Suitable material for build up around slab

slacker878 · Dec 01, 2023 7:17 pm

Hi,

Building a waffle pod slab (m class) on piers due to historical uncontrolled fill. Pretty much flat land. I am on the highest point - ie no slope towards my slab.

Builder used crusher dust (not compacted) with a plastic sheet around the perimeter.

Is that even suitable? I thought crusher dust is porous? He also omitted the garage portion saying that driveway doing to be poured later?
I feel that area should be protected as well given its storm season.

The site can be quite muddy but does dry quickly within 1 day once rain stops.

Thanks

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building-expert · Dec 03, 2023 10:57 am

Foundation flooding is unforgivable, keep your photos in case problems with your foundation material develop and your house cracks.
You will need them for your warranty claim.

Slab edges should always be protected with impervious material, sloping away from the dwelling and into drainage.

stefcep · Dec 03, 2023 1:47 pm

I'd be grateful of any examples of impervious materials that could be used?

alexp79 · Dec 03, 2023 10:22 pm

clay is impervious. However, if you have a perimeter drainage around your slab, then you would use self-draining material around it, to allow water to go directly into the drain.

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ponzutwo · Dec 04, 2023 7:28 am

alexp79

clay is impervious. However, if you have a perimeter drainage around your slab, then you would use self-draining material around it, to allow water to go directly into the drain.

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Looks good, but Ive never seen this done. Most people are lucky to get Gravel shoveled around the perimeter and sloped to look like the requirement is being met.

slacker878 · Dec 04, 2023 8:15 am

building-expert

Foundation flooding is unforgivable, keep your photos in case problems with your foundation material develop and your house cracks.
You will need them for your warranty claim.

Slab edges should always be protected with impervious material, sloping away from the dwelling and into drainage.

What material is suitable?

building-expert · Dec 04, 2023 9:19 am

Concrete apron paving or compacted clay surface with no undulations

Pedro4137 · Dec 04, 2023 3:49 pm

20mm crushed/recycled rock

BuildingandLegal · Dec 15, 2023 8:10 pm

Not recommended!
The image presented is for a sublevel area. The footings are down deep with a load bearing wall supporting the upper floor level. If you did that drain next to the waffle you have just created a zone of influence and created a zone of abnormal moisture next to the slab. ANY movement would be owner related and not covered by QBCC's subsidence policy.
First off when the concretor pulled his form work (the timber boards) the black plastic was required to be folded back up against the slab edge. That plastic needs to finish level with finish ground level to prevent moisture in the soil transfering through horizontally into the slab and rotting the frame/carpet etc etc.
Second the builder should have back bladed, this is where the excess soil is pushed against the slab edge to create ground that falls out from the slab to prevent water ponding against the slab edge.
Third, the stormwater risers the 100mm white pipe sticking up out of the ground, most of those are downpipe points and yard gully points as their are no pipes in the slab near them, so they won't be ORG's for sewer. The stormwater rigid pipes should be cut down at least level or just below the current ground level and flex pipe in a sock connected to the pipe. They can tie a knot in the end of the sock so soil doesn't go down the pipe. This way the stormwater system becomes active straight away (as per the requirements of the BCA, AS2870, the geo's report and the engineers design..just to name a few) and the sites surface water will/can drain.