Having some building work - lime mortar or not?

[russ_all]

Hi all,

We're about to have some minor building work done (bricking up a window, replacing a door with a window). We're in a 1930s semi detached, and we suspect our mortar might contain lime. We've done a white vinegar test and I think it's fizzing enough to suggest it is lime.

However we've pointed this out to the builder, and they've commented that it's unlikely to be lime as our mortar joints are too wide for this. If we would like to use lime, they'd like to charge us extra.

So my questions - (1), does the mortar joint thickness mean anything re the presence of lime? (2) In a 1930s house with a cavity, North West England, is it likely to be lime mortar? (3) House has 70mm cavity filled with blown insulation, does it matter if they use lime or not for the changes?

Thanks in advance!

Russ

 

[^woody^]

My understating is that the reaction with vinegar and the type of lime used in lime mortar and the type used in cement mortar is similar but different and so it is not a reliable test.

The joint thickness is not related to the use of lime mortar

The cost difference is negligible for small works

It won't matter if cement mortar is used in this type o situation, but the mix ratio should be carefully determined so that it is not too strong and the colour matches the existing

 

[russ_all]

Thanks Woody, had a read of a few of your other replies on other topics, and you seem to seriously know your stuff - what a decent bloke you are spending your time helping us noobs!

Thanks again, have a virtual pint on me,

Russ

 

[stuart45]

The 30's was a time when a lot of builders were still using lime mortar, but gauging small amounts of cement into the mix to speed up the setting.
Mortar using only sand and cement is difficult to work with, unless plasticizer or lime is added.
You could ask him to use something like a 6/1/1 sand/hydrated lime/cement mix. The type of sand used will play a big part in the colour.

 

[danlightbulb]

I recently asked about lime myself as I was doing some repointing work and I researched it as best I could.

I came to the conclusion that there's no value in using hydrated lime. It's only a replacement for plasticiser which a chemical one can do with a couple drops rather than having to buy a whole bag of hydrated lime. In the old days plasticiser didn't exist.

Hydraulic lime is different and is what original lime would have been made of. But this type isn't supposed to have any cement and it takes much longer to set.

You can get colour matching powders to mix in to match the colour. I didn't use any as my sand was quite yellow but the mortar still turned out to be very grey even with a 5:1 mix, so I wish I'd added a bit of buff coloured powder.

 

[stuart45]

I recently asked about lime myself as I was doing some repointing work and I researched it as best I could.

I came to the conclusion that there's no value in using hydrated lime. It's only a replacement for plasticiser which a chemical one can do with a couple drops rather than having to buy a whole bag of hydrated lime. In the old days plasticiser didn't exist.

Hydraulic lime is different and is what original lime would have been made of. But this type isn't supposed to have any cement and it takes much longer to set.

You can get colour matching powders to mix in to match the colour. I didn't use any as my sand was quite yellow but the mortar still turned out to be very grey even with a 5:1 mix, so I wish I'd added a bit of buff coloured powder.

The use of lime in a mortar mix for repointing isn't totally about it's workability. The mortar is more flexible, and has self healing properties for minor cracks. It's also more breathable. The cost is greater for using lime mortar however, so for general building nowadays the slight benefits are not considered worth it.
However for repointing, the extra cost isn't so great.

 

[danlightbulb]

The use of lime in a mortar mix for repointing isn't totally about it's workability. The mortar is more flexible, and has self healing properties for minor cracks. It's also more breathable. The cost is greater for using lime mortar however, so for general building nowadays the slight benefits are not considered worth it.
However for repointing, the extra cost isn't so great.

But that is only true of proper hydraulic lime mortar, not cement mortar with hydrated lime added. That's my understanding from the research I did (it seems a topic with alot of uncertainty/misleading information around it).

 

[^woody^]

An additive works by adding air to the mix, this can be detrimental. Lime does not and the resulting mix with lime as a plasticiser does feel different and not "fluffy" like an additive mix.

Lime lightens the mortar too, which is different to a dye.

 

[stuart45]

But that is only true of proper hydraulic lime mortar, not cement mortar with hydrated lime added. That's my understanding from the research I did (it seems a topic with alot of uncertainty/misleading information around it).

Your understanding of the subject is wrong. If adding hydrated lime to a cement mortar mix only worked to make the mix more workable it wouldn't be a specified mix on certain jobs. Plasticizers are much cheaper and easier to use, so hydrated lime wouldn't be used if there was no benefit to it.
There's been plenty of testing done on mortars in recent years, both here and in the USA. You need to read some of the ASTM reports on mortar done in the USA, to know the difference between the different mixes.

 

[danlightbulb]

Your understanding of the subject is wrong. If adding hydrated lime to a cement mortar mix only worked to make the mix more workable it wouldn't be a specified mix on certain jobs. Plasticizers are much cheaper and easier to use, so hydrated lime wouldn't be used if there was no benefit to it.
There's been plenty of testing done on mortars in recent years, both here and in the USA. You need to read some of the ASTM reports on mortar done in the USA, to know the difference between the different mixes.

I'd be interested in your evidence then because I did lots of searching in advance of my repointing job, watched lots of videos on lime mortar including sone which were from the US, and even asked on here myself.

There seems to be no advantage to using hydrated lime in a cement mortar mix.

What is the difference between Hydraulic lime and Hydrated lime? – Tarmac Blue Circle

tarmac-bluecircle.co.uk

I take the point if it changes the colour, that could be a valid reason. But you can get colouring powders for that.

Why did you not reply to my thread when I asked about it? https://www.diynot.com/diy/threads/repointing-do-i-need-to-add-lime-and-if-so-what-type.636050/

 

[stuart45]

I didn't answer your original question, because firstly I didn't see it, and secondly I don't answer every question on here.
PD6678 2005 is a good source of information for mortars in the UK, but you'll have to pay for it unless you have access to the Construction information service. Unless you work in the trade it's not worth doing.
For a simple read, Google Graymont benefit of cement lime mortar. It will give you the basic reasons.
Plasticizer is an air entertaining agent. What it does is to introduce thousands of tiny air bubbles into the mix, which act as ball bearings and make a workable mix, which allows slightly less water to be used.
With lime added it's better at retaining water, which helps the hydration of the cement. Losing water early on in the process leaves voids in the mortar, as well as hydration being restricted.
There are other advantages to lime in the mix as well, but the extra cost means that plasticizers are often preferred.

 

[danlightbulb]

I didn't answer your original question, because firstly I didn't see it, and secondly I don't answer every question on here.
PD6678 2005 is a good source of information for mortars in the UK, but you'll have to pay for it unless you have access to the Construction information service. Unless you work in the trade it's not worth doing.
For a simple read, Google Graymont benefit of cement lime mortar. It will give you the basic reasons.
Plasticizer is an air entertaining agent. What it does is to introduce thousands of tiny air bubbles into the mix, which act as ball bearings and make a workable mix, which allows slightly less water to be used.
With lime added it's better at retaining water, which helps the hydration of the cement. Losing water early on in the process leaves voids in the mortar, as well as hydration being restricted.
There are other advantages to lime in the mix as well, but the extra cost means that plasticizers are often preferred.

Sorry I didn't mean that to be a personal attack. I just only got a few replies and I wanted to use the correct material for my repointing job. I would have been happy to use some lime in my mix if that was the right thing to do but as you can see from my thread, I only got a couple of replies and advice was mixed with a couple saying cement only and one saying NHL lime. Complete opposites, and no-one advised using hydrated lime.

The bluecircle product page for hydrated lime doesn't say much other than its an additive for workability. So again not much use.

It seems to me that the OP of this thread is also trying to do the right thing but coming up against the same problem I had, which is all over the web - inconsistent advice or information.

There are a number of issues I have found in this area, here are my thoughts.

1. Poor use of terminology. People say 'lime' like there is only one product, which isn't the case. There are various strengths of hydraulic lime (NHL3.5 etc) and there is also hydrated lime which is different, and lime putty which is different again. So when people say "use lime" which lime are they talking about?

2. Its unclear what the threshold is for lime use. We can all agree Im sure that in an 1850's stone cottage we should use a hydraulic lime (no cement), and that in a 1980's house we should use cement (no lime). But what is the crossover point and what are the criteria? My house, as with the OP of this thread, is 1930s, which is on the transition point between cement and lime. So which should be used, how do you decide? Both 'might' be fine and so maybe it doesn't matter, but to me that isn't optimum or factual decision making.

3. Huge inconsistency in advice. I could probably find the last 10 threads on here asking about lime mortar and the advice is different every time, with lack of clarity on product choice as I mention above. I notice youtube is full of lime repointing advice, but again poor explanation of product choice. It seems to me that on social media channels and youtube, lime use is a bit 'fad-ish' in that its being used as a way to generate more clicks etc but without clear explanation of when its actually required and when it isn't.

4. I got a few repointing quotes for my job because there was a small area which needed extensive brickwork repairs that I didn't want to do myself. Not one tradesperson who came to see the job mentioned the need for lime.

 

[stuart45]

I can understand you having a problem with the various advice around. I'll give you a more detailed answer to your questions when I get home.

 

[danlightbulb]

I can understand you having a problem with the various advice around. I'll give you a more detailed answer to your questions when I get home.

Thanks, hopefully will help others but its too late for me, Ive already started repointing my house in 5:1 building sand:cement (with a drop of chemical plasticiser) to depth of at least 30-40mm (alot deeper in places as old stuff falls out so easily). Ive completed probably 12m2 already. I cant change now or it will look different.