Guys,
There has been a lot of discussion over the years about CB underlayment, and I’d like an update on the latest opinions. I’ve done lots of bathrooms before, but always used Wonderboard, but never less than 1/2″.
In brief, here’s my project. Indoor, master-bath, marble tile floor, to be put down with thinset, with radiant heating system (Premier) over backer. It’s not for the shower or other really wet area. Floor is old (diagonal subfloor with oak finished floor) totalling 2″ over 16″ oc joists so plenty strong. Because of its rigidity and wanting to keep height to a minimum, I am going with 1/4′ backer board. (Don’t want to use Ditra or other membrane, so let’s not get into a Schluter discussion).
So which 1/4″ product to use? Hardibacker, Durok, or Wonderboard? It’s for my own house so I don’t care that Haribacker is easier or faster — just want the best stuff.
For 1/4″ should I use screws or roofing nails? Seen some posts that say screws will just pull through either product.
Thanks for weighing in!
Rick
Replies
The subfloor and finished floor are both solid wood boards? I'd be looking at removing some or all of that and installing plywood before you install the CBU. Also, be aware that you need l/720 deflection or better for stone, might want to run the deflecto-meter over at johnbridge.com and check your joists.
As far as CBU goes, I prefer Hardi because it's not as crumbly as the others. Aside from that they all work fine.
That's my thought as well....pull out the hardwood and replace with at least 1/2" plywood.
After that, Hardi or Durock won't make much of a difference, although I prefer the Durock if only because it's what I'm used to.
R.I.P. RAZZMAN
Screws won't punch through Hardiebacker if you use screws made for it. They have a different shaped head than drywall screws that some people try to use instead.
I put down Georgia Pacific DensShield over the radiant floor heating system in my tiled kitchen/family room and in my master bath (going on 9 years now with no issues).
The DensShield was 1/4 inch as I had the 3/4" radiant floor system screwed to the joists, which was covered with 1/4" luan (originally I was going to lay the tile on top of the luan - after everything was down the I realized the tile mastic specifically said not use over luan), then finally the DensShield.
I like DensShield over any CBB as it cuts cleanly, is lightweight, easy to handle, and the edges don't crumble when you screw them down.
I'd use good quality screws (no drywall stuff) with a screwgun. I'd also suggest you take the extra time to mark your screw locations on whatever is going over the radiant system as if you puncture one of radiant lines, it will ruin your day.
Art
I like DenShield a lot too. Nice product that gets an undeserved bad rap. Too many folks think it's just drywall -- it ain't.
It does give ya the fiberglass itchies, tho'! ;-(Mike HennessyPittsburgh, PAEverything fits, until you put glue on it.
DenseShield OVER the radiant flooring system?? I was gonna put the mats on top of the backer. This is electric --- basically just a long toaster wire woven through some plastic hardware cloth that you roll out and fasten down. Several companies make it --- Warmly Yours and NuHeat come to mind as competitors to the Premier product I bought. It's only about 3/16" thick.
Then comes the mud and the tile. I am not familiar with putting it under the backer. Anybody else have any guidance on this process? For example: should I embed the mat in self-leveling stuff then come back with the thinset and tile, or do it all in one layer?
Thanks to all for your input.
Rick
Others have already covered joist deflection issues. Pulling the hardwood and replacing with a Sturd-I-Floor or UniFloor rated plywood (in the mill stamp from APA) is a good idea - I would use 3/4".
I like HardiBacker - 1/4" for floors (unless I need to gain height).
Screws - such as RockOn, corrosion resistant, screws specially made for backer boards. Impact driver makes it go faster......
Don't forget to thinset under the HardiBacker before screwing it down. 8" oc - factory cast-in / marked on the sheets.
Jim
Edited 11/24/2009 12:40 pm ET by JTC1
Edited 11/24/2009 12:41 pm ET by JTC1
Also don't forget to MISS the joists when you screw the CBU down. Just the subfloor should attach to the joists, not the CBU.
Roger!
JimNever underestimate the value of a sharp pencil or good light.
Why no membrane?
No help otherwise. Just curious.
s.