# Forum Home Renovation Sub Flooring  Concrete Stump installation

## FelixTheCat

Going to start a pretty reasonable size extension, and just bantering around the way i am going to do the subfloor.
After marking out, doing holes, do i
1) Build the subfloor complete (exc flooring material obviously)with the stumps hanging into the holes, and then get concrete there (but a pain to get to the holes)
2) Assemble the Bearers with the concrete stumps hanging into the holes (good access up the line of the bearers)
3) Get the concrete into the holes, and using a laser-level, get the height of the concrete as close as possible to a 100mm increment (could be alot more difficult than said!) 
The top-of-stump height about the ground varies from 200mm to 1200mm.
There are a total of 100 stumps, all 100mm x 100mm. 
The next question, i would have thought with options 1) and 2) a threaded rod concrete stump would have been much easier to hang than a round rod that is just folded over. 
Any help / suggestions? 
Cheers.

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## jimfish

Generally we set up stumps to a string line about 20mm above desired heigh, put in stumps to string line and back fill before conc in base of hole has gone too hard tap down to finished height using block of timber and sledge hammer.My preference is to use a dumpy instead of laser to tap down to finished height,it requires an extra man but in my opinion you get a much more precise job.

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## FelixTheCat

Thanks for the alternate approach.
With the short stumps, which are easier to manage, i can see how that would work well.
But does it work well when you have such a large amount (being 1.2m) out of the hole?  Is it just a matter of having enough concrete fill around the base of the stump to support it laterally?

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## jimfish

You only put a 200 mm pad of conc in bottom of hole then backfill with soil to hold stump in place.

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## FelixTheCat

Engineer has drawn (see image) stump in concrete.  
I can see how if we wanted to "fulfill his requirements" we could just shovel a bit more in, before tapping the stump down, and backfilling with dirt.
I was actually going to use some 20mPa concrete as the Blinding concrete, as i have some larger mass pads that i need to get Minimix concrete in.

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## jimfish

Never had to put a blinding in stump holes before. The 200 mm pad I was talking about is shown in your diagram as mass concrete. Don't know what the blinding achieves.

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## FelixTheCat

The only thing that i thought it was for, was that you can get the concrete in the hole quickly (in the same day) as the hole is done.  That way if there is any rain, that the integrity of the base is maintained.
i'm sure it can't be to save the extra 200mm of concrete stump (tho each stump would be 5kg less, so i'm not complaining)
The soil report says i need to go down 600mm min, which i'm sure is alot more than the stumps of the existing house are.

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## jimfish

Yeah most stump holes we've dug had to be min 600 deep. Generally we would have holes dug in the morning,(measure and order stumps to be delivered first thing next day,)clean them out and have them inspected in arvo then install stumps next day.

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## FelixTheCat

OK.  Thanks for all the help.  Much appreciated.  It'll be at least a few months before we start, but i like to have as many of these details sorted out.

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