Matching different mortars

[Juju]

We've got the builders in doing various jobs including patch pointing. Most of the inappropriate cement pointing done by the previous owner is in good nick so no point taking it all out as it would be very costly but most importantly, it would probably cause more damage. The builders have today been raking out the worst bits which tend to be around the windows, chimneys etc and one very inaccessible wall which was in a right state so that is being completely repointed. Anyway, I assumed all the repointing would be done with lime mortar but the builder was saying that it wouldn't match the existing mortar so was talking about adding cement to the mix. I'm not happy about this as surely we're just repeating the mistakes of the past but at the same time, maybe it would look daft if the repointing looks completely different. Also I think he mentioned a 1:2:9 mix which having googled it, it seems that some people say it's ok, others say no never use it...

What do peeps think?

Juju

 

[TheForge]

Lime mortar with cement is just a weak cement mix. Lime mortar can be made any colour with the right aggregates and additives, the addition of ash in the right quantity will make the mix look just like cement. It sounds to me that your builder doesn't really understand lime work, what type of lime is he going to use, hydrated?

Those ratios are basically a 3:1 binder to aggregate mix which will be fine (just ideally with no cement!).

 

[TheRoost]

Sounds like the builders want to do what's easiest/familiar/most convenient for them.

I recently sent off a sample of my crumbly mortar to Conserv. It was a bit of a greyish cement colour, similar to some parts of the wall where it's definitely been repointed in hard cement mortar. They have come back with a couple of matches for me in their NHL mortar, a standard mix that is close, and a hybrid that is a 100% match.

I wouldn't let them use cement personally.

 

[essexbearhunter]

a 1:2:9 mix

(1 part cement, 2 parts hydraulic lime, 9 parts sand)
I use this mix on external work to this day. From memory I started to use it because it was the mix recommended by the SPAB in 1970's when I started work. Mixed with a red sand it gives an agreeable yellow colour that goes with my yellow stock bricks and hamstone copings whereas a yellow sand gives a white mortar to go with the flintwork.