Concrete setting time

[howardm]

Hi men,
It's time to get the floating floor in my new shed, 7m x 7m x 140mm thick 14 tons I think.!
After bad experiences with "tradesmen" up here, I was thinking of doing it myself/alone.

So, the question is, how long does it take for the concrete to stiffen/become unworkable.?
If I get it pumped in, then there will be less hard manual work shifting the stiff about.?

I have channel all round the perimeter, so I can use a full-width beam vibrator hopefully just one pass and bob's your uncle.

any input appreciated
thx
Howard

 

[500e]

7Mtr beam hope you are feeling strong

 

[howardm]

7Mtr beam hope you are feeling strong

This type of beam

 

[I'm getting on a bit]

You could specify a curing time when you order.
You should also use a poker to compact it but I would have a few mates round to help you get it spread out before the final floating

Or it will be RIP Howardm

 

[hunter27]

Years ago a mate was enlisting help to concrete his drive. It led from the road to the house,down the length of his house and to his garage behind, so a mixer full. Out of about 6 helpers only me turned up and it was possibly the sunniest and hottest day of the year Well the front drive looks good up to the house but we had to do our best with the rest. You could walk on it after a couple of hours.

 

[eSCHEn]

sunny and hot

howardm - Aberdeen

Not gonna be a problem...

 

[Kent]

as slow as 1mm per day or as fast as you haven't got enough open working time. I was once told allow at least two weeks before doing much with a slab and that has always held up but of course it depends on size and weather also the mix were do you stop

 

[Richardjjj]

Hi.
You will need 7 m3 'all but', a structural concrete has a density close to 2250 - 2400 kg per m3 so closer to 17t.
Workability will depend on the percentage of cement/pfa and water ratio - also humidity and temperature on the day. A polythene membrane will also help to stop water leaching into the substrate and speeding the drying.
Personally wouldn't like to attempt it on my own even with a pump although that would make it a lot easier.
The problem you will have is that a 8m beam, you will need at least 500mm either side, will ride over mounds and those vibrating screeds can also push concrete up behind the beam so you will need at least 2 passes.
Depends on the accuracy you are looking for but I would suggest 2 people as a minimum, preferably 3.
The problem with ready mixed concrete is when it goes, it goes quickly. Breaking out to form a decent joint and finish is no fun.

 

[Wendelspanswick]

You can get a retarder added to the mix to slow the whole process down.
A pal who normally does concrete formwork for a living offered to lay a slab for another pals new workshop, because of the size of the area and the limited labour available he had the mix retarded, trouble was it wasn't ready for power floating till 4 o clock in the morning!

 

[rikrobson]

would it not be better to cast it in sections? asy 2m at one end then 2m at the other and then the 3m in the middle?

 

[mike os]

ou want at least a couple of assistants...

 

[Pete.]

Yep you'll want one on the pipe and two on shovels at the very least. That's with an experienced gang.

 

[mike os]

it will get to unworkable in 4-5hours normally

 

[500e]

Rotary screeder is the way to go (Brandons hire them I think) then the ride on

power float to finish, been there WeSp on more than one occasion 5 loads go off ok the 6th the ride on is great but not at 0500 gmt

 

[howardm]

Thanks folks,
Looks like I'll have to pay through the nose for this part of the job.

Thx
Howard

 

[Richardjjj]

A wise choice I think.
You should also look at adding a couple of expansion joints - a rule of thumb - 40 x the slab thickness as a maximum bay size. Don't know what the slab is for but may save some problems in the future. Would also suggest a soft pack against the channels.

 

[GeorgeB]

It's time to get the floating floor in my new shed, 7m x 7m x 140mm thick 14 tons I think.
any input appreciated

I use concrete quite a lot and I usually add reinforcing bar. Perhaps a few cracks in a shed floor, in a few years time, would not be much of an issue, though.

 

[howardm]

Thanks, I am putting A 393 mesh in, standing on the plastic post thingy's.
What would you put around the edge as a soft pack, would a 12mm soft timber do it.?

 

[Richardjjj]

Sorry, have jumped to the conclusion that the channels you mentioned are permanent, as in a drainage channel or kerb. If the channels are purely to form the shuttering and removed after pour you don't need anything. If they are fixed and the slab once poured could move them you will be able to source rolls of 10mm foam strip (don't know if they do 140 but certainly 150mm) and you place that against the channel and pour against it. Just allows for some movement in the slab.
Probably available from where you sourced the mesh and chairs.

 

[DrDeAtH]

If its a complete slab, get fibres put in for reinforcement. Working time will be approx 90 mins to 2 hrs unless you specify a retarder additive.