Extension foundations

[rahul100]

hello

My builder is starting the foundations for a new 6x4m extension. Builder said he is going to use the crushed concrete pieces which are coming out of an old garden path for the hardcore sub base. Is this ok? Does the hardcore need to be filled with sand? Also does the hardcore need to be compacted before the concrete goes in?

Also how long does the concrete take to mix properly in the mixer, as ive seen builders raking the concrete out after less than 30 secs of mixing.
thank you

 

[tony1851]

No, it is not OK to use bits of concrete path mixed in with the concrete for the foundation.

Any hardcore under site concrete should be well-compacted, otherwise it will settle slightly over time. (there should be no hardcore under the foundation concrete- it should be poured directly on excavated ground).

 

[munchingB]

i thought that you were not meant to use concrete under a foundation at all?

is he doing a trench fill foundation then or a big slab?

 

[rahul100]

trench fill 1100 x 600

 

[rahul100]

.trench/strip foundations