# Cement backer board over concrete slab



## gtimk4 (Dec 20, 2010)

Hi! All, I have a question regarding the ½” hardie cement backer board apply on concrete slab.

The kitchen that I’m working on has concrete slab, I’m putting a 3/8” porcelain tile in the kitchen floor. I want to raise the floor as much as possible to match the adjacent living room floor level (about 1-1/8”). 

So I’m planning to apply ¼” thin set over concrete slab, then put ½” hardie backer board over it, then lay down ¼” thin set on top, and put the 3/8” porcelain tile at last. (the whole assembly may not be 1-1/8” but close enough for me) 

I know that hardie manuf. won’t warranty their product if it applies on the concrete slab directly. I also know that many people in the forum points out that I should not do it either. Here are my questions:

1) If I don’t care about the factory warrant, do you guys think that it is OK to use hardie backer board over concrete? If not, why?
2) How do I secure the board to the slab, would thinset be enough, or do I need to put additional screws to the slab?
3) What screw should I use?
4) What is the better way to raise the floor other than using backer board? I try not to use self-leveling concrete or similar method since it is too difficult for me to do. Do you guys have other recommendation?


Thanks a lot for your help


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## angus242 (Oct 20, 2007)

I don't see a big issue going directly over a clean concrete slab.

However, using CBU over concrete is a big no-no. If you need to raise the height, use a SLC (self-leveling compound).


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## Mike Finley (Apr 28, 2004)

He said leveler is too hard for him to do.

Easy is what he needs.

I'd just lay all the hardi down and duct tape the joints.


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## Tech Dawg (Dec 13, 2010)

Mike, I'll bet ya a roll of duct tape that Angus will disable this conversation and send it to the DIY chatroom....


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## PrecisionFloors (Jan 24, 2006)

Mike Finley said:


> He said leveler is too hard for him to do.
> 
> Easy is what he needs.
> 
> I'd just lay all the hardi down and duct tape the joints.


No. Packaging tape is what you want to use. It's like a moisture barrier too :thumbsup:


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## WarnerConstInc. (Jan 30, 2008)

two layers of tile, duh.


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## rusty baker (Jun 14, 2008)

Just use cardboard, cheaper and it's going to fail anyway.


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## ChrWright (Jul 17, 2007)

Why on earth would you not care about the manuf. warranty???

Do you care how long your installation lasts?

Do you care about who pays for the fix if there's a problem?

Is this for your own house or someone else's?


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## Bud Cline (Feb 12, 2006)

I smell the fragrance of a DIY'er that thinks he is smarter than the rest of us and can learn some trade secrets by lying about his trade. I think you guys are being hoodwinked.


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## Anderson (Sep 7, 2009)

Come on Angus, You didn't recommend Ditra XL that will get him a 1/4


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## angus242 (Oct 20, 2007)

Actually, 5/16" :thumbsup:


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## Anderson (Sep 7, 2009)

I won't doubt you if you say so.


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## MasterBuilt (Dec 17, 2010)

I'm siting here trying to come up with something witty to type but you guys are too good!:notworthy


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## rusty baker (Jun 14, 2008)

gtimk4 said:


> Hi! All, I have a question regarding the ½” hardie cement backer board apply on concrete slab.
> 
> The kitchen that I’m working on has concrete slab, I’m putting a 3/8” porcelain tile in the kitchen floor. I want to raise the floor as much as possible to match the adjacent living room floor level (about 1-1/8”).
> 
> ...


 Exact same post is on the DIY board.


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## angus242 (Oct 20, 2007)

Thanks for posting on ContractorTalk.com. The Moderators of this forum would prefer if you post Do It Yourself related topics on our sister site www.DIYChatroom.com 

ContractorTalk.com is designed for professional contractor's to discuss issues and topics related to the construction and remodeling industries. Many of our professional contractors are also members at DIYChatroom.com and are looking forward to assist you with your needs.

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We apologize for any inconvenience that this may have caused. This thread has been closed.


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