Fiber cement board (hardibacker) question

[cris]

Hi everybody! I just installed hardibacker boards in my bathroom. But I had to remove 1 pc 'coz I made a mistake. Can I still use it again? I screwed it every 8 inches around the edges and along every stud. Can I just cover the hole with thinset? Thanks!

[Basement_Lurker]

The board isn't structural and it's not the waterproofing, so it should be fine as long as it's still in good condition.

[kylee]

I am no master tile layer but, I did just tile my bathroom and kitchen. I would say sure go ahead and reuse it. Those little holes are not going to make much of a difference especially if you are using larger tiles. I had some large gaps between my hardibacker due to the strange shape of my kitchen and I just filled them in with thinset. No problems with it so far. I have one tip I tell everyone, if you are using porcelain tiles make sure to lay them with a thinset that contains laytex or use a laytex addative. Porcelain tiles are very heavy and regular thinset doesnt cut it. Your tiles will become loose if you use a regular thinset. So good luck with the project.

[cris]

Basement_Lurker,

It's still in good condition except for the holes. Thanks!

Kylee,

I'm going to use 1"x1" glass mosaic tiles in 12"x12" mesh. You still think it's ok? Thanks!

cris

[jadnashua]

The holes won't hurt. You need a vapor barrier behind the cbu, or a waterproofer on top of it. If you use one on top of it, then you need to tape and thinset the joints first (assuming you use something like RedGard which is a paint on one). The joints, regardless, should be taped with the cbu specific, alkali resistant mesh tape. It is easier to do this while tiling, otherwise it is easy to make 'speed bumps'. The tape and thinset on the seams is for reinforcement, not looks, so you don't want to create a hump and taper.

[cris]

Jim,

Thanks for the advice! I just finished installing the hardibacker over a vapor barrier. How can I join the hardibacker ends with the existing drywall ends on the wall and on the ceiling? And do I need to apply caulking between the tub and the hardibacker? Thanks again!

Cris

[jadnashua]

For any area under tile, use the thinset and the special tape. Try to plan the tile to lap over onto the drywall at the edges if you can, it is easier to cover those edges, and in a dry area, tiling to drywall is fine. If you aren't going to tile to the ceiling, and you already have cbu up, try covering the area with a thin skim coat of drywall compound, then prime and paint. Since above the showerhead is considered dry, you can tape the ceiling/wall joint with drywall tape and compound...preferably a setting compound rather than the premixed stuff in a bucket. That stuff doesn't soften when it gets wet. If you use a good quality paint and primer, though, you would be okay, but better to use the setting stuff.

Ideally, the cbu comes to within about 1/4" of the tub surface. Caulk that joint unless you opt for something like Dilex from www.schluter.com. If you use that on the tub surface and one of their other expansion joint materials in the corners, you shouldn't need any caulk at all. It is also recommended to caulk the corners at the wall junctions rather than grouting.

[cris]

Jim,
Thanks again! By the way I used the premixed thinset for the hardi joints with the specified tape. Do you think the premixed thinset will be fine?

Cris

[jadnashua]

No, never use premixed (crap) in a potentially wet area. There is no such thing, regardless of what the label says, as premixed thinset. Thinset is a cement product, and must be prepared at time of use. What you have is technically a mastic. It doesn't cure, it dries. If it gets wet, it will turn into a slurry and could wash away. It has no place in a shower. Now, not sure of the best approach here...depending on how dry it is, you can scrub it off or scrape it out. Since you have a vapor barrier behind the panels, you could spray it periodically over the day or so, then it will get soft and you should be able to scrape it out fairly easily, then use the real stuff.

I saw your thread over at www.johnbridge.com. Ask there, I think you'll get the same response.

[cris]

Jim,

thanks for that advice again. i scraped it off! it's a good thing i just used it in 2 joints! One more question. I'm going to install 1"x1" glass mosaic tiles in 12"x12" sheets. when should I apply the thinset and tape between hardis? before tiling or during? bacause i read somewhwere that it causes bumps when thinset is applied before tiling? i just don't know if applies with small glass mosaic tiles. thanks again!

cris

[jadnashua]

It's easier to do this in one step - tape the seams while you lay tile. Otherwise, it's too easy to have a buildup.

[cris]

Jim,

Thanks again!

cris