Recommended way to source lime mortar

[kreyszig]

I'm going to have to re-point a long boundary wall; I'll have to put some pictures up. Anyway I haven't tested it but I think it is lime mortar, and figure that's probably the best thing to use in any case.
I will probably need to colour it too, as in this neck of the woods there's a lot of black ash in the mortar.
I know this site sells premixed mortar, dry and wet, so don't want to tread on any toes in this regard, but could anyone recommend an economical way to set myself up with some lime mortar suitable for re-pointing? E.G: should I just buy some NHL online and get some sand from a builders yard?
Any tips, as usual, most welcome!
edit: sorry if this is a completely daft question! I think I've found a local builders yard that sells NHL, didn't think it would be that easy!

 

[livias]

Well there you are - sorted!

If you can't find a source of black ash then cement pigment is a cheap substitute. Black ash will add hydraulicity to your mortar so you could end up with something more like NHL 5 instead of NHL 3.5 which is not a problem if your stone/brick is reasonably hard, just saying ...

 

[plasticpigeon]

I use 1:1:6 NHL 3.5, hydrated lime,sand. I use a mix of hydrated and hydraulic as it makes the mortar easier to use and ends up being weaker when it is set/cures than straight NHL (it is amazing how hard NHL 3.5 becomes after a year or so). Hydrated is also cheaper than NHL so it saves the cost of buying NHL 2. I use plastering sand as it is sharp but quite fine. Don't use sharp sand from the builders yard, it will make the mortar gritty and impossible to use. Colour can come from soft sand or cement pigments. make it to a dough like consistency. What finish do you want? flush, weatherstruck or something else. i think flush pointing that is flattened of with a piece of wood to make the face or the mortar flat and in the dame plane as the bricks looks really good, if it is a mm or so back from the surface so you can just see the arris (angle) on the brick.

 

[kreyszig]

Thanks both, esp pp for the recipe!
Was planning to use a lime friendly dye rather than actual ash, finish on the house is raked about an eighth of an inch, (and thickness of the joints about the same) but the wall has thicker joints, will have to find a decent bit and see how it's done; I've been too busy looking at the missing mortar to notice the good stuff!
I'd like to get away without redoing the whole thing; we'll see!

 

[FamilyWiggs]

What is the wall made of?

I tend to use sharp sand or bigger, as when brushed back you get to see the aggregate. I have limestone walls though, so this may be an aesthetic thing. A nice brick wall may be more suited to uniform plasterer's sand as suggested.

 

[kreyszig]

It's brick; I'll pop a picture up tomorrow, would welcome opinions on some of the mortar problems too. Thanks!

Here's some pictures of above wall. Is this efflorescence? (this isn't going to be the most interesting post of all time I'm afraid!)






Here's most of it in one shot (excuse the hedge, it's getting done this week!)

 

[kreyszig]

see edited post above - sorry should have added a new post!

 

[Zebra]

I think I'd not worry about the black ash, it'll get dirty in time anyway. Nor would I worry about matching the mortar colour exactly - I've repointed internal walls here with a lime mortar (putty type) which looked very yellowy and wrong when it went in but has now gone much paler and is only distinguishable from the original if you look closely.
I think it's more conservation minded to only rake out the mortar where it's failed, and keep the original where it's good, although this can be fiddlier in a way than doing the whole lot. Shove it in not worrying too much about the finish, fill the joint up, keep it well wetted and protected from sun and wind (a damp blanket and a tarpaulin does well) then bash it with a churn brush the following day to texturise and reveal the larger aggregate.
I used 2 soft, 1 sharp and 1 lime (NHL3.5 on the chimney which has a lot of wind-loading; putty elsewhere, although I like pp's idea of mixing the two). I used both sharp and soft sand from the local builders merchants - I'd agree that the larger aggregate in sharp sand would be a pain if you had very small joints, but the recommended ratio I believe is that the largest aggregate in the mix should be a third of the size of the joint. Too small and uniform and it won't have as much strength.

 

[Feltwell]

I think I'd not worry about the black ash, it'll get dirty in time anyway.

Not so sure on that one Zebra. I have brick arches picked out in pure white lime pointing, and the brickwork around in lime containing black ash - all original - and even after 115 years of many, many local coal fires (I'm in an old mining area), the difference between the pointing is still very apparent.

They won't get anywhere near as grubby now - far fewer factory chimneys and the only coal fires left are supposed to be smokeless round here!

Unfortunately much of the rest of my house has been repointed badly in cement

 

[plasticpigeon]

Are the close ups of the garden wall?

There seem to be 2 things called efflorescence, one is salts crystallising on the bricks which is easily brushed off, and the other is lime leaching out of cement mortar so what you see is probably one of the two!! Is the pointing on you wall cement based?

If you are really concerned about the original finish then you could try and find a part of the wall with an original finish or at least some original mortar and crush it up to see what kind of sand is in it. on the front of my house i found and area of pointing/jointing, just under the bay window roof that was not weathered at all. The pointing was flush with 2 ruled lines in the mortar, one either side of the joint, adjacent to the edge of the brick which gives it a very even look and there were no visible big bits of aggregate. It obviously got weathered back on the rest of the house so it looks slightly recessed.

Also on my place, with perpendicular joints as small as 4mm and the bed joints less than 10mm the sand had to be quite fine to fit the bricks together. It has one or two bigger stones in it, but it is mainly pretty fine as if the big bits got through a hole in the sieve rather than being there by design. I've tried building a wall with joints like on your garden wall using a sharp sand mortar as i thought that was the right thing to do, and it is next to impossible as the mortar just locks up due to the nature of the aggregate. I was having to hit the bricks hard enough to break them to get then into position. Also since it seems that the builders of yore finished the joints as they went along rather than point up after, the finished part of the joint must be of a mortar mix that the wall could have been built with, again which suggests to me a finer finish. It's probably a good idea to spend a day experimenting to get a colour, mix and finish that you like.

Here is my recent bay window base that I built wit the mortar mix I described.

 

[kreyszig]

Thanks everyone. Those are indeed close ups of the garden wall - and I have recently been reading about efflorescence being an issue with cement based mortar. I have assumed that its lime based but it looks like a test is in order.
If there is cement in the current mortar, am I likely to cause any problems by going over the top of it with lime?

I like your work, PP! I'm going to have a go on a bit of broken wall in the garden (tree removal experts dropped the tree onto it!) and see how that pans out.
I will have to break out the wire brush this week and see if I can make a dent in that efflorescence or whatever it may be.