-
source? it's completely opposite to everything I've read online and in this thread so genuinely curious
doesnt lime produce an exothermic reaction rather than 'needing' heat to set.
apc-
Lime is wild - I did a SPAB field trip this year - we put chalk in a kiln - cooked it to 1000 degrees - then put it in a trough (once cool) then slaked it ( sprinkle with water) it starts going bonkers -cracking and steaming and getting v hot. Then sieved it and mixed with sand and water and built some walls. The whole point of solid masonry / lime walls is if they are built right they do let the water in but then back out again. The lime pointing is a sacrificial layer that needs redoing every so often. Inside a an old stone building lime plaster with keim mineral paint - is what you do.
Sheppz
I don't think this is correct. Because gypsum is "modern" it gets lumped in with cement renders, plastic paints etc.
However my understanding is that it is breathable, maybe more than lime plaster (variables depending on lime mix). It is also often lower embodied carbon than lime (gypsum is natural and just needs low heating to dry out, unlike lime which needs heating as part of process).
My understanding is the reason it gets in trouble on old solid wall buildings is because it gets damp, the damp stays, and it encourages mould growth. It's a moisture issue but not the one you think. (I think hygroscopic may be the correct word.)