levelling concrete floor due to subsidence

markyyyyyy · 12 Nov 2020

Over a 4m span, my kitchen floor slopes 3 inches at its most point

I am levelling this up using concrete, followed by self levelling compound.

The floor is currently concrete. Do i literally just dump the concrete on top to level it off, or do i need to apply a primer before?

Once it is level with concrete, i will be using self levelling compound to give it a smooth finish

Thanks

tel765 · 15 Nov 2020

OP,
If your question is still open then come back for a few suggestions?

markyyyyyy · 15 Nov 2020

tel765 said:
OP,
If your question is still open then come back for a few suggestions?

Hi,

Yes still going ahead as planned - i've ordered 10mm ballast and cement.

Was planning on putting timber (starting at high point) along ether side of the room (screwed/nailed to wall to ensure timber level). I was then going to run a piece of timber along these edges while at the same time tamping the concrete down.

Was going to lay the concrete starting at the deepest point? Or is it best to start at the most shallow (highest) point?

Do i need to use a bonding agent? Do i put it on before, or do i add it in to the mix? I'm going to use a 6:1 mix of ballast:cement

cheers

tel765 · 15 Nov 2020

I've not seen the floor but maybe you've jumped the gun.
Given what you say here's what you could do:
1. i'd use the FFL in the next room (dining room?) as my benchmark for the kitchen FFL.
2, You could fix screeding battens - or levelling screeds?
3. Prime the surface with a slurry or a custom primer.
4. mix semi-dry sand and cement and pound each dump down while ruling it off.
5. use kneeler boards to go back on & float the surface smooth.

It maybe that you could fill up the deep area and then finish with bulked up SLC across the whole floor? Depending on unknowns, this would be the best option.

All above assuming you are working in an empty shell/space with no damp issues.
Remember that once you raise the floor you will raise everything that sits on the floor.

23vc · 15 Nov 2020

Whether you use concrete or screed, you’ll get to a minimum thickness like 50mm and have to use a floor leveller and feather it out for the rest of it
The screed is the better idea, but requires a bit of skill, it’s not particularly easy
If you’ve already got a load of ballast, pour that to the deepest bit but don’t go thinner than 50-60mm then get a load of floor leveller and mix with sharp sand for the rest

markyyyyyy · 15 Nov 2020

23vc said:
Whether you use concrete or screed, you’ll get to a minimum thickness like 50mm and have to use a floor leveller and feather it out for the rest of it
The screed is the better idea, but requires a bit of skill, it’s not particularly easy
If you’ve already got a load of ballast, pour that to the deepest bit but don’t go thinner than 50-60mm then get a load of floor leveller and mix with sharp sand for the rest

okay, well i've ordered a tonne bag so i'll just go with that. The drop from living room to end of kitchen is 3 inches in total.
Why can't i go shallower than 50mm with the concrete?

markyyyyyy · 15 Nov 2020

tel765 said:
I've not seen the floor but maybe you've jumped the gun.
Given what you say here's what you could do:
1. i'd use the FFL in the next room (dining room?) as my benchmark for the kitchen FFL.
2, You could fix screeding battens - or levelling screeds?
3. Prime the surface with a slurry or a custom primer.
4. mix semi-dry sand and cement and pound each dump down while ruling it off.
5. use kneeler boards to float the surface smooth.

It maybe that you could take up the deep area and then finish with bulked up SLC across the whole floor? Depending on unknowns, this would be the best option.

All above assuming you are working in an empty shell/space with no damp issues.
Remember that once you raise the floor you will raise everything that sits on the floor.

thanks for your help.

Do you reccommend any particular custom primer?
In terms of bulked up self levelling, are you referring to mixing sharp sand in to it? What ratio of sharp sand do i add to 1 bag of SLC?

I have ordered and paid for a jumbo bag of 10mm ballast so i'll try to use most of that if i can, especially for the deep parts.

tel765 · 15 Nov 2020

google for local available primers - cheap stuff will work.
Sharp or any available sand will do - judge it as you mix and lay - just add a little sand at a time. Read the SLC bag.

23vc · 15 Nov 2020

markyyyyyy said:
Why can't i go shallower than 50mm with the concrete?

it’ll break up/delaminate. To go thin you need much stickier/purpose made stuff like SLC.

^woody^ · 15 Nov 2020

Good luck trying to feather in those 20mm stones.

tel765 · 15 Nov 2020

fwiw 10mm ballast

markyyyyyy · 16 Nov 2020

tel765 said:
google for local available primers - cheap stuff will work.
Sharp or any available sand will do - judge it as you mix and lay - just add a little sand at a time. Read the SLC bag.

Would this stuff do?.

https://www.screwfix.com/p/bostik-cementone-cempolay-universal-primer-clear-2-5ltr/6065p

I've been reading, and If i add sand to SLC I'll need absolutely loads of bags OF SLC to make up 50mm in areas. Surely the 10mm ballast concrete mix would be ok and for anything 10mm and under just use the SLC to give it a smooth edge?

This is the floor I'll be levelling.
It slopes towards the door and is 8cm slope in total from entrance to kitchen to the white door in pic

Or, would another option to be a sand and cement mix? Sharp sand or builders sand?
What ratio?
I can then make the whole floor level using the sand and cement, and then finish off the last 2-3mm with self leveling?

^woody^ · 16 Nov 2020

Will the door open after you've added 80mm to the floor.

Has the cause of the sloping floor been identified and ongoing movement stopped.

You need modified screed to level that floor, not messing about with this and that, hoping that something might do

markyyyyyy · 16 Nov 2020

^woody^ said:
Will the door open after you've added 80mm to the floor.

Has the cause of the sloping floor been identified and ongoing movement stopped.

You need modified screed to level that floor, not messing about with this and that, hoping that something might do

Hi, no the door won't open, as a temporary measure i'm going to cut the bottom of the door, until i get a new door. That's another issue, i will need to raise the door, probably putting a course of bricks in under the frame.

What do you mean by modified screed? Modified in what way? i just think normal screed will do? 4:1 mix of sharp sand:cement....

I will put battons into the walls on edges and use these to run a straight edge over therefore giving a near enough level finish. To finish it off, i'll put some SLC over it in a few weeks time.

^woody^ · 16 Nov 2020

https://www.tarmac.com/screed/screed/sbr-polymer-screed/

What about the door lintel?

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levelling concrete floor due to subsidence

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