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# Subfloor for marble and ceramic - desperatly needing help

#1
10-09-05, 09:03 PM
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Subfloor for marble and ceramic - desperatly needing help

Hi folks,

It's my first time posting here although I have been reading the forum for a while. I desperately need help with issues described below. I will greatly appreciate any piece of advice.
I plan to put A) marble tiles in the bathroom (~50 sq.ft, rectangular shape) and B) porcelain tiles in the kitchen (~100 sq.ft., square shape).
First of all the status quo:
Relatively new house - 7 y.o., joists are 8x2 about 14-15'' apart supported at 11-12 feet, the floor is particle/chip board either 5/8 or 3/4 (not sure).
It is covered with 3/16 plywood (definitely not 1/4 - I measured it) and vinyl.
Elsewhere in the house I have 3/4 hardwood installed directly on the particle board and I would like the new flooring to be at the same level.
For the forementioned projects A) and B) I have already purchased some 1/4 RhinoBoards from Home Depot:
http://www.custombuildingproducts.co...er=diy&lang=en
I was told that they are equivalent to 1/2 - 5/8 plywood and that I should be fine.
I plan to rip off the vinyl and then the 3/16 plywood that appears to be only stapled anyway. On the particle board I want to lay thin-set mortar and put 1/4 RhinoBoard, on top of that I will put thin-set mortar again and then poreclain or marble tiles respectively. This should allow me to ideally "meet the hardwood level (1/8 thin-set + 1/4 Rhino + 1/8 thin-set + 1/4 tile = 3/4 H/W)
Now the problem that I have is whether IT IS ENOUGH?
I am especially hesitant about the marble which is after all quite heavy but also soft and cracks easily.
What are the correct subfloor solutions for my projects A) and B)?
If I have to live with a reducer I will because the last thing that I want is cracked tiles. I am new to this kind of project therefore any help will be greatly appreciated.

Thanks

#2
10-10-05, 01:04 PM
Member
Join Date: May 2005
Posts: 851
First off, that floor doesn't meet specs for marble, second, are you sure that you have particle board and not OSB, I doubt you have particle board as the original subfloor.

Yes, remove the vinyl and it's underlayment, 1/4" backerboard is fine, don't know what they meant by equal, it doesn't add any strength to a subfloor, it's just there for a backer for tile, set it with unmodified thinset with a 1/4" trowel.

Let's first see what you have for a subfloor, OSB looks like alot of small pieces of wood glued together.

#3
10-10-05, 07:54 PM
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Subfloor for marble and ceramic - desperatly needing help

Thanks Tileman
Regarding the subfloor you right on - it's an OSB - I should get the terminology straight first.
The support for joists is actually at 11 ft.
Also in the basement there is a 4 ft hallway going underneeth a half of the bathroom. That, I guess gives some support with 2x4s to the joists under the bath above at 7 ft., the remaining half is 11 ft.

Can you please elaborate a bit on the Rino board? What is it good for then? So Should I return it and get regular plywood instead and put tiles directly on plywood?

#4
10-11-05, 07:20 PM
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Join Date: May 2005
Posts: 851
I wouldn't tile directly on plywood, the CBU is there for a backer for the tile, that's it, it doesn't add strength to the floor, if strength is needed, that's what the plywood is for.

Plywood strengthens a floor between the joist spacing, joists determine the overall flex in a floor.

#5
10-12-05, 07:14 AM
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Yes, but will 5/8 OSB and 1/4 Rino be sturdy enough for marble or should I add plywood between OSB and Rhino??

Thanks

#6
10-12-05, 12:59 PM
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Join Date: May 2005
Posts: 851
I would add 1/2" plywood over the OSB, then the backerboard, also, that 11' span, is that getting the marble?

#7
10-12-05, 06:02 PM
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Yes - marble goes there.
Well, you're not making me happy with this 1/2 inch plywood...
I hoped to make it flush with hardwood

#8
10-12-05, 06:12 PM
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Join Date: May 2005
Posts: 851
I wouldn't tile that floor with stone , 2x8s at 11ft. unsupported not strong enough, guess you really hate me now.

#9
10-13-05, 11:36 AM
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I guess I do..... grrrrr
Honestly, even if it is supported half way at 7ft?

#10
10-13-05, 01:44 PM
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Join Date: May 2005
Posts: 851
If the span unsupported is 7' that is getting the stone, your fine.

You can not go more than 8' unsupported with 2x8s for stone.