Yet another question about mortar mix!

[milleniumaire]

Having done lots of Googling I'm still struggling to determine exactly how I should be mixing mortar to do some re-pointing on my home.  There's lots of advice out there, with suggested mixes and what should/should not be included, but it all seems to be very generic and I'm struggling to apply it to my situation, so here goes.

 

I guess you would call my house modern as it was built in 1998, so is currently "only" 24 years old.  It is built from random stone and around 6 years ago we had an extension built onto the kitchen at the back, which resulted in a very large, long steel beam being installed to support the upstairs walls.  As a result there has been some settlement as well as some water ingress at various points over the years and this is causing issues again.  As well as fixing poorly fitted guttering, I plan to re-point above the extension as there are many cracks due to settlement.  I'm sure water isn't getting through them, but at least if I repoint I can tick off any possible cause of leaks.

 

Attached is a photo of the extension.

 

I've read a lot about adding lime to the mortar mix, but get the impression this is only necessary for older houses.  I've also read that the mortar mix needs to have less strength than the stone otherwise spalling can occur.  Our stone is VERY hard!  When I have to drill holes in the wall, I always try to drill through the mortar as it takes forever trying to drill holes into the stone.  I'm aware that too strong a mortar mix will likely result in hairline cracks and too soft a mix is likely to disintegrate over time.  We also have a stone wall and I have tried repointing a few cracks in this over the years, but the mortar mix, even a 5 parts building sand to 1 part cement, always ends up being very grey, compared to the existing light coloured mortar.

 

So, what mix should I be using for the mortar when I repoint, in order to ensure it blends in and is strong enough, but not too strong?

 

.

 

I've also attached some recent photos of the upstairs wall above the extension, showing the numerous cracks that have appeared since the extension was built. (I only managed to add 2 before I exceeded the size limit!).

 

 

[Bonner]

Can’t you remember if they used Lime mortar? If so try 1:3:6 cement lime sand. Otherwise white cement and sand at 1:5. Unfortunately sand varies in colour quite a bit as well, so unless you know exactly what was used, you will have to try a few mixes

[milleniumaire]

I have no idea how they mixed the mortar for the original build.  I get the impression from Googling, that for modern builds it isn't necessary to include lime, however, I assume lime is white and so I'm wondering if adding it might lighten the mix.

 

I'm using very "yellow" builders sand, which I was told should give a lighter mix, but doesn't appear to as it always turns out grey!

 

I've read that lime makes the mix more permeable and easier to work with, but also that it is pointless including lime in a mortar mix that includes cement as the cement will override the lime and still produce a hard mix.  My limited understanding is that only the cement causes the mortar to harden, so 1 part cement to 9 parts (sand and lime) seems like a very week mix.  But what do I know 🙂

Edited November 17, 2022 by milleniumaire

[Radian]

I think I can see the original buff coloured mortar and the more recent repairs (yours?) with grey mortar.

The original is almost certainly made with yellow sand and may be 1:2:4 which is the same mix as my house was built with in 1998 (snap).

White cement is key to matching your mortar.

[Gone West]

Many years ago I had our semi-detached house repointed to match the original and using yellow sand and white cement we ended up with a creamy colour. In the picture, to the right of the downpipe, the neighbours was repointed using grey cement.

 

[Radian]

When we had steels put in for our garden room extension, the builder started replacing the sandstone with a grey mortar mix. I told 'em to hop it and leave it to me. 🙄

 

 

When we had our house built I made notes of the brick type (Ibstock Chailey), the sandstone (Purbeck from Suttle quarry) and the mortar mix, 1:2:4 white cement, lime, ginger sand.

[milleniumaire]

18 hours ago, Radian said:

I think I can see the original buff coloured mortar and the more recent repairs (yours?) with grey mortar.

The original is almost certainly made with yellow sand and may be 1:2:4 which is the same mix as my house was built with in 1998 (snap).

White cement is key to matching your mortar.

No, the grey mortar wasn't me as I haven't yet done any repointing in this area, only on my garden stone wall.

 

The greyer mortar will have been from the builders who built the extension, which is strange as they managed to match the pointing on the extension to the rest of the house, but then when we asked them to sort out the cracks in the old stonework they did a crappy job.  We also had a roofer come to sort out a leak we had and he ended up filling a lot of the settlement cracks in the mortar with builders sealant.  Quick and easy, but up close, it looks a mess!

 

So, 1:2:4 is 1 part white cement, 2 parts lime and 4 parts building sand?

 

Is there any particular lime that is best to use?

 

17 hours ago, Radian said:

When we had our house built I made notes of the brick type (Ibstock Chailey), the sandstone (Purbeck from Suttle quarry) and the mortar mix, 1:2:4 white cement, lime, ginger sand.

 

I wish I'd had the forethought to have done this myself when the house was built 24 years ago, or even when the extension was added 8 years ago, but alas....

 

I will investigate white cement as TBH I didn't realise it was available.  Is there any particular make that people prefer to use or doesn't it really matter?

Edited November 18, 2022 by milleniumaire

[milleniumaire]

Just had a look at the Wickes website, which is where I purchased my last bag of Blue Circle General Purpose Cement from in July this year.

 

No sign of any white cement!  Same at B&Q.

 

Travis Perkins sells a bag of Blue Circle Snowcrete White Cement for £23.30.  Wow!  That's quite a premium price compared to the £6.10 for "normal" cement.

[Mr Punter]

1 hour ago, milleniumaire said:

Just had a look at the Wickes website, which is where I purchased my last bag of Blue Circle General Purpose Cement from in July this year.

 

No sign of any white cement!  Same at B&Q.

 

Travis Perkins sells a bag of Blue Circle Snowcrete White Cement for £23.30.  Wow!  That's quite a premium price compared to the £6.10 for "normal" cement.

 

£15.23 inc VAT https://www.denmanandsonsltd.co.uk/white-cement-25-kg and sometimes on ebay

[Radian]

Yes, I'm afraid Snowcrete is a premium cement - but if you want it to look right...

The lime you want is a hydrated lime like this one:

[milleniumaire]

3 hours ago, Radian said:

Yes, I'm afraid Snowcrete is a premium cement - but if you want it to look right...

The lime you want is a hydrated lime like this one:

 

Yes, I've just been reading about the different types of limes and realise that hydrated lime is the one that is combined with sand and (portland) cement to make the resulting mix more durable.  Whereas Hydraulic lime binds itself i.e. it doesn't require (portland) cement and simply needs to be combined with sand (and of course water).

 

So, I'm thinking I will purchase a bag of hydrated lime and produce a mortar mix of 1:1/2:4 and use it on my retaining wall to see how it looks.  I've got that mix ratio from a Hanson Hydrated Lime technical data sheet, which I've attached.  I may also try a 1:1:5 mix for the "top" of the retaining wall as this isn't under any force.  I think this mix would probably be better for repointing the house.  Thinking about it, the retaining wall is two layers thick; breeze block on the inside, then a small cavity and stone on the outside, so maybe I could use a 1:1:5 mix for this as I would have thought the breeze block inner layer is the one holding back the earth.

technical-data-sheet-hydrated-lime.pdf