Lime wall smells damp

[Stonehouse]

Good morning all

We are lime outside. Inside, we are St Astier 3.5 followed by St Astier Eco mort plaster.

We haven’t had rain for a while but in the morning I’ve noticed one of the external walls smells damp/musty.

Could it be the wall is drying out or is the water sat there?

I didn’t know at the time how much better a lime putty plaster is. Some people say we’ve trapped water in the walls using NHL. There doesn’t seem to be any sign of damp on the wall and we’ve used a breathable paint over the top.

Thank you

 

[Lacan07]

Good morning all

We are lime outside. Inside, we are St Astier 3.5 followed by St Astier Eco mort plaster.

We haven’t had rain for a while but in the morning I’ve noticed one of the external walls smells damp/musty.

Could it be the wall is drying out or is the water sat there?

I didn’t know at the time how much better a lime putty plaster is. Some people say we’ve trapped water in the walls using NHL. There doesn’t seem to be any sign of damp on the wall and we’ve used a breathable paint over the top.

Thank you

St.Astier is considered one of the best NHL's, even the traditionalists won't bad mouth it. It could just be drying out. What floors do you have? carpets are usually the worst offenders when it comes to damp, musty smells.

NHL is perfectly breathable, the issue people have with it is its strength in comparison to non hydraulic lime.

 

[a twig]

The other thing to consider is ventilation, with this not being the warmest June it could just be internal moisture from everyday life (cooking, breathing, washing…) that isn’t escaping due to windows being closed etc

 

[Stonehouse]

St.Astier is considered one of the best NHL's, even the traditionalists won't bad mouth it. It could just be drying out. What floors do you have? carpets are usually the worst offenders when it comes to damp, musty smells.

NHL is perfectly breathable, the issue people have with it is its strength in comparison to non hydraulic lime.

Thank you so much

I have suspended floors, but it is definitely the wall that smells. I’m hoping it is just drying out.

I’ve been told that due to the hardness of NHL, it makes it less breathable and so now the water can’t leave the wall as well and that’s why a putty should have been used

 

[malcolm]

Wouldn't worry about breathability for NHL 3.5. I use it all over the place and it is breathable enough for me. Yes putty will be even more breathable but the problems with NHL 3.5 are much more to do with it being a bit hard which can make it problematic for early structures that like to move a lot or are built using soft materials.

If the wall was soaking wet behind cement before it was plastered then it will take a long time to dry out. An inch of wall thickness a month is one rule of thumb. So long as you think things are right you'll still need to wait a year.

 

[Stonehouse]

Wouldn't worry about breathability for NHL 3.5. I use it all over the place and it is breathable enough for me. Yes putty will be even more breathable but the problems with NHL 3.5 are much more to do with it being a bit hard which can make it problematic for early structures that like to move a lot or are built using soft materials.

If the wall was soaking wet behind cement before it was plastered then it will take a long time to dry out. An inch of wall thickness a month is one rule of thumb. So long as you think things are right you'll still need to wait a year.

Thank you so much for sharing, Malcolm

We have it over very soft red bricks which were used around windows, door frames and fireplaces. Will this be an issue?

We’ve had some cracks form round where we have the original timber lintels but apparently this is normal due to the movement of the wood.

Have you also used St Astier Eco Mortar at all?

Thank you again

 

[malcolm]

I've been using the Ecomortar ultra fine for skimming. It's only because the plasterers I got in to do the kitchen wanted to use it and I got lazy and just kept on using the same stuff. I don't really like it - it has a fast chemical set so you only get an hour or two per mix and it is tricky to plaster to an existing edge as the fats don't come up easily and the sand size is a bit large. With a lime putty you can get fed up and throw the trowel against the wall, then still have time to sort it the following morning.

For breathability it's fine. It's good for not having cracks because of the chemical set. If something else has moved on the edge a bit of filler should sort it.

For anything lime based being an issue - most people will use cement which does cause issues. I've not heard of anything based on lime causing issues even when it's odd stuff. The breathability is the important thing.

 

[Stonehouse]

I've been using the Ecomortar ultra fine for skimming. It's only because the plasterers I got in to do the kitchen wanted to use it and I got lazy and just kept on using the same stuff. I don't really like it - it has a fast chemical set so you only get an hour or two per mix and it is tricky to plaster to an existing edge as the fats don't come up easily and the sand size is a bit large. With a lime putty you can get fed up and throw the trowel against the wall, then still have time to sort it the following morning.

For breathability it's fine. It's good for not having cracks because of the chemical set. If something else has moved on the edge a bit of filler should sort it.

For anything lime based being an issue - most people will use cement which does cause issues. I've not heard of anything based on lime causing issues even when it's odd stuff. The breathability is the important thing.

Thank you, Malcolm.

I agree about the chemical set. We have it all over really. I also find it sets very quickly and it feels very hard.

 

[Lacan07]

Thank you so much

I have suspended floors, but it is definitely the wall that smells. I’m hoping it is just drying out.

I’ve been told that due to the hardness of NHL, it makes it less breathable and so now the water can’t leave the wall as well and that’s why a putty should have been used

I would give your wall a chance to dry out, come back in 12 months and tell us how the wall is performing.

Changes in weather can affect changes in moisture, previous damp leaves salts which in turn attract moisture from the air. If your walls are breathable from both sides, even if its NHL, then it'll be fine. There are old walls everywhere covered in far worse that still manage to stay dry. Just makes sure your external ground levels are as low as they should be and all guttering, etc is sound

 

[Stonehouse]

I would give your wall a chance to dry out, come back in 12 months and tell us how the wall is performing.

Changes in weather can affect changes in moisture, previous damp leaves salts which in turn attract moisture from the air. If your walls are breathable from both sides, even if its NHL, then it'll be fine. There are old walls everywhere covered in far worse that still manage to stay dry. Just makes sure your external ground levels are as low as they should be and all guttering, etc is sound

Thank you so much.

I know that PVA was used on an internal fireplace

What if PVA was used on the walls before lime plastering argh?!

 

[Lacan07]

Thank you so much.

I know that PVA was used on an internal fireplace

What if PVA was used on the walls before lime plastering argh?!

PVA is only used by modern plasterers using gypsum / modern materials. It's often used on fireplaces to prevent soot stains and salts coming through the plaster. It's also used when skimming lime with multi finish. Its also applied to bare brick when floating out a wall, this is obviously bad news

 

[Stevers]

Whilst I wouldn't recommend it to others, above ground I have selectively used dilute PVA as a binder for weak and dusty plaster (with and without a skim), and haven't noticed any issues with damp as a result. I find this concept of 'breathability' a bit simplistic as in everything is in one camp or the other. PVA in at least some forms is 'breathable', and the problem with gypsum in general is not breathability as much as it reacts badly with salts and attracts moisture - lots of that going on here over the years! Here, it's always that nasty pink finishing plaster that goes bad, whilst Thistle One Coat, even used to fill chases in blown lime plaster, is perfectly sound after 25 years - something I can't explain, but am happy to just live with.

 

[Toby Newell]

Whilst I wouldn't recommend it to others, above ground I have selectively used dilute PVA as a binder for weak and dusty plaster (with and without a skim), and haven't noticed any issues with damp as a result. I find this concept of 'breathability' a bit simplistic as in everything is in one camp or the other. PVA in at least some forms is 'breathable', and the problem with gypsum in general is not breathability as much as it reacts badly with salts and attracts moisture - lots of that going on here over the years! Here, it's always that nasty pink finishing plaster that goes bad, whilst Thistle One Coat, even used to fill chases in blown lime plaster, is perfectly sound after 25 years - something I can't explain, but am happy to just live with.

As I have mentioned in another thread PVAc is one of the most breathable polymers there is, more breathable than many paints, at least some PVA's. D4 exterior PVAc wood adhesive for example is a lot less breathable as not only is it more highly polymerised (HMW = High Molecular Weight) but it has waterproof resins added as well. Cheap PVAc sealer is totally different and is specifically designed to be permeable, try making a garden gate with PVAc sealer and see how many weeks it lasts. This is quite logical if you think for a moment. If you plastered over a Tefal frying pan or glazed porcelain tile then the plaster or paint would simply not adhere and fall off because the finish could not mate properly with the substrate. It is precisely BECAUSE PVAc is relatively fairly breathable that it works as an adhesion promoter! The purpose of diluted PVAc sealers are simply to bind dust and RETARD the passage of water suction into the substrate during the curing phase and specifically not STOP the passage of water, as then it would be the same as plastering onto glass and thus an adhesion reducer. Without sealer some plasters / paints will lose water too quickly via absorption , not cure properly and thus lose adhesion and possibly fail ( come away / peel off ) Some finishes that dry too quickly do not cure completely as either they require water to chemically cure and / or the water content facilitates the transport of other autogenous catalysing agents, or the free movement of dissolved gasses from the surface, such as oxygen or carbon dioxide. Working on the basis that plaster on a now slightly less breathable wall that stays attached, rather than fall to the floor in front of a slightly more breathable wall, is better, it's not always a bad thing. Having said that, a wall with no PVAc IS more breathable and it is a retrograde step if using lime, but for gysum a very thin, hygroscopic and purposefully permeable adhesion promoter is not an issue. I think the issue is ignorance.

Subjectively Poly Vinyl Acetate doesn't sound very 'eco friendly' (whatever that is) I think everyone simply assumes that all plastics are the same, non breathable, that is very much untrue. Nylon is one of the strongest plastics but some forms can absorb 10% by weight of water. I don't know of many plastics apart from PVAc that are so readily soluble in water. PVAc is also digestable by some microbes, so as plastics go, low polymerisation (Low Molecular Weight, LMW) PVAc with no added waterproofing resins absorbs water better than most other plastics. Whilst all you Humanities undergrads were down the pub, us Materials Science Engineers were in the lab two evenings a week for 9 months a year for 3 years. Some of us even had to take modules on Polymer Science and visit industrial plastic factories. You're welcome.

 

[Toby Newell]

And fyi. Plastics are incredibly environmentally friendly. I still have my Nans 1960s plastic sieve. Plastic bags and boxes last multiples of time longer than paper or cardboard ones so over time use less energy per use. Plastic is used to line other materials to waterproof them. Plastic is used in engineering because it is light and strong. Plastic saves weight in vehicles which saves millions of tons of CO2 per year. Plastic is light, flexible and can be waterproof or breathable. Pipes? Iron water and gas pipes corrode and break, plastic less so. What is the energy saving by going from a steel pipe to a plastic pipe? Well, you don't need to have personally visited a plastics factory and Forgemasters in Doncaster where they made the supergun pipes for Sadam Hussein, you just need to know melting temperatures... Steel...roughly 1550°C iirc, PVC and HDPE around 100°C I think the highest melting point of any plastic is about 250 - 300°C. So plastic pipes are more durabke, last longer are lighter, easier to transport and in energy terms use multiples less energy to make, form and transport. Plastics are a wonder material that saves hundreds of millions of tons a year of CO2.

Why are they demonised? So that the sheep can ignore the naked emperor and point at the plastic instead. It's frankly deceptive propoganda aimed at fools, ie all of us! The issue is the needless and pointless overruse of plastic for trivial means. Water bottles are ridiculous, single use bags are ridiculous, why hasn't the world boycotted McDonalds Happy Meals and their idiotic throwaway plastic toys? Plastic is not the enemy, it's our trivial use of it. The problem is the current world order dictates we need to increase revenues, sales and shareholder return which basically translates into 'make more shit'.

No. Make less shit. I have a Festool Trion jigsaw, it was the most expensive one in the UK when I bought it. It has a Nylon body. It was made in 2004, it's possible it will last me another 20 years. That's a sensible use of resources. Instead I could of bought the cheapest jigsaw I could find, 12x cheaper, but guess what, how many cheap jigsaws, with the same plastic body, would I have gone through by now? Without plastic global warming would be much, much worse.

Plastic is a CO2 saviour. It's the broken system that is the issue. Stop pointing at plastic and go find a mirror people.