Share
Hi,
- Dig the trench further to about 300mm deep past the house render exposing about 2-3 layers of brick.
- Waterproof the brick work - 2 coats
- Lay plastic sheeting in the trench making sure it lies against the house wall bricks
- Lay some blue metal or other suitable
- Lay Ag Pipe
- Cover Ag Pipe with a second layer of blue metal
- Cover Blue metal with path/sand gravel similar with what is already there for the path
- I'm thinking 65mm Socked Ag Pipe https://www.bunnings.com.au/brutus-65mm-x-20m-slotted-and-socked-agi-pipe_p0557568
- How much Blue Metal would I need for a trench about 20m long?
- Which Plastic Sheeting?
- Which Water proofing product? I think its something I brush on to the exposed brickwork?
Pictures attached,
Many Thanks
Tim
You’re on the right track, @TimD.
I’m in two minds about the plastic: it can shed water away from the wall, but if any moisture gets behind or under it, the sheet then prevents that water from reaching the ag line. A more reliable approach is to waterproof the wall itself, then let all water that moves toward it fall into free-draining gravel and the ag pipe.
Here’s how I’d do it: extend the trench to ~300 mm deep (deeper is fine if you can maintain fall), clean the exposed bricks/render and apply two coats of a brush-on waterproofing membrane (e.g., an exterior acrylic/bitumen membrane). Once cured, protect the membrane with a strip of geotextile so the gravel doesn’t scuff it. Place a 65 mm or 100mm slotted and socked ag pipe on the bottom of the trench with a continuous fall of about 1:100 (≈10 mm per metre; over 20 m you want ~200 mm drop), then backfill around and over the pipe with drainage gravel to within ~100 mm of the surface.
Wrap the top of the gravel with geotextile to keep fines out, then finish with your path material. Include an inspection/flush point (a tee and riser with cap) near the start so you can clear silt, and make sure the outlet come out to a spot in the garden that won’t cause puddling or neighbour issues; if you can’t get enough fall, consider a small rubble soakaway (a geofabric-lined pit filled with drainage aggregate) rather than a “solid” pit that simply fills with water.
On materials: your 65 mm slotted & socked ag pipe is a good choice. Use 10–20 mm drainage aggregate, geotextile fabric (non-woven) to separate soil from the gravel, and an exterior brush-on waterproofing membrane for the brickwork. For a trench 200 mm wide × 300 mm deep × 20 m long, the total trench volume in 20 kg bags is roughly 81–91 bags. Practically, I’d order ~1.2 m³ in bulk to allow for compaction and a bedding layer—much cheaper and easier than hauling that many bags.
Please let me know if you have any questions.
Mitchell
Hi @TimD,
Yes, the agline would sit directly on the soil. Some guides recommend adding aggregate below the pipe, but that allows water to run through the pipe and travel along the trench beneath it. We want to capture water in the pipe and divert it.
Something more like this: Vinidex 65mm Draincoil Tee. You can then use the ag line to do a small riser to the surface.
90 x 20kg would be closer to 2 tonnes at around 1800kg.
Mitchell
Hi,
This is the finished project. I installed the Ag pipe a day before we had 2 days of solid rain so it was a good test. I may have gone overboard with the geotextile by placing it on the soil then some aggregate and pipe before covering the pipe with more aggregate and then wrapping the whole with geotextile. The soil is pretty sandy and someone recommended it.
With this sort of thing its hard to know if it was a success unless a time comes when it doesn't work! 😀 I still had a slight trickle of water but this was from an area of wall not covered by the Ag pipe. See red line on the above pic. I can't really put Ag pipe there as I've nowhere to drain it and there is a slight slope from the ag pipe to the wall (see yellow arrow).
This dried up within 24 hours.
I may dig a couple of bricks down and paint water proofing on the outside wall (red line).
Last time we had a downpour before doing this project, we had an inch of water in the basement, so I think it went well. (My plumber explained with the lay of this house it will never totally eliminate damp or some water getting into the basement.)
Many Thanks to the Bunnings team for your advice. I never would have had the confidence to tackle this without the guidance you gave,
Regards
Tim
Hi,
I've decided to waterproof the outside wall afterall.
I will use this waterproofing as before. I will waterproof the bottom couple of layers of brick. I've managed to dig down to the slab too. I was wondering if I should apply the waterproofing to the top of the slab (see pic) also - but getting rid of the dirt on top is a problem? Is there a better way of doing it or just clean as much of it away as possible?
Thanks
Tim
