Cob: stucco question

[Mike Wye]

Charmaine/Jay wrote

> Jay said:   I'm guessing that you'd have to be careful with the lime
> mortar that  you used to hold this stonework together in order to ensure
> the
> wall is  strong enough to bear the weight of the house on top of it?
>
>
> Jay and all, the pure lime mortars ( sand-hair-lime) carbonate slowly,
> so setting stones with lime mortar only takes more time from the aspect
> of building tall fast.
>
> Brick layers only could go a foot or less, then curing had to happen,
> this is why cement became so popular..just keep building, no stopping.
>
> BUT the benfit of the lime mortar is tht it CONTIINUES to get strong
> long after the wall is built, which is a good thing.
>
> and in very old stucture with deep pockets of mortar the lime is still
> soft due to lack of air carbonation.
>
> So if you plan the site and building times properly you could excavate
> the stone trench, start mortaring a layer, then go do something else,
> like excavate the interior footprint, then lay more stones, etc. Not a
> lot of mortar is needed to bed the stones.


When working with a lime mortar in foundations and stone plinths they
traditionally used an hydraulic lime mortar either by
1. adding a pozzolan to a lime putty/sand mix to set off some part of the
mix prior to carbonation.
    ( a pozzolan is a burnt clay such as volcanic ash, brick dust, crushed
clay tiles etc which reacts with the lime to     form cementitious
compounds)
2. using a natural hydraulic lime mixed with sand.
Permanently damp stone structures don't allow sufficient air and hence
carbon dioxide into the mortar matrix to carbonate the lime to the extent
needed. The lime mortar would remain a soft paste with little compressive
strength.
regards,
Mike
Mike Wye & Associates,
Traditional & Ecological Building Products
www.mikewye.co.uk