Replies

1. 
   JeffBuck | Jul 27, 2002 09:59pm | #1

   just a quick guess/suggestion.......could ya mastic 1/4 durorock onto the luan......let it set.....then tile away?

   Not sure how the mastic would react with the radiant heat though.

   Would be avan better if you could confidently sink a few nails or screws to hold the sheets in place.....if ya know where ll the radiant lines are! Jeff

      She's exotic ,but not foreign, like an old Cadillac......she's a knockout!

1. 
   jet | Jul 29, 2002 08:06am | #6

   Jeff,  I am probably off my rocker but.....

      Would it be possible to "float" the 1/4 or 1/2"  cement board over the luan? Lay the board down and pull the joints with fiber tape and thinset?

        Just a thought.

1. 
   JeffBuck | Jul 30, 2002 03:21am | #8

   never tried anything even close to that....bet the seams would take a walk away from each other..........but if a science experiment is the way to go......my tile store sells a rubber membrane/crack isolation with a countertop display......showing the subfloor and cement board.......split in 2.....then the membrane....with a tile that spans the two.......and ya crank a knob and screw open the gap......goes from tight to almost 1/2 inch!

   Membrane stretches and the tile stays put......no cracks...no loosening. That would be the ticket.....but I'd just nail/screw tight the cement board as the thinset sets! Jeff   She's exotic ,but not foreign, like an old Cadillac......she's a knockout!

2. 
   C1802362 | Aug 09, 2002 01:42am | #11

   Thanks everyone for the help.

   Here's what i finally wound up with:

   1/4 denshield glued and screwed to the existing floor, as I wanted to minimize buildup.

2. 
   archyII | Jul 28, 2002 02:49am | #2

   This sounds like a disaster waiting to happen.  20" tiles with thin set on 3/4" structural floor.  I believe that you will have lipping problems when you set the tile and cracking tile after. The radiant panels and the 1/4" luan or any other 1/4" plywd. are not structural and do not help stiffen the floor.  The TCA handbook requires 2 layers of 3/4" (I believe.  I know its two layers of ply but I forgot the size and the handbook is in the office) ply in dry areas or a mortar bed (they also have a detail with 1/2" cbu but with a 20" tile I would be concerned about cracking).  You should post your question on the JCL tile forum.  Michael Byrn has left but there are still knowledgeable tile guys responding to questions and some there posted a link to another tile forum.

1. 
   FastEddie1 | Aug 09, 2002 02:07am | #12

   Archy, what are lipping problems?

1. 
   archyII | Aug 09, 2002 03:53am | #13

   Lippage is a tile term that means the tile edges do not align (one tile is higher than the other).  Large tile require that you have enough setting bed to level the tiles.  Any unevenness in the substrate or tiles that are not perfectly flat will cause the edges of one tile to be higher than the next.  The smaller the tile the less of a concern since the the differential in height is spread across a greater number of tiles and you won't notice that the tiles don't align.  Using large tiles the "lippage" can be very noticeable.  Also most tiles are not flat and stone tiles(and some ceramic) can vary in thickness.  A thick setting bed allows you to average out the difference.

1. 
   andybuildz | Aug 09, 2002 03:33pm | #14

   One issue with leveling out tiles (with a thiker mud base or thinset) is when one tries to push the tile a bit too much to "level" it to the one next to it is that it usually squeezes more mud under the adjacent one creating even more problems. I found that there has to be a fine line between how wet I make the thinset so that if I end up trying to do as you suggest, that the thinset oozes up at the grout joint and can simply be wiped away......although too wet and the thinset isnt as strong. I too know that using Admix instead of water adds great strength and some extra flex under the tiles as its an acrylic.almost rubbery. Sux to clean up though but all that means is that its much more adhesive like IMHO. Breaking a piece of thinset mixed in water or mixed in Admix at  the bottem of a spent bucket one can really tell the difference......Just like when doing a wood floor refinish the difference between Moisture Cure and just plain Poly.....The moisture cure is like rubber.

   Good luck

   BE well

              Namaste'

                              Andy It's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM

1. 
   archyII | Aug 11, 2002 02:17am | #15

   Thinset is supposed to be a thin coating.  It loses it's strenght if it is applied too thickly.  Adding more water or liquid than is specified lowers the strenght further.  There are other products that allow for a thicker setting bed and retain thier strength.

3. 
   archyII | Jul 28, 2002 02:55am | #3

   The other tile board was from FHB

   http://www.johnbridge.com/vbulletin/forumdisplay.php?forumid=1

1. 
   C1802362 | Jul 28, 2002 05:08pm | #4

   thanks for the pointer

   I did address the stiffness issue (I think) by designing the floor for L/960 deflection. It sounds like that may not be enough

1. 
   andybuildz | Jul 28, 2002 08:25pm | #5

   I'd use 1/2" WONDERBOARD (just a cpl a dollars more per sheet). Its stiffer and heavier then Durorock and I would think the concrete board will allow heat to be absorbed. Whats under the luon? You have 3/4" Adventec ....can you screw into that (I'm not familiar)? If thats the case then you'd have a total of 1 1/2" of substrate to "screw" into. Use 1 3/8", " Wonderboard screws" and thinset the WB to the luon first.  Your other choice is to staple down wire mesh and do a mud job over the luon if you feel so inclined.

   PS..This all depends on if you can raise the floor that much more ex: using saddles at door openings etc etc....I've done it before with little to no problem. Actually I just finished such a tile job with hose elevation two weeks ago.

   Be well

             Namaste'

                              Andy

   It's not who's right, it's who's left ~ http://CLIFFORDRENOVATIONS.COM

   Edited 7/28/2002 1:35:01 PM ET by Andy Clifford(Andybuildz)

2. 
   archyII | Jul 30, 2002 02:42am | #7

   L/960 is pretty stiff.  If you use cbu it should be set in thinset so that the board has full contact with the substrate.  Luan is not a good substrate for a variety of floors (tile, vct, etc.)  You should check out TCA (http://www.tileusa.com/profile_main.htm) and find out their recommendations.  20" tiles are pretty big to set without the making sure that the base is solid.

4. 
   Scooter1 | Jul 30, 2002 03:59am | #9

   Try Schulter's "Ditra". Specifically designed to go over plywood and act as a de-coupler. Don't know about your thinset problems, as I have never seen a thinset that specifically stated that luan was out of the question. Mapei Keraflex or Ultraflex is just about the stickiest stuff I have ever seen.

   I'd check with Tech Service at Schuleter and ask them to recommend a thinset for use with Ditra over luan.

   Regards,

   Boris

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

1. 
   mhurd0 | Jul 30, 2002 09:12am | #10

   I agree, excellant choice. I recently stumbled over this product at my local dealer.  It is however very expensive. It comes in rolls a good price for it is around $1.36 a square foot.  Another alternative  for using thinset over wood is to use "Ada" mix, it mix's with thinset instead of using water and will give good adhesion.