Concrete Floor

[gjh]

I am in the process of replacing my kitchen floor with a new concrete floor (The old one was only a few inches thick with no insulation, DPM or hardcore beneath).

I intend to dig down the required depth and then fill as follows (top to bottom):

1. Concrete Screed, containing:
Electric floor heating cable
Wire mesh (to lift cable away from insulation)
2. Jabfloor 70 insulation
3. Concrete slab
4. DPM
5. Sand
6. Compacted Hardcore

The question I have is what is the required thickness for each of these layers and what mix (& materials) do I use for the slab and the screed? The surface onto which all this will be laid is quite thick clay which seems fairly solid.

Also I know that I need to put a layer of insulation between the screed and the internal walls, but I have also seen on some websites that this layer of insulation extends all the way down to the concrete slab - so that no part of the new floor is touching the walls, is this necessary?

 

[Static]

how large is the floor area? are there any walls/partitions bearing onto the new slab?

 

[gjh]

The kitchen is 2.8mx2.4m and all that will be going on top is the kitchen units!

 

[Static]

Top - down

75mm screed
Insulation
150dp C30 concrete slab with A142 mesh with 40m top cover
DPM 1200 gauge
50mm sand blinding
150mm min MOT type 1
Well compacted/undisturbed soil

 

[gjh]

75mm screed
Insulation
150dp C30 concrete slab with A142 mesh with 40m top cover
DPM 1200 gauge
50mm sand blinding
150mm min MOT type 1
Well compacted/undisturbed soil

Thanks for the reply, a few questions about the above (apologies in advance if they are dumb questions!).

Whats "150dp C30 concrete slab with A142 mesh with 40m top cover"? How thick should this slab be?

If using the Jabfloor 70 insulation what would be the best thickness? I assume too thick is better than too thin? Would you recommend any other form of insulation?

 

[Static]

Whats "150dp C30 concrete slab with A142 mesh with 40m top cover"? How thick should this slab be?

If using the Jabfloor 70 insulation what would be the best thickness? I assume too thick is better than too thin? Would you recommend any other form of insulation?

Ok, questions are better than assumptions that are wrong
150mm deep (150dp) C30 (C30 is the concrete grade mix) concrete slab with A142 (type of square structural reinforcement should be able to get it at any builders merchants) with 40mm top cover (ie 40mm between the A142 reinforcement and the top of the 150mm slab)

Go for 75mm insulation and youll have a warmer kitchen

 

[gjh]

OK, heres my final (hopefully!) plan:

75mm Concrete Screed, containing:
Electric floor heating cable (have yet to select this item)
Wire mesh (to lift cable away from insulation) using remaining A142

75mm Jabfloor 70

150mm slab
A142 reinforcement with 40mm topcover
30mm x 150mm jabfloor 70 edging strips

DPM blue 1200 gauge

50mm sharp sand

150mm MOT type 1

For an area of 2.4m x 2.8m this gives the following required volumes:

0.5m3 of screed
1m3 of concrete slab

Assuming a mix of [3 parts sharp sand / 1 part portland cement] for the screed and [1 part cement / 2.5 parts sharp sand / 4 parts aggregate] for the slab, can anyone tell me how to work out the required quantities of cement, sand and aggregate? - Assuming that the above mixes are suitable!!

Also, whats the best way to go about laying the slab to ensure that the reinforcement is at the required depth? Do you put in 110mm and leave that overnight, then place the reinforcement in place and pour the remaining 40mm or is there another way? Any advice or links would be most appreciated.

 

[noseall]

don't bother with the reinforcing. the reason why i hear you say? all builders know that large expanses of concrete crack due to their large surface area. so can brick walls . thats why we put in expansion joints. its far better for frost effected rainwater to expand in an expansion joint than a crack, any day. but what about indoor domestic concreting? theres no rainwater, no frost, no heavy traffic and once the concrete has " settled " and the screed applied, no cracks.

sorry if this is provocative, but i've always found it mildly amusing having to fix steel reinforcing in domestic scenarios.

 

[gjh]

Does anyone else share the above opinion? To be honest I was never planning on adding steel reinforcement until it was advised above but I kinda agree with the above sentiment that it would be overkill for a small kitchen - however I am a telecoms engineer not a builder so my 'hunches' don't count for much!

 

[Static]

A single sheet of A142 mesh (2x3m) will cost around £20 per sheet. Finding a local suppliest is the hard part. Yes you dont necessarily need the mesh it depends how confident you are on the compaction of the subsoil, hardcore etc. the mesh is there to allow for soft spots in the ground and heave, its alot easier to fit now than later.

 

[gjh]

OK, thats settled then, a little outlay now could save a big headache later so I guess I'll go for the wire mesh. TravisPerkins have a depot locally so getting hold of some should not be a problem. However back to how do you lay it to ensure it is at the correct depth in the slab?

I would guess propping it up 100mm with bricks or broken paving stones then filling around and over with concrete? Is this the way to go about it or is there an easier way?

 

[Static]

Any non compressible non pourous material.. so bricks dont work, concrete paving slab pieces are acceptable, normally you can buy a few concrete shoes at builders merchants to sit the mesh on.