Levelling a concrete floor

Hi All I have a concrete kitchen floor that is not level enough for my liking. I am about to lay ceramic tiles. It is basically a valley. The high points are along opposite walls, and the low point is 18mm down and about 2.5m from the highest point (roughly 2/3 the way across the room). If I use self levelling compound then I'm going to need 8-10 20kg bags. But, if I manage to reduce the level of just a one metre strip along the high-point wall by 12mm, then all I'll need is 2-3 bags. I have my trusty little angle grinder that I've slowly done a small area by cutting lots of slices and then chiselling the bits out. But do you reckon a grinding cup wheel would be a better/quicker solution? The room is sealed from the rest of the house, and I have a decent face mask. I've made a quick calculation and the amount of concrete that needs to be removed is about 2/3 cubic foot. Ta for any comments or alternative suggestions.
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On 25/01/17 23:21, Grumps wrote:

Do what I did. Buy a spirit level, some string and an awful lot of quick setting tile cement.
And roughly fill in the worst bits with scrap cement and tiles left over from the process as its cheaper to use broken tile and cement to fill that 18mm gap, than straight cement.
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On 25/01/2017 23:31, The Natural Philosopher wrote:

Thanks. That'd work. Or a sand cement screed as John suggested.
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On 25/01/2017 23:21, Grumps wrote:

Sounds like a hard way to do it. I would use a sand and cement screed to half fill the deepest "holes", say bringing them up to only 5mm below level, and then slap half a dozen bags of self levelling latex cement on the top.
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On 26/01/2017 00:57, John Rumm wrote:

Not a bad idea. 3:1 sand cement mix?
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On 26/01/17 08:22, Grumps wrote:

No - like this:
http://www.everbuild.co.uk/image/data/Building%20Products/503%20SBR%20Bond.doc
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On 26/01/2017 08:26, Tim Watts wrote:

That doc says mix using a forced action mixer. How important is this, compared to using a £10/day standard mixer?
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On 26/01/17 10:50, Grumps wrote:

It's not - a regular cement mixer works just fine. I worked to a different document (Cementone IIRC) which did not mention forced mixing.
You could even mix by hand, but mix well and keep the water down as teh SBR acts as a plasticiser so you need less water than expected.
The important thing is to soak the area in 1:1 diluted SBR first and allow to dry, then paint on an SBR/water/pure cement slurry *just* before you apply the screed. This is the primer they refer to (the Cementone document went into more depth).
The end result IME is that the screed is bonded to the top 10-20mm of the substrate.
Don't have high spots as I did in one area, about 10sq inches. It took 30 minutes with an SDS and a scutch comb chisel to cut it back - it really was like iron.
Also - wear gloves and take heed of the cleaning your tools bit in the doc :) This stuff will bond to stainless steel forever - I still have a mixing bowl that has slurry on it.
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On 26/01/2017 08:22, Grumps wrote:

Yup, (possibly with plasters or silver sand - dpending on how thin you want to feather it), and use a good admixture (SBR being idea as Tim suggests)
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On 26/01/17 09:18, John Rumm wrote:

sand + cement alone will crack and lift sub around 20mm
You need sonmethi8ng designed to stay together in thin layers, like levelling compound or - gasp - tile cement.
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On 26/01/2017 10:24, The Natural Philosopher wrote:

With SBR it will stay together at 10mm IME. However we are talking more than that by the time the self levelling is over the top.
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On 26/01/17 00:57, John Rumm wrote:

+1
I would use an SBR regime too - SBR added to the mixing water for the screed, and paint the existing floor with SBR where the extra screed will go.
You can take it down to 10mm without fear of the new screed crumbling and it will bond like iron to the old stuff. Also tile cement loves SBR treated surfaces.
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On 26/01/2017 08:25, Tim Watts wrote:

Ta. When you say "you can take it down to 10mm" do you mean that's the thinnest the screed can be?
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On 26/01/2017 08:37, Grumps wrote:

Yup, sand and cement screeds can normally only go so thin (else the edges crack away when walked on). However you may be able to go a bit under that for something that will be re-screeded in latex since that will protect the edges.
So basically fill all the big holes with sand and cement (+SBR), then cover everything with the levelling compound.
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On 26/01/17 09:21, John Rumm wrote:

That's what I did :)
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On 26/01/2017 09:21, John Rumm wrote:

So, using SBR and Tim's linked doc, the ratio is 3.5:1 plus some SBR. How much sand and cement (in bags) would 1m3 be (not that I need that amount)?
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On 26/01/2017 09:57, Grumps wrote:

One of these will probably do you:
http://www.pavingexpert.com/calcall.htm#focus02
While you are at it, you may find:
http://www.pavingexpert.com/sbr_01.htm
handy...
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On 26/01/17 08:37, Grumps wrote:

Yes.
And you won't do that with regular screed - not without it crumbling.
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I'd say as a first thought, bloody hell, that kind of removal is going to create the mother of all dust problems for years, no matter how careful you are. How did it get to be like this? Brian
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On 26/01/2017 07:10, Brian Gaff wrote:

There would be lots of dust if I went this route, that's for sure.
I think the house was probably built like that. There are no signs of cracks in the floor, although there was subsidence 20+ years ago (that was remedied).
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