Levelling over floor boards

[Jonathanb]

looking for some help to level a floor which is floor boards. I didn’t know how out of level they were until I cut some out to drop the shower tray in. Over 1800 mm it’s about 15mm out of level. It was easy enough to level under the shower tray but I can’t lift all the floor boards up and try to level the rest.
Can I lay a tile backer board or Hardie Backer board then self level it? The tiles going down will be Porcel-thin if that makes a difference.

Cheers
John..

 

[Jonathanb]

You can see how far the floor is out by the height of the ply

John

 

[Old Mod]

You’re a joiner aren’t you John?

 

[Old Mod]

And yes,thin tile does make a difference to how flat a floor must be.

 

[Jonathanb]

Yes I’m a Joiner . The floors flat, but badly out of level, there’s no way I can rip the floor out and level the joists. It would be an absolute nightmare to do and I only have so much time off work
I need a over boarding, self levelling type of option
Cheers
John.

 

[Old Mod]

You only need flat, level isn’t so important, unless the direction of fall causes issues.
But it MUST be flat for thin tile.

 

[Jonathanb]

The reason I want it level as you will see it on the edge of the shower tray. The tray will sit above the tiles about 20mm at one end and 5mm at the other
Most people won’t notice it but I will
John..

 

[Old Mod]

Do you suffer fat fumb syndrome John?

 

[Jonathanb]

Fat fumb ? You have lost me on that one

John.

 

[Old Mod]

Yes you can fix 6mm Hardie with tile adhesive and then screw it down, or you can use their new expanding foam type of adhesive out of a can. However that’s brand new product and I’ve not read anything about it yet.
So I’d advise sticking to what we know works, especially with your choice of material.
So use tile adhesive to stick it down first then anchor with screws afterward.
Hardie screws are not the best, a bit like trying to use dry wall screws, they have a habit of snapping.
Most here use Turbo Golds.
Then tape the joints with scrim style tape and fill joints with tile adhesive.
Then you can slc the floor.
You know it’s not self levelling, right?
Make sure you fill any escape route for the slc, otherwise you might find it in your kitchen table instead.
A pinned roller will help remove the air bubbles and level it.
Mix strictly to instructions and let it slake for 2-3 mins (stand) and remix, it should stay that consistency then.
Don’t be a slouch tho, it won’t be long before it starts to turn.
If you keep an eye on it while it’s drying, you will get an opportunity to rub any high spots back before it cures. But you have to watch closely, it’s a small window.
Once it cures, if it has high spots, use a carborundum stone to rub them back.