Glue Down Durock? Do I Have To?

Michaeljp86

Good thing Im not a tile guy.

Im going to look where I read that at but its says lay a bed of adhesive to the subfloor then lay the cement board and screw it down.

Bill_Vincent

Unfortunately, "adhesive" has WAY too broad a meaning. That could be mastic, construction adhesive, things like that, that woulod be almost guaranteed failure of the floor later. You need to lay it in troweled thinset. End of story. THERE ARE NO EXCEPTIONS OR SUBSTITUTIONS!!

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Jerry T

Not fussing at you Michael ..... but you won't be finding that in any manufacturers installation guidelines or the TCNA handbook.

tileguy51

I wouldn't tear it all back up , i use Fiberock an hardly ever glue it down and never have any problems. Unless you have a really bad floor or the house is not well built I wouldn't worry about it

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PrecisionFloors

So. You know how to do it right.....you just refuse to??

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Bill_Vincent

tileguy51-- How you install is your business. Not that it's right, but atleast when you're installing your floors, you'[re right there to see what kind of shape the floor's in. Can you see the floor this guy's asking about? Do you know what kind of condition that floor's in? Not that it should matter. When giving advice to people sight unseen, the best advice you can give them is by the book, no matter how good or bad the news is.

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Mike Costello

Are you serious?

Bill_Vincent

Yeah, I am. Why?

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Jerry T

I see now what the real underlying problem is.... the topic at hand is gluing down Durock... which as you all know is a backer board for tile. Backer boards fall into several unique catergories or famillies listed on page 10 of the handbook.

Durock is a CBU (cementious backer unit) type or family of backer board. All CBU's (Durock, Wonderboard, ect.) reguire a wet bed of thinset underneath for full support and filling of voids. Hardibacker classifies itself both as a CBU and a "Fiber-Cement Underlayment" family.

Fiberock falls in the family of "Fiber-Reinforced Water-Resistant Gypsum Backer Board/Underlayment" types of backer board. In other words someone can't say "I used Fiberock CBU" because that is a misnomer and makes no sense.

Bottom line is all tile installers should know what type of backer board you are working with and follow the ASTM and ANSI standards for that particular "type" of backer board.

It's all covered in the TCNA Handbook and all of us can get it free now.

Mike Costello

lol not you

Bill_Vincent

Jerry-- Actually, they DO all fall under the generic heading of CBU. Even Denshiled falls under that heading, even though it in no way resembles a cementitious backer unit, except for maybe size and thickness. One way or another-- the one comstant, whether you use fiberboard, cement board, Densheetrock, or whatever, they all have to be bedded in thinset on a floor.

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Jerry T

It falls under the generic heading of backer boards Bill. This is where the problem comes in. It "does" mean the same thing to alot of installers, but if you will read page 10 of the handbook it outlines the definition of what a CBU is and is not. The only commonality Durock and Fiberock has is that they are both backer boards... one is a CBU, the other is not.

I think that's why there are so many guys using subfloor glue under a CBU, they get confused because they think backer boards in general all work the same.

Bill_Vincent

Sorry, but I disagree. The reason people are using glue is because of misinformation. They seem to think it'll make the subfloor stronger, when in fact, it actually weakens the floor, in a manner of speaking. Even if the underlayment is plywood, it STILL should not be glued to the subfloor. ANY time you bond the layers of the subfloor together, you completely eliminate all the benefits of multi layering the floor, which, under tile, is mandatory. Once you glue the layers together, for all intents and purposes, you've created a single layer subfloor, and it'll act and move as a single layer. Guaranteed failure for a tile floor. This is why I say it has nothing to do with Hardi vs. Durock.

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Michaeljp86

Thats how I read to do it, Ive never done a tile floor but after this thread I know what not to do which I would have done. While studying for my GC license Ive learned alot of way to do it by code that are wrong.

Jerry T

The subject started out about Durock (a CBU) then it got switched to Fiberock (not a CBU) somehow.

USG makes both products and both are tile backerboards, but only one is a CBU. In their specs it says to install Durock in a wetbed of thinset.... They do not mention using anything at all underneath Fiberock, they even want the sheets touching.

Two different animals with entirely different installation guildlines but both are tile backer boards. Point of all this is to know the differnce before you go putting it down.

Stacy Moran

Kitchen is a main walk area - 1"14 screws or longer - and you can never put to many screws in - the more screws the stronger your floor and you want strength in a kitchen!!! Let me know If I can help you with any other questions - or explain more!

Bill_Vincent

Hey Jer-- why don't you shoot Dave G. an email about it. I think you might be surprised.

Just for the record-- the folks who started the fiberboard thing (Hardi) DO require thinset underneath.

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framergreg

dont folks use the old mudset and mesh anymore?the tile shops have a product that u mix/with h2o and its self leveling and just like mudset, saw it for the first time this year at a home we framed. saves labor if your in a hurry.

Michaeljp86

I guess the old timers or the high end home builders do mud jobs. I used the self leveling stuff last year and it worked great. Its a little on the pricy side though.

Bill_Vincent

I just did a pretty decent sized mud job down in Connecticut-- all mud floors, walls, and BENCHES in a pair of steam rooms. Other than that, the only mud job I've done in the last five years, other than shower pans, is an indoor pool deck. Most people aren't willing to pay the premium for mud work.

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