Replies

1. 
   chiefclancy | Sep 02, 2002 07:18pm | #1

   Ideally, I would use 1/2" backerboard over your subfloor, but if you must use ply, glue 1/2" exterior grade ply over your existing 5/8" subfloor and screw or nail (with ring-shank or underlayment nails) every 6", hitting the joists as often as possible. I use 16d nails where I hit the joist and ring-shank nails elsewhere. When laying the ply, stagger the sheets so that the joints are not in the same place as the subfloor, and be sure to leave a gap between sheets of 1/8", which will then get filled with thinset when you set the tiles. Also make sure you buy thinset that is specifically approved for use with plywood.

   There is an excellent drawing of this installation on p. 81 of Michael Byrne's book "Setting Tile". I would highly recommend picking this book up, as it makes a great reference.

   Andy

1. 
   JeffBuck | Sep 03, 2002 02:16am | #2

   thinset backer board down to the ply...and nail or screw off. Some say screw only....but I trust roofing nails with the thinset. Thinset and mesh the seams.

   thinset the tiles to the backer. depending on the tiles....maybe modified thinset. Ask at the tile store when you buy the tile. Anything Mapei is good. Use the right size notch trowel. Make your life easy...spend mucho time on layout...shift till perfect.

   grout flat joints. grout caulk corners of walls, etc. grout caulk any dissimilar materials that expand/contract at different rates.....as in tile butted to wood threshold. Sanded grout and caulk usually for floors...unless real little joints....8th or less....

   backer board thinsetted down is a quick and easy insurance for a better lasting job.

   Jeff.......Sometimes on the toll road of life.....a handful of change is good.......

2. 
   Scooter1 | Sep 03, 2002 02:18am | #3

   Tile on Plywood? Doesn't work Jeff. Thats because wood and tile expand and contract at different rates. Use backerboard, a mortar bed, a sheet membrane like NobleTS, or Schulter's Ditra.

   Regards,

   Boris

   "Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1927

1. 
   rez | Sep 03, 2002 02:36am | #4

   Boris,  you still 'dissin'?Half of good living is staying out of bad situations.

2. 
   JeffUpNorth | Sep 03, 2002 07:01pm | #5

   If the ply expands and contracts differently that the tile would not also a backerboard ? When you say a backerboard I am assuming it is the particle board type (more like an MDF...)

   If the floors are in a heated house the expansion/contraction you mentioned would be stable because the temp. is pretty constant, or are you considering moisture as the culprit? What are the membranes made of and what is their purpose?

   Thanks for the advice,

   Jeff

1. 
   Scooter1 | Sep 03, 2002 10:48pm | #6

   Question 1: If the ply expands and contracts differently that the tile would not also a backerboard ?   No.  Both concrete backerboard (Wonderboard Durock) and the fiber type (Hardibacker) both are compatable with tile installations.  While each may have slight variations in the expansion rate, they are more compatable that plywood or anyother wood product.

   Question 2: When you say a backerboard I am assuming it is the particle board type (more like an MDF...)?  No.  Backerboards are called CBU's in the tile trade, Cementious Backer Units.  They are generally made with a cement based product, either wholly (like Wonderboard and Durock) or mixed in with other fibers (like Hardibacker).  There are also some foam based CBU's which are compeltely waterproof like German made WEDI.

   Question 3: If the floors are in a heated house the expansion/contraction you mentioned would be stable because the temp. is pretty constant, or are you considering moisture as the culprit?  Whether the temperature is stable or not, there will be expansion and contraction due to humidity, temperature and the movement of the joists or TJI's.  Tile installed directly on plywood will either fail at the tile level (tile sticks and stays put, but cracks in middle) or will fail at the grout line. 

   Question 3:  What are the membranes made of and what is their purpose? Membranes are made of plastic, CPE, Fiberglass, Polyester and PVC.  Here are some common examples:

   NobelTS- CPE  by the Noble Co.

   DalsealTS- PVC by DalTile

   Kerdi- waterproof polyester I think- by Schluter

   DITRA -plastic I think- by Schluter

   Their purpose is three fold, sometimes two fold: (1) To "uncouple" the tile from the substrate, where there may be issues with expansion and contraction, cracks, etc with the particular substrate; (2) To form a good setting bed, so the thinset can adhere to it, where there may be issues with the setting bed; and (3) To waterproof the installation, and keep water and moisture from the substrate, like a shower membrane.  The above, with the exception of the Kerdi, are not shower membranes, but three of them (NobelTS, Dalseal TS and Kerdi) are waterproof.

   Hopes this answers your questions.  Do not, repeat do not under any circumstances apply tile directly onto naked plywood.  While you may get lucky, this is a method which is not approved by the Tile Council, nor any thinset or tile manufacturer. 

   By the way, the current favorite membrane for tile onto plywood is Ditra, which is fairly cheap and takes up only about 1/8" and is fine for larger format tile, 2" or greater.  I am a backerboard guy or a mud guy myself, and prefer that, but membranes are excellent choices when one wants to apply tile directly to plywood without adding an additional setting bed and the resulting elevation change.  Ditra is spec'ed for 5/8" plywood too, which makes it very popular now, as many of the new tract homes have gone to 5/8" subfloors instead of the typical 3/4" T&G or the upscale inch and an eigth.

   You should get a copy of the Tile Council of America's phamplet which explains all the setting techniques, so you don't make a mistake.

   Regards,

   Boris

   "Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1927

1. 
   traveldogg | Sep 04, 2002 02:01am | #7

   Jeffupnorth

   let me give you a different perspective.  First there is always the text book/state of the art way to do anything (which you'll always get here).  Then there's the way that has worked before and will work again.  Plywood is dimensionally stable as is ceramic tile.  I don't know where the expan/contract comments come from.  If you are not familiar with cem. backer units and thin set then it my be better to use materials with which you are famaliar-the plywood glued and nailed and mastic for setting the tile.  That famaliarity alone may improve your chances for success.  I have used this installation several times and have seen no cracking of tile or grout during there 9 year history.  There are many factors which may cause tiles/grout to crack ie-shifting foundations, material quality control, etc.  Go with your gut. 

   cb

2. 
   chiefclancy | Sep 04, 2002 04:31am | #8

   While not ideal, there is a TCA method (# F150-01) for installing tile directly to plywood. There are several key specifications that go into this method- that the floor be a double layer of exterior-grade ply (i.e. not a single layer of 1 1/8"), that a gap of 1/8" is left between sheets and then filled with setting material, and that the deflection in the floor area is not greater than 1/360 of the span when measured under 300 lb. concentrated load. Additionally, the TCA offers a specific warning AGAINST setting tile directly to any type of composite wood material OTHER than EGP, including OSB, MDF, lauan, and particle board.

   It is definitely better to use backerboard (especially in installations that receive any sort of wet use, like a kitchen floor), however in certain situations if done properly, one can install tile directly over ply and get a long-lasting, stable installation.

1. 
   Scooter1 | Sep 04, 2002 04:38am | #9

   If you are quoting the TCA, I stand corrected. Can you imagine trying to get two layers of EGP with thinset in the middle flat enought to tile on top of?

   I wouldn't do that installation for time and a half. What nightmare!

   Regards,

   Boris

   "Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1927

2. 
   JeffUpNorth | Sep 04, 2002 06:58pm | #11

   Thanks folks, appreciate all the info and experience shared...I was having a time getting my head around the thinset between two layers of ply with a close nailing pattern on the edges. I could see the edges dipped down as the thinset was forced out. I will see what my material options are from the local supplier in the cementious board area.

   Thanks again, Jeff

3. 
   Mooney | Sep 04, 2002 02:58pm | #10

   Once again exellent information was givin. And other options are discusssed. Buy the Michel Byrne book, and order the TCA hanbook. Both will be assets to you library.

   Tim Mooney