You don't need to redo the whole lot. Gently chisel out the cracks to about 15mm either side or to as far as the loose material is. You'll need a little bit of trial and error to get a render mix of the same colour as the original to fill the holes in that you've made. A good start is a 1.1.6 mix. That's 1 part lime, 1 part cement, 6 parts sharp sand. Then you'll need to try and find pebbles of the same size and shape as those on the rest of the wall. Give the brickwork a good pasting of a PVA mix to help the render stick, then trowel it on, giving it the same finish as the rest of it. Throw the pebbles on when it's still fairly damp. You'll never get it looking the same as the original, but with a little care, you'll get a reasonable finish. But may be worth checking when you've got the old render off to see if the brickwork's cracked underneath it. That may be causing the pebbledash to crack. If there's cracking in the brickwork along the joints, then you could have major problems. Get a builder to have a look at it.
As always, be careful when you're mixing the render. Cement and lime are dodgy if you get any in your eyes. If you're not happy doing it yourself, it wouldn't cost much to get a builder in to do it. He'll do it in a fraction of the time that you'll take. Have fun!!
Denis Langley, March 2012
