i don't know is a good idea.

The mortar behind the plaster is generally solid once you get rid of whats crumbled off so I didn't know if more mortar should be used to level it before plastering, or if a lime based bonding plaster could be used, or should it be taken back to brick?

Any help would be greatly appreciated as I would like to crack on it with as soon as I can.

Thanks

 

[Micilin]

Take off any loose.

See if there is damp or any source of damp.

Could be condensation, it that mould on the skirting?

IF the wall is damp free .

Clean it, damp it and plaster on to it.

But see why it is blown fisrt

 

[lee666]

there was but i put that down to my OH leaving something up against the wall for ages which I thought may have stopped the wall breathing as i'm 99% sure I have solid walls with no cavity. There was none before she did that.

It's only when I removed the offending item that I noticed the mould/mildew and the blown plaster as it had bubbled up. And as it was only where it had been covered that's what makes me think it was because the wall couldnt breathe.

The other bigger patch is on an internal wall, the problem I have with that one is that the house on the other side is empty. That wall has blown plaster at the bottom and also a fair bit up the wall and I don't know if the house next door being empty has anything to do with it, it certainly seems to bo the case though as the wall was fine when we moved in and the house next door has been empty for over 2 years

 

[Possel]

If it's an old house built with lime mortar you must use breathable materials wherever possible to let it all breathe. Don't use any plaster based on gypsum etc as it will stop it breathing. If it is lime mortar on your wall (as is most probable) then you might need to remove it as well (back to the brick) but since the plaster has come away from it, it might be OK when dried out.

The issue is, why is the wall damp? There is no point in re-plastering over an area which will become damp again. The most likely cause is indeed the house next door not being maintained properly and thus ingress of water on that side not being noticed. The issue could be a leaking pipe or anything like slipped tiles on the roof, old leadwork, blocked gutters, cracked downpipes, water running along the base of the wall, etc. Check everything.

The house I bought last year has now dried out and it's wonderful. I was careful to use lime products (eleven tonnes of mortar/plaster!) and sort the roof/gutters/drains/high ground. See http://houseintheenchantedforest.blogspot.com/

 

[lee666]

Thanks for the replies.

The wall between my house and next doors is I guess what you would class as an internal wall, so there are is no guttering etc to overflow, also the house is checked on a regular basis so any major leaks would be spotted so i'm certain that's not to blame either.

Could it just be a question that the existing render/plaster has reached the end of it's day? The mortar that is exposed on both holes isn't damp.

The top pic is on an outside wall, and i've been checking it most days to see if it's damp and it's dry as a bone, same for the bottom pic which is on the internal wall.

Assuming that it is just down to it crumbling with age, how would I best go about repairing it?

If I chip off all of the blown plaster, and remove all crumbling render/mortar so that it's solid, should I used a lime based bonding coat, followed by a lime based finishing coat?

The father in law is going to help so I'm not worried about the finish as he is very methodical when it comes to these kind of things and he has done a bit of plastering in the past, but it's just knowing the best way to repair it and in which order.

 

[Possel]

Lime mortar/plaster does not deteriorate unless it gets damp - if it stays dry then it gets harder with age. I guess yours got very wet at some time in the past and so popped off.

You want to get lime mortar and plaster from any supplier (google for it). It is sold pre-mixed by the tub (10 litres) by Mike Wye in Devon (from who I bought the eleven tonnes) and they will give advice on the phone as well; I expect that most other suppliers are equally helpful. Mortar is typically 3:1 sharp sand:lime putty, and plaster is 2:1 using a finer sand.

Basically you will need to apply mortar <12mm thick to about 3mm less than the current surface and then use plaster to finish off when the mortar has gone off. If the mortar has to be thicker you may need to do it in two goes, with a few days between; the bottom layer can have hair which helps it stay on the wall.

 

[peaps]

Lime mortar/plaster does not deteriorate unless it gets damp - if it stays dry then it gets harder with age. I guess yours got very wet at some time in the past and so popped off.

You want to get lime mortar and plaster from any supplier (google for it). It is sold pre-mixed by the tub (10 litres) by Mike Wye in Devon (from who I bought the eleven tonnes) and they will give advice on the phone as well; I expect that most other suppliers are equally helpful. Mortar is typically 3:1 sharp sand:lime putty, and plaster is 2:1 using a finer sand.

Basically you will need to apply mortar <12mm thick to about 3mm less than the current surface and then use plaster to finish off when the mortar has gone off. If the mortar has to be thicker you may need to do it in two goes, with a few days between; the bottom layer can have hair which helps it stay on the wall.

Lime doesn't stay dry, it soaks in water and then it naturally evaporates, is one reason it was used.

 

[lee666]

Lime doesn't stay dry, it soaks in water and then it naturally evaporates, is one reason it was used.

is it feasable then, that depending on the age of the plaster that it has just run it's course after doing it's job for so long? There's been no other telltale signs of a damp problem and I can rule out pretty much most things that would cause a damp problem, other than the DPC, but if that were the case I'd imagine the problem would be a lot worse.

 

[Possel]

Lime doesn't stay dry, it soaks in water and then it naturally evaporates, is one reason it was used.

Eh? The evaporation is just the first (and brief) part of the curing process. Thereafter the process is carbonation where the lime (calcium hydroxide) slowly absorbs carbon dioxide from the atmosphere and thus turns into calcium carbonate (which is what limestone is). In this case "slowly" means years and years, which is why lime mortar used by Romans is rock-hard - it has actually become rock. Lime plaster and mortar does NOT wear out - something must have caused it to deteriorate.

I think your point is that while that process is going on, it is still flexible and so is able to absorb tiny cracks - which is why it should be used on old buildings, and one reason why it is wrong to use cement on them.

 

[lee666]

quick question: If a lime plastered wall is painted with normal emulsion, could this in effect stop the wall breathing, which in turn means it retains the moisture, causing the plaster to crumble?

I'm guessing that for the wall to breathe both sides have to be able to do so, or am i massively wrong?

The main reason I ask is that the previous owners track record for DIY isn't the best, plus there is no blown plaster upstairs, and all the walls upstairs were, and still are, papered, which may let the walls breathe.

 

[Possel]

quick question: If a lime plastered wall is painted with normal emulsion, could this in effect stop the wall breathing, which in turn means it retains the moisture, causing the plaster to crumble?

I'm guessing that for the wall to breathe both sides have to be able to do so, or am i massively wrong?

The main reason I ask is that the previous owners track record for DIY isn't the best, plus there is no blown plaster upstairs, and all the walls upstairs were, and still are, papered, which may let the walls breathe.

"Normal" emulsion? If the emulsion is water based, it's usually breathable, but if it's "vinyl", then it will retain the moisture, and would feel cold when touched.

One side breathing is better than neither side, but both sides are even better. Mine are 18" thick, so it's essential that it all breathes.

Even vinyl wallpaper can stop the wall breathing. My brother has a house on a cliff with lime walls and the vinyl wallpaper refuses to stay attached; he won't agree with me what the cause is . If ever a house needed to breathe properly, it's one that gets continuous sea gales!

 

[peaps]

Lime doesn't stay dry, it soaks in water and then it naturally evaporates, is one reason it was used.

Eh? The evaporation is just the first (and brief) part of the curing process. Thereafter the process is carbonation where the lime (calcium hydroxide) slowly absorbs carbon dioxide from the atmosphere and thus turns into calcium carbonate (which is what limestone is). In this case "slowly" means years and years, which is why lime mortar used by Romans is rock-hard - it has actually become rock. Lime plaster and mortar does NOT wear out - something must have caused it to deteriorate.

I think your point is that while that process is going on, it is still flexible and so is able to absorb tiny cracks - which is why it should be used on old buildings, and one reason why it is wrong to use cement on them.

It's used for it's ability to soak water and evaporate it. Nothing to do with the cure process. Oh it BREATHS

 

[peaps]

quick question: If a lime plastered wall is painted with normal emulsion, could this in effect stop the wall breathing, which in turn means it retains the moisture, causing the plaster to crumble?

I'm guessing that for the wall to breathe both sides have to be able to do so, or am i massively wrong?

The main reason I ask is that the previous owners track record for DIY isn't the best, plus there is no blown plaster upstairs, and all the walls upstairs were, and still are, papered, which may let the walls breathe.

"Normal" emulsion? If the emulsion is water based, it's usually breathable, but if it's "vinyl", then it will retain the moisture, and would feel cold when touched.

One side breathing is better than neither side, but both sides are even better. Mine are 18" thick, so it's essential that it all breathes.

Even vinyl wallpaper can stop the wall breathing. My brother has a house on a cliff with lime walls and the vinyl wallpaper refuses to stay attached; he won't agree with me what the cause is . If ever a house needed to breathe properly, it's one that gets continuous sea gales!

Interesting you should say this