Breathability experiment

[a twig]

Saw this video on YouTube recently - thought someone like @aockenden might fancy doing something similar with various mortars / insulation products in the name of mythbusting

I’m not convinced by this video’s lime results as he uses NHL numbers and mix ratio numbers interchangeably which makes me think he doesn’t really “get” the NHL 2, 3.5 and 5 meaning and of course there is no “fat lime” comparison in there.

My only takeaway was the surprising performance of 5:1:1 sand cement and hydrated lime which made me think it is perhaps less of an evil than it’s reputation suggests

 

[aockenden]

Saw this video on YouTube recently - thought someone like @aockenden might fancy doing something similar with various mortars / insulation products in the name of mythbusting

I’m not convinced by this video’s lime results as he uses NHL numbers and mix ratio numbers interchangeably which makes me think he doesn’t really “get” the NHL 2, 3.5 and 5 meaning and of course there is no “fat lime” comparison in there.

My only takeaway was the surprising performance of 5:1:1 sand and hydrated lime which made me think it is perhaps less of an evil than it’s reputation suggests

Oh cool, this was definitely worth the watch. Thanks for tagging me. I definitely share your concern over his confused mish-mash of ingredient mix ratios and NHL hardnesses, and it forces questions about the rigor of what was done, but overall the story seemed to support our general worldview: namely the less cement you include generally the more moisture is allowed to escape. I recently read a scientific paper about hemp-lime plasters continuing to improve in moisture regulation capability over a 3 YEAR period, so I suspect these results might become even more supportive of our general worldview as the samples aged?

Let me think on this and see if I can find some time to put something together. I’ve just started a new job after 5 months of unemployment so I’m a tad swamped at the minute. I would certainly love to see some more investigation done around this!

 

[stuart45]

Our local lime supplier told me a few years ago that a 1/1/6 was the equivalent of NHL 3.5 and a 1/2/9 was like NHL 2. He knows a lot more about the subject than me so I took his word for it.

 

[stuart45]

My only takeaway was the surprising performance of 5:1:1 sand cement and hydrated lime which made me think it is perhaps less of an evil than it’s reputation suggests

Or NHL isn't as good as first thought.

 

[Stevers]

My re-instated chimney was built in Staffordshire Blues and 1:1:6 twenty years ago, and that's going nowhere despite a bit of shrinkage cracking in the flaunching. In the past I've built garden walls from scratch with 1:1:6 and it's performed well in that use. 1:1:6 isn't evil, but in my experience doesn't stay put when used to repoint a lime mortared stone garden wall. On that basis I'd be sceptical about using it to repoint a chimney built with lime mortar. I've done all my repointing in NHL 3.5 for the last ten years at least and have found it easy and pleasant to use and very reliable.

 

[aockenden]

Or NHL isn't as good as first thought.

Very good point. Without a non-hydraulic lime sample to compare against we can’t know which way to jump on the conclusion.

 

[Kearn]

Or NHL isn't as good as first thought.

That’s probably more the case, studies have shown the carbonation process carries on for up to a decade with strength continuing to increase.

It’s always been one to use with caution, it has its applications but certainly sets solid not flexible like the on site mixed stuff our places were built/repaired with historically.

Breathability is a different consideration, and it will certainly moisture manage. However, the rigid nature means that it is more prone to cracking when it needs to be flexible, and the risk then is water ingress through the cracks.

 

[Robola]

I'm not sure you can generalise about historic lime mortars either. Local variation in the lime, aggregate and other material added as pozzolans must create a huge range of mortar hardness and breathability.

We are coastal and have a lot of shell material added in our old mortar, in some places it is incredibly hard.

 

[Kearn]

I'm not sure you can generalise about historic lime mortars either. Local variation in the lime, aggregate and other material added as pozzolans must create a huge range of mortar hardness and breathability.

We are coastal and have a lot of shell material added in our old mortar, in some places it is incredibly hard.

We’ve some old, very hard poziment panels, you’d assume cement based until investigating - they do manage moisture and have crude clumps of hair in them plus varied aggregate. But god they’re solid!

 

[Cherryburn]

Ah, skill builder. Should have stuck to plumbing, everything else he dives into he seems to have wild unsubstantiated takes on. From what I hear he's quite unpopular in the industry with people who actually know what they're talking about. I gave up on him a few years ago after a rant about heat pumps, and a video in which he plugs that stupid injected damp proofing stuff (in a house with loads of other obvious issues).

It just goes to show that science isn't as black and white as we'd like to think, you can design pretty much any experiment to give you the result you're looking for, consciously or otherwise. This isn't some bombshell discovery, it's very much already a settled question.

An assessment of the relationship between the water vapour permeability and hydraulicity of lime based mortars with particular reference to building conservation materials science

www.ros.hw.ac.uk

https://www.sciencedirect.com/science/article/abs/pii/S0360132322003353

 

[jamest]

His early rant about heat pumps was a bit OTT, but he did then post some videos in collaboration with HeatGeek and they were the ones that introduced me to HeatGeek (thanks skill builder!) - useful discussions in those videos and helpful for people like me with a period house who are thinking of installing a heat pump.