plastering and insulation

[amandag38]

hi there
we are the stage of rendering and plastering half of our house, we have removed the cement render from outside put on a breathable membrane, batons then lath, on the inside we have filled in between the timbers with sheepswool and are ready to start putting on the oak lath, just wanted to check should we be putting anything onto the sheepswool to protect it from the plaster or just simply put the lath straight over.
one other question, we have laid the limecrete floor, which will eventually have underfloor heating and a limcrete screed over, we want to use flagstones but no one seems to be able to advise on a breathable adhesive, can we lay them into the screed as we do it, then use lime to mortor the joints.
thanks

 

[Andrew Bodenham]

re: your flagstone floor I would not recommend bedding the stones in lime mortar as this is unlikely to withstand the considerable shearing forces generated by thermal expansion due to the underfloor heating. A proper tile / stone adhesive recommended for use with UFH applications almost certainly be a better bet. Of course, if the stones are large enough and heavy enough then they'll stay in place whatever. Whilst breathability is desirable this may be compromised by the nature of the flagstones you use - slate is fairly impermeable for example - so that only the lime mortar joints would remain as relatively porous grid. However, as you are going for UFH the subfloor will soon be dried out anyway, and the issue of breathability becomes irrelavant. I've not seen lime mortar used as a grout in UFH applications, so I'm interested to hear how you get on. I presume you have incorporated suitable expansion joints between heating zones and around the periphery of your limecrete slab.
Hopefully someone with more direct experience will share it with us.