I laid out 12x12 marble tiles on top of the hardibacker in my bathroom to determine the pattern and marks for the cuts. There are some areas where there's significant lippage and the tiles rock back and forth. About 4 or 5 tiles out of a total of 25 have this problem, in different spots of the room. I would have assumed that the hardibacker would make the floor perfectly flat, although not necessarily level. How can I remedy this when applying the mortar?? I was told by a friend who owns a kitchen and bath place to use a 1/2 inch notched trowel to help with some of the lippage problems. I'm still worried about unevenness though- even if I try to put more mortar in some spots how can I be sure that it will stay level after it dries?
You're right, that's one reason we have to charge more to install natural stone and rectified porcelain tiles. Takes more time. Sometimes double.
For others, it is impossible for any board or sheet to change the level or flatness of any surface.
You should make the floor flat before you start the installation. You first need to determine how much the floor is out-of-plane. For polished tiles you should try to be within 1/8" in 10 ft. You can use a SLC, self leveling cement, or if 'level' isn't the goal use a trowelable Portland based patch.
Be sure to use the proper thinset mortar, which have you chosen? Half inch trowel may be a little big since the backs of the tiles are flat. Maybe 1/4x3/8" or 1/4x1/2"? But if you fix the floor 1/4x1/4" is best. Again, the proper thinset helps stop drooping after tiles are set.
They also make a few level-installation systems to make things perfect. One that might be good for this small project is LASH by QEP. www.qep.com
TILE GUY - retired- TROY, MI - Method & Product suitability consulting.