Hardibacker tape & float? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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04-11-2005, 08:03 PM
I have put up the hardibacker on the tub surround. I intend to tile over it. Do I need to tape & float prior to laying mastic? Should I also caulk the joints (between the hardibacker pieces)? IF I do need to tape, do I use regular setting compound? Thanks!

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04-11-2005, 08:12 PM
Hi Micha, welcome. :)

Use CBU tape and thinset on the joints and corners. Don't use mastic or joint compound, take it back and get thinset. I use alot of Versabond from Customs. :)

John Bridge
04-11-2005, 08:16 PM
Hi Micha, Welcome. :)

Go to the james hardie site for complete instructions on installing Hardi-backer.


As Davy mentions, it's important to know the difference between mastic and thin set. We don's use mastic for much of anything.

04-11-2005, 08:53 PM
I will take the setting compound (recommended by the guy at Lowe's) back. Two more questions, I inadvertently put the hardibacker flush with the top of the tub. Hardi says to leave a 1/4 gap. Do I need to pull out the sheets and trim them?
Second, I built a two feet deep shelf / seat at the back of the tub, six inches up from the top of the tub. Since it will get minimal water and I sloped it slightly to drain into the tub, do I need to cover it with water resistant membrane such as kerdi? It is Hardibacker over plywood.
Thanks in advance for the help.

04-12-2005, 08:08 PM
Hi Mica.

You really need an expansion gap between the tub and backerboard. That tub will expand and contract and a caulked gap will isolate that movement from the tile. Tile + movement = cracks.

Yes, you should coat that seat with a liquid waterproof membrane. Go to Home Depot and look for a gallon of Redgard in the tiling section, most likely next to the thinset or sealers.

04-12-2005, 08:33 PM
Following on from the mastic/thinset question. I've already made the mistake with the hardibacker around our tub. I used the general purpose joint compount.

Will it be sufficient to sand down to the tape and then apply the thinset, or have I got a major job of removing the hardi, and relaying using thinset at the joints.