Interior wall Lime Repointing confusion!

[Relicah]

Good Afternoon all,

We’re about to have the interior face (random stone on the interior face, squared stone on the outside) of an external wall (approx 300mm total thick) repointed with the intention of leaving this exposed for breathability and aesthetics (I know we’ll lose some thermal properties but research suggests the difference between a damp wall with a few mm of plaster vs an exposed dry wall is negligible)

My question to you helpful lot is what type of lime should we be using for this?

I may be wrong but I gather a non-hydraulic putty would be optimal but potentially the most difficult to get right/ahold of but my question is what would be the preference list from best to worse on the lime scale; putty, hydrated, NHL 2/3.5/5? (Ie. Would a NHL 2/3.5 be better than a blue circle hydrated)

thanks all!

 

[Lacan07]

The best to use would be lime putty based mortar and it shouldn't be difficult to get hold of in ready mixed format. Putty would b closest to the original, it's the most breathable and the most compliant with buildings that move. I would avoid hydrated lime unless you plan to make your own putty and buy the sand. NHL is a newer form of lime, the only issue with NHL is it's been proven to mature a lot harder than it's original grade, so an NHL 2 would be safest. It comes in powdered form and you just add water.

 

[Athers1971]

I have a similar job to do later this year but it’s a 600mm deep and is a party wall with our neighbour.

Once we’ve removed the cement pointing we’ll be repointing it with a Hot Lime mix, Cardewmires aggregate 2.5:1

It’s a standard mix that can be used for pointing, scratch (with added hair) and float coats.

 

[Lacan07]

I have a similar job to do later this year but it’s a 600mm deep and is a party wall with our neighbour.

Once we’ve removed the cement pointing we’ll be repointing it with a Hot Lime mix, Cardewmires aggregate 2.5:1

It’s a standard mix that can be used for pointing, scratch (with added hair) and float coats.

Lovely, will you be slaking your own lime on site? I assume you are if its hot lime.

 

[Athers1971]

I’m not that keen! I’ll be buying it in slaked and ready mixed - just add water!

I did watch them slaking lime when I visited the supplier and it was really interesting, and very hot.

 

[Lacan07]

I’m not that keen! I’ll be buying it in slaked and ready mixed - just add water!

I did watch them slaking lime when I visited the supplier and it was really interesting, and very hot.

Not much water I would imagine though! Just a pinch? the more you mix the putty into the aggregate the wetter it gets

Technically I would imagine all putty based ready mix is slaked lime. Is it not referred to as 'hot lime' when slaked on site and applied fresh and warm?

 

[Athers1971]

I was never very good at Chemistry at school and just scraped by with a C at O Levels.

I think what I saw was quicklime, mixed with damp sand/aggregate which created the reaction and heat. This was then left for 15 minutes or so and mixed up with some water. The resultant mortar could be used there and then 'hot' or stored indefinitely and used cool. I guess that cool 'hot' mix is what I will be buying in.

 

[Relicah]

Thanks both!

I was never very good at Chemistry at school and just scraped by with a C at O Levels.

I think what I saw was quicklime, mixed with damp sand/aggregate which created the reaction and heat. This was then left for 15 minutes or so and mixed up with some water. The resultant mortar could be used there and then 'hot' or stored indefinitely and used cool. I guess that cool 'hot' mix is what I will be buying in.

So this is where I’m getting confused, everything I’ve read suggests that quicklime should be left to slake for 2 months minimum? Did the site office you visited say otherwise?

 

[Athers1971]

Thanks both!


So this is where I’m getting confused, everything I’ve read suggests that quicklime should be left to slake for 2 months minimum? Did the site office you visited say otherwise?

Quicklime and water left for 2 months will make lime putty.

Here, watch this video about mixing hot lime on site (if you have 18 minutes to spare)

 

[saraheamorrison]

What type of stone are you pointing?