Crumbling new Lime Mortar Pointing

Isn't it simply worked out by taking a bucket of dry sand, and working out how much water it takes to make it completely sodden, without any sitting on the top?

Yes - the tricky bit comes from the fact that it was raining on your heap of sand and you don't have a measuring jug. :-)

The best lime is the 'lime putty' that is bought from specialist suppliers, wet, in a plastic tub. This does set pretty quickly. For best results make sure that the bricks a wet and keep the work damp with plastic sheeting or wet sacking if the weather is hot. Don't do it in the winter. Frosts will damage the mortar if they occur before it is thoughly set and this takes many weeks.

If you use dry bagged hydrated lime - the stuff available at any builders' merchants, there is a risk that some of it will already have carbonated. Buy from a merchant with a rapid turnover and when you get it home empty it into a plastic dustbin of water. Once it is under water it will be safe from furter reaction and can be kept as long as you like. When you come to use it tip off the surplus water and scoop out the resulting lime putty to use with your aggregate. You probably won't need any extra water. Just keep mixing till it goes smooth.

Mixing a little lime with a Portland cement mortar may make life easier for the brickie but is usually a BAD idea, despite being a common practice throughout the building trade. There really is no need to use cement in domestic buildings.

Would you please include some context with your replies?

I don't think brickies use lime. Building sand produces a fatty enough mix without plasticisers. It's plasterers that use it to make sharp sand renders more workeable.

What, ever? Is cement now banned totally?

The company which replaced my windows employed a bricky, as one of the windows was to be reduced in size. He used lime mortar, without any prompting from me (it is a lime mortar house). He was quite a young chap too, so I must assume use of lime mortar is not just an old bricky skill. He did a very nice job of it too.

I'll take that as meaning you really are a match for IMM. Maybe the 2 of you'll end up married.

NT

Stuart Noble wrote in news:qRrze.1439 $ snipped-for-privacy@newsfe6-win.ntli.net:

Ah - so that explains why all the cement that I have bought in the last couple of years has plasticiser already added by the manufacturer?

Just answer the question. How does keeping lime mortar damp hasten its set?

Because carbon dioxide dissolves in water to form carbonic acid, which reacts with calcium hydroxide to form calcium carbonate.

Well, thank you for the explanation. So the water in the mix is not sufficient to convert the surface layer to chalk then? Presumably the thicker the layer of mortar, the longer moisture would be migrating to the surface, which might explain why IME it is not effective on shallow re-pointing. As it happens I found myself standing next to a Victorian wall last night where various types of re-pointing had been done at different times. What I think was lime I could just about get crumbs from with my bare finger but it was certainly sound and well adhered to the bricks.

Okay. Lime mortar sets by absorption of CO2 from the atmosphere. Once set is becomes difficult for CO2 to permeate through it so it must get the CO2 from the other side - i.e. through the wall. This will happen but is slow.

Also once set lime mortar actually shrinks a little and the problem is that if this happens just on the surface it cracks.

So over several millenia since Roman times, the established practice for pointing using lime mortar has been to keep the pointing damp using wet sacking for several months so that it sets evenly throughout the whole width of the wall.

Does this answer your question ?

Sort of, except that you are effectively *retarding* the set, much as you would with concrete on a hot day, to ensure a better quality overall set. Keeping a wall covered in sacks for several months is all well and good but how practical is it in this day and age? And how many people realise this when they buy their tubs of lime putty? Is it worth going through all that hassle to end up with a mixture of chalk and sand which does not accommodate movement any more than cement. The self healing aspect whereby cracks miraculously re-seal themselves when the surface gets wet is wishful thinking imo because, once carbonated, the mortar is no longer re-wettable. Chalk cracks, cement cracks and falls out. Either way I don't see how, in the case of re-pointing, all this hysteria about lime is justified. I still think modern additives could be capable of modifying cement to get the best of both worlds but zealots are not interested in discussing that.

Well I've been managing it for three years. It sort of goes with the task of restoring a historic building.

:-) You do after the first wall cracks badly and you then decide to ask the experts.

This assumes all the lime is carbonated. That takes about 100 years or more. Once this happens, as it had on my 200+ year old property, it is indeed time to rake it out and start again. But on an old building without deep foundations you have to assume the building will move a lot and lime does adapt far better than cement.

For many people it isn't hysteria, it's the law.

On the contrary. I've been mixing old and modern methods, looking for the best of both to restore my house. For instance using lime mortar on a chimney stack above roof level is senseless as the stack will only be supporting its own weight and has no need to be flexible. Portland cement will hold it far more rigidly and protect it from the weather more. One up for modern techniques.

Conversely the previous occupier had poured a Portland cement concrete floort which had both failed due to damp building up below but far worse had pushed most of the damp into the walls where carious containment bodges had failed one by one. Ripping the whole lot out and replacing with a poured limecrete floor and some ventilation has resulted in dry floors and walls. Old technique wins.

What I will agree with you totally though is the zealot thing which gives restoration a bad name. English Heritage is quite bad but bodies like SPAB are far worse and unfortunately a lot of conservation officers seem to take their word as law. As a result some of our listed buildings are being forced to use totally unsatisfactory techniques just because they are 'authentic'. IMO the only rule for all buildings should be to use to best available technique.

So the longer the lime remains uncarbonated the better then? Assuming a reasonable depth of mortar, it would actually be more water resistant if the bulk could be prevented from carbonating.

Hm. I can see some flack coming your way.... I was kind of thinking about even more modern innovations. Plasticisers, polymers etc. SBR produces a slightly rubberised mortar, which sounds horrible but doesn't affect the texture or the appearance at all. It's the basis of latex floor screed but I'm sure there are other applications for it.

And to keep things in perspective. Houses are for people to live in, so either compromise on the restoration standards or knock the bloody place down. I know of one such edifice that is visited by people with clipboards now and again, and hopefully it will eventually fall on them rather than the family who live next door to it. Shame, because it is (was) a superb example of a small industrial building. It is, however, quite near the Olympic Village site so maybe there will be some money for a quick Victorian makeover.

He appears to be in the minority then... I had arguments with abricky (Who told my wife to shut up & that she didn't know what she was talking about. Unfortunately when I wasn't present) when he insisted that Lime Mortar was sand/cement/lime. And that you HAD to have cement in it.

Needless to say the company didn't get to finish my conversion... Sadly they're still in business.

People who dont know to be more careful often get cement and lime wrongly described as 'lime mortar.' The other common problem is they add 5% cement when youre not looking to make it go off quick. Beware of builders bearing cement.

NT

Right, got some advice from the chap who sold me the lime mortar.

Something I didnt mention in the original post (sorry), the reason I was raking out the new lime pointing was that it was very white on the surface. ( I hadnt buffed it when I should)

My supplier said that this is lime and has been brought to the surface by the lime drying too quickly. Leaving too little lime "in the mix" to harden everything nicely. Now I did wet down the joints, but I and going to do moreso in my next attempt. The pointing I have done previously which isnt white, (its a nice yellowy colour) has set nicely.

Ill let you know how it goes!

James

snipped-for-privacy@meeow.co.uk wrote:

replying to biff, Bob wrote: There are at least three types of lime and it can be confusing.

Only a couple of feet (height)of wall can be built and then it has to be left to harden/dry out for a couple of weeks. Outside walls have to be covered to aid drying and stop rain leeching the lime out.