Mixing Lime Mortar

14 Jan 2008
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United Kingdom
Hello folks,

I planning to make a lime mortar for some brickwork in a fireplace using hydraulic lime NHL3.5. Now I now that when using non-hydraulic lime you usually make a lime putty well in advance and then wait a few days before adding the sand. I just want to know whether the same applies for hydraulic lime or can you just mix the mortar and use straight away?

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I would have thought the pozzolanic materials in the hydraulic lime would make it start to go off if you mixed it with water. Therefore I'd be inclined to just mix it and use it straight away. I could be wrong, though. Lime is a subject that seems to have a lot of conflicting information.
I've used St Astier Hydrated lime straight from the bag into the mixer and plastered/rendered with it.
Instructions on the bag confirmed this.
It's a little more open texture than I'd like but that's due to the sand rather than the lime, (in France).
Cheers Kevin, I suspected as much.

As for using hydrated lime, I was under the impression that hydraulic and hydrated are not the same.
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NHL 3.5
you can mix and use it strieght away.
We usually mix it 3-1 with light yellow bulding sand and it will give you a nice white finish.
you can also chuck a bit of silica sand in there aswell for an even more smoother finish.
All good advice just make sure it's well mixed, don't make it too wet either or shrinkage will be a problem.
Mortars like this, unlike cement, can be "knocked up" even once they seem to have started going off after a few hours in a bucket without adding any further water. Just takes time so be patient!

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