Floor Height/Level Issues

[CoastalE]

Hello all.
I have a rather large project that I am working on and need some real world advise. Here is the what is going on:
We have 1100sf of plank tile(8in x 32in)to install in a commercial project. The building is built in the 70ies with standard wood construction. The sub floor is 3/4 exterior grade ply(t&g) nailed over 2x12 at 16in. We need to go up 1in including tile of 3/8 thick. The have old doors with 1in thresholds.
My plan before demo was 1/4in hardy board thin-set and screwed as per recommendations. Then install the Latacrete Strata mat XL (5/16 thick) which will get me a little over 1in depending on how much thinset I use.
Then after demo my plan kinda fell apart as nothing is even close to flat let alone level. I did a test area of 12x8ft with levelor and it took an excessive amounts to get it correct.
The floor has multiple rises and fall up to 3/8 along the long length we are installing the tile. I still have 1100sf of untouched area to figure this out.
My options with existing materials(1/4hardy and strata mat):
1. Apply levelor between the sub-plywood and hardy backer with primer. Then install the 1/4 hardy with screws. Worried that screws will not penetrate the levelor or break up the levelor.
2. Float the floor with thinset on top the stata mat as best a possible. Then final height set as installing tile. (very time consuming)

Scrap that plan with the thick Strata mat.
1. Uncoupled motar bed with metal lath and using the thiner normal strata mat. The mortar bed will be 1/2in thick. I think the minim thickness is 3/4in.

The owner is very adverse to change orders

Any advise would be welcome.. I need to start this part of the project this week...

[cx]

Welcome, Eric.

Nothing you've suggested there meets any manufacturer's requirements nor tile industry standards, best I can tell.

1. What is the intended use of this floor?

2. What is the species, grade, and longest unsupported span of the floor joists?

3. Given that you're apparently well short of the industry standard requirement for flatness for those large format tiles, have you considered one of the self-leveling compounds over the entire floor?

4. If you're required to adhere to that total thickness requirement, have you considered recommending a different floor covering?

5. You say the customer is averse to change orders, but what's being changed? What are the current specifications?

[CoastalE]

Thank you for answering.

Answering your questions.
1. What is the intended use of this floor? It is a lobby of a hotel.

2. What is the species, grade, and longest unsupported span of the floor joists? Not 100% sure of this but I can find out. maybe the span is 16ft for most of the floor and the joist are 2x12. Have no Idea about the grade of the joist. Built in the 70ies so assuming better than what we can buy now.

3. Given that you're apparently well short of the industry standard requirement for flatness for those large format tiles, have you considered one of the self-leveling compounds over the entire floor? Yes but it would have to be min 1/2 with a about a 30% at maybe 3/4-7/8.. That is a lot of self-leveling compound so worried about that much weight. That is why I as trying to use the Strata Mat XL so there would be some voids instead of 100% solid.

4. If you're required to adhere to that total thickness requirement, have you considered recommending a different floor covering? Yes but it is a AOAO and they take forever to come to a decision.

5. You say the customer is averse to change orders, but what's being changed? What are the current specifications? Unforeseen conditions of the subfloor. The specification is plank floor with 1/16th epoxy grout.

[Sharon @ LATICRETE]

Eric - have you given our Technical Services Team at LATICRETE a call yet on this project? They can go over the specifics and help to determine an approved method. They can be reached at 1.800.243.4788 x1235

[Fast eddie part deux]

Why do you have to raise the finished floor an inch?

If you have uncovered a hidden condition that prevdnts you from installing what thd contract documents call for, then you should notify the owner and/or architect in writing and ask for direction. If they leave the solution to you, then you need to provide a proposed solution with cost differential, and wait for direction. You also need to advise the person who your contract is with that you are being delayed and may not meet the schedule.