lime mortar - indoor flags

[diamondrobbins]

Hi,

I have been asked to point up the perimeter of the ground floor of a barn conversion.
Originally, lime mortar was used to lay and point the stone flags that are laid throughout.
I understand the pointing between the flags started to crack and fall out, so the builder used a cement-based mortar to point between them.
Now the perimeter is breaking up, hence the need to re-point here, but I can't find a ready mixed lime mortar that is dark enough to match the re-done pointing. (I've sent samples to Mike Wye, suppliers in Devon)
Can anyone please advise what mix is recommended for this job. I have been told that adding normal cement colourant won't harm the mortar, anyone got any views on that?
I've never used lime mortar before, so any assistance gratefully received.
Oh, and one further thing, there is under-floor heating under the flags.
Many Thanks for any pointers.

 

[Blagard]

I would be wondering if the perimeter pointing is breaking up because of movement in the floor above the under floor heating. Maybe pointing it up in a mortar is not the long term answer.

It seems an unusual combination to me - Flags and under floor heating.

As for the mortar colour I have not come across any situation where the colour additive is an issue. You will find it tricky to get it right with the colour usually lightening upon drying out. If it is critical do a test mix and get it agreed.

 

[stuart45]

You need to know what you are doing with lime mortar. What type to use, how to mix it up properly and how to look after it.
Underfloor heating will dry it out too quickly.

 

[diamondrobbins]

Thanks for this guys.
Do you think that underfloor heating is incompatible with lime mortar?

 

[stuart45]

It would be OK if the heating was left off while the mortar cured. Lime mortar hardens by absorbing CO2, and needs to be damp to do this. That why you have to protect it from the sun when repointing and keep it damped down.
If the rest is cement pointing, why do they want this bit done in lime?
You would probably be better using NHL 5 for a floor.

 

[Blagard]

Thanks for this guys.
Do you think that underfloor heating is incompatible with lime mortar?

No I don't think that should be a problem except as Stuart says if the heating is on it will dry it out too quickly.

Be aware there are many different types of lime mortar.