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ehoman
01-17-2003, 12:26 PM
I'm looking at a job to retile a kitchen floor. The current floor has ceramic tile on top of a subfloor that is 1/2" plywood on 3/4" tongue and grove on 2 by 10, 16 o/c joists. The origional tiles were set in thinset and a number have cracked. Which would be the better approach to install the new tile. 1- Tile over the existing tiles. 2- Remove the old tiles and nail down 1/2" cement board with thin set mortar before I retlile.

If the tiles should be removed what is the best method to remove them?

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bbcamp
01-17-2003, 01:44 PM
The cracks tell you not to tile over them. You have to correct what ever is causing them, or they will be back.

Are the tile adhered directly to the plywood? 'Cause if they are, we've found the problem. Otherwise, your subfloor seems OK. How about the maximum span of the joists? 2x10s are good for 14 feet.

As far as the demo, an electric demolition hammer with a wide chisel seems to be the weapon of choice. You can rent them. You may ding up the plywood, but get the tiles up and let's see what we got.

ehoman
01-17-2003, 02:07 PM
Thanks. The span for the 2x10s is 11' so that shouldn't be a problem. The tiles I want to remove are adhered directly to the plywood with thinset.

Once I remove the old tile some of the thinset, from the original tile setting, will still be on the plywood subflooring. Can I apply a new coat of thinset and nail down the CBU and still have a good bond between the plywood and CBU?

bbcamp
01-17-2003, 02:27 PM
That old thinset will have to be very thin (1/16" - 3/32") so as not to make a bump under the CBU. Otherwise, it should be OK, since you are not trying to bond the CBU to the floor with the thinset, just make a good, solid bed.

Do your best to remove the old thinset so there will be one less thing to lose sleep over. :D

Bill Vincent
01-17-2003, 03:17 PM
BB-- not to start any kind of controversy, but tiling directly over the plywood is not the problem. He has 1 1/4" of plywood in atleast two layers, which is what thinset manufacturers require as a minimum. Being that he has 2x10's under an 11' span, and the recommended subfloor, it would be a good idea to look elsewhere for a problem. I've been tiling over floors like that for years without a single problem related to the subfloor.

bbcamp
01-17-2003, 03:21 PM
Wrong thinset, perhaps?


In any event, the question was to remove or tile over. What's your take?

Bill Vincent
01-17-2003, 03:33 PM
I would say absolutely to remove the old tile, but before retiling, as you suggested, find out the cause of the original problem, first, otherwise it's just going to rear its ugly head again in the new floor.

Bill Vincent
01-17-2003, 03:39 PM
I'm trying to think here (a new experience) what could be causing the floor to crack, being that it sounds like it's a sound subfloor. And Dave G., before you say it, I know it's movement, but how is it moving? The only three things I can come up with are either when the subfloor was laid, both layers were laid the same instead of overlapping them, or the top layer was nailed to the joists, or there's pressure from the perimeter of the floor, but in the third case, you would hear the floor getting hollow and possibly see it buckling before it cracks.

Dog paws
01-17-2003, 03:40 PM
"The current floor has ceramic tile on top of a subfloor that is 1/2" plywood on 3/4" tongue and grove on 2 by 10, 16 o/c joists. "

Does 3/4" tongue and grove automatically mean plywood or could that first layer be plank?

Wrong thinset?
Not enough thinset?
Improperly applied thinset?
No 1/4" perimeter gap for expansion?
Yada yada ?

Bill Vincent
01-17-2003, 03:54 PM
If it was the wrong thinset or not enough, the tile would pop loose, not crack. As for the perimeter gap, that's one of the possibilities I thought of, too, but I would think that again, it would pop the floor up, rather than crack it.

John Bridge
01-17-2003, 04:45 PM
Well, I haven't had a good argument for a couple hours now. :D

I don't think it's a good idea to tile directly to plywood. I was around when the practice took root decades ago. I didn't like it then and I don't like it any better now. With all the neat stuff we have nowadays to separate the wood from the tile, why chance it?

And Dave G. and I and others around here have discussed the attributes of modern plywood vs. the plywood of 30 years ago. The modern stuff is made from spindly trees and sometimes the species are mixed. Even the plywood association has recognized the problem and now specifies that the panels be spaced apart. They've even shortened the sheets a tad to acommodate that.

I repeat. Why chance it?

And another thing. Who says the top layer of a double plywood floor can't be nailed into the joists? I'm not doubting you; I just don't know.

bbcamp
01-17-2003, 06:43 PM
Go get 'em, John! :D

Bill Vincent
01-17-2003, 07:02 PM
John-- As for why chance it-- because 90% of all residential installations up here are done over plywood, and if I refused, I'd starve. As for who said it, I copied this from the floorstransformed forum:

Name: Dave Gobis
Date: January 12, 2003 at 20:04:57
IP Address: Logged
Subject: floor backer board requirements

Reply 6
Engineering studies and field experience have shown that attaching the top layer of underlayment to the joint subjects it to all the stress of the structure including seasonal moisture expansion and contraction. Long term, cracked grout and possibly tile will result. Long term is a keyword. It has been a number of years since the plywood or sheathing industry recommended attaching underlayment to the joist.


any questions?

tileguytodd
01-17-2003, 08:51 PM
Bill, I am so very sorry to hear of your predicament.Having to tile over plywood to be competitive is one of my worst nightmares.I hope it never comes true.Plywood tilejobs have a very high failure rate in my neck of the northwoods.Many people have success.I wont risk it.I'll change careers first.As far as the tiles cracking goes. If the morter has sheared beneath the tile we all know how easily they will break (and or crack) after the fact. These cracks may be attributed to the subfloor ,and in a roundabout way they are.But, if the morter is sheared there is no strength to the body of the tile.Step on it wrong and it will crack. Drop something and it will crack.Roll the refrigerator out and several will crack.
I for 1 based on the very little information available am going to have to side with Bob and John on this one.While there may be additional problems that need to be found,The first and foremost problem is the Method of Install.

Easiest way to remove this floor.Remove a Row of tile. Saw through the Plywood and remove the plywood underlayment with tile still attached. Use large breaker bars etc.If Need be, remove all edge tile and using a toe kick saw,saw through plywood flush with cabinets, walls etc. This tool can be rented.
Install new plywood. 3/4" would be best if you have the room.

Bill Vincent
01-17-2003, 10:00 PM
If plywood installations have a high failure rate, then I must be some kind of miracle worker, because as I stated before, I've yet, in approximately 12 years of installing over plywood, to have a failure as a result of plywood being the subfloor I'm setting over.

cx
01-18-2003, 12:39 AM
I think we're gonna hafta get DaveG in on this, Bill. Are you sure of the context of his comments you quoted above? I know their testing indicates not fastening the CBU to the joists below the subfloor, but I don't think that has anything to do with multiple layers of wood.

I think what they are trying to isolate from the subfloor movement is the dimensionally stable tiling substrate, not a second layer of wood subfloor. I don't think that is the same thing at all.

How about you start a thread about this over in the hangout and we'll get DaveG to hold forth, then maybe we can all get on the same page about this issue without further confusing our customers here on the Advice Board (not to mention each other) :)

Garrett
01-18-2003, 06:44 AM
ehoman, have you inspected the back side of the cracked tiles??? From what I've read, one cause of cracked tiles was that the tile was improperly set in the mortar, i.e., there are places where the tile is not attached or supported by the thinset.

In your case, I would take up that 1/2" layer of plywood and put down either 1/4" or 1/2" CBU, depending upon where I would want the ultimate floor height. Also, if your tiles are 10x10 or larger, I would definitely back-butter the tiles. Just my humble opinion.

As far as tiling on plywood is concern, my opinion is that it is best left to professional tile setters unless there is no option. Probably tiling on plywood requires superior technical skills that many DIY'ers don't have, i.e., selecting the right thinset, mixing it 100% correctly, applying the right amount, etc.;)

Garrett
01-18-2003, 06:56 AM
By the way, ehoman, welcome to the John Bridge Tile Advice Forum. :) Could you give us a first name?

Bill Vincent
01-18-2003, 10:04 AM
CX-- this is EXACTLY what the string that quote was taken from was about. I was having exactly the same argument in the other forum, and Dave came in and posted to back me up. I've been told this for years-- ever since I was taught that layering plywood would drastically reduce the possibility of failure.

Bill Vincent
01-18-2003, 10:07 AM
Name: Bill Vincent
Date: January 11, 2003 at 19:40:39
IP Address: Logged
Subject: floor backer board requirements

Reply 1
It sould be enough subfloor, but there IS a problem. By screwing the top layer of plywood into the joints, you've effectively cancelled out the benefits of using two layers of wood. If a couple of screws hit the joists as you're screwing down the plywood, although it's not recommended, it's not the end of the world, either. But if you purposely try to screw the top layer down to the joists, chances are you'll have problems later.

Name: Davy
Date: January 11, 2003 at 22:45:32
IP Address: Logged
Subject: floor backer board requirements

Reply 2
Peter, is this saltillo unglazed? Have you ever layed any saltillo before? Grouted any before?

Name: Judy
Date: January 11, 2003 at 22:53:45
IP Address: Logged
Subject: floor backer board requirements

Reply 3
Go for the backerboard is my advice. My husband and I are tearing up our 2 year old ceramic floor because we laid it with no backerboard. Thought we had floor level, but apparently not. Tiles cracked and grout came out from day one. More work and expense, but worth it to avoid the redo.

Name: Bill Vincent
Date: January 12, 2003 at 00:19:53
IP Address: Logged
Subject: floor backer board requirements

Reply 4
Judy, I'd be very surprised to find that the fundamental reason your floor failed is because of laying tile on plywood instead of backerboard. There's got to be something else going on there, and I'd strongly suggest you look into it before you end up ripping up another floor.

Name: peter dowd
Date: January 12, 2003 at 19:41:01
IP Address: Logged
Subject: floor backer board requirements

Reply 5
bill, why will screwing down the ply to the joists make things worse. i thought i wanted a very solid floor.
pete

Name: Dave Gobis
Date: January 12, 2003 at 20:04:57
IP Address: Logged
Subject: floor backer board requirements

Reply 6
Engineering studies and field experience have shown that attaching the top layer of underlayment to the joint subjects it to all the stress of the structure including seasonal moisture expansion and contraction. Long term, cracked grout and possibly tile will result. Long term is a keyword. It has been a number of years since the plywood or sheathing industry recommended attaching underlayment to the joist.

John Bridge
01-18-2003, 08:54 PM
Okay, Bill,

Let's take it to the Hangout. Go ahead and start a thread there, and we'll all jump in. Nobody here is doubting what you say, and I suppose it IS controversial. Let's take it out of the shallow end.

BTW, I know Larry Glass over at floors transformed. Good man. I pop in over there once in a while to keep things on track. ;) Lately, that wiley Gobis has been slipping around the net, and I caught him over there a week or so ago. I'll argue with him about the plywood thing too.

But in the Hangout. No more of it here. :)