lime render or cement render ?

I have a question, I hope you guys can help !
I have a building built in 1875 It has already been rendered with cement render on the outside some years ago and painted with a waterproof dulux weathershield or similar, but left with lime plaster on the inside which is in poor condition would it be ok to hack off the old lime on the inside then cement render then tank it with a waterproof tanking slurry then dot and dab PIR Plasterboard I should mention the walls are 18" thick but built with cob and lime render and plaster on the inside I would like to get some insulation in the building to make it a little more efficient I would also like to poor a new concrete oversite internally to support my new suspended timber joist floor good idea or not ?

 

thanks, I keep reading that you shouldn't use cement render when a wall is built with lime or cob but because it will not breath but it has already been hard rendered on the outside so therefore it is already been sealed up from the weather I thought it should be ok but i did wonder would it then suck up water and moisture from the ground as there is no damp course and then be trapped in the wall !!

 

not sure injecting an 18" solid thick cob wall would work very well !! it hasn't had one for the last 140 years but having said that that might be why the lime render is practically falling off from inside !! i dont know !!

 

That's agood idea to stud off which we have done in other areas of the building but I dident want to lose to much room we used 3x2 cls and put the studs the 3"way keeping a very small cavity between the cob and stud and used long fixings but I can't do that every where do you think it would be ok to render it up then tank it and dot and dab PIR board certainly make the room warmer
And help bind everything together just a little worried of trapping moisture

 

They are stone and cob mortar very roughly built with lime render and plaster on the inside and modern cement render and masonry paint on the outside we think the outside render was completed about 15 years ago

 

Yeah the only problem with that is the curing time with the lime. The walls are bone dry at the mo also its not such a good job dabing on to lime i am so tempted to SBR it then cement render with a 2 shovel fulls of lime and tank it with slurry i would not do this normally but because its cement rendered on the outside its already messed up we done a test patch on saturday the tanking slurry gives an excellent key for drywall adhesive so i think i'm gonna do that what do you think ?

 

yeah thats pretty much the ratio what we normally mix depending on the scenario
Got another one for you the foundations are stone laid on dirt about 9" wider than the wall all the floor joist are completely rotten sat on 2 parallel stone bearers that are all over the place !!!the plan is to remove all the joists and old stone bearers poor a new concrete oversite then bed a corse of brick with a DPC and sit new joists on top then they would like underfloor heating sat between the joist with 50mm celotex between the joist below!, i'm now thinking will that sweat if warm air escapes around the edges the plumber wants to use them stretcher tray plates between the joist we have done it before with no problems but they have all been in newer buildings with though ventilation under the floors looks like we might have to try to fit air bricks though that 18" thick cob/lime/render wall nightmare !!!! people think these jobs are easy!lol