Out of Level Floor

[dave2]

Didn't know if this should go here, or under Floors?
I have a utility room which has a concrete floor in it. The room width is 3m but in that distance, the floor is out of level by 20-25mm. Any suggestions in how to level it without taking up the existing screed?
Levelling compound would be the solution, but is it OK for that thickness?

 

[barryo]

Depends what you're going to cover the floor with afterwards. If e.g. T&G floorboards you can do it by shimming the battens that you mount the boards on.

You can't use self-levelling successfully to that thickness. Max approx 3-5mm per coat; if you want more (say up to 10mm) you can add clean gravel to the mix.

You could use a 3:1 sharp sand:cement screed if you're going to cover with carpet/laminate.

Check that existing concrete has DPM underneath and that concrete and screed is absolutely dry. If in doubt lay down a plastic sheet (say 1m2) on the floor for >24 hours and check there's no damp underneath the sheet after that time.

 

[barryo]

Forgot to mention that if you go for sand/cement screed, lay it fairly dry. Should hold its shape when you squeeze it, but no moisture dripping out.

 

[dave2]

I don't want to increase the level at the high point, so want to feather it from 0 to 25mm.
Wi;; be putting the timber floor (the type similar in size to normal laminate flooring).
There is a dpc, the screed is solid and no dampness.

 

[JIM456]

Hi Dave,
If you wan't to use latex screed then it is safe to a thickness of 10-12mm. After that you have to mix in fine washed granite chips into the mix. Build up with a couple of heavy coats with granite chips mixed in, then wash over with an ordinary mix, scraping off to a feather edge at your highest point.
It should be fine for most floorcoverings, although if you were planning to lay linoleum or a ceramic tile theres always a slight risk.
Be sure to make sure it has a good key on the original surface, which should be dry and dust free. Then give it ample time to dry out before laying a timber floor.