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Metal dust or roadbase to grade around the house?

Hi everyone,

I'm redoing the stormwater and drainage around my house due to significant water entering into the subfloor from the high side of my block and making its way through cracks in my brick foundations and into the subfloor.

I'm installing ag pipes 900mm away from the house that are around the high side of the property to catch any water before it hits the house.

Im also regrading around the house as it previously had a negative grade and allowed water to sit around the foundations. Currently I've excavated all the permeable sand mix that pavers sat on and brought it down to expose the subsurface bricks and the top of the concrete foundation. Im then going to fill any cracks in the brickwork, apply liquid rubber and then corflute to protect the liquid rubber from backfill.

Im unsure on what to backfill with.

My thought process is to grade away from the house using a non permeable material, like metal dust, to ensure any water that hits, makes its way towards the ag pipe. Or should I use something like road base that allows more water to flow through. I've been recommended to use gravel or roadbase to use around the foundations but wouldn't this potentially allow water to sit at the foundation due to the ag pipe being 900mm away and not being flush with the foundation.

The final finish will be decorative pebbles to sit on top of the metal dust or road base or any other material that is recommended.

Any advice would be great,

Cheers.

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Comments

EricL

Hello @trev21

Welcome to the Bunnings Workshop community. it's sensational to have you join us, and thanks for sharing your question about what backfill to use.

This is definitely a question for your plumber. However, I do agree that gravel and road base will allow water to pass through at a much faster rate. I'm under the impression that it has to be a material that will slow down the water and divert it towards the agi-pipe. But at the same time if the regraded side of your house directs the water at a lower point, then it would be best to use the metal dust. I believe this would be the best option.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let me know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/51729#Comment_51729

Good Evening @trev21

Now that sounds like a fair job and that you have stepped through the thought process 🙂

Any chance of a few pics to make it easier for us to understand what you are asking?

The 900mm from the house with Ag pipe, is there a reason you choose 900mm? And yes an ag pipe will catch some of the subsurface water but have you considered what is on the surface? I wonder if a large grill drain might be an idea (waiting on pics to confirm 🙂 )

Is there a way to stop the surface water from actually getting to the houses edge?

You mention "corflute" after using a rubberised sealer on the exterior brickwork. I really havnt heard a lot about that product so I would ask your plumber if its needed. I say plumber but a builder would know as well.

With the gravel around the agpipe I would think that would allow the water to funnel into the agpipe and away. (I have gravel that my stormwatar pipe sits on and is covered by it and I am sure that it also carries the subsurface water away down my hill as its predomitary clay where I live) So depending on what material you have between the 900mm point and the house it could change things.

Dave

trev21

https://www.workshop.bunnings.com.au/discussion/comment/88006#Comment_88006

I appreciate the reply mate.

The 900mm distance for the ag pipe is the centre of the blind side of my house. I wanted it to be far enough away to get a proper slope away the house and drain straight into the ag trench.

The only surface water that will reach the house on the blind side is rainwater, so to be fair, there shouldn't be a large amount of surface water that should reach the house.

My house is at the bottom of a mountain and is adjacent to a large creek, so I cop every other houses water, predominately sub surface. Im putting in two 100mm ag pipes side by side with 20mm blue metal filled to the top of the trench to try and allow the water to get away as quick as possible.

The corflute is just a protective sheet to protect the rubber sealer, but yeah I will confirm with a plumber if it's required.

Between the 900mm point and the house, there was sand and pavers. I've excavated and brought the level down to show the foundations and it is also clay. Its currently a boggy mess due to massive rains.

Ive attqched photos of whaf it used to look like, then when i ripped the pavers back and finally how it looks at the moment before it regrade and dig the trench

EricL

https://www.workshop.bunnings.com.au/discussion/comment/88006#Comment_88006

Hello @trev21

Thanks for sharing those photos of your house and the area you are working on. I noticed one of your photos had paving installed, will you be paving the surface again? This would be an excellent way to redirect any rainwater falling into the area.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/109620#Comment_109620

Good Morning @trev21

Ahhh playing in clay 🙂 know that feeling so well and the $#&@&@ words that sometimes may follow 🙂

Sounds like you have it well thought through. If you havnt paved/concreted yet I was thinking of a Gully type gutter down against the retaining wall to capture the runoff from up the hill. I have the same issue with houses behind me and I have an idea of a low styled gutter drain across the yard (yet to be implimented of course) to capture the water and funnel it the way I want it to go.

Makes sense your expalanation about the 900mm by the way 🙂

Dave

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/109617#Comment_109617

Hi @trev21

I feel your pain on this situation. I used to live on the side of the hill and also suffered from underground stress as well as surface run-off.

Appears to me by your original photo that the wall vents were essentially at ground level, which would have been a far great area for water ingress than wall cracks. This is how I would consider tackling it with the guidance from your plumber who you will need to make the legal connections to the stormwater.

I would grade the area to create a V 3/4 distance away from the house and at least 200mm below the wall vents. You could then apply a bitumen paint along the wall and if you really want to go all out, then apply blue-board, not Core-flute, which will collapse overtime. Plus nothing will stick to it like any waterproofing coating like more bitumen paint.

Down the channel install a Gal steel grated drainage system. Not plastic as thats just problematic with it not holding shape etc. This would run to one or more pits that carry the water to the stormwater system. Then as @EricL noted I would re-pave or concrete etc the surface so the water will not soak and always have a softness to it even when compacted. Plus you will potentially get water run-off tracks and be forever bringing stones in to the house. A solid surface will make the water runoff far more efficient, and faster to disappear completely once the rains stop.

Nailbag

Screenshot 2025-05-01 at 7.33.23 am.png

trev21

https://www.workshop.bunnings.com.au/discussion/comment/122162#Comment_122162

Thanks for the reply everyone and the advice.

I agree with you about the vents, do you advise 100mm or 200mm distsnce?

We won't be reusing the pavers as they don't fit in with the landscape design and concreting is currently out of our budget. Do you have any ideas of backfilling material to use against the house to grade and divert water towards the drains?

Cheers

MitchellMc

Hi @trev21,

Weep holes must have at least 75mm clearance from concrete, so 100mm to pebbles will be fine.

You could grade the base back materials, whether that be sand or soil, back towards the agline. Add Builder's Plastic starting at the drainage and up to the house wall. Cover over this with your decorative pebbles. That way, water will penetrate through the pebbles, hit the plastic and then run out towards the drain.

Please let me know if you have any questions.

Mitchell

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/51783#Comment_51783

Good morning @trev21

I like @MitchellMc's suggestion, or even if you graded a slope(grassed it even) but down the center where the ag pipe is have gravel up to the surface with the white pebbles the last 8cm or so. You could even edge it with some of those pavers. Just a single paver wide either side to keep the stones in place and something the mower and whipper snipper can go along. I was going to suggest a core 10 style but then thought "Im creating a dam again" lol

So looking at the house to the retaining wall would be

A 100mm gap,

Slopped ground with grass towards the 900mm pipe,

A row of pavers

White pebbels with gravel then ag pipe,

Another row of pavers,

Slopped grass,

Grill drain next to retaining wall,

Maybe more pebbles,

Retaining wall/fenceline.

Dave

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