About to lay Hardibacker on Subfloor w/ mortar

[Edthedawg]

Alan - someone's gonna merge this w/ your other thread about subfloor sistering, i'm sure.

I'm a little concerned that you added a 2x6 spanning underneath all this, but there are still gaps to the pre-existing joists in some places?? If that's the case, then you have flex in the floor still. Shimming those gaps is necessary. I wouldn't start doing any thinset/CBU or thinset/tile installation until that's all taken care of.

Trying to shim later on, after installation, is a sure-fire way for tiles to start poppin' loose.

[Alan D]

The reason I decide to lay it on top of the hardibacker, was because the wall of the tub it not a straight line, It has a shape to it.
I figured it would be much easier to have the hardibacker come out from underneath and join it away from the tub wall, so I would not have to try and cut that shape.

But it would be ok to walk on the hardibacker after i have mortared and screw it in. dont have to wait 24hrs

[Alan D]

Ed,

Why are you concerned about my 2X6 joist span??

Dont worry, I will do the shims before laying the floor, Just trying to get my all my eggs in one basket before the weekend.

Thanks

[Alan D]

whoopsie,

I said 2x6 joist span, I actually was meant to say 4x6

Does that fix your concern

[Edthedawg]

You could park a truck under there. Heck, you could park a truck under each individual joist if you wanted. If the truck ain't touching the bottom of the joist, then it's doing nothing to support the floor and reduce the deflection in the under-engineered system.

If you go down there w/ a stack of shims and a hammer to close up all the gaps, you're gonna wind up invariably moving the floor surface a little. If you've already put any thinset down to hold either your CBU or your tile, then you stand a good chance of inducing cracks and popping and crunching...

Hence the recommendation to get that all firmed up ahead of time.

(4x6 or 2x6 - either way sounds great. Bigger = better, definitely. Just gotta have it in contact w/ every one of the joists down there.)