My house is a double brick construction on a concrete slab. At the front of the house the slab is about 90cm below ground level. The block has a moderate slope so the back is about 20cm above ground level. While we don't have major damp problems the lower level of the house often smells quite musty and we have recently discovered the carpet along the side of the wall is damp to touch at the edge.

So I have decided to dig a drainage trench at the front and side of house which I will fill with agpipe and aggregate. This I am happy with.

Given the effort of digging the *&$%#& trench, I would like to also damp proof the brick work which is below ground while it is exposed. Can anyone suggest any good product to either paint on the bricks which will work well when I refill the trench, or some sort of membrane I can install between the aggregate and the bricks (or both!). I'm in NW Sydney (Beecroft, near Epping) if anyone can suggest a good store I can visit which sells this sort of stuff. I know Bunnings does sell some of this stuff but would prefer going somewhere which can give good advise...