Pointing With Lime Motar

[thiambal]

HI All,

I was mooching around this site and the web looking for hint and tips on pointing with lime mortar.

I found this which I thought was a very good summary.

http://www.hullcc.gov.uk/pls/portal/docs/PAGE/HOME/PLANNING/CONSERVATION/LISTED%20BUILDINGS/LIME_POINTING.PDF#search=%22repointing%20with%20lime%20mortar%22

Enjoy

 

[biffvernon]

Nice to see a Local Government leaflet showing how to slake your own quicklime. Well done Hull.

 

[thiambal]

had a go at my first bit of pointing today - quite a neat job really and I am pleased. However, as the mortar is drying it is going bright white - which is a terrible contrast to the rest of the wall.

Is this normal - does it mellow with time?

 

[Nemesis]

Yes - although you will need to leave it until tomorrowish and then rub it back (the end of a small pointing trowel is good) to expose the aggregate.

Then when it's more carbonised you can rub some muck on it, dilute cow muck, a used tea bag... whatever gives you the best effect. But lime is white. Modern stuff is very pure.

Now eveyone else will chip in and tell you that's not the way they do it and their way is MUCH better!


However - the rubbing back with the end of a pointing trowel is as taught to the other half by Marianne Suhr no less, so as far as this household is concerned that's that.

Keep it damp, don't let it dry too quickly - cover with some damp hessian or whatever if it's warm tomorrow.

http://www.robinkent.com/articles_mortars.html

http://www.buildingconservation.com/articles/toolsoftrade/toolsoftrade.htm


http://www.minervaconservation.com/articles/theuseoflime.php

 

[biffvernon]

Modern stuff is very pure.

It can easily be de-purified. Just add some earth into the mix. Bit of trial and error to get the proportion and colour you want. Smear a little of a piece of cardboard and leave in the sun to dry and you will see the final colour in a few minutes.

 

[thiambal]

Cheers chaps,

The old mortar appears to be very yellow in colour - maybe the local sand. Not sure that mixing dirt in with the mortar will get it the right colour - not sure what else would though.

I will go for the tea bag idea on the stuff I have already done. Will let you know if it is successful.

Oh, one other thing that has been bugging me- all the guides tell you that pointing should not be more than such and such deep as the mortar will not go off. So how does in work when laying bricks then?

 

[Gervase]

Slowly! Afer all, you don't want to rush things... :roll:

There's a common chemical indicator called phenophthalein, which turns pink in the presence of strong alkalis (like uncarbonated lime). I've seen some drops put onto some bedding mortar for a rubble-stone wall laid in 1850 (at the latest) which turned bright pink.
There are tales of lime mortar found under paving which was still uncarbonated after several centuries.
As a rule of thumb,the first few millimetres will carbonate within a week or so, but the rest will be much slower. On brickwork (which is porous) carbonation can take several months. But with non-porous ingeous rock like granite or bluestone in damp conditions, complete carbonation may never take place. Which is one reason why massive masonry constructions are able to move and flex without major damage when made with lime mortar.

 

[biffvernon]

Phenolphthalein changes from clear to pink at about pH=9. I don't suppose you need much uncarbonated lime to get that fairly modest degree of alkalinity.