Help - Concrete Mix for Stumps

[OBBob]

Hi Guy's - I have posted this in another forum a couple of times with little response ... anyone viewing this one have a comment?

I am putting in stumps for a timber extension and have holes bored 750mm, which is about 250mm into the clay in my area. Anyway I had to put a 200mm concrete layer at the bottom of the hole, insert the stump and back fill. However I was told to use the mix ratio of the back of the GP concrete bag listed as 'foundations'. I'm a bit worried now after some more reading that this is too weak. The mix is 1 concrete, 3 sand, 5 stone.

About a quarter of the stumps have been done like this. Is this of major concrne given that it is well into the clay and that the actual amount of cement in the base of the hole is in reality about 350mm dia. by 300 - 400mm deeep?

Any advice would be appreciated.
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[thebuildingsurv]

I would say that would be a pretty much standard mix (I could be wrong) for footings. Cant understand why you mixed it urself though.

[OBBob]

I'm working on my own so I do a bit each night after work ... I wasn't sure that if I ordered a truck and pump etc that I would be able to get all 50 odd holes done.

[Pulpo]

I would have if possible tried to get some mates and had the whole lot done in one go by having ready mix delivered.

The mix you have and with the depth of the holes sound fine with me and I would not be too concerned.

Normally when mixing myself I get a pre-mixed sand a gravel mix [concrete mix] which I think is by memory 3:5.

I use the general use mix 1:2.5:4 and if I'm building a concrete wall or the like I use high strength.

I would move to the mix of general use for the remainder of the holes.

When mixing yourself be careful in trying to get the amounts or ratios right.

As a side point what sort of stumps are you using? Termites?

Good Luck

Pulpo

[ozwinner]

I use the general use mix 1:2.5:4 and if I'm building a concrete wall or the like I use high strength.

1 to 11 doesnt sound high strength to me.

Al :confused:

[Pulpo]

1:11 is not high strength, in fact a very poor mix and certainly not structural.

General use mix on the back of the cement bags

1 cement
2.5 sand
4 gravel

High strength which I did not list but also on the back of the bag is

1 cement
2 sand
3 gravel

And my bias is to mix more towards high strength when estimating amounts/volumes.

Also be careful with the amount of water, I would recommend a stiff mix as the concrete is being placed in a hole.

Too much water can really reduce the strength of the concrete, not sure why or how but in my experience it does.

Cheers

Pulpo

PS I read somewhere there is a spell checker now, can someone point me in the right direction.

[ozwinner]

Ok got it, I read your post "I use the general use mix 1:2.5:4"
As 1 to 2,5,4.

Al

[Robert34]

Pulpo

PS I read somewhere there is a spell checker now, can someone point me in the right direction.

The spell checker is third symbol from the right (ABC) .
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Robert34

[Wood Butcher]

The spell checker is third symbol from the right (ABC) .
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Robert34

Only if you are using Microsloth Internet Explorer :mad:. No good if you are using FireFox

[OBBob]

Thanks for the response guys. Not one of the things you can easily check or change, which is why it makes me worry ... I guess we'll find out down the track! I guess worst case scenario if it did move at some point I can get the restumppers that did the old part of the house to jack it up and add a few more!! One of many lessons to be learnt first time round I'm sure!

[OBBob]

Pulpo ... I'm using COPE concrete stumps. I don't know that much else is used in Victoria these days? Very easy, cheap and helps with the termite problem.