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-   -   How to handle the tub flange. (https://www.johnbridge.com/vbulletin/showthread.php?t=130108)

Billy12 11-22-2020 09:07 PM

How to handle the tub flange.
Hi folks. I used to spend quite a bit of time lurking here but it's been a while as i haven't had a tile project in years. I'm doing a full bathroom remodel and will be installing a new bathtub. The tub fits the 30" alcove space perfectly and i have no plans to fur out the studs The face of the hardiboard will sit a little proud of the tub flange but will not overlap it. I would like to use Redgard for waterproofing and would like advice on how to handle the tub flange to hardiboard transition. The areas on both ends of the tub front that extend to the floor do not have a flange and are areas of concern as well. Thanks in advance.


ss3964spd 11-23-2020 07:30 AM

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Welcome back, Bill,

Since you're going to terminate the Hardie just above the tub flange you don't have a lot of options. You might consider using a band of water proof membrane, like Kerdi, to cover that gap. Install it on your Hardie with a somewhat lose mix of thinset mortar,, keeping the edge of the band in contact with the tub deck, then use Kerdi Fix to seal the band to the deck.

The down side of the Kerdi is that you'd then a little bit of a bump down there, If you're using large format tile, necessitating a larger notched trowel, you can likely compensate for the bump by adjusting the amount of mortar. Smaller format tile, using a smaller notched trowel, will be more of a challenge.

Moreover, given the lack of a flange at the front of the tub, the "legs", you'd really want to cut your Hardie as precisely as possible so that it follows the radius of the front of the tub, where the deck rounds over to the front, in order to keep that gap to 1/16th to 1/8th so that it can be effectively caulked with silicone. Or here again you could use Kerdi, cutting it carefully so it conforms to that radius.

When planning your tile layout don't forget about that front radius. Ideally you want to cut your tile to conform to as this fellow did with his in the photo below.

Tiger Mountain Tile Inc 11-23-2020 09:37 AM

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I think a banding, like Kerdi band, is theoretically the best way to handle the tub flange. However, in addition to what Dan mentioned above, I've found the corners to be annoying with banding material. The tub flange is typically inset and you have to cut the inside corners to get them to conform properly.

What I usually do is just use alkaline resistant mesh tape and apply sealant over it. I use either Wedi board or GoBoard for backer board so the sealant that I am using is for whichever product that I am installing. You wouldn't want to use silicone, for example, in this application and smear it on the surface as that would create a bond breaker.

Attachment 216470

For the sides, it's best, from a water management perspective, to have a tile "leg" go down the side of the tub. Just like the photo in the post above. It's also best to have tile backer board behind that leg.

If that's what you have then you simply need to seal the gap between backer board and the tub.

Sometimes, I've run into a situation where drywall will be up against the tub. In this situation, I've addressed it as shown in these photos.

Attachment 216468

Attachment 216469

edit: I consider 1 out 3 upright photos a good post!

Billy12 11-23-2020 06:45 PM

I was hoping that Kerdi band and Kerdi fix would be an appropriate solution. I'll be using 6X 24 tile so i think ill be able to manage the buildup situation just fine. I appreciate the advice and useful tips guys.

Thank you.

jadnashua 11-23-2020 07:26 PM

KerdiFIx will work, but it's expensive. You'd need some for the overlap to bond to the tub, but elsewhere, thinset is preferred. For that application, you could probably get by with the smaller tube, but the larger one that goes in a caulking gun may be easier to get a consistent bead. As long as you have enough to spread and embed the membrane, it's fine, though.

Before tiling or applying thinset, make sure to wipe down the cbu, as, especially HardieBacker, it's quite thirsty, and will suck a lot of water out of the thinset making it hard to embed the material. Keep in mind, thinset gets it strength by curing, not drying...it incorporates the needed moisture into its chemical structure...the excess (which makes it spreadable) evaporates.

Billy12 12-01-2020 08:52 PM

Should i bond the Kerdiband to the Hardi before applying the Redgard to the Hardi?


cx 12-01-2020 09:29 PM

Bonding Kerdi to cured RedGard with thinset mortar does not guarantee a waterproof joint. Bonding RedGard to Kerdi does not guarantee a waterproof joint, but at least your joint would be "shingled" in that application method.

Best option would be to use Kerdi for your wall waterproofing.

My opinion; worth price charged.

Billy12 12-04-2020 02:33 PM

I don't think my ocd is going to allow me to deviate from what the manufacturers specify so I'll be returning the Hardibacker for Kerdiboard. I think that will allow me to sleep a little better. Thanks for informing me.


Billy12 01-22-2021 06:43 PM

I have a question about installing long metal trim pieces. They're Custom's version of a Schluter Jolly and i'm using them in place of bullnose tile along the top edge of the wall tile and for outside shower corners. I'm used to bullnose tile and being able to install it with the field tile as you go. Some of the trim pieces are 8 ft or more in length and need to be installed in one shot without being able to install every adjoining tile on those walls at once. How does one install an 8 ft trim piece a little at a time when it needs thinset under it?


Billy12 01-23-2021 03:16 PM

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I've attached a photo. I'm essentially working my way up the wall with the trim piece in place and pulling it away from the wall slightly so i can smear thinset under it as i go. Also using tape and shims to hold it. Any additional tips for this would be greatly appreciated.

Thank you.


ss3964spd 01-23-2021 03:31 PM

Sounds tedious, Bill, but about as effective as any other way to install that tile edge trim.

Billy12 01-23-2021 03:56 PM

It is very tedious. Niether wall is perfectly plumb nor is my job perfectly flat so the cuts on both sides are scribe cuts. The tile saw is down a flight of stairs in the garage as well so it's taking forever.

ss3964spd 01-23-2021 04:04 PM

Had the same undesirable tile saw location when I did my master bathroom not too long ago, Bill, lots-o-trips up and down the stairs, and in and out the door to my tile saw station just outside of the garage. Fortunately it was warm outside.

I recently started on my guest bath. I'll probably not be as lucky with the weather when it come to tile cutting. I'm also using smaller tile this time around, so even more trips to the saw. Boo.

cx 01-23-2021 04:12 PM

Type tent into the Advanced Search and you boys can find lots of suggestion for ways to bring those saws indoors and even upstairs to make all those cuts.

ss3964spd 01-23-2021 04:17 PM

The water control on my old MK ain't so hot, CX, I'd need to search for tent and tub.:twitch:

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