What mortar beneath ground level?

[Roger H]

Hi all. Some advice needed please. I am studiously repointing my coarsed, random rubble, sandstone house with lime mortar. However, on the ground floor the builders have removed a depth of masonry beneath the threshold-width of the rear door to run new drains. When replaced this will be at or below ground level, with dpm, slab, ufh and screed on the indoor side. Does it matter if they use cement mortar or is it worth pressing to use lime?

Thanks for views.

 

[Ian Bond]

Do not let them use ordinary portland cement anywhere near your sandstone!

Might want to compromise with a Naturally Hydraulic Lime (not the hard stuff) if you're worried about fat lime mortar not setting in contact with damp ground.

I've banned cement from my millstone grit masonry - woe betide anyone caught with a bag of Bl*e C*rcle!!

 

[Gervase]

Definitely stick with lime. Either carry on using what you've used so far but with an added pozzolan like Metastar or brick dust, or use a hydraulic lime (to a maximum strength of NHL3.5). Stonework below ground level is still prone to movement, and cement isn't going to tolerate that.

 

[Nemesis]

Dpm and

slab,

Dare I ask...

 

[Gervase]

Dpm and

slab,

Dare I ask...

Perhaps best not to... :roll:
Actually, having registered that, there's still good reason to use lime below floor level as the inevitable damp displacement towards the walls may be partially alleviated - particularly if the outside ground levels can be lowered. In an ideal world, of course, cement would be banned from the slab, too (and the DPM dispensed with).

 

[Nemesis]

I think I need to pay a visit Roger... cricket bat in hand... :roll:

 

[Roger H]

Thanks for thoughts, alas, apart from Ian's too late for the zealous pro-cement builders. Will have to compromise with lime from ground level up.

Slab is concrete, as limecrete deemed too expensive. Done-deal now but the floor needs to be insulated, so cellotex etc.. would be as much of an impediment to a 'breathing' floor as DPM I'd guess. Also, have read elsewhere that lime screed unlikely to set very well under stone flags. If I had a bone-dry floor I'd have skipped the DPM. Batched up lime for them last night and hid the blue circle bags.

Thanks for thoughts anyway.

 

[Nemesis]

Insulated breathing limecrete floors:

http://www.limecrete.org.uk/

 

[pandora]

I have a fab limecrete floor with underfloor heating in it powered by a GSH pump and reclaimed bricks set onto it. The house has never been drier or warmer. You are right about the cost. But putting the right material in to start with is not nearly as expensive as digging up concrete in a few years time because all of your walls are soggy and there is a strange smell. Sorry!