Making lime putty - Elementary questions

[michael]

I’ve never tried making lime putty before, so could you please refresh me on what to do.

Questions:-

Standard 25kg bags of lime hydrate from the builders merchant, Blue circle or otherwise.
Or some other specialist make of lime hydrate?

Add water to hydrate or hydrate to water?

What proportions of water to hydrate?

What type of container for the above mix, plastic dustbin, galvanized bath or dustbin or doesn’t it mater? Would old discarded vessel such as an old tin bath with a bit of rust on it affect the mix?

What should the mix initially look like before it slakes - milk, cream or porridge?

After mixing in the above vessel, how long before you have lime putty? I understand mature is better. Dose the water get absorbed by the lime and dose the mix need topping up with water from time to time?

Do you keep the unsightly container (bath) of putty lying around the house for weeks /months on end or can you transfer the mix to plastic containers with lids almost immediately (topped with water of course)?

When you come to use the putty, I guess it would be very wet having stood in water, also the sand will probably have some moisture as well. I believe the standard mix is 3 sand to1 lime putty. No water required I presume?

Many thanks

 

[andrew gayton]

Use an airtight plastic container - You can get plastic drums with screw down lids in either 20 or 40 gallon sizes. mix non hydraulic hydrate into the water within the drum (easier than adding water to hydrate) and thoroughly mix until you have no dry lumps. use as much water as you like, this is not important as the putty will settle leaving excess water to the top (just 'dig out' the putty and leave the water cover......). the longer you leave it, the better. this method has worked for me and a number of other people, although in one instance the putty 'set' in the drum and it was proven that the manufacturer had let some opc in the factory silo that laterly contaminated the lime............ we were compensated by the supplier though, for 20M3 of coarse stuff (lime and sand mixed and left to mature)

use the putty at a ratio of 1:2 - 1:3 is not limey enough in my opinion. everyone specifies 1:3 when historic spec of 1:3 refers to ratio of quicklime and aggregate.......... and of course quicklime can double in volume once slaked. saying that, recent analyisis of mortar on one job showed a range from 1:1 - 1:12!

I would use 1:2 as a basic mix for most jobs.

 

[MdB]

I’ve never tried making lime putty before, so could you please refresh me on what to do.

Questions:-

Standard 25kg bags of lime hydrate from the builders merchant, Blue circle or otherwise.
Or some other specialist make of lime hydrate?

Blue circle etc is fine. Just make sure it says lime hydrate on the bag.

Add water to hydrate or hydrate to water?

Doesn't really matter. I add hydrate to water so as to keep the amount of powder blowing around to a minimum. Wear a mask and gloves.

What proportions of water to hydrate?

I start with the bucket 1/3 full and then add water as required.

What type of container for the above mix, plastic dustbin, galvanized bath or dustbin or doesn’t it mater? Would old discarded vessel such as an old tin bath with a bit of rust on it affect the mix?

I use old plastic tubs with lids so I don't have to move it around.

What should the mix initially look like before it slakes - milk, cream or porridge?

You are not slaking. That is for quick lime. You are basically just mixing. Milk is too thin, porridge is too lumpy. Cream cheese is what you are after.

After mixing in the above vessel, how long before you have lime putty? I understand mature is better

You can use it straight away though some think it is worth leaving for a few months first. I find that it is best to leave for a week or so to settle. You can then pour the excess water from the top which you need to do.

Dose the water get absorbed by the lime and dose the mix need topping up with water from time to time?

No need to add extra water. Absorption happens almost straight away.

Do you keep the unsightly container (bath) of putty lying around the house for weeks /months on end or can you transfer the mix to plastic containers with lids almost immediately (topped with water of course)?

Mix is in the plastic containers. Far easier.

When you come to use the putty, I guess it would be very wet having stood in water, also the sand will probably have some moisture as well. I believe the standard mix is 3 sand to1 lime putty. No water required I presume?

If left to stand for a while, it will settle with water on the top (it will keep like this for years). Pour this water off before use. The putty will be like cream cheese and could be cut with a knife so more solid than you might think. If you use dry sand, you may need to add the smallest amount of water when mixing mortar. 3 sand to 1 lime is correct and a paddle mixer is a lot better than a normal cement mixer. If your sand is wet, you may end up with soup which is very easy to mix but useless to use. If it ends up too wet, you can either leave it for a couple of weeks and the water will end up on the top and can be poured off or you can just add some dry hydrate and more sand (1:3 again) to dry it out.

Others just forget the putty stage and just mix water sand and hydrate together.

 

[Flyfisher]

Others just forget the putty stage and just mix water sand and hydrate together.

What are the pros and cons of making lime putty from hydrate and letting it 'mature' for a few weeks before use vs mixing hydrate/sand/water as required?

I appreciate putty can be stored for long periods whereas bagged hydrate will go off, but assuming an easy supply of fresh hydrate as required what's the benefit of putty?

 

[andrew gayton]

hydrate will not 'go off' in the bag, as most manufacturers employ a plastic liner bag - as per opc bags - to prevent this.

put it like this, if you add water to quicklime you can produce either hydrate or putty........... the magical difference is the amount of water added........... less for hydrate, more for putty.

lots of people won't specify or use hydrate as they believe the myth put about by putty manufacturers/suppliers that it is 'substandard'.......... which really is not the case.


cynical me suggests that perhaps spending more money on putty gives certain people a sense of security??

 

[MdB]

hydrate will not 'go off' in the bag, as most manufacturers employ a plastic liner bag - as per opc bags - to prevent this.

Hydrate will go off in the bag if the bag is opened. Rolling the top down is not enough as I found out. I've also not found any plastic liners in the various manufacturers bags I've purchased but I might not have been looking hard enough.

 

[andrew gayton]

bar one manufacturer, the liner is there.

 

[michael]

Thanks for the useful information everybody. I’ll give it a go one day when the need arises
.
Up until now I’ve been making up small mixes of dry hydrate, sharp sand and water to do a few patch repairs to internal brickwork i.e. resetting a few bricks on the internal face of a solid 9” wall and a bit of repointing etc. The mix seemed to be pretty good for this type of work and I guess I can carry on doing the same.

I would imagine it would be a different kettle of fish however for plastering work where the creamy texture of the lime putty would no doubt give a much better finish. I suppose the other advantages of lime putty, are that there is less potentially hazardous lime dust to contend with if you’re doing large jobs and also the potential for it to keep for many years unlike dry hydrate. I’m not sure if this latter point really matters though as bags of dry hydrate from the builder’s merchant aren’t that expensive and can be bought fresh as and when required.

The bit I’m not to sure about is the maturity of the putty vs. fresh dry hydrate as Fly fisher pointed out. What are the advantages of this or in other words are there any weaknesses in my brickwork jobs for not having used a matured lime.

I should mention that I did a small outside repair job last summer to the 130 year render which covers some of my building using the 3 sand to1 dry hydrate mix. When I say small, I mean a small patch about 3 or 4 inches long by 1inch high by about half inch deep. I went to inspect the repair about six months later and it was soaking wet, soft and could be dug out with a pencil. I redid the repair using 3.5 NHL hydraulic lime and the repair has held up pretty well. I’m not so keen therefore to use hydrated lime outside. I also don’t like the idea of having to drape Hessian over every repair I do to protect it while it carbonates. I live in a seaside location by the way albeit about 500 yards back inland but fairly elevated and therefore exposed to salt ridden sea spray winds. I don’t know if this had something to do with the failure.

 

[biffvernon]

Like wot the others said.

But Andrew, why did you say airtight container? Mine is in an open plastic dustbin. I know I should have put something over it because quite a few leaves dropped in over winter so I shall have to fish them out, but I'm sure the lime putty below will be fine.

And, more importantly Andrew, your recommendation for 1:2 ratio. Now for fine plaster work where an excess of lime makes for a smooth finish on the top coat that could be good, but for other work I think that such a lime rich ratio may give a weaker mortar. If we consider the gritty mechanics, the load should be transferred by the aggregate, the very strong particles of quartz that make up the grit and sand. The lime serves to bind the aggregate so you don't want any more than enough to fill the voids between the aggregate grains. Too much and the sand gets pushed apart which means that mechanical loads are felt more by the weak calcite crystals. If the aggregate is well graded, from coarse grit through sand to silt, an even smaller proportion of lime, say 1:4, can be used without loss of strength.

 

[DaveBrigg]

Do you keep the unsightly container (bath) of putty lying around the house for weeks /months?

I think my wife would have words to say about this, although at least the kids would come out glowing and clean each night.

 

[MdB]

But Andrew, why did you say airtight container? Mine is in an open plastic dustbin. I know I should have put something over it because quite a few leaves dropped in over winter so I shall have to fish them out, but I'm sure the lime putty below will be fine.

Air tight so as to not to dry out. I believe that it is all that is important. Your dustbin will, I assume fill with rain water so it will keep indefinitely.

 

[andrew gayton]

But Andrew, why did you say airtight container? Mine is in an open plastic dustbin. I know I should have put something over it because quite a few leaves dropped in over winter so I shall have to fish them out, but I'm sure the lime putty below will be fine.

Air tight so as to not to dry out. I believe that it is all that is important. Your dustbin will, I assume fill with rain water so it will keep indefinitely.

As above; to ensure that it does not dry out, fill up with debris.

As for the 1:2, this comes from analysis of mortars in the eastern region.

I am fully aware of the arguments for 1:3/1:4 mix............. but comparing them to historic mortars tells me that they can be too sandy and certainly not as forgiving as thos with a higher lime content. see summerlings work on lime/chalk aggregate/hair renders and plasters.

salt laden air? probably has a lot to do with failing mortar.....................

 

[Flyfisher]

Would there have been many local variations of lime mixes around the country in the days of lesser communication and 'word-of-mouth' recipes passed down between master and apprentice?

Is it possible that the East Anglia lime/chalk mixes that Summerling describes eventually fell out of favour because word got around of 'better' mixes? Summerling himself admits that durability of such mixes was a concern and that it needed a lot more aftercare than sand-rich mixes.

Interesting stuff though, particularly the increased flexibility ("plasticity") of such mixes and the ability to apply in single coats of up to 20mm thick.

 

[andrew gayton]

there might well have been more variety due to both the lack of communication and the reduced availability of materials on a 'national' basis pre industrialism.........................?

 

[michael]

Thanks Andrew for your last comment “salt laden air? Probably has a lot to do with failing mortar.....................” Dose anybody else agree with this? Do lime mortars (at least lime pointing) generally fail on seaside properties and is that why most historic seaside properties are rendered?

 

[skier-hughes]

I had my lime tested and it came back as a 1.2 ratio, but also as there was so much large aggregate in other parts of the mortar mix they recommended I use a 1.3 mix.

 

[Flyfisher]

I'm probably taking this all too seriously (I have a hunch that the modern preoccupation with the scientific method, quality control and repeatability was not as well developed in days of olde!) but, based on modern knowledge, is there an optimum ratio for lime mortars?

I guess 'optimum' could have different interpretations but, for example, Biff's description of the lime only being required to fill the gaps between the sand particles, which should themselves be touching for maximum strength, seems intuitive enough. I've no doubt there is some mathematical calculation that can determine the volume of space between an aggregate with a specified range of particle sizes, which would give the precise ratio of lime required - so surely this must have been done by someone, somewhere? Is this where 1:3 comes from?

And, if 1:3 is the optimum for strength, what are the pros and cons of increasing or decreasing the lime ratio? For example, would more lime 'keep apart' the aggregate to create a mix that would better accommodate subsequent movement in the structure, or would that requirement be better achieved by reducing the lime content, leaving more of the aggregate to move amongst itself?

 

[Gervase]

You can work out the optimum ratio easily with a straight-side glass and a measuring jug. Fill the glass with your sand/aggregate and measure how much fills it. Then fill your measuring jug with water and pour it onto the sand in the glass. When the water comes to the top of the sand, stop. How much have you used? That will tell you how much lime you need. Say you had 300ml of sand and needed 100ml of water to saturate it and fill every void in the glass; that's 3:1. Your mileage may vary...

 

[Flyfisher]

That seems a good way to do the 'maths' !

Assuming this gives the optimum mix for strength, are there other benefits of using more or less lime? (accepting that the mix would be less strong, presumably).

 

[Gervase]

There's not much to be said for using less lime, but using more lime gives a 'fatter', stickier mix which can take a smoother finish. It has to be used thinner, though, as it will be more prone to cracking. Best done with finer aggregate, though - as an example, finish plaster is often 1:1 silver sand and lime