Laying ready mix concrete slab

DIYer Damo · 9 Sep 2018

Hi all,

I've ordered some ready mix concrete for a ground floor slab in my renovated house. It's about 75m2 (9m3) and is mostly open plan apart from the living room. I'm having it pumped in due to access and my question is how many people should I get round to help level it off?

The concrete supplier said the pump guys will help get it in but won't help to level it out. He said I'd need max 2 people but speak to others since I'm being told I'm massively underestimating the amount of effort it takes and will need many more. I've currently got about 4 people arranged.

Current plan was to make a couple of levelling sticks out of cls that could be dragged, tapped on surface. Anyone have any advice, never done anything like this before.
PS I've a laser level but not sure how best to make good use of IT? Was thinking of setting it up in a corner and just marking a length of wood to determine correct height.
PPS: the slab will be covered with insulation then self level screed so doesn't need to look pretty but does need to be pretty level.
Cheers

bobasd · 9 Sep 2018

i'd stop right there if i was you.
posypone the mix and put your guys on hold.
i now this is a DIY forum but with your nowledge doin what you propose is best done by professional concrete guys - watch how they prep an establish benchmarks an how they set about doin the job.
you can probly jump in an labour for them

if you make a mistake you might have to jackhammer large areas out.
small outside areas are good for learnin on not full ground floors.

DIYer Damo · 9 Sep 2018

Thanks bobasd,

I appreciate your concern however I’m not a complete newbie to big diy tasks. I’ve self built a rear extension inc installing 8 rsj’s, dogging footings, putting tiled roof on and x4 velux windows, so tackled some pretty major elements so far. Surely their must be a way of doing this decently without coughing up even more for pros. If it were that difficult I’d have expected concrete firms to offer that service but none of them do.

bobasd · 9 Sep 2018

offer what service? what do you mean by concrete firms?
there are gangs who do nothin but sub to prep, pour an finish to whatever specs.
the mixer firms that i now are supply an deliver only.
its not difficult but its unforgivin.

endecotp · 9 Sep 2018

There have been other similar threads, you will learn a lot if you can find them.

DIYer Damo · 9 Sep 2018

Thanks endecotp. I did a quick search before posting but couldn’t see anything similar. Maybe I was in the wrong section. Didn’t know if to look in flooring or building. Cheers

dazlight · 9 Sep 2018

Most pros Cant do it right to be honest. I lay over 1 in 10 decent screeds.

KenGMac · 10 Sep 2018

Ok it will be a back breaker, get as many people as possible, and search around for someone that has done this before???

Suggest you have a look at -
Acra Screed Ground System, Acra Screed Concrete Systems ...

other systems are available? research google for "Concrete Screed systems"

Set these things up about 400.mm or so from the long wall in each room, that will set the level in that room, using your Laser Level you can get a reasonable level established overall. you can then use the CLS you mention [ something more robust may be worth considering?? 150.mm. X 50.m Generally referred to as a Tamping bar]

But, there is generally a BUT? ensure that your CLS or whatever will "fit" into as many spaces as possible, not practicable to make your CLS [or whatever] fit the largest space but cannot fit smaller areas?

OK This System will cost, but is is easily removed when the concrete has set a bit.

Have you organised a vibrator? you will need one, if nothing else it assists in moving Concrete around, and many gangs that do so called "Ground work" use rakes to move the wet Concrete around.

Depending on the pump you are to use, you will have to be quick so get everything in place well ahead of the action.

Ken

KenGMac · 10 Sep 2018

Forgot to ask how deep is the screed? Is it reinforced?

Manpower projection? [Approximate]

If the Concrete supplier has manpower to lay and adjust the pump hose OK, these things are bitches to fit together and pull apart. Large lump hammers rule.

Two men on the tamping bar, they can also spread. it is not possible for one man to work this tamping device.

One man on the vibrator, almost full time, can assist spreading.

One man spare to assist where needed, if possible a back up man would be a good idea? they can follow the concrete pump placing and assist in preliminary spreading awaiting the tamper to finish of.

The tamping bar needs to have "handles" so the men can stand at either end, and either drag or, in unison lift the bar up and down to level the concrete, the tamper bar must hit the screed bars [if possible] so when completed the top surface of the screed bar is visible.

Several shovels, two or three rakes and a load of bottled water?

There will generally be a load of re assessing of who is doing what during the process.

Ken.

endecotp · 11 Sep 2018

DIYer Damo said:
Thanks endecotp. I did a quick search before posting but couldn’t see anything similar. Maybe I was in the wrong section. Didn’t know if to look in flooring or building. Cheers

Mostly in “Building”. More than a “quick search” will find lots of people doing similar jobs, e.g.:

https://www.diynot.com/diy/threads/troweling-slab.480013/
https://www.diynot.com/diy/threads/concrete-slab.481674/
https://www.diynot.com/diy/threads/power-floating-advice.506500

cdbe · 11 Sep 2018

I suppose it's too late to put the insulation under the slab.
If you don't have time to do anything else I would knock a load of pegs in, level to them as much as you can (big rakes as above) and blind the finished slab with a layer of sand if it's too uneven to support the insulation.

As you're having a screed on top you'll be fine.

Don't forget your wellies.

DIYer Damo · 12 Sep 2018

Thanks so much everyone, as always I can count on this site to give some good advice.
After struggling to get enough spare bodies to help out and struggling to work out how I’d get this slab level given that it’s internal with Dpm lapped up the walls preventing easy fixing of rails + quite a few obstacles to work round (nibs, a central brick pier) I’ve decided to delay my concrete and seek help from the pros. Not had a price yet. I must say I’m really deflated at having to make this decision. There is so much I’ve diy’ed during my house refurb that most people would have told me not to tackle I’m feeling a bit defeated with this job and expect to now have to fork out 7/800 notes on top of the materials price. Still, as a few have pointed out it could have cost me a lot had I gone ahead and made a mess of it.

KenGMac · 12 Sep 2018

DIYer Damo, good evening.

OK Deflated but if it had gone wrong a serious volume of additional very hard work.

It is OK for someone who has undertaken this type of work and understands that preparation is all in this area of building, the actual placing of the material comes in almost as a secondary less important aspect, if you are not prepared then it all goes west very fast [see the DONALD for further comments??]

To place what is about one and a half concrete mixers worth of material is a big ask, OK it can be done in sections? but alas some things are not suitable for DIY

Hope you get a decent price for the proposed work.

Ken

DIYer Damo · 12 Sep 2018

Thanks Ken,

I suppose it’s that balance between risk and ability.
Had I asked people if I should self build my rear extension with zero building experience I’m sure (quite rightly) that most people would have told me to stop and think. That’s what’s bugging me so much about giving in on this one job before I’ve even tried. I do trust the advice I’ve gotten though from the likes of yourself. Building the framework alone would have probably taken me a couple of days!
I’ll be super intrigued to see how the pros tackle it and hope that when I see it being done I’ll realise that I couldn’t have done it myself.
I’ll post an update once it’s complete - cheers

lostinthelight · 12 Sep 2018

As this is pumped oversite concrete would it be almost self leveling enough if screed is going on top
Could you not have pegs or bricks dotted around leveled with your laser and remove them as concrete fills.

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Laying ready mix concrete slab

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