Floor leveling

[knothead]

I am going to tile a floor that has a hump front to back from a beam that is directly beneath it and want to know what is the correct procedure to flatten it out. Hump is approximately 3/8 high. Should the floor be leveled with leveling compound and then put backer board on top of that or does the backerboard go down first and level it while setting tile? Tiles will be 12x12. My experience with putting leveling compound down first is that the compound tends to break up when fastening the backerboard.

[SLS-Construction]

Level the floor first, then Backerboard or Ditra, then tile

Are you sure the floor is done settling, and does the existing floor meet deflection standards - quick unofficial test, jump up - does it deflect or bounce any / dishes rattle in a nearby cupboard?

[neolitic]

I'm with Sean.
I always want to know the
root cause.

[orson]

You could also use a self-leveling underlayment(SLU) instead of a leveling compound and then set your tiles directly on that.

I use Mapei UltraPlan M20 SLU

Be sure to leave an expansion joint at the perimeter of your leveling compound or SLU in any case.

One easy way to do that is to use foam tape around the perimeter of the room (and just leave in place).

Make sure when you pour the compound there aren't any gaps or holes it can run out of as it will create a low spot as it cures.

Note that "self" -leveling compounds and underlayments are a bit misnomered, take your socks and shoes off and work the product with a trowel until it is generally level and it will do the rest. (Don't forget to have a messy foot landing pad outside the room)

Make sure to follow the manufacturer's recommendations concerning acceptable substrates and liquid bonding agents that may need to be applied so the SLU doesn't delaminate from the sub-floor.