to cut or not to cut? the suicide tile floor job

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ShowerDude

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I have to tile this foyer/entry w/6x20 porcelain wood tile its rated i believe as C1 or commercial floor rated. 3/8"nominal thickness.

The client demands it time out with their old 3/4 hardwood.

Its currently a failed mosaic over a thin mud bed on top of roughcut 3/4"x 8"cross planking....... this mudbed cant be much more than 1/2"!

The joist system is, with its span and not including the sisters rated at L/1955 OFF the charts....yet this vintage thin mud bed is failed and tiles have been popped up and grout. But it lasted nearly 70 years or so!

heres a few pics and a crude sketch of my proposed cleating of joists to recess new subfloor and build up from that. Ill now have 1-5/8+ to add cross grain 3/4" exp 1 ply uncoupled from joists, and topped with im thinking strat mat which ill tile on and easily time out with the origional floor.

The big question regardless how good my blocking /sister system is " CUT or not to cut" out the old cross planking and cleate in a recess to build up from.

Or screed another even thinner reinforced mudbed ( suicide)

The clients been educated, they understand the risk vs. reward and the wife absolutely needs her floor timed out with that wood floor.

Roberto? John? vegas? !! (vegas!)

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mat kristi subfloor plan.jpg
 
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DougB

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Both my engineering and computer science degrees - tell me - don't mess with that diagonal sub floor - it works. I've learned not to mess with things that work.

The bath room floor that I replaced was similar in design. I think they call it a jersey mud job - frowned upon. However my bath room floor was 65 years old - and was perfect. It was damn hard to rip up - just metal lath stapled to the subfloor and cement? I don't know if they had thinset in 1950.
 

ShowerDude

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So Doug being a smart man quickly spots the dangers.......nice eye Doug.

So lets say we go old school 15#felt 2.5 staple lath and add to It A latex modified 1/2"mudbed?

Also very scary for the tile setter....

Now i may be able to go with a scary combo of 3/8 exp 1 ply with say noble cis over the cross plank. Still not approved by any standards....

So many ways to attempt this......none approved.

If i look to standards i need at least 5/8 exp1 ply and a membrane on top of that ...... Now were looking At reducer thresholds and the unhappy wifesituation

Normally I run......and look to Ansi and TCNA and science here AKA deflection ratings...
 
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ShowerDude

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I feel like at the school test :D


Well Roberto, if we were at school you would be teaching us all... You have the master tilers years of experience behind you.......

This is a friends home, he is a scientist and has a say in how we build this floor up...... We are ready for a challenge, dare i say breaking some rules as well!!!

Dare I ???on this web forum!

Lets hear? how you would approach this ? Rules aside...???
 
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Eurob

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I won't bite .......... rules are hovering over me ........... I am doomed !!!


To cut or not to cut ......LOL

 
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Jadnashua

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Dimensional wood changes with seasons aren't as big if the house has a/c and can maintain a good humidity level throughout the winter as well. Hassle is, someone leaving for vacation, turning things either off or down, the changes in dimension can wreck havoc with directly bonded things. A way that will work is to cut out the planks, recess the first layer on cleats as you indicated, then a full coverage layer of ply with an approved tileable layer (cbu, or maybe an uncoupling membrane). As many know, sometimes you can get away with not following the guidelines, but what some do not want to deal with is that the failures often can take a long time - occurring a little bit at a time until it finally lets go.
 

ShowerDude

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But yes Roberto clear access from below with
Clean joist bays really nothing in the way and good access......
 

JohnfrWhipple

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I would be asking myself why the old floor failed now. That is the elephant in the room.

Has there been any changes to the home? Any walls moved? Did you have a new roof put on?

For the old tile to fail over that old mud job I'm thinking you either have some kind of rotting floor joist or a shift in point loads. You might get a tell tale sign over laying the wall layouts for your homes different floors.

The other scenario might be something heavy was dropped over the messy area.

As far as thin build up over tar paper and expanded lath - I have done lots of this. Of course every job failed and I needed to use Ditra later !!! LOL - NOT.

Maybe your tile saw some moisture. Maybe the old nails are finally done.

I saw cut some of that floor out and look closer. AFTER YOU DO AN OVERLAY....
 

Eurob

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The plank subfloor is clearly not recommended , even with the use of an uncoupling membrane -- and Without adding a minimum of 1/2 inch ply on top -- bridging gaps -- . I could also say that the T&G recommendation is also no respected , even with the addition of a ply on top .

Playing by the rules -- TCNA -- I would say you can not achieve the desired '' floor timed out with that wood floor. ''

Then there is the other option -- not sanctioned by the TCNA but "S" -- where the

D-W16-T-14

is shown . I would prefer to have blocked joints , instead of the T&G , but there is really careful work to be performed .

Do you want to take the risk ? "S'' is manufacturing only the uncoupling membrane ......the rest of the job rely on structural wood construction , mortar and grout products choosing and the so called experienced installer .
 

JohnfrWhipple

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"S' over Ship Lap. Not in a million years. Maybe in a lab setting I would try it. But not if I wanted to stay in the home more than four seasons.

Why block the shiplaps ability to breathe and move with thin-set? Makes no sense. Unless all this time me leaving expansion room between sheathing and ship lap has been wrong.
 

Eurob

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Just to make it clear , you can not install the uncoupling membrane directly on top of the wood planks .
 

Koa

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I'm curious If you think the following would not work and the reasoning behind it:

Gluing down backer board over the planks with a urethane adhesive (something Bostik makes for example). You could still do a membrane over the backer board and then tile.

Bostik can be used to glue solid wood flooring to concrete. What I suggest is similar but upside down. The adhesive allows a wood floor to move when adhered to concrete. Wouldn't it allow the planks to move separate from the concrete board? A membrane on top of backer board would allow additional movement without affecting the tile.
 

ShowerDude

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I'm curious If you think the following would not work and the reasoning behind it:

Gluing down backer board over the planks with a urethane adhesive (something Bostik makes for example). You could still do a membrane over the backer board and then tile.

Bostik can be used to glue solid wood flooring to concrete. What I suggest is similar but upside down. The adhesive allows a wood floor to move when adhered to concrete. Wouldn't it allow the planks to move separate from the concrete board? A membrane on top of backer board would allow additional movement without affecting the tile.


KOA. 2 reasons.

A.Not enough room to work with is the simple answer....

B. Structural integrity of cement board is crap even at 1/2" unless its set/bonded in thinset which I would never do over cross planking anyways. CBU not a smart option for subflooring which would have to be 1/4" backer with a membrane. In order to time out with 3/4" hardwood. NO GO.
 

ShowerDude

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"S' over Ship Lap. Not in a million years. Maybe in a lab setting I would try it. But not if I wanted to stay in the home more than four seasons.

Why block the shiplaps ability to breathe and move with thin-set? Makes no sense. Unless all this time me leaving expansion room between sheathing and ship lap has been wrong.

Exactly lets concern our selves with expansion contraction and uncoupling any layer that goes over the shiplap (cross planking.)

John to answer your earlier comment the Joist, and shiplap is IN immaculate clean condition. I would never consider cutting a "Part of it out" typically but were trying to time out here...you know do the impossible.

FWIW very easy joist bays to get at almost completely uncluttered.....So sistering cleating blocking is very doable and could be done in a day or so........

thinking outside of the box here.

lastly I believe the homeowner damaged the floor rather than it failing my client has just told me...

No jersey mudbed here not while setting thicker porcelain. Not me......!
 
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