Salts ruining Lime/Clay plaster

[Platypus13]

Hi all,

First post, long time reader of the forums. It has been hugely helpful in tackling our renovation over the past 6 years.

Our house is a late 1700s (as far as I’ve been able to work out from old deeds etc) end of terrace cottage. Once it was a larger farmhouse which during the 1800s was split into terraces and added on to. Downstairs construction is thick sandstone walls, whilst upstairs is old soft brick on the front and back, but still stone all the way up the gable side. Seems a little odd to me but so much of this house is.

Over the past few years we removed the cement render outside, and have been removing the gypsum and cement from the inside. All going fairly well bar the odd wall collapse!

My current issue that I’m battling is in the living room. About 3 or so years ago I removed all the cement and gypsum from the walls. Let it sit for around 9 months then repointed in traditional lime. It then had 2 coats of cornerstone insulating plaster, and top coats of Clay plaster. All seemed well until after drying out salts slowly started to creep back through. The worst areas had the clay removed and re applied in the hope the clay had pulled out the worst of the salt contamination. Since then in a few areas the salt has come back and pretty much turned the clay plaster to loose dust that falls off the walls.

What’s the options here for remedying?

The worst wall is an interior wall between the living room and kitchen, but there are no pipes or anything around or above that wall that could be leaking.

Is it possible that the walls are still drying after all this time?

Are there any lime plaster additives that allow the walls to remain breathable but block salt? I assume not but worth asking.

Short of continuing to plaster and remove when slats appear, sort of like using a poultice, I’m a bit lost as to what else to try.

Thanks for any advice which you might be able to give.

 

[Kearn]

The salts are coming from within the walls. As you say, lime can pull them out. But they can also damage the integrity of the lime itself.

Most likely option is that the wall was saturated and plastered before fully drying out. While the plaster extracts the salts it also slows down the abut for the wall to dry out.

Assuming both sides are now plastered internally, so there’s no bare material to speed up evaporation.

How thick is it?
How wet was it?
9mths would be about right for traditional 9” solid brick wall, but I’m assuming you’re much thicker and with sandstone, more absorbent.

It could be that there’s more moisture still entering the wall, but that would need to be fairly significant ingress, not just a bit of rain buffeting the external surface.

No, there’s no magic product to apply.

Best bet is probably patch repairs as and when, but leave the affected areas to dry as long as you can before repairing.

Any pics?

 

[Platypus13]

I can get some photos this evening.

The worst wall is actually just an interior wall between two rooms. This is a single brick thickness wall, so about 4”. It was strange as it seemed bone dry before plastering, and hadn’t suffered with any damp previously like the external walls did.

The other side of the wall currently has the kitchen units on, but they will be removed shortly. That said, looking behind them, there’s no pipes or anything that could be leaking.

I wonder if it’s just with one side still having the old possibly gypsum plaster on it, and the re plastered side being lime if it’s pushing condensation through to the ‘easy’ side and depositing salts that way.

 

[Cubist]

While you're still looking for the 'smoking gun' you should first look into a mirror for 'whodunnit'.

Assuming this internal wall was near bone dry before you applied the plaster then its most likely that the exposed brickwork sucked in and absorbed much of water used to mix the plaster coating and to damp the wall down before it was applied. That absorbed water diluted the salts inherent and natural in the old bricks and mortar and, as the new plaster began and now continues, to dry out, those salts are being drawn to the surface to appear as efflorescence on the plasters surface.

Your accomplice and co-conspirator is your heating and ventilation systems but these will also become your best and most effective long term solution. For now though you should not consider painting or decorating the new plasterwork until you are sure that it has thoroughly dried out. While waiting for that you should merely brush or wipe off the surface salts and make good any damage.

BTW - the same culprits are responsible for any salts appearing on your external walls and this begs a question - what are your plans for the exterior elevations?

 

[Platypus13]

That would make sense I suppose. So the salts would have been in the wall all along and are now being ‘moved’ out to the surface?

It’s not getting painted anytime soon. Until the whole house is finished with removal of plaster and fitting out I’m leaving all decorating right till the end.

Heating is being worked on at the moment so the living room is not very well heated via central heating. It will have a large radiator on the gable wall. I have installed a multi fuel stove recently and that is being used as much as possible to keep the space warm. Windows are always on catch to allow some airflow and the bathroom down the hall has a continuous running fan fitted with humidity monitoring for when the shower is run.

90% of the time the humidity in the downstairs is around 50%.

The exterior walls have been re rendered and I’m sure everyone will tell me that this was a bad idea, we used k rend.

I must state though we spent a good 4 years trying to get the exterior line rendered but had no luck. We had a list and spoke with well over 50 people about doing this, yet not one single one would take the job. Being that gable is on the road I don’t think anyone wanted to deal with the hassle of permits etc. We really did try but just couldn’t find anyone willing to do the work in lime.

As a result everything inside is being made breathable to hopefully compensate a little. So far the damp that was present on the exterior walls mostly seems to have been sorted. 2 years later and we haven’t had anything like before. Just a little salt here and there.

The ground level of the gable is too high, but again with this being the road you can imagine how that’s gone down trying to rectify it. Years of speaking with the council, local councillor, mp and ultimately there is no way they are granting any permission for works to better drainage or lower the ground on the gable elevation.

 

[Cubist]

So the salts would have been in the wall all along and are now being ‘moved’ out to the surface?

Yes, all bricks will include some salt inclusions with the clays used in their manufacture and natural stone possesses these too.

Barring for its marketing blurb I'm unfamiliar with K Rend but the claims regarding its ability to repel water while remaining breathable are intriguing. My guess would be though that there would be some difference between the rates of moisture transfer from the interior to the exterior of the external walls that may cause some build up of damp at lower sections - something perhaps to keep your eye on.

 

[Platypus13]

Yes I’m not buying into it being 100% breathable either but our hands were pretty much tied on that. Same with not being able to lower ground levels on the gable. Frustrating but we just have to do the best we can.

I think the clay was probably a mistake, as it really doesn’t stand up to any kind of water damage at all. Perhaps the worst areas can be patched with lime. It’s all a sponged finish anyway as I’m not a fan of perfectly flat and smooth walls in such a wonky house.

 

[a twig]

Out of interest how long did you wait between applying the nhl based cornerstone insulating plaster and then applying the clay?

 

[Platypus13]

About a month or so. It was all done in stages quite slowly. The walls had been bare for around 9 months or so if I recall correctly

 

[a twig]

Sounds about right - I know I struggled with salts when I didn’t leave NHL based plasters / renders long enough before doing the finishing coats but 4 weeks is usually enough

 

[Platypus13]

It’s been a huge learning curve. We bought the house as ‘fully renovated’ and knew nothing 6 years ago. A few months in and it started falling apart. Clearly had just been bodged and tarted up. Survey was about as much use as you’d expect. So the past few years have been removing plaster, repointing, learning to plaster, rewiring, repairing joists and all that good stuff.

It’ll be worth it when it’s done is all we keep telling ourselves. Either way, I’m too deep now to stop!

 

[Lacan07]

It’s been a huge learning curve. We bought the house as ‘fully renovated’ and knew nothing 6 years ago. A few months in and it started falling apart. Clearly had just been bodged and tarted up. Survey was about as much use as you’d expect. So the past few years have been removing plaster, repointing, learning to plaster, rewiring, repairing joists and all that good stuff.

It’ll be worth it when it’s done is all we keep telling ourselves. Either way, I’m too deep now to stop!

Join the club, its certainly an interesting journey