Subfloor thickness requirement for porcelin floor tile


Old 01-31-12, 03:52 PM
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Smile Subfloor thickness requirement for porcelin floor tile

I need a pro's opinion on this 1 1/4 inch minimum thickness under floor tile.
My application is new construction.I have 3/4 inch tung and grove AVANTECH subfloor, screwed and glued to 12inch Engineered I joist(n80), 16 inches on center,with an unsupported span of 9 ft.
I have radiant heat under the avantech.The finished space is an entry hallway that extends 32 ft. with laundry room and bathroom on one end.
I will be installing Engineered hardwood flooring on adjacent floors and want to minimize the hight diference to the tile floor.
If I use 1/4 inch hardee board with my 5/16 tile, my hight delta is 1/16.
If I use 1/2 dura rock , instead of the 1/4 hardee board ,my delta is 5/16, or the thickness of my tile.
Will I have a problem if I shave the minimum by 1/4 inch?

Last edited by Martyk; 01-31-12 at 06:34 PM.
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Old 01-31-12, 06:43 PM
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I have both in my house installed over 3/4" Advantech with a 19.2 truss spacing and have had no trouble with either. The 1/4" Hardee is in our entry foyer which gets less use than the 1/2" Dura Rock floor in our master bath but both are crack free after 10 years.
Old 02-01-12, 01:57 PM
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First things first. Is the tile you are installing ceramic tile or natural stone?

Cement board adds no structural strength to the floor. It only serves as a good bonding surface for thinset and tile. Using 1/4" or 1/2" hardi will not make a difference.

In general, the 1 1/4" rule you mention is for 2 layers of plywood when bonding the tile directly to the plywood (not the best method). If you are using natural stone, you also need 2 layers of plywood, but not so for ceramic/porcelain tile. If you are using natural stone, its also likely that your joist system is not adequate.

So, if you are installing ceramic/porcelain tile. The 3/4" advantec and 1/4" hardi is ok. You could also look at sheet membranes like "Schluter Ditra" instead of the hardi. Its only 1/8" thick and will do a better job than the hardi will.
Old 02-01-12, 04:19 PM
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My tile is Porcelin so I should be ok.

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