Repointing with lime

Apodemus

I rebuilt a very small section of a north-facing, road-side, rubble-stone, retaining wall with lime mortar and it has held up well, while the remaining cement-pointed section has cracked with minor movement.  If I was doing it again, though, I would go for an NHL 3 or 4 or get hold of some pozzolan.

Just this afternoon, I've been fixing vine eyes into a wall that repointed in lime perhaps ten years ago.  The mortar is certainly quite soft in places, but still hard enough to drill into and hold a rawlplug.

I think technique is quite important and I'm a useless amateur, so if you are a professional and experienced with cement and mortars in general, then you are much more likely to get good consistent results.  However for the amateur there is no doubt in my mind that lime is much more forgiving than cement!

Grenage

I was reading the bluecircle hydralime sheet earlier (as on does..); it was about the only hydrated lime in the area.  I notice that it said as it was non-hydraulic, it wasn't suitable for mortars without portland cement.

Hydrated lime is hydrated lime, surely?

stuart45

It's probably that they don't want anyone to think it's a hydraulic lime. The normal hydrated lime you get in the builders merchants is normally used with cement in the mortar or render. It's only sets by carbonation. Hydraulic lime sets by part carbonation and part hydration, so is often used for building or external pointing. 
The problem with pure lime is that the outer skin carbonates first and stops CO2 getting to the inside and carbonating properly.

stuart45

Apodemus said:

I rebuilt a very small section of a north-facing, road-side, rubble-stone, retaining wall with lime mortar and it has held up well, while the remaining cement-pointed section has cracked with minor movement.  If I was doing it again, though, I would go for an NHL 3 or 4 or get hold of some pozzolan.

Just this afternoon, I've been fixing vine eyes into a wall that repointed in lime perhaps ten years ago.  The mortar is certainly quite soft in places, but still hard enough to drill into and hold a rawlplug.

I think technique is quite important and I'm a useless amateur, so if you are a professional and experienced with cement and mortars in general, then you are much more likely to get good consistent results.  However for the amateur there is no doubt in my mind that lime is much more forgiving than cement!

Sounds like you have done a good job. Good thing about doing it on your own property you can experiment and if it goes wrong you can have another go. 
I was only taught about cement mortar as an apprentice, so lime mortar is an ongoing learning curve for me, as for everyone else in the trade.

Grenage

stuart45 said:

It's probably that they don't want anyone to think it's a hydraulic lime. The normal hydrated lime you get in the builders merchants is normally used with cement in the mortar or render. It's only sets by carbonation. Hydraulic lime sets by part carbonation and part hydration, so is often used for building or external pointing. 
The problem with pure lime is that the outer skin carbonates first and stops CO2 getting to the inside and carbonating properly.

That makes sense, cheers!

stuart45

As it's your house and you are paying out for scaffold and putting a lot of work into the job, you might be better to talk to your local lime supplier about the best mix for your house. I often get advice from ours, even though I've been doing lime work for around 20 years. 
The last thing you want is to do all the work and 5 years down the line the joints starting to fail.

Grenage

This is probably a daft question, but how large can particles be in sharp sand for pointing?

I've got some about the right colour, but there seem to be a fair amount of small bits of shell and stone:

stuart45

Depends on what size sieve it went through. That one looks like 6mm down. If you got it from the merchants and asked for sharp you get a bag of concreting or flooring sand for screeds. The true meaning of sharp sand is the angular shape of the particles.
They can be all small 2mm down which is called fine or larger which is coarse. Building sand for cement mortar has rounded shapes known as soft.

Grenage

Ah I see, so this will be no good?

stuart45

You can use it, there's nothing wrong with it. I've used it myself for pointing larger joints on stonework. If the joints are small it easier to have a smaller grade of sand. I used a mix of 2 sharp to one soft building one NHL 3.5 on this job as the stone  joints are quite big. 1mm down for the brickwork.