Sand type for lime mortar?

[vards01]

Hi All,

Does anyone know what type of sand should be used in the mixing of lime mortar for brick laying / re pointing purposes. I see plastering sand and sharp sand mix seems to be what is being advised on youtube (1 lime (hydraulic NHL 3.5) / 2 plastering / 1 sharp). Is there a reason why you couldn't use building sand?

 

[stuart45]

It's to do with the pore structure of the mortar, which allows moisture to pass through it.

 

[vards01]

So is the mix that I mention above the right way to go about it?

 

[stuart45]

The sand you use can also depend on the joint sizes. Really small joints need a finer sand. Some people use 50/50 sharp/building sand, others as you have seen.
Mix up for about 20 minutes with not too much water to start with, then leave for 20 to fatten up, then mix for a couple more.

 

[vards01]

That is the issue I have here quite small joints 5mm - 10mm. on the arches I had to sieve building sand as even that was too gritty as some were 2mm, originally lime putty. Im just starting so do not want to use a sand that is a complete no go. I was just using travis general building sand but I'm now worrying this isn't the right sand for the job.

 

[vards01]

It also seems that tooling a lime joint isn't the done thing as you have to leave the surface open. i.e overfill joint scrape back and then light taps with the churn brush.

 

[stuart45]

Rough guide, max grain size one third of the joint size. No use using a sand gone through a 4mm sieve with 2mm joints. For arches with small joints use a lime putty, or silver sand and lime. Some of the best arch joints had a mix of white lead and shellac.
Churn brush finish is quite common now.

 

[vards01]

So a weathstruck joint in lime would still be OK technically? I tried with this but even when wetting the bricks the lime just pulled in too much. The impression I was getting is that you have to leave the surface open i.e scrape and churn brush to maximise vapour release.

 

[stuart45]

For striking joints you have to catch them at the right time. Tooling with metal brings laitance to the surface and makes a smoother but slightly less breathable joint(so the experts say)
However I think one of the reasons that the flush joint/churn brush is so popular is that many of the older buildings now have larger joints as the edges have either worn away or been knocked away during a repoint.
Larger joints tend to look worse when they are tooled up, whereas the flush joint/churn brush finish seems to match the rustic look.

 

[vards01]

So would you say there is anything wrong with using just building sand?

 

[stuart45]

http://www.stastier.co.uk/nhl/guides/sandmort.htm
This article explains it better.

 

[vards01]

Yes I had come across that article myself when trying to reason my argument of changing my plan.........as oppose to using the logic of some guy on youtube uses it.

As I really have no idea what is in travis building sand its difficult to say in relation to that article but I guess due to its orange colour there is some clay in there.

I'm looking at the original mortar on my house and it is quite yellow in colour similar to what the mortar colour is when using just building sand, although the original does have some larger aggregates in there.

If I use the plastering / sharp mix the colour is no where near the original colour its more white in colour.

 

[stuart45]

Mix the building sand with some sharp sand, it's what most people round here do. It's been done like that for the last 20 years without any failures as far as I know of.

 

[vards01]

http://www.stastier.co.uk/nhl/guides/ptgnhl.htm#nhl

According to that the sharp sand and plastering I have just brought from travis couldn't be used as max size is 4mm according to the packaging. There' no way there are 4mm stones in the plastering sand though........

 

[stuart45]

https://www.limebase.co.uk/sands-and-aggregates
The lime suppliers near me have a variety of different sands for different situations. You may need a local lime supplier if you need to match to colour and have smaller joint sizes.