Replies

1. 
   timkline | Aug 22, 2004 04:51pm | #1

   Certified by whom ? 

   The Tile Council of America currently does not approve the use of any DW in shower and tub wet areas.  I had a GC argue with me last year  (after his shower stall tiled over green DW fell apart 3 times in 3 years )  that the drywall manufacturers approved its use in these locations.  I couldn't get it through his thick head that it didn't matter what the DW manufacturers said, it's the manufacturer of the finished product who have the final word in what base material goes under their surface.

   The cost of the callbacks on just this one house would have covered the additional cost of using cement backer board on the entire group of homes in the development.

   After arguing his drywall point till he was blue in the face, he later quietly mentioned that they were now using CB board for these applications.

   carpenter in transition

1. 
   jhausch | Aug 22, 2004 07:43pm | #3

   So if I'm planning on doing a bathroom with a drop-in tub and separate shower.  The shower will be full tile, the ledge around the tub will be tile, the floor will be tile, and the walls will be tile up to about 4' from the floor.  Do I:

   1)  put DW (or green board) on all the walls and the cover the DW with Cement Board up to 4' and fully in the shower area?

   2) put DW (or green board) on all the walls / areas that are not getting tile, but cement board only for everywhere else (all the areas getting tile)

   3) DW (or greenboard) on all the walls and only CB under the floor and in the shower area (and in the shower it goes on top of bare studs or on the DW)

   Im so confused. (seriously - I need guidance)

1. 
   PaineB | Aug 22, 2004 08:39pm | #4

   I pick #2. Actually, when I have my druthers, I use cement board for all of the walls and the ceiling above the shower. I don't always get my druthers but I just won't tile a wet place on top of greenboard. I have quit jobs over the issue.  

   I wouldn't put cement board over drywall. The good thing about cement board is that if moisture migrates to the inside of the wall, it can dry out again. If it is in continuous contact with drywall, the drywall will wick the moisture and the place where they meet will stay wet.

1. 
   Isamemon | Aug 22, 2004 11:22pm | #5

   I go for #2 also

2. 
   DANL | Aug 22, 2004 11:42pm | #6

   I agree with option #2.

   Anyone ever encounter exterior drywall? On a fairly upscale house here in Michigan it was used on a soffit/fascia where the fascia was something like 16" from top to bottom. The DW had the consitency and integrity of dry oatmeal. I asked the boss whatever possesed them to use such a thing and he said it was/is? quite common. We had a fun several days replacing it with signboard, which turned out really well. My boss impressed me by just eyeballing the angles and replicating them. Every so often I'd have to bring a piece down to him for a second cut.

1. 
   JohnSprung | Aug 24, 2004 10:36pm | #10

   > We had a fun several days replacing it with signboard,

   I haven't heard the term "signboard" before.  What is it?

   -- J.S.

1. 
   IMERC | Aug 24, 2004 10:48pm | #11

   MDO... Medium Density Overlay..

   Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming....                                                                   WOW!!!   What a Ride!

2. 
   ronbudgell | Aug 25, 2004 01:57am | #12

   I've seen a tile underlay priduct for sale here that looks interesting - it's an extruded polystyrene coated on both sides with fiber mesh and a thin layer of thinset. It comes in different thicknesses, 1" 2" 2 1/2" and, they say, can be used to construct walls for showers without any framing as long as there are tiles on both sides and the spans aren't too big. No Framing! No cement board! You need one framed wall to put pipes in, I suppose.

   It's a Schluter product and that's a company that knows tile.  They call it Kerdi board. They also sell an extruded polystyrene shower base with a drain system made for it. Very cool, I think.

   http://www.schluter.com/english/products/2002/sectionh/overview-h/section-h.html

   Ron

3. 
   DANL | Aug 25, 2004 02:36am | #13

   Yeah, what IMERC said. MDO is apparently called "signboard" because it's so often used for signs. I know highway departments use it for signs. Its wonderful to paint because it has a phenolic resin impregnated kraft paper facing. I guess it is like particleboard under the paper overlay, though it seems more like plywood. Stuff I've used was 3/8" thick. I'm getting confused on these messages because someone else asked a similar question about the best material to use for an outside sign or something. Gotta find that discussion.

3. 
   JeffBuck | Aug 25, 2004 03:34am | #15

   2.

   and as far as I'm concerned ... greenboard is useless.

   I'd say just use regular drywall ... actually I perfer 5/8th ...

   and use a good quality latex primer and paint. PermaWhite is great for kitchens and baths ...

   that .. and install the correct size exhaust vent that's vented to the outside.

   build it right ... fight excess moisture in the first place ... I see no need for greenboard.

   and always a backer board behind any tile ... aside from adding a little decoration to the kitchen backsplash.

   JeffBuck Construction, llc   Pittsburgh,PA

        Artistry in Carpentry                

2. 
   Zano | Aug 23, 2004 05:44am | #7

   By the International Residential Code. Here is the link:

   http://www.wconline.com/CDA/ArticleInformation/news/news_item/0,3303,131501,00.html

1. 
   timkline | Aug 23, 2004 06:03am | #8

   Z.

   thanks for that link. finally the heads come out of the sand.  i see they still allow fiberglass reinforced drywall.  i know that it is a popular product around here because it  saves time, but i just can't see saving an hour or two on a tile job that needs to last 25 years.

   danno, if you are talking about brown board, the gyp board that comes in 24" width with the brown face paper and the radiused edges, yes, i've used it.  throwing a piece in a bucket of water will help show its value.  i had hoped they stopped making that stuff.

   i also vote for #2.  at the points where you make your drywall to cement backer transitions, you should put blocking in the wall behind the board edges to strengthen the joints.

   carpenter in transition

1. 
   jhausch | Aug 23, 2004 01:10pm | #9

   Thanks for the advice.  #2 it is. 

2. 
   DANL | Aug 25, 2004 02:41am | #14

   I don't really know what this stuff was--it was painted, so I don't know the color, but it was horrible. It was a gypsum product. It may well have been "brown board" and if it was, it was appropriately named because it was crap.

2. 
   xhammerandnailsx | Aug 22, 2004 05:06pm | #2

   This is kind of depressing. Those tile on drywall tearouts are sooooooo easy.