making a solid floor

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Can someone explain the various layers of materials in making a solid floor; am I right that you can have , hardcore; sand; DPM; kingspan insulation; and screed on top. But NO ACTUAL CONCRETE?

Or do you need concrete on top of the insulation, just under the screed? And what are the thicknesses of each layer?

Thank you
 
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Typically it will be:-

Screed
Insulation
Concrete Slab
DPM
Sand Blinding
Hardcore

MIs may call for a VCL between the insulation and screed and the insulation may be put below the slab in some details. Perimeter insulation will also be required. Depths will vary dependant on spec.

hth
 
thanks.

Now about laying the screed - my extension is only 2200 x 2100 mm so once you deduct the 300 thick walls, the actual floor area is even less.

But what is the easiest way of laying the screed perfectly level, and to finish so it is same level as exisisting floor level?
 
But what is the easiest way of laying the screed perfectly level, and to finish so it is same level as existing floor level?

I personally do not like the insulation beneath the screed. We fit it beneath the slab. I understand that UFH requires this method, but i don't like UFH either.

Anyhoo, the screed will be the last thing you will install once the knock through has been completed. It is then a simple case of marrying-in new to existing levels.

With this in mind it is then a case of working out finished screed level and deducting the thickness of screed (plus insulation, if adding above slab)) and working down from this.

We sometimes knock a hole out right the way through so that we can get a level through onto the existing screed. It is then a case of measuring down from this and set your concrete slab at the required height.

Remember to knock a hole out where you intend doing the final knock through.
;)
 
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As noseall says, knock through at floor level (either side of the wall where your extension is going and transfer the FFL. Use the FFL as your datum for digging out etc, then do your stuff
. ;) ;) ;)
 
OK, but when laying screed, do you screw battons around the walls to act as guides to the height , and then move a straight edge over these?

My question is how exactly do you get the screed surface flat ans level over the whole room?

One method I saw was to first make long lines of screed to the height you want, like bays, and then fill inbetween...
 
how exactly do you get the screed surface flat ans level over the whole room?

One method I saw was to first make long lines of screed to the height you want, like bays, and then fill inbetween...

Correct. You use the screed material as levelling guides.

We usually go around the perimeter of the room with the screed and a 1200mm level. We would typically lay a 450mm wide screed around the perimeter then fill in. Once you have an edge screed you then use a longer feather-edge to level between screed runs.

With large rooms, it may be best to have a central screed as well as perimeter screeds.
 
Noseall - I'm new, and you've been posting for years - so you're in a better position to advise what to do -- it seems to me that the screed estimator on this site is wrong - and badly so.

I've seen a fair bit of contradictory stuff on this site, and from other estimating tools on the web, so I've resorted to weighing cement powder! -- and it seems to me that it weighs about 1.3kg per litre -- or 1.3 tonnes/cu m -- which agrees with the Blue Circle and Lafarge data sheets. (e.g. http://www.lafarge.co.uk/CementDatasheet/Mastercrete.pdf ) Of course cement powder can get compacted, but I'm trying to weigh it as it usually comes out of a bag.

I'm also assuming that a cube of sand weighs 1.6 tonnes - is that near enough? In other words sand weighs a fair bit more than cement.

You have posted elsewhere that a tonne of sand, for a 4:1 mix, needs about 8 bags cement -- and if I can quote another poster - "Plstering" - he says "I base most my mixes 4:1 6/7bags per tonne m8, if that helps"..

You and he seem to be correct to me, according to my weighings of sand and cement - it equates to about 5:1 by weight. (Skip these calcs if you're bored already :- if cement is 1.3 t /cu m then 1 tonne is 0.75 cu m - therefore eg 8 bags (200kg) is a fifth of 0.75 = 0.15 cu m. If you want 4 times as much sand by vol you need 0.6 cu m of sand - which should weigh a tonne, if a cube weighs 1.6 tonnes. 200kg cement is therefore a quarter of the volume of 1 tonne of sand [hence a 4:1 mix], obviously 5:1 by weight)

But the estimator sticky on this site has a 4:1 mix as 3:1 by weight ! -- it says 14 bags cement per tonne of sand ! - and the densities at the top of the estimator say that cement weighs more than sand - by a big margin - This seems just plain incorrect, but I don't want to attack a sticky without double checking..

The Source4me estimator - which lots of people seem to be trusting - looks identical to the one on this site - same bizarre densities..

By the way - 3:1 by weight gives 2.4:1 by vol (at correct densities) - that's a dangerously bad floor ...

Could I be correct?
 

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