setting timber stumps in concrete

[4woods]

Hello all,
the plan for our major addition calls for treated pine 150mm round stumps to be set in 800 deep x 450 wide holes and set in concrete.(inc. 200 mm concrete below the stumps) Just wondering if anyone has any ideas about the best way to do it? I'm thinking of mixing enough concrete for the 200mm and just enough to set the post ( maybe 100-150mm?), I can do this in groups over say, a week ( there are 60 holes!) and then get a readymixed delivery to backfill the remaining 600mm in each hole.
Does this sound reasonable or are there better ways. ( I don't have a team of helpers on hand!) Thanks in advance.

[Bear]

I just went through the process of having the house restumped. I was suprised when they didn't conccrete the stumps in. They said they didn't use concrete anymore as it sped up the rotting of the redgum posts. These guys have a real good name in the area so I trust them. When I done my alcove and decided to concrete in my stumps I was advised to use H5 pine posts (I'm sure that was the rating) it was the rating used for poles that could be immersed in water make sure you cover the cut ends with the correct chemical and don't have them in the ground

Regards

Bear

[4woods]

Thanks Bear, yes H5 treated pine posts are what we're using.

[TermiMonster]

I would do a rough calculation to determine how many stump holes a truck of mini mix will do. Prep that many holes (plus a few for good measure). Then do it in batches of that size. I would do each hole complete in one hit. You have a certain amount of time after putting the concrete in the hole to work the post. It would be a lot easier if you have at least one fit young thing to help though (those barrows don't get any lighter as you get older.)
Be aware the concrete truck is free for 15 min or so, then you pay for their time, so you do need to be efficient about moving the mix (unless your loaded, in which case you can hire a team of lackies, sit back and enjoy the show.)

[joe greiner]

In my humble and professional opinion, timber embedded in concrete is an inferior solution. Bear got a better job done. Replace your concrete dimensions with gravel, tamped every 150mm or so. Gravel allows water to drain below the timber, so less chance of rotting. (Or at least longer duration until.)

Joe (retired structural engineer)

[ausdesign]

If the 800 deep concrete is nominated on the drawings it sounds to me that there has been a 'bracing capacity' incorporated to the stump to meet the subfloor bracing requirements.
That doesn't help with what your asking but if it is the case it will rule out using another material to backfill the holes.
You can buy precast round concrete pads - used a bit where distance makes ready mix expensive or sites that have problems with access - that would do what you want to set up the columns & then top them up after but I haven't seen them in that large a diameter. Usually 230mm