Being limed to?

[Doug]

Hey there! So, I recently started working on pointing some lime mortar for a 200-year-old grit sandstone house. The guys I hired showed up with a bag of blue circle hydrated lime. They're mixing it with river sand and builders sand, nothing else. I have to admit, I'm not entirely sure if this is the right kind of lime for the job. But when I questioned them about it, they insisted that it was. However, now that I'm looking at it today, the mortar seems very white and brittle, with lots of hairline cracks appearing. It's not at all like the lime mortar I'm used to using. Do you have any advice for me? I'd really appreciate your input!

 

[Zebra]

You can use hydrated lime for a job like that... whether it's necessarily the best choice...? Hydrated lime is generally best made into putty and left to mature for 3 months before mixing it into mortar. And then there's the question of whether you would have been better off with NHL (hydraulic lime).
As for hairline cracks appearing the next day, they should be bashing the work with a churn brush the following day to compact it remove any trial marks and reveal the aggregate.

 

[Lacan07]

Hydrated lime needs to be made into to lime putty before use, I'm not sure whether mixing it dry is good form.

As a product its fine to use, probably more desirable than NHL, but the problem with hydrated lime is it goes off pretty easily and you don't know how long its been lying about at the builders yard. Its usually advisable when mixed to putty to put a small 'briquette' to one side and observe whether its sets hard.

 

[Doug]

Really appreciate the info and advice Lacan07 and Zebra.

 

[stuart45]

We used that type of lime at Tech for building with, but the work was knocked down and the mortar reused. It's normally used as an ad mix for cement mortar. Properly matured air lime is preferred, especially for inside plastering. For external work a Hydraulic lime is normally used.
Hydrated lime in bags has already started to carbonate.

 

[Athers1971]

The data sheet says...

"Blue Circle Hydralime is used to improve the plasticity, cohesiveness and water retention of Portland cement mortars and renders....
Note that as Blue Circle Hydralime is non- hydraulic, it is not suitable for use in mortars and renders without a Portland cement."

Is this just not the wrong product to be using for the job in hand? Asking for a friend.

 

[Zebra]

The data sheet says...

"Blue Circle Hydralime is used to improve the plasticity, cohesiveness and water retention of Portland cement mortars and renders....
Note that as Blue Circle Hydralime is non- hydraulic, it is not suitable for use in mortars and renders without a Portland cement."

Is this just not the wrong product to be using for the job in hand? Asking for a friend.

That's probably arse-covering as the result would be so dependent on factors outside of the manufacturer's control, not least the mix, method and choice of application.

 

[stuart45]

I've never used hydrated lime on it's own myself, as I wouldn't want to experiment on a customer's house and risk it failing. All the info on it points to it being unsuitable for use on it's own straight from the bag.
Using the correct sand is important as well. The OP says that the sand was a mix of river and building sand, but most building sand comes from rivers because of the need for rounded particles used in modern cement mortar.
It could be that all of his sand has rounded particles, which are more likely to suffer from shrinkage cracking.

 

[Stevers]

Highly experimental, and really the wrong time of year for this sort of work, even if a hydraulic lime had been used.

 

[larry]

I asked a similar question on a different forum earlier in the year for rendering. https://forum.buildhub.org.uk/topic/33725-hydrated-and-hydraulic-lime-renders-without-cement/

We had it done in NHL, no hydrated lime. Very happy so far.

 

[alexander]

hydrated lime needs an additive to make it set which is usually cement defeating the purpose of what they are trying to achieve, sorry your current builders do not have a clue about the correct lime to be using , you need to get rid off them before they do any more damage to your property