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Frequent Contributor
drgene
Posts: 84
Registered: ‎10-23-2009
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Ditra membrane verses Hardy backer board

Thanks to Dad4Taylor I found out that the particle board that was on my bathroom floor was placed upon plywood. I am going to start to tear the particle board out tomorrow and replace it with plywood.

 

A few years ago, when I was tiling the bathroom in my shop that has a radiant heat floor, I asked how to tile on a concrete slab and someone recommended the Shluter-Ditra membrane, an orange felt back membrane with honey combed square on the other face. I used it and have had no problem at all with the floor in my shop bathroom.

 

Now I will be retiling my master bath floor and using the Hardy cement board will raise the height of the floor. I checked out the Schluter-Ditra website and reading the installation PDF makes it look like a good solution to avoid raising the floor level as much as if using cement board. It said that you can embed the membrane directly onto OSB or plywood in thinset and once dry, lay your tile on top, exactly as I did when I tiled on my radiant heated slab.  

 

Has anyone tried using the Ditra membrane on plywood? I found a few testimonials on the web like in a Fine homebuilding magazine article. But I thought I would see if someone out there has had a good experience using it.

 

Best regards,

 

Ron

"We see farther because we stand on the shoulders of giants" Sir Isaac Newton. Seems to fit this board too.
Senior Contributor
dad4taylor
Posts: 223
Registered: ‎10-27-2009
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Re: Ditra membrane verses Hardy backer board

Your floor is probably not thick enough to use just 1/4" Hardie but if it were the difference in height between Hardie and Ditra would not be that much... Ditra maybe 1/8" lower??  If you need 1/2" Hardie then the difference is huge.  Be that as it may, because of it's membrane quality, Ditra is an excellent choice for using in a bathroom.  Ditra comes in two sizes, regular and XL.  The regular size can be used over a single layer of ply with joists 16" O/C.  In theory the regular Ditra can be used with greater joist spacing but that scares me a bit. So assuming you have a sound underfloor, good ply on top and 16" spacing you're good to go.  Schluter (the makers of Ditra) wants you to use the same adhesive to lay the ditra as you would for the tile.  My mantra is always use thinset from a bag that you mix with water and I'm going to ammend that for adhering the Ditra to the ply by saying to add liquid laytex additive to your mortar mix per the manufacturers directions.  You can even make that floor nearly waterproof by using Kerdi-band at the seams and at the wall.

 

The Schluter company makes a whole host of really great tile products.  I would encourage anybody to look at their catalog.  They have an endless variety of waterproof systems, edging, transitions etc.  At the area where you are going to transition I would suggest using the appropriate thinset embedded transition from them.  Their website offers the most comprehensive installation instructions I've seen anywhere and includes videos for many installations. 

 

Good choice Doc!

Lead, follow, or get out of the way.
Senior Contributor
Tool Guy - Kg
Posts: 196
Registered: ‎02-02-2010
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Re: Ditra membrane verses Hardy backer board

[ Edited ]

Ditra is superior and would be my choice over HardiBacker. 

 

I'd like to add one little thing to dad4taylor's post for clarity.  In general, Schluter instructs to use unmodified for above and below the Ditra....except when you're installing it on plywood.  The plywood introduces the need for a modified mortar.  If the Ditra happened to be installed over a cement slab, the same unmodified thinset would be used under and over the Ditra.

 

So use a modified thinset (meaning it adheres to ANSI standards 118.4) to install the Ditra to the plywood and use a high-quality unmodified thinset (ANSI 118.1) for installing the tile onto the Ditra.  That's a very important detail.  Finding high-quality modified thinsets are easy because there's a lot of choices available.  But finding a high-quality unmodified thinset can be a challenge, so I'll name some specifically.  Durabond makes one called "DitraSet", Mapei makes one called "Kerabond", and Laticrete makes one called "272" that are all high-quality unmodified thinsets

 

And I'll do something I've never done before...disagreed with our friend dad4taylor on the "your floor is probably not thick enough" comment.  He's a reliable source of info and I've been reading his comments here or on the John Bridge Forums since 2004.  But cement board doesn't add any significant structural strength to a floor and the use of thinner cement board isn't inferior or weaker.  The floor's strength comes from the plywood.  Use the thinnest backerboard unless the added height of the 1/2" version helps in your adjacent flooring transitions.  :smileyhappy:

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handyman john
Posts: 361
Registered: ‎10-21-2009
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Re: Ditra membrane verses Hardy backer board

Two completely different products for two completely different applications. YES both are for tile and that is where it ends.

 

DITRA is a waterproofing membrane which additionally AIDS in tile adhesion because of its shape (geography).

 

Hardi board is made to STRENGTHEN and stiffen the sub-straight and bring it up to a level of thickness needed to provide a stabile installation. Hardi backer board, for instance, also can be used as a backing for TILE WALLS without other support.

 

It's OTHER strong point is cement board GRIPS thin-set bonding well to the adhesive (LIKE DITRA) but it does NOT provide a water-PROOF membrane. Cement board will withstand water but it is NOT WATER TIGHT.

 

If your floor is only 3/4" or even 5/8" thick you NEED to bring it up to a MINIMUM (meaning the LEAST it CAN be and not what it SHOULD be) Hardi-board is the answer OR more plywood; its especially critical when installing bigger tiles, and the bigger the tile the greater the need for THICKER/stiffer sub-floors.

step one; understand the problem - the correct answer will follow
Senior Contributor
Gbotha
Posts: 305
Registered: ‎11-05-2009
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Re: Ditra membrane verses Hardy backer board

[ Edited ]

I would use Ditra on concrete with cracks, EASYBOARD [only $1 more than other backers] 1/4" on plywood. If you remove 3/4" particleboard, and replace with 3/4" plywood, over the 1/2" ply existing, you are plenty solid enough for any kind of backer board. Ditra is too PRICY for me, and not sold in small quantities. At least from Home Depot. 50' plus roll?

Senior Contributor
dad4taylor
Posts: 223
Registered: ‎10-27-2009
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Re: Ditra membrane verses Hardy backer board

Tool Guy,

 

Thank you for disagreeing with me in a respectful manner... it seems like this world could use a little more respectful disagreement.

 

I went to the Hardie website and you certainly are correct, 1/4" Hardie can be placed over 5/8" ply which would not result in a floor greater than 1 1/8" thickness.  For anybody who has ever read a post of mine regarding floor tile you will see that I always put out that number.  I wracked my brains for a little bit trying to figure out where I got that information.  I try not to say anything on this forum unless I know it to be valid, after all I owe this forum a huge debt of gratitude for the things I've learned over the years.  I was able to find the source.  I got the information out of a book called "Setting Ceramic Tile" by a guy named Michael Byrne.  It's the source for my technical knowledge of the art and over the years I have touted this book as the bible for laying tile on this forum.  Page 89 reads as follows:

 

"For floors that get regular use, a sturdier underlayment of 5/8" thick plywood or 1/2" thick backer board should be laminated and nailed to a subfloor that is at least 3/4" thick, giving the substrate and subfloor a combined thickness of more than 1 1/8"  "

 

I probably bought this book 20 years or more ago and things have probably changed over the years... I don't even recall Hardie being available back then.  I have always used the 1 1/8" rule and even after reading the Hardie website I would be hard pressed to go less than that purely because I've been successful with what I've always done.

 

With regards to the assertion that "cement board doesn't add any significant strength to a floor"; When somebody steps on a piece of ply between joists the ply will want to bow between those joists.  By laminating a layer of anything you effectively stiffen the ply because the laminating layer will to some degree offer a counteraction to that bow through lateral compression.  As an engineer, not having data on the product and relying on my gut instinct I would submit that rises to the level of significant strength... after all I know for sure that adhering tile to 5/8" ply only would be a disaster and the difference between disaster and success is surely significant.   My gut feeling also tells me though that it's entirely within the realm of possibility that the difference between 1/4" Hardie and 1/2" Hardie could surely be insignificant.

 

You're absolutely right about the unmodified thinset for tile on Ditra.  That was surely something I left out.  My typing skills don't allow me to get into great detail on subjects so I always tell people to read the instructions and install products per the manufacturers directions.

 

Thanks for the exchange, I appreciate your clarifications!

 

Lead, follow, or get out of the way.
Senior Contributor
Tool Guy - Kg
Posts: 196
Registered: ‎02-02-2010
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Re: Ditra membrane verses Hardy backer board

[ Edited ]

I didn't see the original poster's other thread talking about the removal of the PB.  According to Gbotha's post 2 posts back, they are going to be reduced to starting with a subfloor of only 1/2" ply? :smileysurprised: Yikes, get some 3/4" ply over that like suggested!! 

 

Getting back to some discussion:

That 1 1/8" thickness number has been out there for a long time and I wouldn't dare point any fingers for anyone building up the floor or using that number (and if all other things were equal, I'd want a double layer of ply on all floors).  In fact, the Tile Council of North America Handbook shows a method detail for tiling directly over a double layer of plywood (residential) with 5/8" T&G and 1/2" ply.  And if you called technical support for Durock up to a few years ago, they also wanted the same 1 1/8". 

 

Touching on something you mentioned about Hardi's website:  Hardi specifically states you can use their product over a 5/8" T&G subfloor, but...................I firmly believe they are engaged in a marketing game of numbers to compete with the other manufactures.....keeping up with the Jones' mentality.  New products are allowing the use of thinner subfloors and manufacturers don't want to appear as inferior.  I sure wouldn't want to work over a single layer of 5/8" T&G ply.  Only possible way I'd touch it is if it were new, in perfect condition, and was installed exactly to specs.  I don't have easy access to 5/8" T&G plywood....even if I did, I would use 3/4" T&G instead.  I've seen a ton of houses built with a 5/8" ply subfloor, but they have never been T&G.  So the 5/8" stated minimum kinna makes my eyes roll. 

 

Onto the subject of stiffening a floor with cement board.  I'm not looking to "convert" anyone, but love engaging in learning.  I would readily agree that laminating a layer of Hardi to the ply stiffens it.  Sure.  But I would respectfully submit that this very bond between the ply and Hardibacker only lasts a few seasons before it starts shearing the bond.  There is too much differential between the expansion and contraction rates of the plywood and Hardi.  Once it's sheared, the floor stiffness reduces back to the layers of the plywood.  Yes, using better thinset prolongs the bond, but will still shear.  If Hardi needed this bond, they'd require higher quality thinsets for installing the board down....but they don't....in fact, they are totally okay with using cheapie thinsets under their board.  As long as the tile is well bonded to the top of the Hardibacker with good thinset, the Hardibacker becomes the buffer between the tile and plywood's movement differential.  And as long as the Hardibacker is taking on the stress, the tile stays safe and remains solid for a long-lasting life.

 

Ditra works in a different way, but for the same reason.  Ditra is technically an "uncoupling membrane".  The tile is well supported by hundreds of vertical columns of thinset within the waffle pattern of the membrane.  But the air space between the columns (which permits physical distortions/movement), along with the locking dovetails (which continues to holds the tile down when the membrane is being distorted), and forgiving bottom fleece allow the tile and plywood to independently expand and contract without building up any significant shearing forces.  Ditra doesn't have to take on the bigger forces Hardibacker does because it deals with the problem differently. 

 

:smileyhappy:

Frequent Reader
tamtiki00
Posts: 3
Registered: ‎08-16-2011
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Re: Ditra membrane verses Hardy backer board

Hello,

What material would you choose if you need to use Onyx floor tile 18X18 size and 3/4 thick - Hardy backer board or Ditra membrane

Thanks

Senior Contributor
Tool Guy - Kg
Posts: 196
Registered: ‎02-02-2010
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Re: Ditra membrane verses Hardy backer board

Hi Tamtiki,

 

Interesting question.  But be prepared for an answer far longer than you were expecting.  :smileytongue:

 

Onyx, being a natural stone material, falls under a more stringent set of installation methods than man-made tiles (like ceramic or porcelain).  You see, natural stone is generally weaker and needs more support from the underlying plywood.

 

I'll try to cut right to it.  Generically speaking, natural stone tiles need two extra things (with wooden floor structures) that man-made tile installation don't:

 

  1. The first is a double layer of plywood (before your tile membrane or cement board) is installed.  Why, you ask?  Because a single layer of ply exerts a much higher amount of plywood deflection onto the tile than you'd have with a floor consisting of a double layer of plywood.  One of the areas of highest deflection on a single layer ply system is between the seams of plywood over a joist...the movement is enough to sometimes crack tile.  By installing a second layer of ply over the first, the stresses are dispersed and the tile isn't subjected to such harsh stresses.  Some stones are fairly strong, but many are much weaker than man-made tiles, including onyx.  Ideally, you'd start with 3/4" T&G plywood, then add a second layer of plywood (layer thickness minimum is dependant upon the membrane or cement board that you're using).  But, in no case, should you ever add a layer less than 3/8".  Plywood less than 3/8" isn't rated at adding structural value...(and is especially prone to warping during installation of membranes).
  2. Another huge consideration is that natural stone tiles need a far stiffer joist structure to cut down on joist deflection.  Let's talk about that for a second.  Engineers will express the amount of deflection a given floor has by telling you the amount the joists may bend downward when exposed to loads.  In modern homes, floors are built to a minimum deflection rating of L/360.  Simply put, this means that the floor joist may deflect downward (at a maximum) one unit of measure for every 360 units of measure laterally.  Unfortunately, a natural stone tile needs a floor that's twice as stiff.  It needs a floor structure rated at L/720.  Rarely is that seen in homes...usually the only time you have a floor stiff enough is when the architect specs the floor structure specifically for natural stone tile.  

 

I'm sorry to say that these two extra things needed for natural stone are not commonly acknowledged by many remodelers or by the sellers of tile.  They are actually industry standards you'll find in the TCNA Handbook (the bible to the tile industry), but so commonly unknown by many installers.  My point of this last paragraph is that you won't find a lot of widespread support for my statements by checking around town.  But it's your floor and if it fails in a few years, YOU'LL be the one that has to replace it at your cost (or live with a cracked floor). 

 

Now that I've dispensed with a bunch of technical data, let me ask you a question or two.  If this is a polished onyx, do you realize it will scratch quite easily and can be damaged by a single mis-application of common household cleaners?  What room will this be used in?  Would you consider a man-made porcelain tile that mimics natural stone?  I ask because using porcelain would eliminate the extra requirements of natural stone and would be very durable.  I can't say I've shopped for an onyx look-a-like, but there are plenty of great-looking marble and stone look-a-likes that are made from porcelain that will serve you well and require much less maintenance.

 

:smileyhappy:

Frequent Reader
tamtiki00
Posts: 3
Registered: ‎08-16-2011
0

Re: Ditra membrane verses Hardy backer board

Hello and thank you so much for your  detailed explanation. I picked this material (onyx)  because of its colour. May I ask you about the tickness of this tile 3/4 of an inch. Does this fact make any difference to the praperation of the subfoor?

 

Thank you again

 

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