Time To Ask The Professionals: Tub To Tile Sealing

[PGB1]

Hello All!
On this forum, I've learned a lot & I appreciate the time people spend sharing their knowledge & experience.

I'm re-doing a bathroom and wanted to post a picture of what I plan and wish to ask you all if I'm OK with the plan or if I goofed. I read many posts here about sealing tub-to-tile and managed to confuse myself. (Not hard to do...)

It's a little hard to explain, but I installed Durock brand cement board on the wood framing. It stops about 3/32" above the very short (3/16" tall) tub "nailing" flange. (Not really a nailing flange, as tub is cast iron & flange has no holes)

After taping & thinsetting the joints & corners, per Durock, the cement board will have Mapei Aquadefense membrane on it.

My idea was to get long lasting caulk and caulk the gap between the cement board and the flange so no water can escape to the framing.

But, if I also caulk the bottom of the tiles to the tub, how does water that penetrates the grout & lands on the Mapei Aquadefense escape?

Would I be better off leaving the tile-to-tub un-caulked and finishing the tiles' edges with a trim, such as a Schluter tile edge trim so any water can roll out? (Or even an upside down bullnose)

Thanks For Helping. I appreciate it very much.
Paul

[cx]

Welcome, Paul.

Difficult questions, both.

Those cast iron tubs with the little "curb" at the edge, rather than an actual tiling flange, are very difficult to properly waterproof in a tub/shower installation. But you gotta try.

Caulking a joint between the bottom of the wallboard and the tub is not really a useful way. And if you do that at all, you do not want to use a caulk, you want to use a flexible sealant. Yes there is a difference. A very important difference. The sealant will say it meets the requirements of ASTM C920 and will indicate its Type, Grade, Class, and Use. A Class 50, for example, indicates the material is capable of 50 percent expansion or contraction of the joint without failure. Class 25 is more common in my experience. And it is extremely unlikely that you would get the correct shape for your sealant in the joint you have. Considering that there will be differential movement of that joint, I don't trust such a joint filled with sealant as the only waterproofing of that area.

Use of a sheet-type waterproofing membrane, bonded to the tub and to the wallboard would make me a lot more comfortable. Use of a reinforcing fabric along with your HydroBan might better fit the bill, but I honestly have never tested the bond strength between that liquid and something like the tub's enameled surface, but it would likely be better than just the sealant. And you want to continue that all the way around the top corner of the tub and down the tub leg, too. See my warranty information below.

As for using a continuous sealant between tile and tub, I've opined here many time that I disagree strongly with that industry recommendation. I've probably been guilty of calling it a terrible idea. If a fella would at least leave some open gaps for moisture to escape, it probably wouldn't hurt as much.

One of the "profiles" made for tile edging might work there, too, but I don't particularly like the look of any of them, so I've never really tried it.

My opinion; worth price charged.

[PGB1]

Thank You, CX for taking time to reply and for the explanation that you gave of the options and materials.

I will most likely use your plan of membrane bonded to the board & the tub. Does Kerdi Band & Kerdi Fix sound like an appropriate combination?

Thank You again,
Paul

[Bdobz]

When I did mine a couple years ago I used Window and door flashing tape on the flange and up on the studs before installing the backer board. I then filled in the gap below the backer board with thinset as I installed the bottom tiles. Then finished it off with a 1/8th inch bead of silicone.

[PGB1]

Hi Everybody!

I installed some cement backer board (USG's Durock brand) on walls to be tiled with porcelain or ceramic (to be decided).

To install the alkali resistant mesh tape on the seams, I looked my partial bag of Mapei Keraset dryset mortar that's left from installlng Ditra a couple of years ago.
But...

On the bag, it says one of the suitable substrates is cement backer units when mixed with water. On the Mapei technical document for it, the statement is only on CBUs when mixed with Keraply. Conflicting information, to be sure.

The instructions for Durock say to use "modified", so I think that leaves dryset out.

(The field tiles will be installed with the appropriate mortar for the tiles on Aquadefense coated cement board.)

Out of curiosity:
Is dryset OK to tape & mud the joints?
What does the polymer additive contribute that makes modified different?

And, if I may double-up with a second question:
When I was picking up the cement board at the wholesaler, I commented to the counterman than taping the outside corners always challenges me. A customer said to NEVER! tape & thinset the outside corners. It wasn't like a "you don't have to", but more of a "the world is going to end if you tape the outside corners" tone. He also said not the "bother" with inside corners.

When doing the seams, I've always taped & thinsetted inside and outside corners. Have I been goofing up?

Thanks For Helping & educating!
Paul

[cx]

This is part of your shower installation, Paul?

Yeah, that would be confusing. It's not uncommon to find errors of one kind or another on thinset mortar bags, and even when pointed out to the manufacturer, the error continues until they run out of that batch of bags. The website is usually the more up to date and correct information.

In this case, the manufacturer of the CBU calls for a modified thinset mortar for filling and taping the seams. Unfortunately, they also call for the use of an organic adhesive (mastic) for the same purpose. We've known for years that USG (when they still existed) had some problems in the technical information for their ceramic tile installation products. Apparently, that hasn't changed with the change in ownership.

Not only would I recommend you throw away that old bag of mortar, I'd recommend you use a modified thinset mortar (ANSI A118.4) for all tile applications. Well, except for bedding the CBU over a wood subfloor. That's a good application for such mortars, except where the manufacturer calls for a modified mortar there, too, for reasons unclear to me.

Unless "A customer" was also a representative of the particular CBU manufacturer in question, I'd pay little attention to his advice, preferring instead to read and follow the manufacturer's written installation instructions.

My opinion; worth price charged.

[PGB1]

Thank You, CX for explaining. (It is the shower project you have been helping me with)

I appreciate your help & explanation. It'll help the job be longer lasting, then me I hope.

[cx]

Let's keep all the project questions on one thread, Paul, so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

[Tiger Mountain Tile Inc]

Outside corners should be taped with mesh tape and mortared over. 3 or 4-inch mesh tape works great for that but you probably don't want to purchase a whole roll just to do one corner.

What I've done in the past is use 3 strips of mesh tape. 1 on the very corner that gets folded and one on each side that overlaps the first.

The idea is to try to get the side strips to hold the fold on the corner. It doesn't work perfectly but it can work long enough to get some thinset on there to hold it even better.

[PGB1]

Hello All!

I am remodeling a bathroom with tub & shower faucet.
There are two holes to cut for the faucet rough-in box and the wall elbow for a hand held shower hose gizmo. (Drawing is attached)

I have not been able to figure out the best way to cut the holes.

I can't install the tiles and then drill with a carbide hole saw because the rough in box protrudes about 2 inches from the wall. (It gets cut off flush with the tiles after grouting.)

Tools I have are a 4" angle grinder and a MK tile saw that is the kind that has an upside-down angle grinder and a sliding table. A rotary Dremmel type tool is also available, as is an adjustable carbide hole saw.

How would you attack this?

Thanks for sharing!
Paul

PS: The tile size might change a small amount and we have not decided porcelain or ceramic. That will depend on what tie "we" pick.

[cx]

I'd cut the individual tiles after marking in position using either your angle grinder or your Red Screamer. Sometimes easiest to make multiple cuts perpendicular to the marked curve and break off the thin pieces. Doesn't hafta be real pretty, but you can sometimes smooth out the cut if you want using your wet saw blade. Not a blade manufacturer's recommendation, but it's commonly done.

For the little one-inch hole I'd use a hole saw.

Porcelain tiles are ceramic tiles, by the way. Just a harder, more dense version.

My opinion; worth price charged.

[ss3964spd]

Before you start cutting for that rough-in box, Paul, check the instructions for how close the cut out needs to be to the circumference of the wall box. I recently finished a job with one of those rough-in boxes, a Grohe unit, and the tile cut out could be no more than 1/4" more. I used a combination of my own red screamer to get close to the cut line and then a dremel for the final shaping.

[PGB1]

Thank You both CX & ss3964spd for taking time to reply and for your suggestions. I also appreciate the reminder about distance to box for the holes.

I apologize that I somehow, accidentally stuck this hole cutting post into a previous post instead of on its own.

Thanks Again!
Paul

[cx]

Paul, you did make a new thread for your hole cutting post. I combined it with your project thread. See Post #8.

[PGB1]

Thanks CX for fixing my posting goof.

You guys mentioned "Red Screamer" tool. I searched the web and came up empty. What's a Red Screamer?
Thanks,
Paul