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What thinset for Hardi Board

Posted by saxmaan1 (My Page) on
Mon, Sep 3, 07 at 18:07

All the manufacturers installation instructios say is to:

Apply a supporting bed of mortar or modified thinset to subfloor using a 1/4" square-notched trowel

OK...so what do I use...Flexbond, Masterblend, Versabond, etc???? Does anything go?


Follow-Up Postings:

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RE: What thinset for Hardi Board

I just tiled my third room today...I didn't put thinset between the subfloor and mortar...I spoke to many people on this....from my experience...40% don't even put hardibacker down, of those who do less than 50% use thinset between it and subfloor and almost no one taped and mortared the seams (1/8th inch thick)...granted I have only spoken with about 30 folks (5 being professional installers) on tiling but interesting results...
I also didn't use the recommended number of screws...most don't use Hardibacker screws, just roofing screws which were cheaper and do just as well. I used about half as many as it called for.
Now I did use Versabond between my tile and the hardibacker...

My take on it is if you are a professional and warranty your work then follow the manufacturers instructions...if you're looking for a floor that will last 10 years then do what I did...if you want it to last 20...stick with the manufacturer's instructions...John Bridge's forums mention the mortar to use between the two...Logically, I just couldn't see the layer of thinset below the hardibacker then screwing all those screw on top it making a big difference...with as many screws as they recommend, that board is not moving no matter what is under it.

Tara


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RE: What thinset for Hardi Board

saxmaan,

An unmodified thinset (Masterblend) is fine between the Hardi and the subfloor.

Tara,

The reason for the layer of thinset between the cement board and the subfloor is to fill the voids/gaps between the two. It'll keep the cement board from moving up and down. That long term flexing can lead to problems down the road.

Shame, shame, for building disposable housing.

Mongo


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RE: What thinset for Hardi Board

It's unfortunate that this attitude is so prevalent, and not just among DIYers, either.

And then people wonder why their floors don't last.

It's just IMPOSSIBLE to make a tile floor last more than a couple of years!

I actually had a GC say this to me about two years ago. I came in to do a tile floor, where he'd already put down the cement board, and of course, there wasn't a drop of thinset between the CBU and subfloor. When I mentioned this as a problem, that was his reply.

No wonder.


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RE: What thinset for Hardi Board

I heard a reply that modified thinset should not be used because if you tear the floor out, it will be hard to get the backerboard up. Is this true. If I use modified, is that technically a better beefy cement board installation? What about Versabond...is that kind of between unmodified and modified?

This might be a strange question...but how do you gut a new installed bathroom floor? The old mud jobs with the wire mesh and tar paper actually tear out with relative ease once you get underneath and get sections to break off. I am thinking, with a new installation, you have thinset and cement board with tons of screws, and then more thinset and tiles. And then you have thinset all over the plywood versus the tar paper and mesh that keeps the plywood nice and clean?

Is it recommended to put tar paper under a cement board installation????


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RE: What thinset for Hardi Board

In my limited tiling experience, I followed the instructions exactly. How could one not realize that the thinset helps prevent the Hardibacker from flexing downward and the screws help prevent it from flexing upward?


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RE: What thinset for Hardi Board

I heard a reply that modified thinset should not be used because if you tear the floor out, it will be hard to get the backerboard up. Is this true. If I use modified, is that technically a better beefy cement board installation?

It depends on who you talk to as to whether or not it should be used. It's a big debate in the industry. The manufacturers say to use modified, and TCNA who is completely unbaised, says that you're better off using UNmodified thinset for all CBU. Personally, I'll listen to TCNA before I listen to a thing a manufacturer has to say, because TCNA has nothing but the welfare of the industry at heart when they do their r&d. They're sort of the Consumer's Reports of the tile trade. Also, it makes sense. Why use a modified thinset, when the LAST thing you want to do is bond one layer to the other?

What about Versabond...is that kind of between unmodified and modified?

Actually, it's a midrange modified thinset, about equivalent to Mapei's Ultraflex II, Laticrete's 253, or Hydroment's Single Flex.

Is it recommended to put tar paper under a cement board installation????

The ONLY time tar paper should be used under tile is either as a vapor barrier BEHIND the cement board for wall installation around a tub or shower, or as what's called a "cleavage membrane underneath a thickbed mud installation. NEVER under or over cement board on a floor.

How could one not realize that the thinset helps prevent the Hardibacker from flexing downward and the screws help prevent it from flexing upward?

Good question.


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RE: What thinset for Hardi Board

IF YOU CARE ABOUT YOUR COUNTRY CARE ABOUT ITS STRUCTURES...people give they're lives for the sake of this country...it's a disgrace to not spend a few miserable bucks for the sake of it.

To assure less trouble upon future removal I have specified best 3/4 " plywood screwed down with lifetime coated screws..with a 5/8" plywood over that..THEN thinset/hardie board. And best honed carrera mosaic marble tile on that..then seal with best stuff.
Even this job is INFERIOR to a tile set of 60-100 years ago.
In a minor country like Lebenon everything..cielings..floors and all are poured CONCRETE.
Don't say America is the "Best Country on Earth"..PROVE IT.


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RE: What thinset for Hardi Board

I'm in the process of laying Hardibacker cement board over 3/4" plywood in my kitchen. The manufacturer says to use mortar or modified thinset with 1/4" trowel. Has anyone used mortar between wood subfloor and the Hardiboard?


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