bathroom floor - leveling the underlayment

I'm going to lay a good grade of Armstrong sheet vinyl. Its not perimeter bond. Needs adhesive underneath all. My bathroom floor is not level, and unfortunately, angles toward the tub and towards a corner of the tub that is tucked back in a small area between tub and vanity. Being that it's in a rental unit, I'd like to change that. Last tenant didn't think not using a shower curtain liner tucked into tub would be a big deal. I'd like to have the water not all gravitate right next to the tub and the corner where it's less likely to be a *bother* to tenants that don't have their heads on straight. However, I'm not up for tearing out the subfloor to the joists and doing it right. I plan to remodel the bathroom in the future, and that will wait until then. For now, I want a fix that will hopefully last a few years until I remodel.
The bathroom is about 4.5' wide, sloping downward from the left end of the tub to the right. I can't correct the whole thing, but plan to use some pyramiding of 3/16" or 1/4 underlayment material to get the right side where the vanity and deepest corner are level very slightly sloping back towards the left side, so that I don't have water finding it's low point at the edge of the vanity and trying to get underneath it. [The pyramiding will be beneath the final solid sheet underlayment layer that will go from one wall to the next. It will be almost entirely under the vanity and tight space between vanity and tub that will get no foot traffic, except for a few inch transition beyond the vanity.] In this way, I will end up with both sides sloping slightly to the center.
In other words, it won't be perfectly flat. It will gently slope about 1.5' from left wall to about a 1' level area where the person will be standing in front of vanity, and then start gently sloping upwards again for the remaining 2' to the right wall (beginning a few inches in front of the vanity.
So after that unwieldy description, my question is, is this a big deal? Having a perfectly flat floor is supposedly a necessary prep for Armstrong sheet vinyl, but is it *really*? What terrible things will happen if I follow my plans, and what "physics" would be at work? :)
Again, I really just need this to last a few years in a tolerable condition for a rental unit until my resources and *time* are there to remodel.
Thanks!
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I answered your other post. You can float this off with Skimcoat (brand name) under the hardibacker and before the plastic. This will last more than a few years. The risk of not having a "very close to level" surface is buckling of the vinyl. IMO, the dips are more of a problem than a uneven surface.
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Just saw this post which explains the situation in more detail.
Thoughts in random order...
First of all, you don't need to have a level floor, just a flat (smooth?) floor. Bumps, nails depressions, etc. all can "translate" thru the vinyl. If your vinyl is a bit thicker (sounds like it) than it'll be more "forgiving" as far as these depressions, but you still want to get as flat (vs level) as possible. The slope you seem to be talking about (that's going to make it not level) shouldn't matter.
I'd stay away from the hardibacker as it's overkill (you're not putting down ceramic tile) potentially thicker, and more expensive.
Sounds like you don't want to build up this floor too much or it'll differ in height from the rest of the house (based on your planks that ARE the finished lfoor).
Based on the idea I have in my mind from your statements, you might want to try laying down some 1/4" luan over the planks. THen you could get some cement (or similar) to do the build ups in the various areas you want to slope toward the center. You're not building up more the 1/4" from what I read so the cement appropriate for thin applications, or even floor leveling compound is good.
However you do this build up to correct your slope and low spots, you gotta produce a smooth surface with no bumps, ledges, etc. That's why I'm suggesting trowling on someting like floor leveling compound (which is like cement).
I'm suggesting the 1/4 luan so that you don't have an issue with gaps between the planks, to prevent any cement work from dripping down below, and for easier removal (while saving the plank floor) in the future when you decide to remodel for real. If these aren't an issue, forget the luan.
BTW, you can have some decent difference in height between the hall floor (that's presumably right outside the bath door) and the bath floor (ceramic tile might cause this), and they do sell thresholds for these situations. The idea is not to make it such a height that one trips cause it's not flush and not a step.
Renata

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