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Unread 05-28-2020, 05:06 PM   #31
ss3964spd
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Quote:
Originally Posted by Vignesh
...why would a hardiboard on top of plank isolate movement just like plywood on top of plank?
Because the manufacturer does not state that installing Hardie directly over planks is an acceptable method, it suggests it wouldn't. That your previous tile installation survived with just such an underlayment is probably an aberration. The manufacturers test a lot of configurations, then determine the best installation method that will virtually assure success in all circumstances. It amounts to a CYA exercise for them; claims wise and reputation wise. IMO, natch.

Installing anything outside of manufacturers and industry recommendations/guidelines is a risk. Can it work? Sure. I installed tile directly on plywood in my laundry room 4 or 5 years ago and it's still there; no cracks and all are still stuck, the grout isn't disintegrating. My rational for taking the short cut was "it's juuust a laundry room". Will it still be in great shape 5 years from now? I dunno.

If I'd done it correctly I would know.
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Unread 05-30-2020, 02:49 PM   #32
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Thanks Dan . you are correct. Doing it the right way makes sense.

Your reasoning and to avoid the excess lip, im thinking i should rip out the plank subfloor, put in a 5/8" OSB and use hardiboard on top.

Let me know if you think thats not a good idea. Im ok for the excess work. i would take the safe approach instead. My joinst span is 14" between joists.
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Unread 05-30-2020, 04:05 PM   #33
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Vignesh, keep in mind also that there was a time when James Hardie did recommend installing his backer board over sawn board subfloors. He changed that recommendation years ago and I bet you can guess why.

Quote:
Originally Posted by Vignesh
My joinst span is 14" between joists.
That would be your joist spacing rather than the span and I would guess it's closer to 14 1/2" between joists, indicating a spacing of 16" on center.

You also need to know the unsupported span of your joists as well as the species and grade to effectively calculate the design deflection.

If you elect to remove the existing subflooring I would suggest you use nothing less than nominal 3/4" exterior glue, T&G plywood with no face of grade lower than C or a similar OSB product. I would not even consider anything thinner.

My opinion; worth price charged.
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Unread 05-31-2020, 06:13 PM   #34
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As an aside, unless Schluter has changed things up, light blue membrane is not Ditra. Could be a similar product, but I think if it was sold to you as Ditra, you got ripped off! Maybe I'm missing something.
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Unread 06-03-2020, 10:48 PM   #35
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no it wasnt DITRA. It was Dural, but i also have DITRA 1/8. I was just using Dural to show that I am off a lil. Both Dural and Ditra are 1/8 thickness
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Unread 06-03-2020, 11:08 PM   #36
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Sorry. Yes Spacing = 14". Unsupported span = 13 ft.

Current plank subfloor is only 5/8". I am afraid if I use 3\4 instead, I will go over the adjoining wedi board in the shower area.

i have to do some measurements to see if I really can go with a 23/32 T&G board + 0.42" hardi cement board and be at the same level as the Wedi Shower pan.

I am only thinking about removing existing subfloor so I can get pefectly level with the Wedi board (by avoiding DITRA). Else I don't think its worth the hassle.
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