"New" type of tile backer board

Has Art been cheatin' on us? What's this about another board?

Art???

[chip]

I would never cheat on you, ya' know I'm a one forum kinda guy!

Getting kind of possesive, aren't you?

I haven't had time to check in here as much as I would like, let alone hit the other forums.

Prep and paint this week-end. The entire interior. For a guy like me, that should take about 1 1/2 hours. Then I'll lay 1250 s/f of tile on Diag. w/ dots, and go to lunch.

It's off to work I go. High ho, the merry Oh!!!!


Art

Geez, I just noticed the Travelin' Salesman designation.

I like it.

Well, Art, I'm just going to mud a tub deck and a bathroom floor. I wish I had your rate of production!

Rob

[Dave Gobis]

Easy on me Art,
This "uncoupling" word is going to have to get defined in documents a little better. For something to uncouple it would have to have been coupled in the first place. Your right, with dryset it wouldn't bond so it could never uncouple. The theory behind dryset and the reason it remains in the TCA and ANSI handbook is the majority feel it allows a minor interface of stress relief as opposed to forcing it to become part of the structure. The latest studies show that attaching underlayment to the floor joist should also be avoided. APA/EWA says underlayment should be staggered 2" off the lower panel and floor joist. Backerboard will be following suit.

[Bud Cline]

"YES, YES" There's one I won't have to argue about! How 'bout that?

[JC]

Well as long as you are nailing the stuff, regardless of actually hitting a joist or not. Does'nt this indeed increase the margin for error and decrease the effectiveness of the "movement action"?

Just what are the nailing specs for these backerboards again?

Seems the less nails the better if you follow that theory.

The whole thing about having a detached underlayment and then nailing it down just does'nt work well for me. I can see it but only if the nails give out(release) before the finished floor does.

Is this why there are the problems with the hardibacker and wonderboard?

[Dave Gobis]

JC,
Obvoiusly there is some disagreement in the manufacturing community itself on this issue. Here is the way I feel and why. If the substrate actually does meet the L/360 and you use dryset, nails/screws, Stay off the joist, tape the joints, and leave a 1/4" movement joint at the wall line, experience tells me you will not see much if any in the way of hairline cracks in the joints or broken tile unless the underside of the structure has extreme moisture or you are over an OSB substrate.

If the floor is marginal a lot of us want to bond the panel and spike or screw to the joist to stiffen up the floor. Some use or prefer to use 4x4 panels so they can hit the joist and then bond the panel to the floor.

In my contract days of recent past we did both. Long term, we had much less problem with dryset and not hitting the joist relative to hairline fractures. Adding 3 years of answering technical calls confirms that it is indeed less problematic. The reason for all this is compressive stress and tensile stress. If you attach to the floor framing you are now part of the structure and structural stress. Addtionally, if you laminate by using latex modified you have done a similiar attachment but now you are subjecting the panel to seasonal expansion of the wood sheathing plus you have added addtional compressive tension under foot traffic. If it were not for all this movement you could put tile in with 50 PSI thinset and not have an issue. Instead we are using thinsets with shears of 250 to 600 PSI. Why? Cause it's all about stress. Actual bonding is not the issue. That is it before this turns into a book.

[John Bridge]

Methinks you go puttin' a ceramic installation over nothing more than 5/8 ply , even with 2x10s 16 in. o.c., you be askin' for trouble. And if the backer board does not, as you say, strengthen the floor, that's what you're doin'.

You guys have me talked into 1/4 in. backer, but so far it would only be over the trussed floors with 1 in. t&g ply. There's not much bounce to that 1 in. stuff.

[JC]

Thx Dave, that did clear it up for me somewhat.

Now one more question if you have time.
The Ditra specs are very liberal in regards to structural conditions. And as John and a few guys pointed out that even if it says you can over OSB board with wide centers, what about deflection?
How can ditra still withstand a weak floor?

I can see horizontal movement and uncoupling but the bouncing sounds hard to believe.

Am I in error about there specs?

I beleive there specs specify various liberal joist/spacing/wood thickness requirements and these requirements would indicate a less then adequate deflection rating.If I am correct that is.
Now what's the deal with this? Should we go by the Ditra specs or with the L/360 specs?

[Dave Gobis]

5/8 5 ply, underlayment grade ( or CC plugged or better with exterior glue ) will make the performance critera. 5/8 CDX or even the above exposed to weather will not. All the tests on the industry standard were done with 1/2 " backerboard. The 1/4" is a manufacturers proprietary standard. I would not do that installation myself and I don't care who blesses it.

[John Bridge]

JC,

You do bond the Ditra to the floor? That should help a little. I'm not saying I'd do it (I won't).

[Dave Gobis]

JC,
They ( Ditra )will do 5/8 on 16", 3/4 on 19.2 and require a double layer 3/4 and 3/8 on 24". That will provide the L/360 between the joist. OSB properly installed will meet the performance from a load perspective. As for the joist themselves L/360 is part of the Universal Building Code. When it gets to a trus your looking at L/480 commomly in 19.2 or in a 24" application L/600. This is IF they are installed correctly. One common problem is they require bridging or blocking if there is no finished ceiling such as a basement. That is not part of building code but the manufactures instructions. It often doesn't get done and rarely does an inspector catch it. They look at the rating, not the instructions.

[Dave Gobis]

Yes, you do bond it. The Catch 22 is no manufacturer recommends thinset to OSB !!!!! You are required to bond with a thinset suitable to the substrate.

[kalford]

OSB: glorified particle-board

[JC]

Let me get this right.

Ditra can be used over 5/8 OSB at 16o.c and you are saying that will give you enough deflection?

In the above post you said you need 5/8 5 ply to meet the criteria? As long as it is not exposed to weather that is.

Now if Ditra can go over OSB as long as the thinset will permit it. BUT there is no thinset company that will permit it...Where does that leave us?

I used Ditra over OSB in the past because I was told that Ditra was the only floor allowed by the TCA? to go over OSB.

In fact it is a major selling point for new construction projects for me where they used OSB.

Never had a problem.But I don't want to have a problem either.

What gives would YOU feel comfortable useing Ditra over OSB?