Tile bond failure, staple up (ME)

Larry Ticknor

I didn't remember seeing a specification for 1" of plywood for Custom Building Products, so I went to their website to see what it says.

Looking on the Custom Building Products website (www.custombuildingproducts.com) under the "Right way to tile" for floors they say:

1.
Subfloor should have a minimum 5/8" thick, exterior-grade or
exposure1 plywood base with 2" X 10" or 2" x 12" joists spaced no
more than 16" on center.

Note: If your wood subfloor is an "I" joist system, the joists must not be
greater than 19.2" on center and subfloor should be ¾" thick or
greater. 1.
Subfloor should have a minimum 5/8" thick, exterior-grade or
exposure1 plywood base with 2" X 10" or 2" x 12" joists spaced no
more than 16" on center.

Note: If your wood subfloor is an "I" joist system, the joists must not be
greater than 19.2" on center and subfloor should be ¾" thick or
greater.

So they seem to allow as little as 5/8" plywood if the joists are spaced close enough. They also do require concrete backerboard.

I believe the Tile Council of America (in the last update I got from them) say s 1" OSB (or is it 3/4" OSB?) is acceptable instead of plywood. I can't remember the thickness right now, but I do remember them allowing OSB instead of plywood. (With concrete backerboard on a mortar thinset and the concrete backerboard screwed of nailed).

Of course 1" is better than 3/4" or 5/8". I do think as the tile setting materials improve the thickness required has dropped. Though nothing can make up for a floor with too much deflection.

Larry Ticknor

ADDED: I just read this and realized I didn't write what I intended. I believe the bags of Versabond and others do say 1" plywood if you placing the tile directly over plywood with no backerboard. The website allows for thinner plywood subfloors, but I think it applies to floors with a cement backerboard. Both places say not to put it over OSB or luan plywood, but I think that is when not using a cement backerboard. Ie. they allow direct application to plywood if the plywood is 1" thick. They don't allow direct application to OSB. They prefer application of tile over a cement backerboard, in which case the plywood subfloor may be as thin as 5/8. That's the way I read it. Sorry for the long message.

Larry

Mark Eatherton1

Tile Bond Failure with Staple up.

This gent sent me a question with which I have no personal experience. Sounds like something that needs to be investigated tho... His question follows.

After years of experience of setting tile over hydronic systems, Recently set porcelain tile over a floor that had the hot water tubes stapled to a 3/4 inch wood subloor, and a 1/4 inch cement board. The flexing of the floor,
heating and cooling, resulted in numerous tiles coming loose, has this ever happened to any one else?
Thanks, Mel

I notified him via e-mail that I was posting it here, so expect him to show and answer any questions you all may generate.

ME

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Bill Clinton

Have done hundreds of bathrooms

and don't know of a single failure. None however involve cement board, so the way that was used might bear some looking at.

Bill

Duncan_2

Tile failure

Mark I've got tile in both the entryway and bathrooms, 3/4" OSB subfloor, 3/8" plywood underlayment, thinset mortar and 8" tiles.

In the heavily travelled areas, tiles are coming loose.

NEITHER floor is radiantly heated.

Flex (deflection) comes a lot into play here, as well as adhesive.

I would like to ask your friend: "How could you specifically determine if heat caused failure, rather than normal deflection? What are the telltale signs that allow you to differentiate between heat failure and deflection failure?"

I believe these tiles are also porcelain... that is, they are so glass-like and hard, they can only be cut with a saw, not a glass cutter type of cutter.

Mike T., Swampeast MO

Having done many tile installations

and many more tile repairs (some over radiant) I offer these possibilities for failure between the cement board & tile.

1) Porcelain tile is extremely hard and slick and sometimes hard to get to stick to anything. A latex add-mix in the mortar is a MUST.

2) Deflection. 1/360th of the span is the acceptable highest deflection with tiles up to 12" or so. (Larger tiles require considerably less deflection.) With 16" centers, modern lumber and 3/4" sturdi-floor 12-13' should be considered "tops" for a 2x10 and 9-10' for a 2x8. You can extend this range a couple of feet by adding a second layer of sturdi-floor and staggering all joints. A first-rate installation with GMMU (cement board) will find the GMMU adhered to the subfloor with mortar AND acrylic add-mix.

Mike T., Swampeast MO

More on deflection

Forgot to mention this. If a relatively narrow section of tile is installed mid-span on joists that do not meet the previous criterion, watch out for trouble! The deflection is greatest mid-span. Doubling the sub-floor and adhering the cement board to the sub-floor with mortar and add-mix will help, but sistering (doubling) the affected joists, or mid-span support is often called for.

If installed on one side or the other of mid-span, you're generally OK even with a single layer of floor.

Mike T., Swampeast MO

Hi Duncan! Applying tile directly to wood has always been tricky. The acrylic add-mix is an ABSOLUTE must! I've repaired many 60s/70s/80s era entries and baths with tile attached this way.

Large, well-adhered tile will literally crack from excess deflection. Smaller tiles will fail at the mortar joint allowing in water (common in an entry or bath) and breaking the tile bond.

If plain mortar is used to adhere tile to wood, normal traffic will often break the bond even if there is little or no deflection. Once any water gets in, the process accelerates. The add-mix does two things: it makes the mortar "stickier" and it makes it somewhat flexible.

Even with the add-mix, this is not the best way to do tile. Since the advent of GMMU (cement board) there is rarely excuse for a job of this nature. The old mud bases were often so heavy that they harmed the structure--now with Glass Modified Mortar Units, we can get nearly all their benefits with none of their drawbacks.

hr

Inadequate substrate

The Cermaic Tile Council, and other tile associations have a MINIMUN required thickness for the substrate. Generally 1-1/4" is the least they will accept and approve. You would need 3/4" ply wood ant at least 1/2 backerboard to meet their specs.

Of course over spanning the joist will cause the floor to bounce with the additional weight of the tile application, sometimes adding an additional post or support beam will handle this. If the floor is springy as you walk across, it probably will not hold a "tile job" very well!

Send them to the various online tile web sites they will show the correct way to do the install. Sounds like an installation issue more than radiant application.

What temperatures are they running? There is a temperature number that makes the engineered plywood manufactures mighty uncomfortable and may actually cause irreversible wood cell and fiber damage. The plywood manufactures would be able to give you their take on that

hot rod

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Duncan

Got acrylic admixture?

Well you about nailed it, Mike. 3/8" ply was used simply to bring two different floor systems flush to the same surface. The contractor may have been trying to save some pennies by not using cement board.

I wouldn't have used thinset on wood, myself, probably would've gone for a flexible adhesive. On concrete, sure. He did use acrylic additive, though.

Anyway... Mark's tile guy seems experienced.

I mostly wanted to know HOW he determined it was heat, heat only, and not some other factor that made 'em pop, some signature telltale sign. Figured an experienced guy would know what sticks and what doesn't, but then why would he ask? Hmmm.

hr

www.laticrete.com

will answer some questions.

hot rod

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Earthfire

thinset and wood

quoting from a bag of Custom Building Products VERSABOND thinset mortar."Unacceptable surfaces include hardwood,Luan plywood,parquet,particle board ,cushion,sponge-back or asbestos containing vinyl flooring or their adhesive residue,metal,fiberglass and OSB panels." Quote # 2 "Floors of APA exterior grade plywood must be a minimum of 1 inch thick with deflection not to exceed 1/360 of the span " This is the MINIMUM requirement for a Flex mortar with polymer additives already in it. 3/4 inch plywood with 1/4 inch backer board does not make 1 inch of plywood. Too many times we don't read ( follow ) the factory directions and cut a corner . Then some look to spread the blame. How many times have the words " But we always did it that way" been uttered when the proverbial cow excrement goes flying thru the fan. The "TILESETTER DEADMEN "used WETBED . My personal minimum spec.is 1 1/2" thick with galvanized chicken wire. 1 part portland cement, 4 part concrete sand. and just enough water to make it crumbly like crumb pie topping. Pack it in well by hand . I smooth it with a mag float & let cure for about 3 or 4 days ( longer is better if time is available)

Mike T., Swampeast MO

GREAT WORDS!

Too many times we don't read ( follow ) the factory directions and cut a corner . Then some look to spread the blame. How many times have the words " But we always did it that way" been uttered when the proverbial cow excrement goes flying thru the fan.