Lime Mortars

[Bailout]

I have a query.
I am abit confused, I want to make up some lime mortar for internal pointing and rendering on old stone wall.
In local builders merchants I see bags of hydrated lime for around �7 per 20kg bag.
my neighbours are doing a similar thing and bought a pallet of hydraulic lime that cost them �12+ per bag, I asked them what was the difference and can I use the cheaper stuff but they didnt know, they just bought from same place as a friend of theirs had been buying, so they werent too sure.

Can you shed any light, and also can the hydrated stuff be used for lime wash? As I have tried a small patch externally and it seems fine.

And if its not to be used then why?

Thanks for any help.

[stanleyman]

This is a very interesting and complex subject and you and your neighbour need to know if you have the right traditional lime for the job. Hydraulic lime can set under water and hydrated, classed as a feeble hydraulic lime is not so durable for adverse conditions but perfectly suitable for particular jobs.

Check out this site:

http://www.buildingconservation.com/articles/lime/hylime .html

[stanleyman]

Just to add to this, hydrated lime is unsuitable to make limewash, you need lime putty.

[Bailout]

Hi Stanleyman

Thanks for that article, but to be honest I am still confused because if you look at the paragraph entitled

"USE OF LIMES
Non-hydraulic to feebly hydraulic lime"

It says there:

'Non-hydraulic lime is available from over 40 suppliers (UK and the Republic of Ireland) in the form of putty and from most builders merchants in the form of bagged hydrate'

Then it goes onto say:

'To use a feebly or non-hydraulic lime today is perfectly acceptable'

The great merit of mature putty lime is that it is often highly compatible with weakened, weathered stones and bricks, is able to accommodate minor building movement'.

Well I really am confused, as it seems here that the lime putty is made from Hydrated lime, and can be used.

And I have made what I think is lime putty, I bought a bag of hydrated lime, added it to water (not vice versa) in a plastic tank,,,i keep it wet, and go in every few weeks and give it a good stir, then cover with a plastic bag. and I have used it to make a lime wash, mixed with milk and water on a fairly decent size test area, which was already limewashed, and seems fine 6 months later. I have even done a smaller test patch externally and that seems fine too.

I really am confused, as I have had someone from a conservation company tell me it cant be used. but thats not what that article seems to say, or my test results.

further help is most welcome, as I want to save money if I can but dont want to do the wrong thing

Regards and thanks again

[stanleyman]

I'm not an expert but as I understand you can have limewash from hydraulic or feebly hydraulic lime putty made directly from the slaking process but putty made from bagged hydrate which is a dried powder by a slightly different process is considered inferior because it has already started to go off in the bag as soon as it is made, like cement does. You can of course try it.

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

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