Mortared Tops / Lime Mortar

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Mortared Tops / Lime Mortar

Postby Vladimier » Sat Sep 27, 2008 1:28 pm

Has anybody any thoughts / experience of which sort of lime to use for the lime mortar?

Whilst personally I hate the thought of mortared tops I have been asked to do some despite voicing my reservations (wall settling etc) but the client is adamant!

In the BCTV handbook Sean Adcock describes the technique, but do I use hydraulic lime , or non-hydraulic if non which one? EH2 EH3.5 or EH5 or re-hydrated as per builders mechants.

Thanks in anticipation
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Postby jerryg » Sat Sep 27, 2008 3:32 pm

I agree with you that mortaring tops onto a dry stone wall should not be done but sometimes you have no choice.
I assume that you are being asked to mortar the top stones because you are walling with limestone, which is much sought after by unscrupulous landscapers. Around our way there are only two ways of stopping said landscapers from pinching the limestone top stones is to either mortar them on or paint them with tar or some other horrible paint. Poor farmers use paint everyone else just mortars the top on.

Non-hydraulic lime is made by mixing lime putty with sand. It arrives ready mixed but takes time to cure. This is often called traditional lime and it is used mostly in the restoration of historic buildings.

Hydraulic lime comes in 25kg bags dry packed and requires mixing with sand on site. It cures much faster than non-hydraulic lime. This is the lime that you ought to use. The most common mixes are a 1:1:6 or 1:2:9 ratio mix using cement, lime and sharp sand.
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Postby rabbit » Sat Oct 04, 2008 4:05 pm

I would use Hydraulic lime at a ratio of 1 part to 2.5 sand, sand being a coarse mix, sharp sand will suffice for under the copes. Try and use on days where the temperature is above 5 degrees and cover at night if there is frost.

I wouldn't mix in cement as you are already paying for an expensive product that contains naturally hydraulic clays that will allow the lime to go off. Adding cement only pollutes the Lime with a non natural chemical mix which will degrade the self healing properties of natural lime that help in the settlement of a dry stone wall.

Also, I wouldn't use Hydrated lime or 'Bag lime' as this has already been partially hydrated with water and contains no natural clays to help the lime to cure.

As for pure lime putty, this would be overkill for a dry stone wall, for use in solid wall construction such as a barn wall or dwelling. Only use Lime putty between April and Sept as it requires a temperature above 5 degrees to go off plus CO2 from the atmosphere.

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Postby Carole » Mon Oct 06, 2008 9:25 pm

Hydrated or bag lime available from the DIY sheds and mixed with water and sand is fine for copes. And building. Even though the bag says not.
You can make perfectly good lime putty out of bag lime too.


Hydraulic lime, will do a chemical set and comes in different strengths.
The stronger it is, the less flexible it is. You might as well use cement instead of nhl 5 unless you are avoiding cement for environmental issues.

Rabbit, which strength hydraulic lime are you saying to use?


Vladimier I think you may be a bit muddled up.
Hydraulic limes are the nhl 2, nhl 3.5 and nhl 5. (nhl means naturally hydraulic lime)
Non hydraulic would be the hydrate in bags and the putty.
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Postby Vladimier » Thu Oct 09, 2008 6:34 pm

Back after a computer registry re-build

Thanks for the help, Carole, I guess your second paragraph leads to the obvious!? question - Why use lime mortar at all?

I know, I know - because lime is self healing, allows settling of wall, probably better environmentally, etc. :roll:
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Postby Carole » Thu Oct 09, 2008 7:52 pm

8)

and also means the stone can be recycled for ever as lime can be cleaned off.
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Postby jerryg » Thu Oct 09, 2008 10:40 pm

Which goes back to my point which is that if you don't mortar the tops on securely then the top will be recycled sooner than you think by landscapers pinching your top stones.
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Postby bhutcheon1 » Tue Oct 14, 2008 9:48 am

Slightly off topic,but has anyone found a good solution to the problem of blending in,tinting or ageing a lime mortar repair. I have tried various "witches brews" but have never really found a perfect solution,particularly in matching the sooty appearance of so many old victorian lime mortars.I have found a mortar tinting kit available in the UK at www.dyebrick.com that looks like it may be some kind of answer......have any of you guys tried this?Any and all tips appreciated.
Hope the winter is good to you.
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Postby rabbit » Tue Oct 14, 2008 9:39 pm

Have you tried crushing to powder a piece of the stone you are trying to match and mixing that in with mortar?
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Postby Carole » Wed Oct 15, 2008 3:41 pm

jerryg wrote:Which goes back to my point which is that if you don't mortar the tops on securely then the top will be recycled sooner than you think by landscapers pinching your top stones.



It isn't THAT easy to clean off 8)
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Re: Mortared Tops / Lime Mortar

Postby Inspire » Tue Nov 13, 2012 11:11 am

A response to an old post but should still prove useful to most.

A moderately hydraulic lime mortar would suit best for capping on a dry stone or daubed wall, whether it is a flaunch or a whole capping. The mix should be a 4 sharp sand: 1 soft sand and 1 NHL mortar mix to give a good textured finish and strong/supple bond. The mortar colour will be made with the correct coloured sands. Mortars are either white or cream, the whiter the mortar, the whiter the final capping will be. If you wish to tint your mortars you can use brick dust, stone dust, dry pigments in the wet mix or blow them over the pointing when they are still slightly wet. You can also make the colour in a water colour paint and paint it on to dry mortars to tint that way.

You can get some good quality mortars on the market now and there are several to choose from. French mortars are best and they have a great history in producing reliable and strong mortars. St Astier is probably the best one available.




Hope that helps.
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Re: Mortared Tops / Lime Mortar

Postby stonedyker@talk21.com » Thu Nov 15, 2012 10:44 pm

Lime mortars can take a couple of months to mature properly, which can be difficult in the colder months of the year.

Try a five or six to one mix (Portland cement to local sharp sand - NOT soft building sand). Lay that up the middle of the top of the wall and set the copes on top.

If properly done with good wide copes there should be a very minimum of mortar showing, brush that back to expose the aggregate within the mortar. This will 'green over' a lot faster.
If there is a lot of mortar showing brushing back with a churn brush, just before the mortar cures, will roughen the surface. Throw on some soil to hasten the greening. Initially it may look a bit untidy but the inevitable rain will wash most of it off.

Mortaring copes on drystone walls was often recommended in the late 1700's and early 1800's.
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Re: Mortared Tops / Lime Mortar

Postby George Gunn » Wed Nov 21, 2012 8:22 pm

I think the Hydraulic lime mixes sggested are a bit low on lime content. 1 1/2 to one or 2 to one lime is better. Sharp sand is the right sand. Don't use lime if the temperature can drop below 8 deg c.

I've always said that if a dry built wall has coverbands on top which are a foot long, and it is accepted that this is best practice for a strong wall, then lime mortaring copings on but leaving an un-mortared bit between two copes every foot will act in the same way and settle with the wall in the same way that a cover-banded wall does.
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Re: Mortared Tops / Lime Mortar

Postby Nigel » Wed Nov 21, 2012 9:28 pm

The member 'Inspire' is clearly here just to flog his own goods, he had to trawl through 4 years worth of posts here to make it look like he was not just posting spam. I too would go with a stronger mix, but then, I guess he is the expert?

I will be removing his website from his profile (as per this post viewtopic.php?f=2&t=1471 that he clearly didn't read) and passing his details on to one of the Trustees who may well call him to ask him if he would like to advertise here on the forum and invite him to become a member.

If this was a pub or any other place in the real world we would not put up with somebody barging in, talking just to flog his stuff to a group of people he has not even been bothered to get to know.
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Re: Mortared Tops / Lime Mortar

Postby Tracey B » Thu Nov 22, 2012 6:50 am

Morning Nige. Good catch.
I always enjoy your metaphor about the forum resembling the local pub.
Mine's a gin and tonic, landlord please.
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