# Forum Home Renovation Sub Flooring  Setting Concrete Stumps

## beefabear

G'day all, new to the site, but about to owner build so could be here often! We have a kit home laying in the paddock, a house site cut with partial fill at front, in S class soil. Concrete stumps was part of package. they are 1500mm stumps, we are putting 500mm in ground, 1m above. holes are 300 dia, and a 200mm pad is required. I have had conflicting info on fill of holes. One person told me to partially concrete the stump in and fill the rest with site soil (mainly clay), because concrete stumps can snap/break if fully concreted. Someone else said that the stumps with load bearing walls above should be fully concreted, and that this was Aust Standard, but wasnt sure about S class. Can anyone clarify!? Cheers, Beefabear

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## ausdesign

The 200 of concrete under the stump is all that is required (generally). Taking the concrete up to ground level will provide some extra lateral bracing to the stumps but this would normally be noted on the bracing layout or subfloor layout if it is required.

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## beefabear

Thankyou Peter, your info is greatly appreciated!

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## Eastwing

I personally always fill the hole with concrete no need to brace the stump until the concrete sets (unless it's really long). 
Pour the concrete into the hole, then push the stump down until the laser tells me it's level. it help if your string line is close to the ground.  
Make sure your stumps are 200mm short if you sit them in the hole before the concrete goes in.

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## ausdesign

I would assume most 'Chippies' would know how to lay stumps with the most economical use of concrete. In this case with pre-delivered 1500 it would be more of a case of ensuring the hole base is 1700 (plus) below bearer level
.

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## dib

The way my carpenter & I did my stumps. A 15 litre bucket of concrete in the bottom of each hole to start with. ( This generally works out to be around 200mm in the bottom). One person holds the stump plumb and level (We used a string line) when he/she has it in position the other fills the hole with whatever dirt came out of the stump holes, which holds the stump in position while the concrete goes off. A standard that I read suggested that some situation required corner stumps to completey filled or rammed for bracing as ausdesign suggested.

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## wombat200

I am currently building in 'S' class soil in Melbourne. My plans show the stumps on 200mm concrete pad, stumps sat on the pads, then another ~200mm concrete place around the stump, the remainder of the hole filled with soil. 
Hope this helps.

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## ausdesign

To clarify for readers of this post - the soil report nominates the depth required at the base of the hole to achieve the soil type (& bearing capacity) that can support the load required. The size of the pad (thickness & area) is determined from the load  that the stump supports.For a concrete pad the nominal thickness ranges from 100mm to 250mm depending upon the footing type as tabled under AS1684. The pad area likewise varies from 230*230 to 430*430.
Any extra concrete in the hole is a waste unless the stump needs to be designed as a bracing unit, whereby the concrete is taken to the top of the hole & the bracing capacity can be calculated in regards to the volume of concrete.
In theory, although obviously not practical, a concrete stump can be placed upon a timber sole plate to achieve bearing capacity. For example for a type 1 footing with 'unreinforced' concrete pad footings the size required is 230*230*100 & for a timber soleplate the required size is 200*235*38.
Hope this clarifies.

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