footings concrete

[terence7556]

is lean mix acceptable in a footing or not allowed? as compared to 4;2:1 wet concrete
(please answer buildersmate)
my builder on my extension has used lean mix in a footing (1200mm x 1300 ) up to 100mm from the top and covered it with wet concrete . the trench is 9mts long , dug in 2mt bites at a time and is 650mm from my neighbours garage wall, so the original footing 600mm wide has been extended to 1.2m wide to support this wall
the engineer on my site says its old school, and serves me right for accepting the cheapest qoute(17k difference, would you give that up?)but its adequate to support a two storey extension. he said lean mix will support 25 newtons but wet concrete will carry 40 newtons.
the building control inspector has said the footings are satisfactory but the covering used makes me suspicious

[laptopsteve]

wonder why he didn't use wet concrete and done in 2mtr (bites) is wary (why not the whole 9mtrs so that the footing is one complete support, especially in a two storey construction in rare cases that you need to do footings in (bites) you have to use starter bars which is steel bars set in the first bit of concrete gone hard to the other i would explain to inspector as at this stage it REALLY needs to be correct also take pics of everything and show a freind in the trade good luck.....

[terence7556]

it was carried out in 2mt bites because of the close proximity of the garage wall and the risk of the wall subsiding.
think underpinning, you know dig under ,fill in for 4feet, miss 4 feet etc.

[buildersmate]

If a (structural) engineer is happy with it, and so is the BCO, I can hardly say against them - they are on the site and I'm not.
But, like you, if it was my house I wouldn't be very happy. The structural strength of concrete comes from having the correct mix, cast in a single piece - but I guess you knew that already.
Is the BCO satisfied that the loading of a two-storey extension along the foundations doesn't exceed 25N? Sounds a very light structure to me.

[laptopsteve]

ahh under pinning,, makes better sence now can see why he used lean mix and in 2mtr blocks but its still good to use starter bars (metal rods) so that when you do the blocks left in between the bars help join them together still take pics though..