Lime

[Anonymous]

I've been looking through these pages gathering info on lime use on the brickwork for older properties. I thought I'd grasped it and was ready to tell any builders I spoke to that "I want it done in 1 part NHL 3.5 to 3 parts sand, etc". I then took a look at an article elsewhere on the site and I am confused again. The article, by Jeff Howell, says:

Lime mortar is easy to make and use. The only problem is trying to find a bricklayer prepared to use it. There is a common myth amongst builders that lime and sand mortar will not harden unless cement is mixed into it, and a common myth amongst building conservation experts (who really should know better) that the only suitable material is hydraulic lime. In fact, hydrated lime - available in 25 kilo sacks (costing 3 to 4 quid)from practically every builders' merchants in the land - makes a perfect lime mortar for bricklaying and pointing. Mix it with washed coarse sharp sand, around 1 part lime to 4 of sand. Keep it wet in tubs or buckets, with an inch of water on top of it, and it will be ready to use whenever you need it. No need for expensive tubs of slaked lime putty, or expensive sacks of hydraulic lime. And definitely no need for cement.

What is the general consensus on this? For example, if I had a small patch of re-pointing to do could I go with the above advice? If so, how is it mixed and prepared?

Many Thanks

 

[Anonymous]

The best thing by far is non-hydraulic mature lime putty, along with of course your chosen aggregate, unless it's for building something under water, or a chimney. Hydraulic is what is better then.

That article by Jeff Howell has caused a great deal of trouble and aggravation. Apart from the bit about do not use cement, I'd ignore it. I know there are others who tell you differently, but I have spent a great deal of time considering all this and I would not use bagged hydrated lime at all, I'd only use hydraulic under specific circumstances, and in general I'd stick to non-hydrualic.

If you want more specific advice, try called Mike Wye or Ryedale, and read Jane Schofield's little book on lime. That has details of wider reading.

It's getting very late in the year to use lime - frosts etc.

 

[Anonymous]

Thanks Evelyn. The bigger picture is that a previous owner saw fit to 're-point' using sand and cement to a grand depth of about 4mm, almost like a skim, if it's too late this year, which I suspected it might be, it'll have to all be re-done next year.

So, as an emergency fix to the poor pointing (about .5m square) what would you suggest? At the moment these is nothing there as the cement has come away in places dragging the mortar that was behind leaving some nice gaps which, in some places, have some nice moss growing where the mortar should be. There is also a section where they used some sort of mastic that is acting as a poor skin. This has to be done now as with the recent rain we actually saw water come into the house inside directly behind this section.

 

[Anonymous]

Regarding frosts/cold, would it be OK to make a repair/point a small area and cover it with plastic sheeting, or is it best just to wait for next year.....If covering is an option how long to leave it covered - and how often would it be best to check on the setting process?

 

[Anonymous]

Well, it depends where you are and how much frost you are liable to get soon. You may just get away with it, especially if you use a pozzolan to aid the cure, although that will make your lime a little less breathable.

It sounds a nasty bodge job!

I can't think really of anything temporary - quick setting will also be cement based and hard to remove without damage.

 

[Anonymous]

It wouldn't need to be that quick setting. I don't think frost is likely too soon. Is there nothing lime that I can get and use to repair this section, even if it has to come out with the 'real job' next year. Something 'plugging' the holes would be better than nothing. I'll even cover it in hesian to keep that rain and wind from washing it out for a couple of weeks!

Or shall I just buy a couple of buckets ;-(

 

[Anonymous]

It's useful to cover it anyhow, we use hessian. It's a cure not a drying process so keeping it most helps prevent cracking. However, if it can wait I'd leave it - we did try some lime work once late in the year and it simply went crumbly. It depends though on where you live and how bad your frosts are.

We have had frost already oop north - enough to kill off the squash plants.

 

[Anonymous]

Have a go then with lime, it depends where you live and how severe the frosts are! We live not so far from Hadrian's Wall, the frosts are pretty severe and very early. You would be wise to try covering anyhow, it stops the surface from drying out quickly and cracking a little.

 

[Anonymous]

I'm guessing you'd recommend lime putty with aggregate then rather than the NHL 3.5 mix? It's not easy stuff to get hold off though (Merseyside), that's why the article caught my eye as a quick fix, especially as you say it's probably too late to get the whole job done this year.

 

[Anonymous]

The problem is it's going to be hard to remove. I've never tried using it but it seems to me that you'd be wasting time and money on.

Give one of the lime suppliers a ring - they will send it to you - and have a chat. They are always very helpful!

 

[Anonymous]

I know this risks upsetting Evelyn, but I ve used dry bagged hydrated lime from a builders' merchant and found that it works just fine. Buy from somewhere that looks like it has a quick turnover and as soon as possible empty it into water. I find two 25kg bags fit conveniently into a standard plastic dustbin. Stir well to make sure all the lime is wet and there are no trapped air pockets. Leave to stand for a few days or longer if possible. I find that a mix of 1:4 lime:sharp sand works well. It sets quickly enough to brush off any surplus mortar that accidentally got onto the face of a brick after half an hour. By next day the pointing is quite firm to finger pressure and in a few weeks it is as hard as ever you want it. Like any lime mortar, it's lovely to use beacause you don't have to hurry, worrying that it will go off. If there's mortar left at the end of the day you just put it in a tub under water and then pour off the surplus water when you next come to use it.
The frost problem, of course, depends where you are. Its been a few years since we had a frost that would do serious damage to fresh pointing, but we live by the seaside. Maybe this next will be a cold winter.

 

[Anonymous]

I had a conversation with Peter M-H about this. His opinion I valued highly, and I will miss his expertise.

Let's just say you pays yer money and you get what you pay for! I know many another lime person who wouldn't agree either with this use of bagged lime.

It's a long term thing. I reckon do it once do it right.

 

[Anonymous]

I've just read all the posts below, and must say that I'm all for the putty route, unless an area is extra exposed (chimney etc) when I would recommend a mix with NHL 3.5.

I still have a few bits to do for a neighbour, and here in Northants I think it will be OK to continue for a few weeks yet, but I will cover it with both hessian and plastic. I've rigged up various sizes of covers on battens that allow easy secure fixing to the walls. A light frost won't get through that.

However, I wouldn't attempt a lot of work now. In your case I'd go round and fill all the obvious holes and worst areas, look after it and cover it, but go with the idea that next year I may just knock it out again and do it properly with the rest of the work. I did just that at the end of last year and it was fine.

Order your putty from Mike Wye or Old House Store or someone else (those are the two I know of) and get it delivered. Or, if you just want a few bags to do the emergency filling, order the stuff ready mixed for pointing. Costs a bit more, but you just open the bag, bash it about a bit and use it. If you need to find a suitable sand (well graded, sharp and of suitable colour for your building) it could slow you down. I always have a few bags on hand as it keeps really well, and even if it seems a bit dry years later, I can still knock it up for use with a bit of elbow grease.

Sue

 

[Anonymous]

I've revised my estimation of bagged lime somewhat downward, although Jeff Howell did make some good points. He was highlighting the fact that the confusion and mystery surrounding lime putty causes many people to go for the easy option - cement. After all, modern builders are familiar with it and it's easily available. I think on reflection that Jeff had vastly oversimplified the issue.

I reckon the bagged hydrated lime makes a good enough putty for scratch coats of internal plaster, providing it's done carefully. Biff makes a very good suggestion about using suppliers with a high turnover, so you can hopefully avoid stuff that's been lying around for ages and carbonating in the bag.

The linked article may be of some interest to you.

"Lime putty + pozzolan v hydraulic lime powders v cement gauging. Analysed by Mike Wye"

I'm currently in a lime related dilema. I need to repair and partly rebuild a chimney stack (sandstone, badly eroded, pointed with cement) but am unsure what type of lime to use for the mortar mix. From what I've read, a non hydraulic lime would not be durable enough for an exposed location. On the other hand, you don't want the mortar stronger than weak, decaying masonry as it will accelerate the erosion process. Added to all this is the problem of frost getting at the mortar before it has set sufficiently, causing it to fail. It seems to me that I've left it too late for this year, and should really delay the work until spring.

However, it might not be too late to make an emergency repair to a small area of pointing, providing you protect it with hessian sacking.

The critical things seem to be:
* Do not use cement
* Don't make the mortar hard and impermeable
* Don't repoint entire elevations when only small sections of repair are needed. Perfectly sound, historic pointing is often needlessly removed.
* Don't do something to the building that can't be undone
* Don't use cement



http://www.ihbc.org.uk/context_archive/63/limemortars/hydraulicity.html

 

[Anonymous]

Thanks Sue, you may have answered my question before I asked it (see my reply below).

I have used NHL5 for bedding a roof ridge, but this may well be too strong for my chimney stack rebuild. NHL3.5 may well be a sensible compromise between durability and flexibility.

Ian

 

[Anonymous]

Sue mentioned 'well graded, sharp sand'. I think this means that there is an even grain size (well graded) and large grain size (sharp). I believe this will tend to give a microstructure with voids, unless there is more lime in the mix than is usual. This is useful if breathability is important. The void structure is a significant factor in vapour pereability. If a not well graded sand is used, i.e. a sand that includes both fine and coarse material, there are likely to be fewer voids for the same lime ratio. This may be less breathable but more resistant to the environment of a chimney top.

That said, I bet the men of old just dug up whatever vaguely sandy stuff they could find within wheelbarroing distance and made do.

 

[Anonymous]

I seem to be having posting probs tonight - I hope this appears!

Last year Geoffrey had problems with the chimneys at Knedlington. I think someone had just dug up whatever was available and eventually it reverted to mud!

It was the end of the seasaon, frost was a consideration, he had the scaffolding up, and chimneys to both rebuild and repoint.

After much discussion and deliberation it was decided that non-hydraulic maybe wasn't the best for chimney rebuilding - exposed, single layer, etc. A form of hydraulic was decided would be the best. SPAB was consulted and said a feebly hydraulic, Mike Wye a moderately hydraulic. He went ahead and chanced the frost, and it all seems to have turned out well. I am sure he will expand on this and post a pic when he reads this!

 

[Anonymous]

Quite right, although I can't remember all the details, you must have looked up the post. NHL 3.5 I think it was, Mrs 51 swung the trowel.

I have to say, though, that c***** was used for bedding the ridges in accordance with a roofing expert's recommendations. I didn't see a problem with this as breathability was not an issue and no historic brickwork was harmed in the process. I used white cement per AG's suggestion and it looks white.

I did point a whole run of tile to brick fillet in the lime putty (non-hydraulic) stuff and it fell to bits within days (very mild frost).

The two chimneys seem perfectly good, though. Absolutely no problem.

 

[Anonymous]

No, I simply remember all the angst! And the details! Frost does have a pretty dramatic effect though.

 

[Anonymous]

I think one has to be pragmatic. I'd rather see someone useing hydrated lime and sand than using cement. I'd much rather see someone using putty and sand, but that's the ideal world and won't always happen.

Given that in the current time most builders will only use cement or a mix of cement gauged into hydrated lime and sand, anything that drops the cement is great by me!

There is a very interesting article on the Building Conservation web site (below) about guaging lime with cement. I think this just about says it all.

Sue


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