Concrete Cavity Fill Techniques For Large Houses and Volumes

[jwoodhead978]

TLDR: Efficient ways to concrete cavity is ready mix possible?

 

Architect has specified a standard cavity construction from footing to DPC, this obviously needs to be filled with concrete to 225mm below FFL.

 

After some rough calcs the concrete will be ~6 m^3. Although possible, it is unreasonable and inefficient to use a site mixer and wheel barrow.

 

So just wondering if anyone has any experience trying ready mix and potentially pumping, I'm aware of the mix design being lean compared to standard ready mixes. Or any other techniques to speed up the process.

 

The build has already commenced so no turning back now

 

Thanks in advance

Edited November 22, 2023 by jwoodhead978

[Conor]

2.5tonne mini digger. Set an area with polythene sheet for the mix to be dumped out. This time of year, you'll have a good couple of hours or more working time, at least. Have a mate with a shovel to help get it in evenly and spread out.

 

Mini digger hire will be less than half of a concrete pump. And I'm sure you'll have a few other jobs for it to do while you've got it.

 

If you've never operated one before, get it the day before and get practicing. Valuable skill to have.

Edited November 22, 2023 by Conor

[JohnMo]

Concrete pump, easy to do, may cost you, but easy and quick enough. Wonderful things, we hire one, 5 times during the build.

 

 

[Chanmenie]

Concrete pump would be a bit of an expensive luxury for just 6m3 plus I think you’d need to check if they will pump a leak mix.

 

with a little help i mixed 4.5m3  put it in buckets, on a conveyor belt and filled the gable ends of my ICF build, so 6m poured into footings cavities should be a breeze 

Edited November 22, 2023 by Chanmenie

[Canski]

Getting the concrete quickly into the cavity is key. Mine were 130 mm cavities and I made a hopper / trough out of timber to allow the concrete to be loaded in and guided down the cavity quickly.

 

6 m3 is quite a bit of concrete. I would have 2 x 3m3 deliveries over two days and would still want a mini digger and a dumper to get the concrete round to my trough then into the cavity.

[Iceverge]

Curved ball here. 

 

How about filling the cavity with closed cell polyurethane foam.

 

It'll be more expensive than concrete but no labour for you and make an excellent job of that wall to floor thermal bridge. 

[JohnMo]

A full concrete pre mix lorry contains 8m3, so 6m3 is quite a bit. 20 barrow loads per m2, so around 120 barrow loads to give you some perspective.

[Canski]

I was just looking at my 2 houses cavity fill whilst working on some other stuff. I only used just under 3 m 3 of cavity fill for 2 houses. Are you sure your calculations are correct ?

[Gus Potter]

5 hours ago, jwoodhead978 said:

So just wondering if anyone has any experience trying ready mix and potentially pumping, I'm aware of the mix design being lean compared to standard ready mixes. Or any other techniques to speed up the process.

Self building means you need to build a relasionship with the folk you are working with on site.

 

I know you are trying to get a price for everything but that is not the best way.

 

Six cube of concrete equates to a 15 tonne load of concrete ballast and a few bags of cement. Talk to your guys on site as this is the kind of job that can be done when the labourers have not much else to do. Bung a bit of cash their way and it will work out fine.

 

If you know what you are doing then hand mixing six cube of leanmix over a couple of day is not that hard.. I have done it many times over the years. I think a lot of folk have gone far too soft.. it is less onerous than picking Asparagus in Linconshire and you don't smell so bad in the toilet after.

 

 

 

[jwoodhead978]

8 hours ago, Canski said:

I was just looking at my 2 houses cavity fill whilst working on some other stuff. I only used just under 3 m 3 of cavity fill for 2 houses. Are you sure your calculations are correct ?

100% certain

 

 

[jwoodhead978]

5 hours ago, Gus Potter said:

Self building means you need to build a relasionship with the folk you are working with on site.

 

I know you are trying to get a price for everything but that is not the best way.

 

Six cube of concrete equates to a 15 tonne load of concrete ballast and a few bags of cement. Talk to your guys on site as this is the kind of job that can be done when the labourers have not much else to do. Bung a bit of cash their way and it will work out fine.

 

If you know what you are doing then hand mixing six cube of leanmix over a couple of day is not that hard.. I have done it many times over the years. I think a lot of folk have gone far too soft.. it is less onerous than picking Asparagus in Linconshire and you don't smell so bad in the toilet after.

 

 

 

I'm not even bothered about the price. There's a difference between people going soft and understanding heavy machinery increases efficiency.

 

I have enough respect for my employees to not waste ther time shoveling and borrowing such large amounts over such large distances. The distance between each end of site is over 60m.

Just wanted to see if anyone else has had experience pumping it in

[jwoodhead978]

11 hours ago, Conor said:

2.5tonne mini digger. Set an area with polythene sheet for the mix to be dumped out. This time of year, you'll have a good couple of hours or more working time, at least. Have a mate with a shovel to help get it in evenly and spread out.

 

Mini digger hire will be less than half of a concrete pump. And I'm sure you'll have a few other jobs for it to do while you've got it.

 

If you've never operated one before, get it the day before and get practicing. Valuable skill to have.

Decent idea currently have a digger on site. Got decent hours on a digger. Might built some form of ply funnel to help get in as cavity is only 65mm

[jwoodhead978]

10 hours ago, JohnMo said:

Concrete pump, easy to do, may cost you, but easy and quick enough. Wonderful things, we hire one, 5 times during the build.

 

 

Used a couple normal line pumps but never a boom. The cavity is only 65m. And other times the pump has been used it seems a bit wild. Although a boom pump with a ply funnel may be the best option. Cheers mate

[Conor]

Why is the cavity only 65mm? What's your wall buildup?

[jwoodhead978]

2 hours ago, Conor said:

Why is the cavity only 65mm? What's your wall buildup?

Timber framed mate. Inner 140mm block, cavity 65mm then 100mm brick/block depending on finish

[JohnMo]

22 minutes ago, jwoodhead978 said:

Timber framed mate. Inner 140mm block, cavity 65mm then 100mm brick/block depending on finish

If you are filling the cavity with concrete, you obviously don't need a cavity, so why not build as a solid structure. Block on its side 215mm, plus block 100mm wide installed normally, gives you 315mm. Your build is 315mm wide also, plus all the faff of concrete fill.

Edited November 23, 2023 by JohnMo

[joe90]

1 hour ago, JohnMo said:

If you are filling the cavity with concrete, you obviously don't need a cavity,

That’s what I thought, so why not fill it with more insulation, poly beads 🤷‍♂️

[ETC]

18 hours ago, jwoodhead978 said:

TLDR: Efficient ways to concrete cavity is ready mix possible?

 

Architect has specified a standard cavity construction from footing to DPC, this obviously needs to be filled with concrete to 225mm below FFL.

 

After some rough calcs the concrete will be ~6 m^3. Although possible, it is unreasonable and inefficient to use a site mixer and wheel barrow.

 

So just wondering if anyone has any experience trying ready mix and potentially pumping, I'm aware of the mix design being lean compared to standard ready mixes. Or any other techniques to speed up the process.

 

The build has already commenced so no turning back now

 

Thanks in advance

Why on earth are you building the sub-floor in cavity? Build it in solid blockwork to the underside of the slab. Use a stepped DPC no need for a 225mm gutter.

[Iceverge]

Maybe some pics would help if the stage you are at and the access? 

 

Would it be impossible for a concrete truck with an unloading belt to back up to the site? 

 

 

[Gus Potter]

On 23/11/2023 at 07:21, jwoodhead978 said:

I have enough respect for my employees to not waste ther time shoveling and borrowing such large amounts over such large distances.

Ouch!

 

On 23/11/2023 at 07:21, jwoodhead978 said:

I'm not even bothered about the price. There's a difference between people going soft and understanding heavy machinery increases efficiency.

Here is a suggestion, from someone with a Contracting backgound.

 

Get a load of ballast and a few bags of cenment delivered to site. I take it you have a machine with a bucket on site and a bag mixer knocking about, not a mini Belle.. a proper mixer. Batch up the lean mix for the cavity and take that to where you need it with your idle machine and pour it into the cavity, all you need to do is tamp it in carefully so you don't burst the walls. No need for a barrow.

 

Any left over ballast you'll use it elsewhere for bottoming, slabbing etc.

 

Lean mixing cavities is a great way of teaching apprentices as it is low risk. Say you need a small batch as you always do on site. Are you going to get a spot mix in for half a cube, the delay and time it will take you to organise that? If you take a bit of time to teach your employees (especialy apprentices) and get them to recognise that they need to be working all day for a fair days pay, but that you are not thrashing them to death then this make good buisiness sense.

 

There is a time for heavy machinery and a time for thought and finesse.

 

On 23/11/2023 at 07:21, jwoodhead978 said:

I'm not even bothered about the price.

You future looks bleak as a Contractor. I'm sure you are making hay at the moment but the good times will come to an end.. they always do.

 

 

 

[ETC]

27 minutes ago, Gus Potter said:

Ouch!

 

Here is a suggestion, from someone with a Contracting backgound.

 

Get a load of ballast and a few bags of cenment delivered to site. I take it you have a machine with a bucket on site and a bag mixer knocking about, not a mini Belle.. a proper mixer. Batch up the lean mix for the cavity and take that to where you need it with your idle machine and pour it into the cavity, all you need to do is tamp it in carefully so you don't burst the walls. No need for a barrow.

 

Any left over ballast you'll use it elsewhere for bottoming, slabbing etc.

 

Lean mixing cavities is a great way of teaching apprentices as it is low risk. Say you need a small batch as you always do on site. Are you going to get a spot mix in for half a cube, the delay and time it will take you to organise that? If you take a bit of time to teach your employees (especialy apprentices) and get them to recognise that they need to be working all day for a fair days pay, but that you are not thrashing them to death then this make good buisiness sense.

 

There is a time for heavy machinery and a time for thought and finesse.

 

You future looks bleak as a Contractor. I'm sure you are making hay at the moment but the good times will come to an end.. they always do.

 

 

 

Again. Build it solid.

[Gus Potter]

1 hour ago, ETC said:

Again. Build it solid.

Thanks ETC for the advice.

 

I'll see where I can apply that method more often, has given me food for thought so thanks again.

 

[joe90]

1 hour ago, Gus Potter said:

There is a time for heavy machinery and a time for thought and finesse.

This is the one line I liked and always repeat, “work smarter not harder”.