switching type of thinset on subsequent CBU panel [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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01-08-2003, 06:21 PM
Hi all, I have some update photos I should send of my tub/shower project. It still needs to be grouted, but it turned out fine.

Okay, the topic at hand: I am in the middle of laying CBU's on my OSB bathroom subfloor, so I can tile it. So far, I have been using Master Blend thinset mix, modified with acrylic latex admix, then attaching with hardibacker screws. I have done 3/4 of the floor, but I ran out of Master Blend. I have one more panel of CBU to put down.

Should I drive 20 min to HD to buy some more Master Blend, or can I use the Versa Bond I already have here? If I can use the Versa Bond, should I mix it with water or latex?


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01-08-2003, 06:41 PM
The thinset under the CBU is really for filling the minor voids between the floor and the CBU. No bond is required, therefore there is no need for modified thinset (latex). So, I guess this means "get back to work, no trip to HD for you!" :D

01-08-2003, 07:13 PM

Okay...back to work.

John Bridge
01-08-2003, 07:34 PM
You better get those pictures in here, Victoria!


01-09-2003, 05:27 PM
Hi John!

Okay, I'll send those photos :)

Just wondering...will the thinset + latex between the OSB subfloor and the hardibacker help keep water away from the OSB when my two boys flood the bathroom floor?

Bill Vincent
01-09-2003, 06:43 PM
It won't keep the water away, but your necessity for concern is dependent on whether it's really OSB, or particle board. If it's particle board, then you might consider putting a waterfroofing membrane over the CBU. If it's OSB, their big claim to fame is that in testing they were submerged in water with no ill effects, and although I wouldn't want to put them to that extreme a test, I wouldn't worry about it, either.

John Bridge
01-09-2003, 07:35 PM
I got your pictures, Vic. Looks like a shower! ;)

John Bridge
01-09-2003, 07:38 PM
And here's the current state of affairs. I think it's going to be a wonderful shower. I do like the style. ;)

01-09-2003, 08:03 PM
Thanks! I am quite pleased, as a matter of fact. And after grout, drywall, more quarter-round trim, and fixtures(!) it'll be much nicer. I just got a toilet (as I was typing, the UPS guy dropped it off) and I have just discovered it is an identical color match to the trim tile! I am so happy, cause with white everything, I wanted the toilet & pedestal sink to provide a little contrast.

Yes, my subfloor is OSB (oriented strand board, the real McCoy) and the guy at the Tile Council of America (after reading it in the HD tile book-go figure) told me that OSB is not good under wet areas & to thinset some 1/2" backer board over it before tiling. What kind of membrane could I put over the CBU and under the tile? Anything that is available at HD?

My boys are really wild in the bathtub and do flood the floor!

Thanks for all this great advice!

John Bridge
01-09-2003, 08:28 PM

There are all types of waterproofing membranes, some brushed or rolled on and others that are a fabric or mat. I think one of the best ideas is Schluter Ditra. It not only will waterproof the floor, but it will enhance the mechanics of your tile installation as well.

And it's user-friendly. Say hi to Missy. Missy is the national accounts manager for Schluter Systems.