Lime Mortar - suppliers

[Nigel]

Hi

Our (Grade A listed) house and surrounding walls need a tad of repointing; nothing serious just a few patches here and there. The house comprises two parts, built in 1610 and 1775. The front walls are (new house) dressed, cut, stone and (old house) harled (pebble dashed) but the rear walls are pointed rough blonde sandstone. It is the rear walls that need a few areas touched in.

Being a regular visitor to this site I am aware of the need to use lime mortar and not the dreaded cement but finding lime mortar is proving very difficult. This is sad, not particularly because of the inconvenience to me, but because it is a reflection of the fact that local builders are now repointing all the old buildings with cement, something I notice everywhere.

A few quick questions on which I would welcome assistance:-

- Not having used lime mortar before is there a particular type I should be seeking, for external pointing?

- Is anyone able to steer me to suitable suppliers, the nearer to Ayr, Scotland, the better?

- Is it an easy DIY job or is there an art to pointing with lime - direction to any brochures/aides would be helpful


Any assistance much appreciated

Cheers


Nigel

 

[MdB]

(I'm new to this too but I think the following is correct)

Option 1:

Go to your local builders merchant and buy a bag of hydrated lime. Look for stuff that has turned up recently and hasn't been hanging around and has been stored in the dry. If it gets damp it will carbonate and won't be as good.

Dump hydrated lime in a bin and add water. A bit of a stir will help get the air bubbles out. Make sure there is a layer of water on the top and then seal the bin. Leave for as long as possible (a couple of weeks is good, a couple of months is excellent, but you can get away with a day or so). You now have lime putty. Don't breath the hydrated lime and don't eat the putty (it looks like cream cheese). Safety glasses and waterproof gloves are recommended.

To make lime mortar, mix 3 parts by volume of sharp sand to 1 part lime putty (*). If you use a mixer then give it a longer mix than you normally would with cement. You don't want any lime lumps left in the mixture. The mortar will keep for years if sealed in a tub.

Option 2:

Buy ready mixed lime mortar from a lime supplier. Mine is in Devon which won't be much help to you. It costs roughly twice as much as making it yourself but is a lot less hassle.

You may want to experiment with different sources of sand to get a match with the old mortar. As you are in Scotland, you also might want to consider using a hydraulic lime mix which will set in wet conditions. Others will advise better on this.

(*) Some people suggest 2 parts sand to 1 part putty.

 

[Nemesis]

I wouldn't use hydraulic for pointing. Not necessary or always desirable.

If you have existing pointing then try to retain the historic and match to that.

The Scottish Lime Centre is a source of useful information:

http://www.scotlime.org/

 

[andrew gayton]

- Not having used lime mortar before is there a particular type I should be seeking, for external pointing?

bearing in mind taht sandstone tends to suffer from lime run off (hence you never see limestone built at a higher level than sandstone as rainwater runoff from the limestone tends to corrode the sandstone) go for an exercise in minimal repointing as opposed to wholesale renewal. use a 1:2 non-hydraulic mix with a sharp sand (3mm > 150 microns [as per 'concrete grade' sand] make it quite stiff so it does not slump on the trowel and pack the joint tightly, going back to recompress/take up initial shrinkage when it has started to carbonate/harden. don't use hydraulic as it will be far harder and denser than the sandstone................ sorry, what was the other stone??

- Is anyone able to steer me to suitable suppliers, the nearer to Ayr, Scotland, the better?

go to j*wsons etc etc and buy hydrated non hydraulic lime by the bag; most builders tend to use this now as a plasticiser for a compo mix. just as good as tubbed putty.

- Is it an easy DIY job or is there an art to pointing with lime - direction to any brochures/aides would be helpful

diy - rake out friable pointing/brush out joint/wet joint/point/recompress/point and finish with a stick and tapped stiff churn brush/cover with hessian in hot weather/keep damp ish to aid a good carbonation and strong joint.......... expect to do about m2 a day if done properly. respect appearance of existing sound work............

 

[Mark]

http://www.masonsmortar.co.uk/

are reasonably close I think ?

 

[NT]

Any BM will stock bagged lime. Some diy sheds do too. Repointing is easy enough to get stuck stright in.


NT

 

[Nemesis]

Actually I disagree that in this case repointing should be easy enough and getting stuck in is required.

This is Grade A listed, and a pretty ancient building, possibly with historic mortar which should be considered. Only the minimum of repointing should be carried out and I think that this may require consent, or at least discussion and agreement withHistoric Scotland for the conservation and repair.

So much damage can be done to historic structures by those who mean well but...

Historic Scotland has an advice note on the use of lime mortars it may be worth considering sending for.

http://www.historic-scotland.gov.uk/index/publications/technicalpublications/technicaladvicenotes.htm

 

[NT]

This is Grade A listed,

Ah, I missed that bit. Nem is right, maybe mortar analysis is called for.

NT

 

[chuckey]

tools for re-pointing:-
Cheapo thin wood chisel from market stall (£1) for raking out.
Stainless steel wire wall tie straightend with one end bent into a little (1/4") hook for fishing loose bits out.
STIFF 1" paint brush (mine is polypropolene from Carrefours in Calais), to brush out the grot. or if your stones will take it, a narrow wire brush.
Narrow striking irons to finish the joint. If you have a disc grinder, cut the blade of a stainless steel table knife down length ways,leaving a bit say 8mm wide X 60mm long, kink the blade to provide clearance for your knuckles.De-burr it. Do lots of funny shapes, one I use a lot has the "blade" bent around a 1 1/2" diam, it is useful for finishing around ragged stones that stick out a lot.
Frank

 

[MdB]

This is what I've been using. Seems to work very well though I did increase the angle of the narrow bit using a blow torch so as to reduce the loss of skin on the knuckles... (Cost under £3 though you can pay £12 if you go to the wrong place (TP))

 

[chuckey]

Yes I've got one too. I find that the blade is a bit too wide for my joints and unlike a table knife after using it for 6 Hrs, it gets uncomfortable. I forgot to mention, I made a small Hawk about 5" square. Suits my low speed of pointing - no point in holding 2 Kg of lime for 10 Minutes on a standard size hawk. Yet another tool I have made is a rectangular trowel. Its basically a Brickies trowel, cut down so its 3 1/2" at the handle, 3" at the end with two straight sides (about 9" long). I made it to mix stuff in buckets, but its also useful as a hawk in tight corners. I sold my first one for £20 to a builder!!
Frank

 

[Nigel]

Thanks everyone, very helpful, as ever.

I have spoken with Masons and found them extremely supportive (they have a great web site). Sad to say they are the only supplier in Scotland, which is indicative of the fact that much repointing up here these days is done using cement.

With Mason's guidance I have chosen ready mixed lime mortar that should be a good match for that existing. I am only doing occasional localised repairs where old cracks have opened up, or the odd lump has fallen out. I will start at a low visibility place and see how it shapes up. If it is a decent match I will charge on, if not I will call in an expert stone mason that I know.

Cheers

 

[stickybeak]

.

 

[Nemesis]

Mortar repointing is one of the parts of conservation where 'new work being clearly identifiable' definitely does not apply!

That's interesting - it's the exact opposite of what the late Peter Maitland Hood used to say! He was very much of the opinion that it should be.

However, as I said earlier - before touching anything I'd consult the CO and Historic Scotland. Not a stone mason, not a lime supplier...


http://www.historic-scotland.gov.uk/building_conservation_resources.pdf

 

[stickybeak]

There has been room for a lot of different approaches to conservation over the years and Peter Maitland Hood was indeed one of the movement's staunchest allies.
However, current conservation thinking is in favour of matching mortars, for a number of reasons. This link http://www.scotlime.org/faq.asp explains all. It's the Scottish Lime Centre's own FAQ page and discusses this very topic. Not only that, but they'll do your mortar analysis for you as well.

 

[stickybeak]

I nearly forgot: if you're going to do a mortar repair with a mix which is not an exact match, it probably doesn't qualify as a like-for-like repair (which doesn't need LBC) and may affect the building sufficiently to qualify as an alteration- which does need consent.

How did P M-H get around that conundrum I wonder?

 

[Nemesis]

I can't recall - although he did a great deal of work in Scotland - and I can't now give him a ring and ask him, more's the pity, but as I keep saying - I'd seek some consultation before doing anything.

He did used to get very irate about people not differentiating old work from new though. In fact he used to get very irate about a great deal of current conservation thinking. Myabe of course he sought consent and discussed things before jumping in?

I am aware of the different opinions on the matter - hence my view that this is all OK'd before doing anything.

I've just blackleaded my hobgrate with some stuff made from a historic recipe for me by Peter. Lovely stuff.

 

[chuckey]

Mortar analysis consists of disolving out the lime with an acid and examining the remaining sand particle under a microscope to determine their colour and size. Your problem is to duplicate this mix. It is likely that it was obtained from the nearest source, which might or not be available . The big question what do you do now?, go to B&Qs with your sample grains and see if they sell anything comparable?. I have been to a sand specialist and fancied some thing like Frith-End but sharper. No chance, not even a suggestion of where to go next! I wish you the best of luck.
Frank