3/8" Travertine Subfloor Specs

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Old 02-25-10, 03:26 PM
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3/8" Travertine Subfloor Specs

I'm installing 3/8" travertine tiles in a 80sf. entry way where I previously had 90 year old hard wood with several old vent opening patched with plywood. There is 3/4" x 7 1/2"w floor boards on top of 2x10 joists at 16oc. Beaming and foundation walls support the joists pretty well and nearby. I was planning to lay 1/4" cement board, 3/8" thinset and then the tiles. Will this suffice?
 
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Old 02-25-10, 08:48 PM
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NO WAY!

First start by measuring the unsupported span of the joists to the inch, and check for condition and also see if you can find a stamping that tells you the species and grade. I know they're old, so probably no luck with that but try. Since they are old, measure the actual size of the joists. Today's 2x10's are 1.5x 9.25, yours may be bigger.

Natural stone tiles require a much stiffer subfloor system than ceramic or porcelain. It is also rare for a home to be built to these higher standards unless the stone tiles are being installed when new. You may have to do some work there.

Then if/once the joists are at par, you will need a sheet of min. 1/2" underlayment grade plywood, then a cement backer or membrane.

Jaz
 
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Old 02-25-10, 10:58 PM
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The joists are 9.5" and the max span is 4ft below. This entry way happens to be in an area where there is a concrete foundation wall beneath that runs through the center of this floor area and another that runs perpendicular through the middle. I ran the numbers on the deflection and appear to be within range. This is a 80sf area.

2x9.5 joists with 4'span
3/4" floor boards
1/4" thinset
1/4" cement board
3/8" thinset
3/8" travertine

Still think I need that extra 1/2" plywood? Please say no...!!

Thanks again.
 
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Old 02-25-10, 11:19 PM
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Hey, it's late, but I've got the late shift.

Yes you need plywood, can't install any backer board on planks. Way too much movement.

BTW, those numbers you have there for thin set are wrong. That may be the trowel you use, but not close to the thickness it'll raise the floor once set.

1/4" trowel for backer ends up adding no more than 1/16".
1/4x3/8 trowel for tiles, adds about 1/8" max.

A good alternative would be to add 1/2" or thicker ply, then use Ditra (1/8" total), instead of cement backer.

Jaz
 
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