Whats the best way to install a level concrete subfloor?

[keycare]

Hi,

I'm DIY rennovating an old farmhouse in Wales. My current job is lifting the badly installed ground floor and installing a new floor with insulation, UFH and flagstones.

My dillema is, having dug out to approx the right depth to accomodate the various layers, I now want to pour a level slab so that installation of the insulation slabs is nice and easy.

As it is a very old house (early 1700) nothing is level or straight. So how do I ensure that the 11m x 4.5m concrete is nice and level?

Hoping to pour Friday, any help appreciated.

 

[fastneattrowel]

make it wet find its own level

 

[Shytalkz]

Lafarge do a super plasticised mix, can't remember the name, but it flows miles and, to get it level, you merely walk through it - honest! About £30/m3 more but you can do it on your own, saves on labour costs; they're doing deals on it atm to get more people to use it. Needs dpm under it, to stop water being drawn into the subbase material, but that's about the only prep needed.

The problem with mega-wetting up a normal mix, as per Effenntee's suggestion is that that can lead to uncontrolled cracking as it cures.

 

[^woody^]

make it wet find its own level

Concrete will not find its own level however wet it is mixed.

You need to set some levels or a timber guide around two sides, so that you can pull a straight edge across the surface.

Or if not too wet, just lay a spirit level on the surface and rake it .

Is this to have a troweled surface or are you screeding afterwards?

 

[puggles]

The stuff from Lafarge is called Aggelia (self levelling concrete). Easy to pour.

 

[Shytalkz]

Here's the info, it's called Agilia: http://www.lafarge-aggregates-construction-materials.co.uk/main.htm. Don't need anything other than a hole to fill, Woody, no levels, nuffink

 

[Shytalkz]

The stuff from Lafarge is called Aggelia (self levelling concrete). Easy to pour.

Beat me

 

[puggles]

At least you spelt it correctly, and added a link, very impressive!!!

 

[Shytalkz]

What a daft name for it though, hardly trips off the tongue, does it?! Have you used it? I'm going to use it on my barn project. As I specify (lots of) concrete, they're letting me have it at the price of normal concrete, too, hahah

 

[puggles]

Yes, I laid 250 square meters on a factory floor in cambridgeshire a couple of years ago. I cheated though, I told Lafarge I didn't know how to use it and got the rep to come and give me a hand, all for the same price as normal concrete!!! It is very easy to use. I used a 2 inch static pump to pour and then tamp finish concrete with tubular steel bar.

 

[Shytalkz]

They might have modified it since you did that, as you don't need a pump, unless you need it to go more than 11m or so, I think.

They do a screed as well, although the prep work is a bit more involved, as you have to keep sunlight off it when it's curing; but it means you can reduce the thickness to 50 for UFH set ups, so you're saving up to 33% volume of a normal screed anyway, which will go some way to offsetting the EO cost of it.

 

[emphasis303]

Sidi?

 

[Shytalkz]

No, this: http://www.lafarge-aggregates.co.uk/Screed Bro_1.pdf

 

[keycare]

fantastic stuff gentlemen.

Can I specify this lafarge stuff in readymix? I reckon on about 5m3 for my floor.

The floor construction is...

Sand blinding, DPM, Concrete 4-5in, 3in insulation boards, DPM, UFH pipes with 2.5in screed and 2in flagstones.

My problem with tamping level is where and how do I install the timber guides for the tramlines. They'll need to be fixed to something and as the walls are rubblestone I can't nail them to the walls. Screwing them is one hell of a job cos they're not even and I would need to SDS them to get a hole in the stone.

I had a brickie and his labourer lay the concrete in the Kitchen/Utility but I wasn't happy with the finished surface. It was too bumpy especially around the edges. It made laying the insulation slabs a nightmare cos I had to blind almost the whole concrete floor with sand otherwise they wouldn't sit properly. I'd like to try to do a better job this time.

 

[keycare]

Just rang Lafarge, and in typical style, they are no plants in my area (Swansea). This is the story of my life with this bloody rennovation.

Back to traditional methods then...

I need to accurately tamp and level this subfloor.

One method I thought of using was to shutter the floor about 4in in from the walls, drape enough DPM over the shuttering so that when the concrete is nearly set I can remove the shuttering and lay the excess DPM up the walls. I can then manually mix enough muck to fill the gap between the slab and the walls and trowel flat.

Would this work or would the fill-in concrete break away from the main slab and cause problems?