Levelling a concrete substrate before tiling.

[ajlelectronics]

Tiles are all up and the water underneath dried out! The substrate is very uneven, with about a 10mm depression (Pussy marks the spot). Also there is an area going into the conservatory which had a concrete step, now removed and requiring repair.
My instinct was to reach for sand and cement at 1:4 and fill or skim as appropriate. However, Internet research tries to tell me that sand and cement mix will always be a bad idea and using mortar mix is even worse because it will crumble.
Area is around 7.5m square and using leveller is going to need 7x 20Kg bags according to my calculations from the back of the No Nonsense Cement Leveller I bought From the dating agency. I don't fancy the expense of that when I have sand and cement in stock, so I would be grateful for some expert advice please.

 

[RobCox]

Firstly, I'm no expert. My experience of preparing a floor for tiling was when we took up the lino tiles from our kitchen diner. They were stuck down with bitumenous adhesive which was impossible to shift. I was advised to screed the floor with latex based screed which could be spread out 3mm thick, which is what I did.

30 years on, the quarry tiled floor is still good, just a bit grubbier.

 

[gaz1]

just use quick drying floor tile cement float it level it will be set in an hour and carry on after that

 

[julianf]

Watch out for "self leveling" compound.

In my experience, self smoothing would be a better name for it. Self leveling, in my experience, is not what it does.

I used it once, and then for all subsequent jobs, I've gone with sand and, normally, lime, but cement would work, I'm sure.

 

[julianf]

A trick to get levels across an awkward job -

Screw in screws at points across the job. Screw them in and out to level up a level.

Get them to the point where you know they're all the same.

Lay the job, and remove the screws.

I'm sure there are many other ways also.

 

[Neilj]

10mm is a bit thin for sand and cement, it won't have a lot of strength. Far better to use latex compound. Where was the water coming from?

 

[ajlelectronics]

Where was the water coming from?

A very good question; I was only told about it by 'indoors who took it upon herself to lift the tiles and so give me another job I didn't want! **
My assumption is that it was cleaning water that had got underneath through missing / damaged grout but otherwise I am stumped.


** I got home to find the concrete block largely gone, her using my Bosch SDS chisel (after breaking another chisel bit). I picked up the drill body and got a nasty burn off the handle because she had run it to within a whisker of its life!

 

[ajlelectronics]

10mm is a bit thin for sand and cement, it won't have a lot of strength.

That is a far more sensible reason. Didn't know that and I think you are telling me to go to the dating agency and bend over (again)?


I will use a 1:4 cement : sharp sand mix to repair the damage where the step was removed.

 

[brightspark]

That is a far more sensible reason. Didn't know that and I think you are telling me to go to the dating agency and bend over (again)?


I will use a 1:4 cement : sharp sand mix to repair the damage where the step was removed.

give it a coating of sbr bonding agent before you lay it . its water proof bonds to damp substrate and seals. lay covering while still wet

 

[mike os]

If you want to do it properly get a decent leveller, fine flow 3000 or levelflex are my go to.

Prime with sbr following the instructions on the container

Mix the levelling compound with the maximum permitted water, don’t exceed it.

Buy or borrow a spiked roller


Watch a few YouTube vids

Do not use sand and cement unless you want a crap job that you redo soon

If there is water coming through it will show as damp on the leveller, in which case apply a liquid Dpm

Edit:

The flatter you get it the easier and better the tiling gets, but if it’s within 6mm tiling is much easier than bigger , 4mm is a doddle.

Use a tile levelling system, it’s not worth the fee quid saved not to

 

[brightspark]

If you want to do it properly get a decent leveller, fine flow 3000 or levelflex are my go to.

Prime with sbr following the instructions on the container

Mix the levelling compound with the maximum permitted water, don’t exceed it.

Buy or borrow a spiked roller


Watch a few YouTube vids

Do not use sand and cement unless you want a crap job that you redo soon

If there is water coming through it will show as damp on the leveller, in which case apply a liquid Dpm

as above you can prime with sbr 1st and let it set then a wet coat when leveling that is then the dpm

 

[Neilj]

A very good question; I was only told about it by 'indoors who took it upon herself to lift the tiles and so give me another job I didn't want! **
My assumption is that it was cleaning water that had got underneath through missing / damaged grout but otherwise I am stumped.


** I got home to find the concrete block largely gone, her using my Bosch SDS chisel (after breaking another chisel bit). I picked up the drill body and got a nasty burn off the handle because she had run it to within a whisker of its life!

That's ok, I was just wondering if the floor was damp under the tiles that was all. As others have said, hit the floor with a few coats of SBR (not PVA) and lay your coating when the last coat is still wet it will help things flow and level out (self levelling doesn't self level very well as already mentioned!). If you've got a decent area to fill to 10mm depth you could use 1:4 sand / cement to bring that up close to finished level and then a bit of latex compound over the whole area to level it. I find sand / cement tends to rub up whereas a latex compound is very fine and is far more hard wearing. Also depends on what your finished floor is going to be as well, is the repaied section going to see foot traffic or are you covering it with say tiles?

 

[mike os]

Unless you can apply at least 40mm do not use sand and cement…

 

[500e]

I expect the No Nonsense Cement Leveler has further instructions, it seems to be self motivating which can be quite wearing.
The quick drying would be my go to

 

[mike os]

Some flow better than others …

 

[RWD3M]

A very good question; I was only told about it by 'indoors who took it upon herself to lift the tiles and so give me another job I didn't want! **
My assumption is that it was cleaning water that had got underneath through missing / damaged grout but otherwise I am stumped.


** I got home to find the concrete block largely gone, her using my Bosch SDS chisel (after breaking another chisel bit). I picked up the drill body and got a nasty burn off the handle because she had run it to within a whisker of its life!

I think before you splash out on any levelling compound, sand or cement, you need to invest in some new security for your tools!

 

[gaz1]

A very good question; I was only told about it by 'indoors who took it upon herself to lift the tiles and so give me another job I didn't want! **
My assumption is that it was cleaning water that had got underneath through missing / damaged grout but otherwise I am stumped.


** I got home to find the concrete block largely gone, her using my Bosch SDS chisel (after breaking another chisel bit). I picked up the drill body and got a nasty burn off the handle because she had run it to within a whisker of its life!

ive chuckled about this since you said it

my assumption is she didnt like the tiles so up they came due to them being unlevel didnt look right in her eyes

good on her for getting on with the job though now its your turn to finish off

 

[colnerov]

On the contrary if she's started it let her finish it, whether you heckle comment from the sidelines is up to you. Let us know how that goes.

 

[mtt.tr]

What people miss with self leveling is it will only manage X thickness at a time try to much you get a mess

 

[mike os]

What people miss with self leveling is it will only manage X thickness at a time try to much you get a mess

Definitely no more than 50mm