Lime and cement mix mortar?

[Pogonation]

Hi everyone,

I have just finished repointing various areas on our 150 year old property. I got a builder who was familiar with heritage properties and said yes it needs to be lime mortar (as I explained) however when I arrived after they had finished working on it I saw a bag of cement next to the lime. He said they make lime mortar using some cement in the mix and I didn’t think much of it as he is the expert..

Now I have read on this forum that generally speaking, any amount of cement should never be added to the mortar?? This is has been done on the front of our brick terraced property (west facing) and now I’m worried about whether this will cause an issue? Some patches were done, particularly around the sand stone windows where most the pointing had gone.

Is this a disaster?.. should I be getting it all redone with 100% lime before it hardens? The last thing I want is a damp problem when we don’t have any existing problems with damp!

 

[Feltwell]

No, there shouldn't be any cement in the mix. Some builders though are just addicted to the stuff...

Will it cause problems? Not necessarily, but no one can say for sure. It won't be as breathable or flexible as a pure lime mix. It's probably better than having knackered pointing though.

Pointing goes off pretty quickly. If you didn't have a damp problem with knackered pointing, I can't see why you'd have one now. I'd chalk it up to experience for the future - quiz tradesmen before they start.

 

[Lacan07]

As Feltwell says cement should not have been used but it's not a disaster so I wouldn't get too disheartened about it. Just goes to show however that you have to 'know' the job you're asking the builder to do and watch them like a hawk.

 

[stuart45]

Nowadays it's not considered the correct thing to do, adding OPC to lime mortar. The older period house books used to recommend a 1/2/9 mix.
It was after the Smeaton project that it was decided that even small amounts of OPC will affect the mix slightly. Back in the 1920's it was normal to gauge a bit of cement into the lime mortar mix.