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Old 11-05-2008, 07:31 PM   #1
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Thinset under Hardi backer


I'm wondering if you have to let the thinset dry before you screw down the Hardi backer? And is there a right and wrong side to the Hardi backer?

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Old 11-05-2008, 07:58 PM   #2
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Thinset under Hardi backer


I'm not an expert but why would a person put thinset 'under' hardibacker?

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Old 11-05-2008, 08:49 PM   #3
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Thinset under Hardi backer


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Originally Posted by Speedball View Post
I'm not an expert but why would a person put thinset 'under' hardibacker?
Because you're supposed to. Screw the hardibacker down while the thinset is wet, then get off of it and let it dry overnight. Most 1/4" hardibacker I've seen has a grid and screw pattern on the "up" side.
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Old 11-05-2008, 08:53 PM   #4
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Thinset under Hardi backer


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Originally Posted by Speedball View Post
I'm not an expert but why would a person put thinset 'under' hardibacker?
It fills the minor low spots in the substrate, thus eliminating the potential for an area that could flex under load, and when the backer is fully bonded to the substrate, it is much more solid. Of course this step is skipped more often than it is done, even though all cement backer manufacturers state to do this in their instructions.
Generally the rough side is up for thinset applications, and the smooth side is up for mastic applications. This is found either on the label stuck to each board, or sometimes printed directly on the product.

Last edited by troubleseeker; 11-05-2008 at 08:59 PM.
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Old 11-05-2008, 08:54 PM   #5
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Thinset under Hardi backer


Speedball,
Because it is a requirement of the hardibacker manufacturer. Actually all cement board manufacturers state this in their literature.
Divinepoodles,
You want the thinset to be wet because the board needs to bed into it and it helps take up any variations in the floor. then mechanically fasten the board while it is wet. One side of the board has indents to help people locate the required spacing between fasteners.
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Old 11-05-2008, 09:40 PM   #6
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Thinset under Hardi backer


Thank you all for the help. It all makes sense now.
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Old 11-05-2008, 09:40 PM   #7
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Thinset under Hardi backer


Speedball,

That's a fair question coming from you, a regular homeowner DIY'er. Problem is there are many tile installer "Hacks" that ask the same question. Those guys are ripping their customers off with poor workmanship.

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Old 11-06-2008, 06:23 PM   #8
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Thinset under Hardi backer


Appreciate the good replies and no, I'm not in the business.
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Old 11-06-2008, 08:29 PM   #9
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Thinset under Hardi backer


instead of backer board, we put 1/2" plywood down for 5 x 9 bathroom floor. we put a million screws in the plywood to minimize any movement. is this bad? i'm not in the business either. it feels solid.
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Old 11-06-2008, 08:34 PM   #10
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Thinset under Hardi backer


Drewhart,
What was just under the 1/2" plywood?
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Old 11-06-2008, 08:39 PM   #11
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Thinset under Hardi backer


nothing. just kidding! 3/4" sheathing. six inch wide boards. older, we nailed them down as secure as could first.
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Old 11-06-2008, 09:49 PM   #12
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Thinset under Hardi backer


Drew,

Plywood as the underlayment in a bathroom is not a very good idea. It's not a good method anywhere, but it can work in dry floor installations. Tile doesn't make the floor waterproof you know?

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Old 11-06-2008, 10:25 PM   #13
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Thinset under Hardi backer


is backer board waterproof? in new constuction i have rarely seen anything other than plywood used. my parents house has four bathrooms. the house is fifteen years old and there has never been a problem.
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Old 11-07-2008, 06:53 AM   #14
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Thinset under Hardi backer


The concrete based backer boards are not waterproof, but they are dimensionally stable when it comes to moisture. Wood is not. It will expand and contract as moisture content changes. Now you could put a membrane like Ditra over the plywood and it will make it much more waterproof and uncouple the tile installation from the wooden subfloor.
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Old 11-07-2008, 08:52 PM   #15
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Quote:
Originally Posted by drewhart View Post
3/4" sheathing. six inch wide boards. older, we nailed them down as secure as could first.
I'm getting ready to do the exact same thing!.... only maybe screw the boards down. Then plywood....but if something is better I need to find it.

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