breaking up hardcore

[jtc]

Hi I am about to build up a concrete floor on an extension. I intend breaking up a mountain of old bricks and concrete for the hardcore. What size should I be looking to break them down to. Also once laid does it need to be compacted afterwards by machine or is it possible to do it by sledgehammer.

 

[Softus]

Size doesn't matter, but the smaller the bits the more concrete you'll have to mix (or get delivered).

The maximum size is dictated by the depth of the slab. When I put pieces of broken bricks into the mix I try to ensure that the frogs (if any) are facing upwards so that there are no air pockets that could later result in fracturing.

 

[joe-90]

Size doesn't matter,

It does with most of the 'hardcore' I've ever seen.

 

[Softus]

OK, that one is darned witty.

 

[jtc]

Size doesn't matter, but the smaller the bits the more concrete you'll have to mix (or get delivered).

The maximum size is dictated by the depth of the slab. When I put pieces of broken bricks into the mix I try to ensure that the frogs (if any) are facing upwards so that there are no air pockets that could later result in fracturing.

Thanks for that but now I am more confused I thought you laid all the hardcore material in the hole and then compacted it (not concrete it together). Cover with sand, DPM then concrete over it. Then insulate and screed.
Does the hardcore need to be concreted together ?

 

[Softus]

I thought you laid all the hardcore material in the hole and then compacted it (not concrete it together).

Er, you do compact it, but then you pour concrete on it.

Cover with sand...

Yup.

DPM then concrete over it.

Nope - that would puncture the DPM.

Does the hardcore need to be concreted together?

Yes.

 

[Thermo]

break the hardcore down as this will allow it be compacted more easily and with a better result.

Cover with sand to fill the gaps and give a smooth surface that will not puncture the dpm.

put the dpm down

pour the concrete job done.

You dont need to concrete the hardcore if its compacted. If the dpm is laying on a blinded snad bed then the concrete wont puncture it.

 

[Softus]

Well, I stand corrected. I guess there must alternative and equally acceptable methods, then, because that isn't how I've done it.

Apologies to the OP if I've misled.

 

[alpcon]

So what happened to the insulation!!

Sorry softus its not an alternative its the right way to do it. You do not lay concrete over the bricks without first laying down a sand blinding

The Right Way

An awful lot of hard work breaking up old bricks which incidently have to be clean and conform to a certain size! Are you having this job inspected by building control? If so I don't think they will pass it.

Use scalpings - type 1 MOT £30 to £40 per tonne
Compact these down well with a wacker plate - easily hired.
Lay in 2 inchs of sand minimum on top of the scalps as a blinding and use the wacker plate to pack this down.
Lay down your DPM lapping it up the walls and then the insulation, the thickness of which will be detailed in your building reg specs - if you have any.
Then pour your concrete on top and leave to cure.
Then lay in and level your floor screed

Scalps pack down much better than bricks and you will always end up with a few voids using bricks as hardcore.

 

[Softus]

Sorry softus its not an alternative its the right way to do it.

Why are you apologising?

You do not lay concrete over the bricks without first laying down a sand blinding

Please tell me where I said, or implied, that one does.

 

[alpcon]

Softus wrote

Please tell me where I said, or implied, that one does.

Please see your post in this thread sun oct 14 @ 7:38

 

[Softus]

Please see your post in this thread sun oct 14 @ 7:38

...in which I wrote "Yup." in reply to "Cover with sand...".

 

[alpcon]

I give up!

Banging heads, brick walls comes to mind

If jtc sticks to the method I posted he cant go wrong - tried and tested and it works

 

[Softus]

I give up!

That'll be because you're wrong.

Banging heads, brick walls comes to mind

Next time, read the notice on the wall that says "Don't bang your head here.".

 

[Thermo]

did you not say that the hardcore needs to concreted together?