Is modern breathable render a scam?

[Spadez88]

Hi,

There seems to be a lot of conflicting information online. There doesn’t seem to be any doubt that putting sand and cement on a solid wall Victorian is a dumb idea but is it really the case that you have to resort to lime render?

A lot of companies quote that their render is breathable. Krend, Parex, Weber, Vimark, Baumit etc then refuse to publish any stats about the breathability of their product. It seems like it’s a positive quality you want in your render for older properties but none of these guys can back up their claims.

Modern breathable render. Does it exist or is traditional lime rendering the only serious option for Victorian properties even today.

 

[markyspread]

How can one product be stated as waterproof and breathable at the same time ?? even goretex sweats
Modern renders will be like artex , i.e people will pay to have it taken down/off
Good marketing by the said companies, but its a crap product, that wont stand the test of time in our damp climate
Also bit of a dig , but traditional rendering is a skill that most "plasterers" cant do ,
There will be some along in a minute to digress !!!!

 

[Stewie03]

Depends if the Victorian wall is stone or not theres some knowledgeable people on here who know there stuff about renders and lime plastering they will guide you better

 

[smoother09]

How can one product be stated as waterproof and breathable at the same time ?? even goretex sweats
Modern renders will be like artex , i.e people will pay to have it taken down/off
Good marketing by the said companies, but its a crap product, that wont stand the test of time in our damp climate
Also bit of a dig , but traditional rendering is a skill that most "plasterers" cant do ,
There will be some along in a minute to digress !!!!

True!

 

[martinemj]

Mono St astier esp has mostly lime/sand with only small percentage of white cement

Agree with your Comments though ...they don't really want to tell you exact proportion cause it's a secret...

 

[Cockney]

 

[Deleted member 32554]

2 coats of lime cement and sharp.
No waterproofer , involves a lot of water before and after

 

[worthwords]

I think the most reasonable view is that it's still an area of uncertainty.
If you read Hot Mixed Lime and Traditional Mortars by Nigel Copsey it's clear that the word 'breathable' is not sufficient.
Traditional hot lime mortar and mixes were often mixed with crushed lime stone and the result was a compound which had specific structures - small channels (or capillaries) which act to draw moisture away from the masonry to the surface allowing it to efficiently evaporate.
By protecting the masonry from frost cracking, the whole wall may have 100s of years of durability. Also by wicking the water , salts are deposited in the mortar surface or the render which also protects the masonry.

So the key is that traditional lime mortars are permeable to water and not just water vapour but it's the functional properties - the way the water is buffered away from the stone and released that makes it useful.
This functional property is not appreciated and if someone specifies NHL or a mix containing portland to speed up the set - the function is lost and may be just as bad as S&C render over time.

Modern renders pass lab tests for certain threshold of vapour permeability and are labeled breathable. Even a milk carton has some vapour permeability as anyone who has stored left over curry next to plastic milk bottle i a fridge which attest to.
Plastic bottle would be considered water proof and vapour permiable(but only very slightly).
I don't know of any independent testing over 20-30 years to look durability and unintended damage over time for these products.

The advantage of modern buildings is that they are usually specified with a vapour barrier. A large source of trapped moisture in a wall comes from humidity within the house. The idea of vapour permeable exteriors is that for solid walls the water in the vapour phase is not trapped between the render and he masonry - but rain from the outside has limited penetration (and if so can re-evaporate though the render).

I think every house has it's history and idosynchracies so it needs proper assessment.

Please however protect our british heritage of cob houses though - these have been destroyed by inappropriate renders.

Gaping hole left in Devon house after cob wall collapse

A gaping hole is left in a house built of cob after an outside wall collapsed.

www.bbc.co.uk

 

[The Hobo]

How can one product be stated as waterproof and breathable at the same time ?? even goretex sweats
Modern renders will be like artex , i.e people will pay to have it taken down/off
Good marketing by the said companies, but its a crap product, that wont stand the test of time in our damp climate
Also bit of a dig , but traditional rendering is a skill that most "plasterers" cant do ,
There will be some along in a minute to digress !!!!

here is one