Gettin ready to tile my bathrooms, laundry and kitchen. Planning on using ultraflex 1 thinset over 3/4 OSB, then 1/4 hardie, then the same ultraflex 1, then tile. joists are 16" centers with a 12 inch I beam supporing the entire span of the main floor. Sound ok? I have read about the evils of thinset over OSB but I also find just about the same amount of data that says its ok. Ive done a little tiling before but Im just a tad nervous. Just looking for opinions. Thanks!

 

Sounds good. Thinset on OSB, then tile is a No NO, but using the thinset to embed the cbu is a must. It gives level stability which you need.

 

I wouldn't put tile over OSB, but that's me.

 

Sam, I am hoping it is advantech or other subflooring as opposed to sheathing, too.

 

The issue with thinset and osb is that you should not bond tile directly to the osb. In this case the thinset is used to fill all the voids between the hardie and osb, not to bond them together. The mechanical fasteners will hold the two together. No problem here using thinset and osb.

 

It will probably be OK. I am just saying, as a pro flooring installer, I won't do it. OSB does not handle moisture well.

 

I appreciate your guys' opinions. If its a disaster it wont be out of place with the rest of my existence . I have the mortar and hardie down, and it seems very sound. At least I really hope so. Thanks!

 

sam floor said.
As others already mentioned, he is not putting tile on OSB. The tiles are going on Hardie.

sam floor said.
On the contrary, quality subfloor-grade OSB is better than plywood in handling moisture during the time the structure is open to the elements. Some are coated with a repellant for that purpose. I still prefer high quality plywood though. You may be thinking of the cheapo $9 a sheet sheathing which does suck moisture.

Jaz

 

JazMan, you know thinset won't adhere to OSB.

 

Wrong! Thin set bonds to OSB very well. Lack of a good bond is NOT why you don't bond direct to OSB. Even regular dry set is good for the purpose of installing Hardie or any other CBU.

Jaz

 

Just to add fuel to the fire, it doesn't matter if the bond is there or not. You are looking for leveling properties for the cbu. Once it is determined and the thinset laid, the cbu is screwed in, you have achieved all you can.

 

Absolutely right Chandler. Although I would not say "leveling", I think "supporting" is a better description of what the thin set does. Many people still don't understand why you need thin set under all CBU's and what it does.

Jaz

 

My understanding of the thinset is support as well - it fills all of the voids so pressure from above (like someone walking on the floor) does not cause deflection movement into those voids.

 

The OSB used as subfloor here falls apart like particle board if it gets wet. I have worked in houses where it was so soft it wouldn't hold tack strip, and that was from rain during consruction.

 

Yeah, but use Advantech or an equivalent, and all those problems go away. It has a wax type impregnation that beads water up during construction so there is virtually no puffiness even after many weeks of rain. We just sweep it off and keep on rollin'

 

How on earth do you think osb will hold thinset over cdx sanded. Have you ever seen osb? I'm sorry Jaz but osb is only good for carpeting in my book.

 

Deflection has to do with joists, size plywood and how it's layed out. If you cover that part right and you put thinset to plywood that doesn't adhere I don't care how many screws you put into the cbu that will be the only movement you will end up in the end is the failed thinset between ply and cbu.

 

Below info is from the James Hardie Website. It clearly includes osb subflooring. Every other cbu manufacturer includes osb as well. CDX on the other hand is not an acceptable subfloor or underlayment for tile and should not be used. Isola I have no idea where you get your info from. Just so that you are aware, it is the mechanical fasteners (screws/nails) that hold the cbu to the subfloor, not the thinset. The thinset is there to fully 100% support the cbu so that there are no voids between the subfloor and the cbu.

For all floors:
• Use minimum 5/8 exterior grade plywood or 23/32 OSB with Exposure 1
classification or better, complying with local building codes and ANSI A108.11.
• Joist spacing not to exceed 24” on center.
• The floor must be engineered not to exceed the L/360 deflection criteria (L/720 for
natural stone), including live and dead design loads, for the specific joist spacing used.

 

All I'm saying is I wouldn't use osb with thinset and yes I'm not afraid to say its possible to use cdx in pretty much any case for flooring and I have not had a tile fail yet with it.
We're are you getting your info from?
It takes engenniers to figures load spans and deflections out no website is going to tell you those numbers based on joist spans.

 

I get my info from the TCA handbook, ansi standards, manufacturers literature and 35 years of installation experience. Where do you get yours.

Heres a website you can go to for deflection calculations just in case an engineer isnt available.

Maximum Span Calculator for Joists & Rafters

Keep installing on cdx and you'll soon have your first failure. cdx is cheap crap and has to many voids within the layers to be used as a substrate for ceramic tile.

 

Cdx is cheap crap but it works & we are in a tough economy. I do give the the option to consumers wether to use cdx and tell them exactly about voids in the cdx.

Thanks for the link

 

a great conversation, I havent logged in a while. Its all down and the fllor meets the deflection specs. Ive been gone so I havent tiled it yet but it feels rock solid with the thinset under the hardie and screwed down per hardie specs. I cant wait to tile it and gwet my kitchen back. If it all fails and cracks and breaks im not above a controlled burn! Thanks for all the discussion.

 

I missed Isala96 comment about my post a while back, mainly posts; 8,9,10 and 16.

Isala96, I doubt you will ever learn the right way to do things. You've shown that for a long time It's not a matter of chocolate or vanilla, you just don't have a clue about certain things.........like how to install tiles in a manner that after much testing and experience is determined by industry experts as the best way to ensure success.

I doubt that if a CDX ply failure happened, the customer would know it was because you wanted to save a few bucks or just settling or other structural movement. And the comment that modified thin set will not bond to OSB is foolish. We do NOT install tile directly to OSB, but thin set (even dry-set), will bond like crazy to OSB.

And how can you axe me if I've ever seen OSB? What are you smoking?

Jaz

 

Osb shouldn't be use in a bathroom reguardles in my book And what you don't know Jaz is mosture will move through osb way more then plywood. Yeah it will adhere to thinset but not for long and cbu won't prevent it from happening. Moisture = expanstion = movement.

 

OK, I think we've beaten this horse about to death