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Do I need anything between OSB and backerboard when installing porcelain tile in a bathroom?

The HD on-line project instructions say that when installing porcelain tile, that it should be over exterior grade plywood, but that "Oriented strand board, or OSB, and exterior-grade plywood will work if first covered with a latex-modified mortar and a tiling backerboard."  However, all latex-modified mortar that I looked at says not to put it on OSB.  Do I need a latex sealer on the OSB prior to putting down the mortar and backerboard?  If so, what should I use?  Or if I use a latex sealer, do I even need the mortar under the backerboard?

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Posted 2014-01-17T17:46:59+0000  by ayresclan86 ayresclan86

DO NOT install tile directly over OSB (that's what the thinset manufacturers are referring to).


It's ok to put a layer of thinset between the OSB and backer board.  The backer board should be screwed down according to the manufacturers specifications.  Typically 8" along the edges and 12" in the field.



Posted 2014-01-18T06:06:26+0000  by Adam444

Hey ayresclan86,


Thank you for your question and welcome to the community!


In order for any tile to be placed on a bathroom floor, almost any manufacturer and tile installer will tell you to use tile backerboard over a plywood subfloor. But, there are certain tricks to doing it.


I'm glad you were doing your research, and it sounds like you have a good grasp of the installation process.


You can still use an exterior grade OSB and THEN backerboard, but instead opt for using non-modified mortar alongside backerboard screws to fasten it down. It is optional, but you can still seal the OSB but it really isn't needed.


Make sure the backerboard sheets are installed perpendicular to the OSB sheets to ensure better stability. As for the non-fortified (the absence of latex additives) thin-set mortar, use this one below. It is sold in our stores and is the only one that is not latex modified.


Click on the image for pricing and more information.

Although the bag says use for concrete floors, it can used used over OSB and underneath tile backerboard. Remember you are also using backerboard-rated screws for them alongside the mortar. This is done to ensure the best installation for your porcelain tiles.


You can click on the image below to find out additional information regarding getting a lifetime warranty out of your backerboard, tile, grout, and sealer.


Lifetime Warranty



As long as the backerboard is installed correctly with the information I provided above, you'll really get a tile install that lasts a lifetime.


Please do not hesitate to ask me any further questions, and I hope if this has assisted you.


Posted 2014-01-18T16:02:53+0000  by Joseph_HD_ATL
I have the same question. Was going to buy the above pictured thin set but all the bags were rock hard at HD. I bought VersaBond Professional Thin Set Mortar (unmodified). 
Hardibacker says use unmodified thin set but versaBond says not to use it over OSB. 
Can I use constructions adhesive and then screw down the Hardibacker or should I just use the thin set and screw it down?
I will be applying Schluter Ditra over the Hardibacker before applying the tile.
THanks for your help!
Posted 2017-05-06T21:30:42+0000  by kfaith
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