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Old 09-20-2012, 02:44 PM   #1
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thinset b4 cement board on OSB?


a couple of my buddies, who often do flooring work, told me not to put the cement board in a bed of thinset before tiling. they said to glue the cement board to the OSB then screw it per instructions. they all said the OSB will absorb the water out of the thinset and swell like a sponge and start popping tiles. true? if so, what glue do i use? ive got 2X10 floor joists then 1X8's then 3/4 OSB...am going to use 1/2 in backerboard.

second, what size trawl do i use on some 6X24 wood plank porcelain tiles? .25 or .5?

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Old 09-20-2012, 06:15 PM   #2
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thinset b4 cement board on OSB?


Use the thinset----they are wrong----the thinset is there to fill any voids and keep the backer from flexing----

To verify what I said --read the tcna manual---or look at the instructions for Durrock---

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Old 09-20-2012, 08:19 PM   #3
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thinset b4 cement board on OSB?


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a couple of my buddies, who often do flooring work, told me not to put the cement board in a bed of thinset before tiling. they said to glue the cement board to the OSB then screw it per instructions. they all said the OSB will absorb the water out of the thinset and swell like a sponge and start popping tiles. true? if so, what glue do i use? ive got 2X10 floor joists then 1X8's then 3/4 OSB...am going to use 1/2 in backerboard.

second, what size trawl do i use on some 6X24 wood plank porcelain tiles? .25 or .5?
I read on JB's site that you should not use OSB when tile is involved. Can someone confirm that is the case?
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Old 09-20-2012, 08:28 PM   #4
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thinset b4 cement board on OSB?


I would try a .375 trowel frist, but have a 1/2" handy.
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Old 09-20-2012, 08:42 PM   #5
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thinset b4 cement board on OSB?


Quote:
Originally Posted by deputy View Post
a couple of my buddies, who often do flooring work, told me not to put the cement board in a bed of thinset before tiling. they said to glue the cement board to the OSB then screw it per instructions. they all said the OSB will absorb the water out of the thinset and swell like a sponge and start popping tiles. true? if so, what glue do i use? ive got 2X10 floor joists then 1X8's then 3/4 OSB...am going to use 1/2 in backerboard.
Sorry, but your buddies don't have a clue in this case. But, is this 3/4" OSB subfloor grade or cheapo generic, what brand? All CBU are required to be set into fresh thinset mortar, fastened and seams taped.

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second, what size trawl do i use on some 6X24 wood plank porcelain tiles? .25 or .5?
Neither of those. How about .375. So, 1/4x3/8x1/4.


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Originally Posted by garlicbreath
I read on JB's site that you should not use OSB when tile is involved. Can someone confirm that is the case?
Perhaps you miss understood what someone was saying. OSB as a subfloor is fine. You install a backer or Ditra then the tiles and you're good. What they were saying, (or should have been saying), is that you can not install tiles over OSB.

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Old 09-20-2012, 11:39 PM   #6
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thinset b4 cement board on OSB?


its going on top of 3/4" OSB t&g screwed down to the joists through the 1X8's with 3" screws. the floor is about 160 or so sq. ft. and i used almost 5lbs of screws. the markings on the OSB is Blue Ribbon 22/32" THIS SIDE UP...got it from lowes.

Looking at my sub-flooring job, i accidently have one board flipped over...does it matter?

Last edited by deputy; 09-20-2012 at 11:47 PM.
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Old 09-21-2012, 08:19 PM   #7
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thinset b4 cement board on OSB?


Deputy,

It's best to fasten the underlayment only to the subfloor and not the joists too. This allows a bit of separation from the twisting of the joists. Not the end of the world if you already installed the 3/4" ply since you'll have another layer over it.

We normally have you tell us how the framing is built and with what materials. Give us the; type and size of the joists, (2x10 in your case), their species and grade will help a lot, on center spacing, (usually 16"), and the span, to the inch. We will refer to a span chart and let you know.

I wouldn't worry about that one sheet much. BTW, can you confirm exactly which Blue Ribbon OSB product you bought?

Jaz

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