old cinder/cement wall (not cinder block) help

[birdy13]

all the walls in my house interior and exterior are made from what I can only describe as a mix of ash bits of charcoal and cement, they are about 2 foot thick and rendered each side. Fixing anything to the wall is a nightmare, where the original render has come away I can dig a hole through the wall with just my hands, Internally this is not such a problem as I have dry lined all the walls. Ok for outside, I was thinking of using some old railway sleepers I have to sink into the walls then use a 6mm rebar grid between these and render over the grid leaving the front fcse of the sleepers exposed like the old style cottage will this work or will the movement of the wood crack the render?

 

[theprinceofdarkness]

Those walls sound a nightmare!. What you suggest seems to be really dangerous, as you will have to dig out the walls to almost a half of their thickness.
The way I would proceed is to drill a hole 8mm diameter every 30cm in the wall at least 150 mm deep. Then bend up "hair pins out of stainless steel wall ties which will hold up sheets of stainless steel mesh. Then use injected polyester resin to glue the hair pins in, which will hold the mesh back to the wall. Then render the whole wall..
You could try Googling for "straw bale construction", because your walls seem to be a close relative to straw!
Frank