Lime putty

[tobydog]

Potential dumb question alert. I recently bought 3 tubs of lime putty (25kg each) from Anglia Lime. Way more than I need but as it lasts forever when looked after properly, matures with age, and was relatively cheap at £14 per tub, I stocked up. The tubs have settled well and have about an 1" of water above the putty. When I use the putty I will drain off the excess water and only remove as much putty as I need for each batch which will not be much. My dumb question is, how much denser is the putty at the top compared to the bottom?. I know I can poke a cane in but that's not very accurate and I could end up with a sloppy mix. Once I've removed the excess water, should I stir the whole tub before taking out just what I need or is scooping off the top okay?

I've been using NHL to date but would prefer a more breathable / softer mix for what's coming up.

Thanks

 

[plasticpigeon]

My limited experience with lime putty is that when it settles it gets much thicker and dryer at the bottom of the tub. If the whole thing is mixed up is it not a good consistency? I imagine you could take out what you need with a trowel and ad water to the required consistency if you think it will be too thin all mixed up. You could pour the water off the top, but I believe that it is best to store the putty with a film of water on top of it.

I have found that a substituting NHL 3.5 with a 50:50 mix of NHL and hydrated lime gives a much more workable mix that isn't as hard and seems more absorbent than straight NHL mortar just like a 1:1:6 cement lime mix, but with NHL instead of cement. It is certainly more convenient than putty, and it is possible to colour match by choosing appropriate sand.

 

[tobydog]

how much denser is the putty at the top compared to the bottom?.

Believe it or not I did honestly mean this the other way round . I am beginning to wish I hadn't bought the stuff now. My concern with not mixing (knocking-up) the whole lot is that I will have an inconsistant / unknown proportion of lime, as opposed to an inconsistent proportion of water which I could add if necessary, if that makes sense. Due to the water element in putty I was going to use a 2:1 mix rather than a 3:1 mix that I might use with NHL, hence the reason why I want the lime content consistent.

 

[worms]

I can't speak for the store-bought stuff, but my home-made putty doesn't vary much from top to bottom. if it is mature, i would have thought you should be able I to slice out chunks with a spade, like cutting a cake. That way if there is any variation, each slice should have the same proportions.

But, hey, it's lime! More art than science, so what's wrong with a bit of variation between batches!

 

[Zebra]

Only very limited experience but I would say that yes, slightly thicker in the bottom than the top, but not by much. No harm in knocking up the whole tub every time you take some out but I haven't been doing that. I haven't been altering the amount of putty in the mix unless it were really quite thin, but would just make small allowances in the amount of water added.

 

[tobydog]

Thanks for the feedback. I'll have a go on Sunday.

 

[MdB]

Lime at the top of the bucket will be wetter than that at the bottom but the lime content is identical. There is no need to mix up.

If you are mixing with wet sand you may find that the resultant mix is too wet for immediate use. If so, leave a day in a sealed tub and then pour off the water that rises to the top and remix.

Putty has more lime in it by volume than hydrate or NHL. You therefore need less of it not more. With the sand you get in Cornwall (not very good stuff) you need a lot of lime. I typically use 2.5:1 when mixing with putty and 2:1 when mixing with hydrate / NHL. You may be able to get away with weaker mixes if your sand has more very fine stuff in it.

Mixing is the most important job and makes a big difference to workability. I use a cheap (£40) geared sds drill with a chuck and paddle mixer. Don't use a normal drill as you will burn it out. I mix half a tubs worth at a time and remix if I leave it for a few hours - it really is better when recently mixed up. Mixing by hand never seemed to work well.

Oh and you will add to much extra water the first few times you do a batch... Don't worry - leave in tub with the lid on and pour off the water the next day.

 

[Zebra]

Putty has more lime in it by volume than hydrate or NHL.

That's interesting, I didn't know that. But yoghurty putty would have less lime in it per volume than cottage cheesey putty? I mean, if when you make it from hydrate you put a bit too much water in and it's a bit runny, that water won't settle out overnight. The next day it will still be runny, in my experience, and for some weeks. If you needed to use it straight away nonetheless, could you compensate by using a little more lime?

 

[plasticpigeon]

Putty has more lime in it by volume than hydrate or NHL.

How so???

Also I thought that finer sands needed more lime due to the greater surface area of the fine particles which all need to be coated, and rounder particles having a greater surface area than sharp ones. I suppose a well graded sand needs the least lime.

 

[MdB]

Putty has more lime in it by volume than hydrate or NHL.

How so???

Fill a bucket with hydrate then add water. You will end up with 3/4 of a bucket of putty. Water allows the particles to sit closer together than with air I guess.

Also I thought that finer sands needed more lime due to the greater surface area of the fine particles which all need to be coated, and rounder particles having a greater surface area than sharp ones. I suppose a well graded sand needs the least lime.

Round particles have a smaller surface area than sharp ones (for the same mass)...

Builders sand with similar sized medium grains needs lots of lime. Builders sand with medium and fine grains needs less.

Well graded sharp sand needs the least lime as you say - it is just that Cornish sharp sand doesn't seem to have the very fine grains (dust size) so needs more lime to fill the gaps.

 

[plasticpigeon]

I'm an idiot sometimes. I am familiar with spherical things having the smallest surface area to volume ratio but for some reason my mind gave up on me and I thought it was the other way around!!!!

 

[tobydog]

Well, a few weeks later than planned :roll: , I did finally make my first lime putty mix. After I poured the water off the top of the putty I stuck a garden cane in to test the density. It was pretty much the same top to bottom. I started with a 1:2 mix which was way too sloppy given the lovely Greek yoghurt I was working with. I added extra sand to make it 1:3 which gave a much better batch and after mixing thoroughly, leaving for a while, and knocking up again, I was left with wonderful putty to work with.

My only concern is that whilst it was great to work with, it was still a little too wet. I got away with it (just) on the plinth walls I was doing but there was a small area where it cracked fairly quickly. This was probably down to me not wetting the bricks thoroughly enough but after a little compression the crack was gone. I will be doing some repointing shortly but what suggestions do you have for making the mix slightly drier? I didn't add any water to the batch and the sand, whilst not dry, was only damp. Would adding a small proportion of NHL 3.5 to the putty mix help or should I simply dry the sand out thoroughly on a sunny :? day?

Thanks

 

[Zebra]

it cracked fairly quickly. This was probably down to me not wetting the bricks thoroughly enough but after a little compression the crack was gone. I will be doing some repointing shortly but what suggestions do you have for making the mix slightly drier? I didn't add any water to the batch and the sand, whilst not dry, was only damp. Would adding a small proportion of NHL 3.5 to the putty mix help or should I simply dry the sand out

I believe a mix that's not too wet is good, as then there is less water separating the particles of sand and lime, and so it can be denser when set. However there is a point at which too dry is unworkable. I don't think (with my limited experience let me add) that the mix is the problem. What the pros recommend is to use a churn brush the following day after repointing each section. You bash the mortar with it, using it as if it were a hammer not a brush, and it compresses the mortar and gets rid of any cracks. It also texturises the surface of the mortar to get rid of any trowel marks and leave a rough texture.
http://www.oldhousestore.co.uk/churn-brush-205-p.asp
I have two, you'd be welcome to one.

 

[DJH]

I've come across a very useful book (which I'd forgotten I had) while cataloguing my little library which I think all PP owners should have. It's title is Conservation of Plasterwork Technicle Advice Note 2, and is pubplished by Historic Scotland, ISBN 0 9517989 5 2 published in 1994. Part one of a series of three (could be more by now) deals with the Preparation and use of Lime Mortars which is it's title as well.

The first book has four pages of tables giving answers and reasons for Cracking, Crazing, Separation of coats,Separation from background, bulging, partial or total collapse, Crumbliness, Efflorescence, Staining, Fungal growth, and Flaking of surface decoration, There's also a useful bibliography at the back.

Sorry about the flash...



Some of the Q & A pages



I should thank Historic Scotland and Simpson & Brown Architects for using these pictures and here's a link for buying it.Good value at 6 quid I reckon and it has been updated since my copy was published.

http://conservation.historic-scotland.gov.uk/publication-detail.htm?pubid=7135&searchterm=Plasterwork&category=&date=&page=1


Doug

 

[tobydog]

Thanks Zebra. What I have now is a putty mix that's setting nicely but still very slightly soft after 3 days. There's no rush where it is and it will get a few coats of limewash in due course. I do have a churn brush and have already given it a bash. It's come up well but it is an odd colour. When I used the same sand with NHL 3 it was a greyish colour. For some reason with putty it's a dark mustard!. The sand is quite orange.

I think I will dry the sand for pointing to get a slightly drier mix. I will need to compress the mortar quite a bit and probably do it in stages because there are some areas where all the old mortar came out as dust, and others where I will need to remove whole bricks and replace them.

Doug - when I get home I'll get my magnifying glass out and see if I can read those pages without buying the book