# Hardibacker thickness for bathroom floor



## oh'mike (Sep 18, 2009)

Marble will need a very stiff floor---the 3/4" osb is not stiff enough--adding 1/2" BC plywood will be needed---then 1/4" cement board set in thinset and nailed or screwed.

These 2x10 floor joists---what is the unsupported length?--( from foundation to beam or from outside wall to bearing wall if it's a second floor)


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## JazMan (Feb 17, 2007)

Mike is absolutely right, you need more strength between the joists. Probably won't meet minimums for joists' deflection either. Let us know what the span is along with species and grade if you can find that info stamped on the joists.

Jaz


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## amakarevic (Apr 12, 2007)

i doubt the beams will be sagging because they are only 12 ft long and there are two load bearing walls on the floor under perpendicular to them (powder room - load bearing wall - hallway - load bearing wall - utility alcove).

having said that do you think the existing 3/4 OSB + maybe 1/2" DUROCK maybe will do? i heard durock is stronger than hardibecker (although i like hardibecker cause it seems easier to cut).

besides, if i did what you suggested, it would be so much higher than outside the bathroom (carpet on top of subfloor) that it would look awkward, kind of like half a step up almost ... LOL


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## oh'mike (Sep 18, 2009)

Backer board adds no strength what so ever--so 1/4" is plenty.
OSB is weak and flexible--add plywood on top or live with cracked stone.

If your joists are 2x12 and the spacing is 16"---and the span is 12 feet---it's a chancy install for stone.

Your deflection is 558-----stone requires 720 and tile 360----good floor but not great,


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## amakarevic (Apr 12, 2007)

so for the 1/2" additional subfloor support on top of the normal 3/4" OSB subfloor, should i use OSB or plywood?

also, since it will be a big jump up when you get in the bathroom, what do you recommend for the threshhold divider, considering it is marble tile inside?

thanks


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## Bud Cline (Mar 12, 2006)

Use "underlayment grade" plywood (Exposure 1).


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## amakarevic (Apr 12, 2007)

thanks, Bud. one more question: for the walls, does that require 1/2" cement board?


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## Bud Cline (Mar 12, 2006)

> for the walls, does that require 1/2" cement board?


Always 1/2" on wall studs, never anything less.


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## amakarevic (Apr 12, 2007)

what is everyone's favorite cement board brand? hardibacker or durock?


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## oh'mike (Sep 18, 2009)

They are both a fine product---I prefer Durrock or Wonder board --but only because that is what I learned many years ago and have never had a failure--

Many installers use mostly Hardi---personal choice--


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## amakarevic (Apr 12, 2007)

Bud Cline said:


> Use "underlayment grade" plywood (Exposure 1).


is this a good kind?

thanks


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## JazMan (Feb 17, 2007)

No, that is sheathing not underlayment. Go down the aisle a little further and you will find it. 
http://www.lowes.com/pd_12227-99999...br|0||p_product_qty_sales_dollar|1&facetInfo=

Jaz


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## Bud Cline (Mar 12, 2006)

What you are looking for should be labeled "underlayment". It will also be "exterior grade". It will also be called "Exposure 1". It will also likely be "B-C". Unfortunately nomenclature varies around the country but "sheathing" definitely is not what you want.


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## oh'mike (Sep 18, 2009)

If plywood were clothing----

Sheathing is like a shirt---it's worn on the sides of a house---to be covered by siding---

Underlayment is like shoes----tough and strong and won't fall apart if you step in a puddle.

For tile---look for BC exposure 1-

The letters mean the quality of the faces--

A-smooth sanded-no voids

b-smooth voids are filled

c-rough small voids allowed

d-nasty--open knots and large voids are allowed


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## mikieb (Jan 17, 2014)

When adding plywood underlayment, cement board, and then tile can create easily over an inch transition between adjacent floors. What wood be the best way to solve this problem?


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## oh'mike (Sep 18, 2009)

I make wood transitions using a table saw and router----works well for most situations---store bought marble ones are an option if you can find a color the looks good--


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