Removing cement render, to replace with lime

[Suzy H]

Hiya
We own an old chapel, which at some point in its history has been rendered with sand:cement, to improve the weathering as the bricks are very soft. We now want to remove this and re-render using lime. (unfortunately can't expose the brick as it has been badly keyed)

We're in the process of hacking off the two coat cement render - does anyone know how fastidious we need to be with this. The base coat of the render is extremely hard to get off without damaging the brick, and we're not sure if we need to go back to bare brick, or just to a sound surface. I know lime render allows expansion / movement and that cement render doesn't, so wasn't sure if having some cement render under the lime render would make it fail?

Any thoughts
Cheers
Suzy

 

[Lime]

Anyone who has been involved with removing cement off soft brick will understand why cement is such a bad idea.
Very sharp chisels are required with the smallest hammer mass possible to minimise damage.
Angle grinders can do a better job (by grinding away the cement surface) if used very carefully but it is tedious work and requires skill and strength.

IMO I would not be happy if I left large areas of cement untouched under a layer of lime render.
The bad properties of slab cement do not alter that much under lime.
However if we are talking about only a few individual separate bricks with cement I would not be concerned so much.

If the cement HAS to be left use an angle grinder to cut out where all the pointing is.
At least the mortered brick joints will then be able to breath and move.

 

[Suzy H]

Thanks for the advice - I agree - Unfortunately as it will mean lots more work ! Off to buy a better chisel now !!!