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Old 11-23-2008, 01:56 PM   #16
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OSB to durock install


Thinset CAN BE USED to install CBU over OSB. It's not there to bond to begin with.
Thinset CAN NOT BE USED to bond tile directly to OSB.

Read all the bags you can find they all say the same thing.


Last edited by Bud Cline; 11-23-2008 at 09:11 PM. Reason: correct dumb spelling
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Old 11-23-2008, 07:37 PM   #17
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OSB to durock install


Andy,

There is no contradiction in using thinset to install backer board or even bonding Ditra to OSB and the directions not to "bond direct to....... They are talking about not bonding ceramic direct to the OSB, not that modified thinset will not stick well to it. Modified thinset bond great to OSB, it's just that OSB is not stable enough to use as an underlayment. Installing a CBU or membrane changes all that.

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Old 01-05-2014, 08:41 AM   #18
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OSB to durock install


Just to clarify, I can apply modified thinset to the seams of durock? I am going to redgard before tiling.

Or would unmodified thinset be fine since I am using redgard?

Thanks!
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Old 01-05-2014, 09:06 AM   #19
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OSB to durock install


I suggest you use modified thinset for any filling and taping---this is what you will be using to set the tile over the Red Guard any way--so why buy a second product---

Be sure you use a thin coating---creating a hump will cause lippage when you set your tile---
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Old 01-05-2014, 09:11 AM   #20
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OSB to durock install


Thank you! That is what I thought, but I wanted to be sure. Appreciate the quick reply!
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Old 01-05-2014, 12:11 PM   #21
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OSB to durock install


Sig,

Sounds like you're doing a tub enclosure or stall shower, yes? Did you happen to have some unmod left over from another project?

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Old 01-05-2014, 12:33 PM   #22
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OSB to durock install


Jaz,

Yep, going a stall shower install, I don't have any unmodified, but you can buy the small bags of it, just to do the seems for the durock, I wasn't sure if it was acceptable. I need to buy modifed anyway for the tile, so I just got it as well.

Thanks for the reply!
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Old 01-05-2014, 01:06 PM   #23
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OSB to durock install


Quote:
Yep, going a stall shower install
OK, good. Most showers are not built completely right, (even by the so-called pros), are you up to speed on the details? The floor, lower walls and curb are the most critical for a shower and where 95% of the mistakes are made.

Wanna share your plan in detail? Tiled floor or molded pan floor?

Jaz
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Old 01-05-2014, 02:23 PM   #24
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OSB to durock install


Jaz,

There was a corner shower unit installed prior. The unit started coming off the walls, it was just glued onto the drywall, this is when I first started to realize I had a problem. Upon removal and further inspection, the drywall behind had rotted away and the got underneath the plastic shower pan and started to get to the sub floor.

I decided to rip every thing out and start fresh. I was down to the studs and subfloor, cleaned it and let it dry for about two weeks (thankfully the house is only 6 months old and I noticed it in time). The subfloor was still sound.

I installed Durock in the shower surround from the floor up 7 feet. I used tile-ready inserts for the shelving unit. I am using modified thinset for the seams, and will apply 2-3 coats of RedGard at 30 mils. I will install and pvc based (Oatey) pan liner to the sub-floor then do a pre-slope pour for the shower pan, redgard, final slope, redgard, then tile over the redgard on the floor and walls using modified thinset.

On the floor outside the shower, I have removed all existing tile, thinset and cement board, I am going to use an UNMODIFIED thinset to apply Ditra then tile over the Ditra with a modified thinset.

On a side note, I also siliconed all the screws in the durock and let dry prior to sealing the seams with modified thinset.

Think that sounds okay, any suggestions?

Thanks!
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Old 01-05-2014, 02:29 PM   #25
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OSB to durock install


As far as the curb is concerned, I used 3 2x4 wrapped in pvc pan liner and used Mark-E-Industries Kirb-Perfect plastic form to provide the appropriate cement backing the tile.
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Old 01-05-2014, 03:52 PM   #26
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OSB to durock install


Quote:
Originally Posted by sig
(thankfully the house is only 6 months old and I noticed it in time)
What?

Quote:
Originally Posted by sig
I will install and pvc based (Oatey) pan liner to the sub-floor then do a pre-slope pour for the shower pan, redgard, final slope, redgard, then tile over the redgard on the floor and walls using modified thinset.
Where did you get this procedure? Too many things going on here.

Why use the pvc shower pan membrane and also Redgard? Gonna create a moisture sandwich.

The pvc pan does NOT go right on the subfloor if you wanna do it right. You want the pre-slope first, then the pvc membrane, and finally the finish deck mud for the tiles. This is the traditional method.

If you want to use a liquid membrane you do not also use the pvc. Does someone now recommend that? Where did you get that info?

I only use the Kerdi Drain & Kerdi Membrane method, but 10 years prior used the traditional method. Kerdi and surface waterproofing is the best way.

Quote:
Originally Posted by sig
On the floor outside the shower, I have removed all existing tile, thinset and cement board, I am going to use an UNMODIFIED thinset to apply Ditra then tile over the Ditra with a modified thinset.
By your description the floor is plywood or OSB. You've got the types of thin set required backwards. You'll be very unhappy if you use unmod for Ditra over ply or OSB.

No reason to silicone screw heads or seams. Now the Redgard may not stick to it. You may not know it but, paints, adhesives etc, do not bond to silicone.

Jaz
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Old 01-05-2014, 04:32 PM   #27
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OSB to durock install


You're correct about the thin set, error in typing, modified to bond to osb. I suppose I could just preslope onto the osb, figured it would give me a barrier to protect the floor.

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