We have had problems with rising damp on our walls to the back of our house and are getting the wall externally injected to combat this. However the Damp Specialists have recommended extending the small drainage channel along the side of the wall where the damp is a problem, which allows surface rainwater to run into a drain. At present as the patio is slightly slopped towards the house, rainwater is collecting against the wall and sitting above the old damp cause and not running away in to a drain.
The current channel is concrete lined; only 20 cm wide, about 3 metres long and say 10 cm deep. It sits below the main patio level. Weâ€™d only need to extend it by about a metre and a half and I was wondering how easy it was to do this? There currently is only about a 3-4 cm layer of concrete acting as a patio, which is old and looks easy to break up and it looks like there is only earth below. Do you think a 2 kg hammer drill with a rotorary stop would be fine for this? I was hoping to gently slope the new channel towards the drain to keep the water away from the wall as much as possible. Is there any advice you could give me on this job? What should I line the earth with before laying the concrete? Should I also line the exposed brickwork with something?