On Thursday, 7 July 2005 16:02:05 UTC+1, Stuart Noble wrote:
wrote:

For the OP, lime mortar should idally be kept damp for a few weeks to
hasten its set. It can be covered with sheeting, or sprinkled.

How would keeping it damp hasten its cure? I think you cover it until
the surface has cured/carbonated/dried sufficiently to withstand rain.
Not exactly a practical proposition, which is presumably why hydraulic
lime was used. Maybe the sand also has a pozzolan effect. How would you
ever get a house built otherwise?

Only a couple of feet (height)of wall can be built and then it has to be left to harden/dry out for a couple of weeks.
Outside walls have to be covered to aid drying and stop rain leeching the lime out.

On Sunday, 10 July 2005 12:02:37 UTC+1, Stuart Noble wrote:
Mike wrote:
"Stuart Noble" wrote in message
...


Just answer the question. How does keeping lime mortar damp hasten its

set?

Okay. Lime mortar sets by absorption of CO2 from the atmosphere. Once set
is becomes difficult for CO2 to permeate through it so it must get the CO2
from the other side - i.e. through the wall. This will happen but is slow.

Also once set lime mortar actually shrinks a little and the problem is that
if this happens just on the surface it cracks.

So over several millenia since Roman times, the established practice for
pointing using lime mortar has been to keep the pointing damp using wet
sacking for several months so that it sets evenly throughout the whole width
of the wall.

Does this answer your question ?



Sort of, except that you are effectively *retarding* the set, much as
you would with concrete on a hot day, to ensure a better quality overall
set.
Keeping a wall covered in sacks for several months is all well and good
but how practical is it in this day and age? And how many people realise
this when they buy their tubs of lime putty?
Is it worth going through all that hassle to end up with a mixture of
chalk and sand which does not accommodate movement any more than cement.
The self healing aspect whereby cracks miraculously re-seal themselves
when the surface gets wet is wishful thinking imo because, once
carbonated, the mortar is no longer re-wettable. Chalk cracks, cement
cracks and falls out. Either way I don't see how, in the case of
re-pointing, all this hysteria about lime is justified.
I still think modern additives could be capable of modifying cement to
get the best of both worlds but zealots are not interested in discussing
that.

They are repointing the medieval church tower close to me.
The scaffolding has been up for months and the whole tower wrapped in woven plastic.
Must be costing a fortune.

Lime in Building: A Practical Guide Paperback €“ 1 Dec 1997
by Jane Schofield (Author)

A practical guide to the use of lime for repairing and redecorating old buildings. Suitable for homeowners, builders or even interested professionals who are unsure where to start or what to do. It contains basic, simple recipes with easy rule-of-thumb measures and advice on preparation, techniques and materials. There is an up-to-date suppliers list.

https://www.amazon.co.uk/Lime-Buildi.../dp/0952434121

I bought a copy years ago from soewhere, amazon seems a trifle expensive

[george]

I seem to remember that you need two weeks without frost for lime mortar to set
[g]

On Saturday, 15 October 2016 12:03:13 UTC+1, Adam Aglionby wrote:
On Friday, October 14, 2016 at 2:13:32 PM UTC+1, DICEGEORGE wrote:

Am now incumbent of 1869 , ex railway, building that has been previously had some well intentioned , but wrong, re pointing done in cement.

Haven`t seen Stuart here in a while, but can assure him that repointing a rock faced stone building with cement is liable to blow the front of the stone off with frost.

The areas with open pointing have actually survived better.

Any tips on cutting cement out of the joins?

I don't think there's any magic formula. The advice is often do it by hand to minimise damage, but it's advice that doesn't make sense. Using an angle grinder very gently puts far less peak force onto the bick/stone than any manual smacking. The gentler the better.


NT