Repointing with lime

FreeBear

Grenage said: I've knocked up a load of putty using a few bags of lime.  Do you normally add any water to the sand and putty when mixing?

Depends if your sand is wet or really dry.

I mix dry(ish) sand in to putty, adding a bit at a time. If the mix balls up in to clumps, add a very small amount of water. Leave for a week or more in a tub with lid and a piece of plastic covering the surface. Just before using, pour off any water and give a good mix.

I've got tubs of plaster & mortar that are three/four years old, and still good to use.

Grenage

Cheers guys! Stuart, do you mean I might over mix it with a paddle, or that under-mixing leads too much water being added?

stuart45

With lime you don't won't to under mix it and have to put too much water to make it workable. When mixing up NHL for pointing work I normally let it mix for 15-20 mins, leave it for another 20 to fatten up, and then quick mix again.
This is using a drum mixer, but it will mix up quicker using a roller pan mixer which is really the best one for lime.

Grenage

Excellent, thank you.

Apodemus

Grenage, will your mixing paddle cope with a sand/putty mix?  I must confess, I've never really managed a good mix for pointing at first mix, it is much better left as Freebear suggests, then pour off the excess water and mix through again.

stuart45

Apodemus said:

Grenage, will your mixing paddle cope with a sand/putty mix?  I must confess, I've never really managed a good mix for pointing at first mix, it is much better left as Freebear suggests, then pour off the excess water and mix through again.

An air lime is much better when left to stand for a few weeks. 
How did you find the lime mixed from Hydrated lime?  All the firms I've worked for have either bought it as lime putty, or more popular as ready mixed. Normally for pointing though NHL was used.
Hydrated lime seems to have a bad name in the trade for lime work and is only used for sand/lime/cement work.
Has the work you have done cured as well as you had hoped?

Apodemus

stuart45 said:

Apodemus said:

Grenage, will your mixing paddle cope with a sand/putty mix?  I must confess, I've never really managed a good mix for pointing at first mix, it is much better left as Freebear suggests, then pour off the excess water and mix through again.

An air lime is much better when left to stand for a few weeks. 
How did you find the lime mixed from Hydrated lime?  All the firms I've worked for have either bought it as lime putty, or more popular as ready mixed. Normally for pointing though NHL was used.
Hydrated lime seems to have a bad name in the trade for lime work and is only used for sand/lime/cement work.
Has the work you have done cured as well as you had hoped?

Stuart, I'm not sure if your question was aimed at me.  I only once tried mixing dry lime + sand + water (by hand) and it was a bit of a disaster, so since then I've always used home-made putty. All the hydrated lime that I have bought has been fine for that.  I think if the lime was "off", it wouldn't form as good a putty, so I would know before using.   But my putty bin is primarily as a source for lime-wash and my pointing/repair work has been a side-use.  Making small batches of mortar does, of course, result in a variable commodity and some batches have cured to a much stronger finished product than others.  There are so many variables in there - even down to the weather on the day - that it would difficult to pin the finish down to any particular cause.

stuart45

Apodemus, yes I was asking you, as I have never made lime putty or lime mortar from bags of builders hydrated lime.
In theory it is the same as the lime putty you get from the specialists, but plasterers in particular seem dead set against using it. 
I suppose I'm not brave enough to try it out on a customers property, so was really wondering if there is any difference, or it's just a trade rumour . The only difference I can see is that once bagged a small amount of moisture could cause some carbonation in the lime.
Hydrated lime and sand is used for apprentices in Tech colleges, as it can be reused again.

Apodemus

Stuart, lime putty definitely improves with age, going from "sludge", through "cream cheese" to "putty" and I guess the plasterers want the best putty, but without the hassle of keeping a future stock maturing.  The conservation builders I've seen have all made their own putty on-site, which is probably fine on a historic rebuild, where they are on-site for several months, but would work less well on a day-or-two job.   

While the advice used to be to only buy hydrated lime from places with a good turnover, my understanding is that in fact for making putty, the proportion of carbonation in even an old bag of lime would be insufficient to adversely affect its ability to form a good putty (unless it has also got damp in storage).  Happily, though, use of hydrated lime has increased in recent years and it is both much more readily sourced, but presumably also with an improved turn-over at suppliers. 

The use of soft lime mortars by the colleges, is part of the problem!  Most bricklayers who have been to college associate lime mortar with being soft enough to take the wall apart again, therefore nowhere near suitable for a long-lasting job!

stuart45

Thanks  Apodemus, have you used the mortar made from hydrated lime for any repointing in an exposed area, and if so how did it do after a year?
In my area the general rule of thumb is to to use  an air  lime for indoor work, and an NHL or a pure lime with a pozzy added for exterior work. Hot lime is becoming a lot  more popular now.