angus242

Plywood Underlayment Method F150-09

"underlayment: residential - 15/32" exterior-glue plywood underlayment"

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"If you're good at something, never do it for free."

plazaman

trust me, older homes are built stronger than todays homes. I am in the rennovation business, believe it or not, we demo baths where they poured 10" concrete between the joist and tiled ontop of it. drop a 1/4 ply on top of that.

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angus242

For plywood underlayment, old doesn't = strong. In the Chicagoland area, most older homes have been built with 2"x8" or even () 2"x6" joists. That's not "strong". Not even close. We're talking deflection here.

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"If you're good at something, never do it for free."

CliffHollen

Angus,

As a matter of fact, I laid the tile this morning.

I did propose the two layers of CBU. I was brainstorming. Splinter informed me it wasn't a good idea. I learned something- that's why I come here. I didn't mention it again.

Alex's plan I still believe is solid. In a perfect world where no compromises had to be made I would have pulled up the planks and reinforced the joists and put down new 3/4" plywood and CBU or the like and everything would be perfect and "right".

What would you have me do about the joist defection, Angus? There is evidence in another room that the joists can adequately support the tile. Nothing could further reinforce my confidence in joist deflection than a decade long field experiment. I did my best to best to create a substrate that was both strong and as thin as is reasonable. The potential joist deflection in this bathroom is not going to keep me up at night. I'm still not worried about it.

I used 3/8" plywood and 1/4" CBU and ended up exactly one tile thickness higher than the hardwood. After I screwed threw the plywood into the joists and sandwiched the hole thing it was quite rigid. I wouldn't be surprised if the 3/4" planks plus the 3/8" plywood deflected less than 3/4" ply. I used a bullnose first row and it looks great without a threshold. If the tiles break or the grout cracks, Angus, I will gladly tell you that I was wrong and you were right.

I appreciate the knowledge everyone. Angus, I'm sure I will now ALWAYS remember that 1/2" EGP is the minimum according to you and the TCNA.

-Cliff

angus242

You make it sound like these are my recommendations and that they somehow don't apply to you.

First of all, I'm repeating the specs set forth by the Tile Council of North America....not the council of Angus. If you think your situation doesn't apply, that's your choice.

As for comparing what you did to the tile installation in the other room, apples to oranges, my friend. You cannot tell me that a mud bed installation and 3/8" unknown grade of ply + 1/4" CBU are the same.


So you screwed the 3/8" plywood into the joists?


Again, nothing to do with me. I apparently just wasted my time here with that one. But now you've publicly posted an installation you did that doesn't meet minimum requirements set forth by the TCNA.


You don't have to admit anything to me. I think everything that needs to be said has already happened.

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"If you're good at something, never do it for free."

R&D Tile

Boy oh Boy.

CookeCarpentry

How does one join this "Council of Angus"??

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Mark
Wayne, PA
"It is what it is."

angus242

$35

or simply buy me a beer

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"If you're good at something, never do it for free."

Celtic

Shouldn't it be:

The Council of Noble Angus [TCNA]?

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Splinter

Old homes around here are often framed with 2x8's and drastically overspanned. Load bearing walls are never supported from below, point loads are often placed on the plank subfloor between the joists... I'm glad they dont build them like they used to....

The mortar between the joists is quite common, it's a --sort of-- recessed mud bed, to keep the floor height equal to the other rooms. They really suck to remove.

I'm curious to know what type of 3/8" plywood you installed. Also, did you use thinset between the ply and the Hardibacker?

The TCA-150 calls for 1/2" underlayment, but that's also assuming it's over a 5/8" plywood subfloor. And my '07 manual shows a lack of backerboard in the sandwich.


Not every situation encountered in the field will be covered in complete detail in the TCA guidebook. 3/4" planks in good condition with 3/8" ply and backerboard over thinset is an acceptable subfloor. Would 1/2" be better? Sure, and so would 3/4"...

The joist size and span should have been researched, and if they didnt meet acceptable standards, some structural work would need to be done. Guessing on joist support from the feel of an adjacent floor is unacceptable. Do the next job better, eh?

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- Alex

angus242

Wow, you're on to something there

Maybe I should switch from using Schluter to Noble products. I could market that name. I suppose I'd owe you something though.

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"If you're good at something, never do it for free."

Celtic

Just once, I'd like someone to make good on that and send me a god dam pie!

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olzo55

Angus, you actually READ the TCNA book? I thought you were just ripping pages out for shimming cabinets.

BTW, I'll join the COA (Council of Angus) if we can hold a meeting at the Twisted Kilt. First beer is on me.

on to topic: I'm with Alex. Old houses, at least where I'm at, are not designed as well for floor loads or point loads as todays homes. Some builders still don't build them right but the design criteria is there for the reading. Same with floor installers. The criteria is there (TCNA / deflection calculators) if you choose to use it.

olzo