Breathable paints

[Stevers]

This chap at Leyland Paints (4:10 on) specifically states that their Contract Matt (cheap as chips) is 'breathable'.

He thinks it should only be used on nearly dry new plaster, though I think we know better! Also mentions the importance of thinning the first coat between 10 and 20%, and that like us, he doesn't consider vinyl matt 'breathable' though he concedes some low level of porosity.

I was only looking at vids about Leyland Paints because I'm just about to tint (to a yellow ochre) 2.5L of Leyland brilliant white Trade Satinwood (solvent based) that also seems remarkable value at £21.99 from Screwfix with good reviews.

 

[Kearn]

This chap at Leyland Paints (4:10 on) specifically states that their Contract Matt (cheap as chips) is 'breathable'.

He thinks it should only be used on nearly dry new plaster, though I think we know better! Also mentions the importance of thinning the first coat between 10 and 20%, and that like us, he doesn't consider vinyl matt 'breathable' though he concedes some low level of porosity.

I was only looking at vids about Leyland Paints because I'm just about to tint (to a yellow ochre) 2.5L of Leyland brilliant white Trade Satinwood (solvent based) that also seems remarkable value at £21.99 from Screwfix with good reviews.

Maybe breathable to humans. Maybe allows some moisture vapour to pass. Will not manage actual liquid which is where the issues start.

I could launch a paint tomorrow, tell you it’s breathable, market it as Conservation Heritage Blend X and there’s no body or affiliation to go through to make such claims…

 

[Lacan07]

Maybe breathable to humans. Maybe allows some moisture vapour to pass. Will not manage actual liquid which is where the issues start.

I could launch a paint tomorrow, tell you it’s breathable, market it as Conservation Heritage Blend X and there’s no body or affiliation to go through to make such claims…

Exactly my point, the whole subject is a mess quite frankly and trusting a reputable 'heritage' distributor like Mike Wye or the Lime Centre won't necessarily guide you either. They all sell NHL plaster and mortar after all despite knowing it has its issues.

 

[CliffordPope]

Maybe breathable to humans. Maybe allows some moisture vapour to pass. Will not manage actual liquid which is where the issues start.

I've never been wholly convinced about the breathability argument. After a discussion some years ago here about breathable external walls vis a vis rain, I thought the point was that breathable meant that water vapour (gas) could pass through, but that water (liquid) could not? Hence it didn't matter that a wall became soaked in driving rain, because a) the wall was waterproof so the water couldn't pass in, but b) it was breathable so water vapour generated inside the house could still escape out.
I could just about accept that in periods when the rain had dried off the water vapour had its chance to escape, but still find it hard to picture the two moving in opposite directions at the same time. Apparently because the molecules are a different size they still manage to jostle past each other.

 

[Kearn]

I've never been wholly convinced about the breathability argument. After a discussion some years ago here about breathable external walls vis a vis rain, I thought the point was that breathable meant that water vapour (gas) could pass through, but that water (liquid) could not? Hence it didn't matter that a wall became soaked in driving rain, because a) the wall was waterproof so the water couldn't pass in, but b) it was breathable so water vapour generated inside the house could still escape out.
I could just about accept that in periods when the rain had dried off the water vapour had its chance to escape, but still find it hard to picture the two moving in opposite directions at the same time. Apparently because the molecules are a different size they still manage to jostle past each other.

I think folks think ‘breathability’ is a regulated thing! What the SD value measures is vapour passage, not liquid. What’s essential in an old building is both. Walls get wet, they absorb moisture but then let it go again. Being hygroscopic is essential… fabric will get wet, but as long as it has the ability to dry again with no ill effect, life carries in.

Old buildings aren’t designed to be waterproof, quite the opposite.

 

[Maria D]

Exactly my point, the whole subject is a mess quite frankly and trusting a reputable 'heritage' distributor like Mike Wye or the Lime Centre won't necessarily guide you either. They all sell NHL plaster and mortar after all despite knowing it has its issues.

I have plasterers coming soon to internally lime plaster (over woodfibre boards). Should I be checking what specific plaster they are using?

 

[Flyfisher]

I've always understood that 'contract matt' emulsion was more breathable than standard modern emulsion as it is mainly used on newly plastered walls that may not have fully dried and needed to breathe that last bit of moisture out before the new-build owners move in and apply the paint colour of their choice. Basically, the contract matt paint just leaves out the vinyl content, which makes it a lot more breathable than a vinyl emulsion, whereas the vinyl makes it a lot more durable because of the plastic content.

I've never been wholly convinced about the breathability argument. After a discussion some years ago here about breathable external walls vis a vis rain, I thought the point was that breathable meant that water vapour (gas) could pass through, but that water (liquid) could not? Hence it didn't matter that a wall became soaked in driving rain, because a) the wall was waterproof so the water couldn't pass in, but b) it was breathable so water vapour generated inside the house could still escape out.
I could just about accept that in periods when the rain had dried off the water vapour had its chance to escape, but still find it hard to picture the two moving in opposite directions at the same time. Apparently because the molecules are a different size they still manage to jostle past each other.

Grasping at the remnants of my A-level chemistry, isn't the direction of movement of water (or almost anything) through a wall (or almost anything) dependent on the partical pressure on both sides? Thus a sweaty hill walker remains dry inside a Goretex (tm) jacket because the partial pressure of water vapour inside the jacket is higher than the outside so water vapour moves outwards. Water molecules are the same size whether they are in a solid, liquid or gaseous (vapour) states but hydrogen bonding causes individual molecules to 'stick' together when in the liquid and solid states, whereas in the gaseous state the water molecules are effectively individual and therefore in their 'native' form. So yes, water vapour can travel through smaller pores than liquid water, but not because the molecules are a different size, more that they are 'clumped together' to form a larger 'blob'. I'll get my Anorak

 

[Lacan07]

I have plasterers coming soon to internally lime plaster (over woodfibre boards). Should I be checking what specific plaster they are using?

Have they specified a 'brand' yet? It might be worth asking, it will mostly likely be an NHL.

 

[Stevers]

It's easy to overcomplicate things in pursuit of absolute perfection. My NHL plastered/rendered basement chimney breast will shortly be painted with Leyland Contract Matt (Drop and Ceiling), Crown Heritage Flat Matt Emulsion (above dado) and F&B Estate Emulsion (below dado). I'm expecting all of those finishes to cope well with the water vapour coming off the chimney breast (that only appears dry), but we shall see!

 

[CliffordPope]

Just to be quite clear - "waterproof" means water lying in puddles or running down walls or woodwork in heavy rain should not pass through the paint?
"Breathable" means that water vapour can pass through however (in either direction) ?

 

[Maria D]

Have they specified a 'brand' yet? It might be worth asking, it will mostly likely be an NHL.

Is there a product more preferable to NHL?

 

[a twig]

Is there a product more preferable to NHL?

A traditional “fat lime” plaster is the ideal, but a good NHL2 based plaster is reasonably close in performance.

Both are preferable to any other sort of plaster though so for me (I know others on here disagree) it’s a case of not letting the perfect be the enemy of the good. I’ve used both to good effect internally - I was DIYing it and got on better with NHL based plasters, and they were also more readily available in my local area so tended towards that

 

[Lacan07]

Is there a product more preferable to NHL?

well, the wood board manufacturers and sellers usually stipulate an NHL, I'm not sure what the reasoning is...whether its performance or just the fact that NHL is the 'trendy, modern' lime. Personally I've ignored the instructions and used non hydrated (putty based) lime.