How to ensure Concrete is level

[bluebaron]

Morning Chaps,

Any tips for ensuring a 50m2 concrete foundation slab is level?

Thanks.

BB

 

[John D v2.0]

For normal trench foundations you'could bang in pegs beforehand and level them with a spirit/water level or laser. Then fill and level to the pegs with a long wood to tamp it.
I guess the same would work for a large area.

 

[bluebaron]

Thans John I've got 6 pegs in Ill check the levels again when the footings are in. I'm assuming i can be a bit out and let the screed take in any slack anyway.

Thanks.

 

[JohnD]

A water level is very handy, because with pegs and a straight-edge plus spirit level, you can get a tiny error which gets bigger as you work along the slab. Turning the level round for every check will help you spot or compensate the error.

 

[garyo]

The ponding that forms on the wet concrete as you tamp it in will give you a good indication if you're badly out too.

 

[John D v2.0]

Yes the watch word is surely cumulative error, the screed can take the wobbles out but not the slope.

 

[^woody^]

concrete foundation slab is level

assuming i can be a bit out and let the screed take in any slack

Which is it, foundation or floor slab?

 

[bluebaron]

Its the floor slab.

 

[Blagard]

For slabs you really want rails set level so you can draw across whatever you use for tamping, then pull out the rails and locally fill to the main concrete just poured. On commercial projects scaffold poles in cradles are often used or even bespoke systems. The good thing about a scaffold tube is that it needs just a few supports and leaves only a shallow hollow to fill when pulled out (wet). You can look up screed rails for more info

 

[^woody^]

Its the floor slab.

Then you would level it off DPC course.

 

[bluebaron]

ok thanks for tips chaps Il see how i get on.

Woody, I can't level to DPC as i need to celotex above slab for UFH and screed so concrete will be 220mm approx below.

 

[Newboy]

level it off DPC course

not

level to DPC

 

[bluebaron]

My bad long day

 

[^woody^]

Woody, I can't level to DPC as i need to celotex above slab for UFH and screed so concrete will be 220mm approx below.

You make a tamp board that be placed on the wall, and the board sits at the required height.

 

[bluebaron]

Hi Chaps I'm pouring this on Monday. Don't think I can add a tamp board to the foundation blocks as I would have to screw it through the DPM.

Another suggestion I had was laying a few bricks on top off the DPM and levelling 100mm off them. It was also suggested I could just leave them in. Might look a bit odd but it's all getting covered up anyway.

I can't see how else I can ensure a 100mm thickness across the whole span with little or no reference point?

I found this can anyone explain it another way I don't understand the logic?

"If using the dpc level walls to establish the level then just use a big 2x4 and screw a bit of ply to the side so that you end up with a squashed T (or L) - both upside down from the letter that I used.

Make the 2x4 longer than the exterior dimension and the ply the same(or slightly shorter) as the internal measurement. You could also add a piece underneath so that you get an I shape
Set the drop to whatever level you need

Move it side to side while moving left or right"





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