Floor tile installation

[Karen O.]

I know tile is to be installed over cement board.  The plan was to install 1/4" durock over the 5/8 plywood subfloor. 

My laminate floor installer took initiative and installed a marble threshold (he was installing laminate in hall) before 1/4" could go down in the bathroom.  The threshold is not coming out without being destroyed. 

Installing 1/4" board would cause porcelain tile to be higher than threshold.

The subfloor is very solid. Would adding a wood preserver before floating a thin layer of floor leveler be a viable alternative to the 1/4" c-board?

I fear the threshold has to come out because he didn't account for the 1/4" durock or the mortar. Or the subfloor has to come out and be replaced with 1/2 durock.

Thanks in advance for your suggestions.

[Jim K.]

@Karen O.

A 4 x 36-inch faux marble threshold that is 3/4 in. thick costs under $20 at Home Depot. That needs to be understood from the beginning. You're going to need to bust the threshold out, and it's not a big deal. Anyone who tells you it is misinformed about the power of a cold chisel and a maul or has something to gain by lying to you. Use the cold chisel to smash and remove the threshold in pieces, and remove the adhesive underneath it. It's not rocket science.

Wood preserver + thin layer of floor leveler is not an alternative to 1/4 in. "c-board." If you want to get all fancy-schmancy about what to call it, it's CBU or "cement board underlayment."

Not too long ago, there were lots of people who would tell you that a thin layer of watered-down modified thinset cement with a layer of chicken wire embedded in it was a viable alternative to CBU. These tile jobs were referred to as "Cleveland mud jobs" in my area and "Jersey mud jobs" in yours. Thankfully, enough of these floors have failed for this to no longer be much of an issue in new flooring.

I disagree with some of @Account Closed's assessment of what should be done. Yes, you should use HardiBacker (we agree that it is a superior product for this application), instead of WonderBoard or Durock. But I believe you should use HardiBacker's recommended installation procedure (please see link for details).

HardiBacker installation instructions

That's a technical disgreement and something endlessly debated among tile installers. It's not so important to solving your problems here. And the rest of what Jonathan writes here is very much correct.

1.  You will need to use 1/4 in. CBU. if you expect the tile to last.

2. The door will probably need to be trimmed on the bottom. This takes a pass with a circular saw. Again, not rocket science.

3. Usually, where laminate meets tile, you have a hardwood transition strip under the door cut to accommodate the various thicknesses of the material. This is usually sold in a tile to laminate transition kit at the big-box stores, and usually costs about $20.

This is not a big deal, Karen. I know you're worried, but in the worst case scenario multiple people here could show you how to easily DIY it and it would be fine.