# calking backer board to tub



## glassman (Sep 15, 2006)

im getting readt to calk my new tub.i was wondering what calking i should use?i put backer board up and will be getting it tiled in a day or so ,so i need to calk the tub before tile man gets here.can you help?


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## AtlanticWBConst. (May 12, 2006)

glassman said:


> im getting readt to calk my new tub.i was wondering what calking i should use?i put backer board up and will be getting it tiled in a day or so ,so i need to calk the tub before tile man gets here.can you help?


There is no need to caulk your tub prior to the Tile installation. Caulking is done after that process....

Caulking used is 'silicone' based.... and color matched according to your grout color and tile...


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## Tscarborough (Mar 31, 2006)

After ripping out the rotted ************rock on my tub, I am going to caulk the hardibacker and the tile. What can it hurt?


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## AtlanticWBConst. (May 12, 2006)

Tscarborough said:


> After ripping out the rotted ************rock on my tub, I am going to caulk the hardibacker and the tile. What can it hurt?


The rotted ********** rock?...Do you mean sheetrock?
If that is the case, then I'm not surprised that you had problems....

In reality caulking cement backerboard is not a common general installation practice. BUT, I absolutely agree in the concept of building on the side of caution and 'precaution'...

That is whay i will now say this:

I do agree with the point about using silicone caulking where the wall meets the tub. I would actually use latex caulking with silicone in it, just to reduce the mess....
Additionally, if you are going to go that route, then you should also caulk ALL seams of the backerboard/cement board with the caulking prior to mesh and thinset application. 

But, before all that:
Prior to installing the cement board, you should install a vapor retarder in the form of 15 lb roof felt - (overlapping the felt's edges appropriately at the seams) - This would be installed over the surrounding enclosure's bare wood/steel studs....ONLY on the walls and the areas of those walls that the cement board will be added to....


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## troubleseeker (Sep 25, 2006)

AtlanticWBConst. said:


> There is no need to caulk your tub prior to the Tile installation. Caulking is done after that process....
> 
> Caulking used is 'silicone' based.... and color matched according to your grout color and tile...


 
I always seal the backer board/tub joint with a flat bead of silicone before the tile. It is cheap insurance, because the one thing you can gaurantee is that this joint will leak , it is not if, only when.:yes:


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## AtlanticWBConst. (May 12, 2006)

troubleseeker said:


> I always seal the backer board/tub joint with a flat bead of silicone before the tile. It is cheap insurance, because the one thing you can gaurantee is that this joint will leak , it is not if, only when.:yes:


Yes, If you read my last post (the one before yours)...you will see that I changed....'my tune' about this point. IT isn't common practice, But now, I can see this as a good 'precautionary' point....


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## mgc7914 (Jan 3, 2008)

did you ripp down to the studs and what did you use aftrer that im in a bath remodel as well and want to tile my walls i have purchased 1/4 hardibacker and have people telling me to use 1/2 inch hardi board for the walls and also place roofing felt behind it to stop moister, im at a loss right now as to what to do?


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## send_it_all (Apr 30, 2007)

mgc7914 said:


> did you ripp down to the studs and what did you use aftrer that im in a bath remodel as well and want to tile my walls i have purchased 1/4 hardibacker and have people telling me to use 1/2 inch hardi board for the walls and also place roofing felt behind it to stop moister, im at a loss right now as to what to do?


I agree with replacing the 1/4" with 1/2". As far as the rest...following the steps Atlantic outlined above is the way to do it. 

To repeat.....staple 15 lb. roofing felt to the bare wall studs in the tub surround. (I start at the bottom and unroll about 11 feet of felt. That is a little more than enough to cover the area. I staple it up horizontally around the tub. Then I put another piece above the first, overlapping it by 6-8 inches. I do this until the vapor barrier is at least as high as the tile will go.) Then I screw the Hardi Backer to the studs using the special Hardi Screws (over the felt), using the marks on the face of the H.B. as a guide for screw spacing. It takes a bit of work to get the screws countersunk into the H.B. I use an impact driver and run the screw in all the way then back it out a little then drive it in, then back it out, then drive it in for the last time. Then, it is ready for tile....unless you feel the need to caulk the gap where the H.B. meets the tub.

The last couple of tubs/showers I have done, I have used the Schluter/Kerdi fabric over the Hardi, instead of the roofing felt under it. It is more expensive (by far) then the felt, and more difficult to install, but supposedly a much better/ more waterproof system.


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## rblaine (Jun 5, 2008)

I am about to do this in my tub/shower surround but I'm still confused about where to caulk. See the little diagram I drew (I have too much spare time at the moment, yes)...from what I have been reading, it is recommended to silicone caulk the gap between the CBU and the top of the tub lip. But the roofing felt should be extending slightly over the tub lip, right? Which means the silicone will be between the felt and the CBU, but I don't see how that will help seal out moisture...it will create a little puddle of water that will sit behind the bottom row of tile.


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## Nestor_Kelebay (Jun 17, 2008)

Rblaine:

1. You should shim out your studs so that the tiles drop down IN FRONT OF the top lip of the tub.

2. If it wuz me, I'd use a plastic vapour barrier instead of the roofing felt and caulk it to the tub lip rather than the cement backer board. Caulking between either the top of the tub lip and the CBU or between the felt or plastic and CBU is kinda dumb in my view because water will pass right through the CBU anyhow. It's kinda like caulking around a screen to keep out the draft.

3. You want the bottom of your CBU to stop about 1/4 inch above the top of the tub lip. The bottom row of tiles hangs down to the top of the tub in front of that lip. Then you caulk between the bottom row of tiles and the tub with silicone.

Please don't set your first row of tiles on the tub. If your tub isn't dead level (and it won't be) then your vertical grout joints are going to lean into or away from a corner and you're gonna have a 1 inch wide grout joint by the time you get to your ceiling.

Instead, fasten a STRAIGHT wood molding horizontally to the wall above the tub. Ensure that the distance from the top of that molding to the tub is about 1/2 inch shorter than the tiles you intend to use. Set all your tiles ABOVE the wood molding first, and then remove the wood molding and cut the bottom row of tiles to fit down to the tub. That way, no matter how out of whack your tub is, your horizontal and vertical grout lines will be horizontal and vertical, making the tiling look like it was properly done. Check before you start tiling that your tub isn't so far out of level that the distance from the top of the molding down to the tub is greater than the height of the tiles you're planning to use. If it is, you need to move your molding even further down cuz you can't stretch your tiles.

Also, set two rows of tiles out on your floor; one row with the tiles end to end and the other with them side by side, both with tile spacers between the tiles in each row. This will help you pick a horizontal starting point along each horizontal wood molding. And, PLEASE tile all the way up to your ceiling to avoid paint peeling and mildew forming on the wall above the tiling. If, using your end to end row, you find that you'll have to cut the top row of tiles about 1 inch tall to fit up to the ceiling, then install a horizontal accent strip of tiles that are wider than 1 inch somewhere on the wall so that top row will now be almost a full tile in height.

If you're relatively new to tiling, use your two floor rows to find out how wide an area to tile at a time. I like to use 6 X 8 inch tiles set in LANDSCAPE orientation because you rarely see that done, and so it allows me to get a very custom look with plane jane tiles. I might measure that with the spacers in place, an area of 4 tiles wide by 4 tiles high would be 32 3/8 inches wide by 24 3/8 inches high. I'll use a carpenter's square resting on my horizontal wood molding strips to mark off an area 32 5/16" wide by 24 5/16" high on my wall and mask those lines off with 2" wide masking tape (and mask off the wood molding too). Then I spread my thin set on the wall and pull off the masking tape. That way I don't have to be careful about spreading the thin set. When I pull off the tape, all the thin set will be spread exactly over the area I'm about to tile, and no further. Then I back butter each 6X8 tile and press it gently into place. Even if the thin set on the wall skins over from drying out, the moisture from the fresh thin set on the back of the tile will reactivate it, and it'll stick like chewing gum to the underside of a church pew.

You can see pictures of some of the messes I've made at:
www.ilos.net/~nkelebay

PS: Unless you live in an earthquake zone, I wouldn't use any additive in your thin set. I own a small apartment block and have tiled all 21 bathroom walls in my building. In 21 bathrooms in 20 years, not a single tile has come off of it's own accord. So, why use any additive (pronounced "adhesive") in the thin set to make the tiles stick better. It's only going to make those tiles EVEN harder to get off in future. Contractors will use those highly polymer modified thin sets because they're only concerned that they don't get called back to the job. If they were also the ones who'd have to be taking those tiles off 25 years down the road, they wouldn't use such strong setting thin sets.


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## rblaine (Jun 5, 2008)

Nestor_Kelebay said:


> 1. You should shim out your studs so that the tiles drop down IN FRONT OF the top lip of the tub.


Yup. I am planning on having the front of the CBU even with the front of the tile lip as shown in the diagram.



Nestor_Kelebay said:


> 2. If it wuz me, I'd use a plastic vapour barrier instead of the roofing felt and caulk it to the tub lip rather than the cement backer board. Caulking between either the top of the tub lip and the CBU or between the felt or plastic and CBU is kinda dumb in my view because water will pass right through the CBU anyhow. It's kinda like caulking around a screen to keep out the draft.


That's exactly my concern. I think I'll just put a bead of silicone under the roofing felt along the top/front of the tub lip. That should prevent water from wicking up behind the felt from the tub deck (and the silicone between the bottom tiles and the tub will be added safety there).



Nestor_Kelebay said:


> 3. You want the bottom of your CBU to stop about 1/4 inch above the top of the tub lip. The bottom row of tiles hangs down to the top of the tub in front of that lip. Then you caulk between the bottom row of tiles and the tub with silicone.


Yup.



Nestor_Kelebay said:


> Please don't set your first row of tiles on the tub. If your tub isn't dead level (and it won't be) then your vertical grout joints are going to lean into or away from a corner and you're gonna have a 1 inch wide grout joint by the time you get to your ceiling.
> 
> Instead, fasten a STRAIGHT wood molding horizontally to the wall above the tub. Ensure that the distance from the top of that molding to the tub is about 1/2 inch shorter than the tiles you intend to use. Set all your tiles ABOVE the wood molding first, and then remove the wood molding and cut the bottom row of tiles to fit down to the tub. That way, no matter how out of whack your tub is, your horizontal and vertical grout lines will be horizontal and vertical, making the tiling look like it was properly done. Check before you start tiling that your tub isn't so far out of level that the distance from the top of the molding down to the tub is greater than the height of the tiles you're planning to use. If it is, you need to move your molding even further down cuz you can't stretch your tiles.


Thanks, this all makes perfect sense and is what I was planning on doing.



Nestor_Kelebay said:


> Also, set two rows of tiles out on your floor; one row with the tiles end to end and the other with them side by side, both with tile spacers between the tiles in each row. This will help you pick a horizontal starting point along each horizontal wood molding. And, PLEASE tile all the way up to your ceiling to avoid paint peeling and mildew forming on the wall above the tiling. If, using your end to end row, you find that you'll have to cut the top row of tiles about 1 inch tall to fit up to the ceiling, then install a horizontal accent strip of tiles that are wider than 1 inch somewhere on the wall so that top row will now be almost a full tile in height.


Good idea wrt the accent tiles to pad out the pattern. I was planning on a single row of glass tiles in there; if need be I can adjust their size or have a second row.



Nestor_Kelebay said:


> If you're relatively new to tiling, use your two floor rows to find out how wide an area to tile at a time. I like to use 6 X 8 inch tiles set in LANDSCAPE orientation because you rarely see that done, and so it allows me to get a very custom look with plane jane tiles. I might measure that with the spacers in place, an area of 4 tiles wide by 4 tiles high would be 32 3/8 inches wide by 24 3/8 inches high. I'll use a carpenter's square resting on my horizontal wood molding strips to mark off an area 32 5/16" wide by 24 5/16" high on my wall and mask those lines off with 2" wide masking tape (and mask off the wood molding too). Then I spread my thin set on the wall and pull off the masking tape. That way I don't have to be careful about spreading the thin set. When I pull off the tape, all the thin set will be spread exactly over the area I'm about to tile, and no further. Then I back butter each 6X8 tile and press it gently into place. Even if the thin set on the wall skins over from drying out, the moisture from the fresh thin set on the back of the tile will reactivate it, and it'll stick like chewing gum to the underside of a church pew.


Good idea with the masking tape.



Nestor_Kelebay said:


> PS: Unless you live in an earthquake zone, I wouldn't use any additive in your thin set. I own a small apartment block and have tiled all 21 bathroom walls in my building. In 21 bathrooms in 20 years, not a single tile has come off of it's own accord. So, why use any additive (pronounced "adhesive") in the thin set to make the tiles stick better. It's only going to make those tiles EVEN harder to get off in future. Contractors will use those highly polymer modified thin sets because they're only concerned that they don't get called back to the job. If they were also the ones who'd have to be taking those tiles off 25 years down the road, they wouldn't use such strong setting thin sets.


I do live in an earthquake zone. Aside from that, I am using modified thinset because I was potentially putting heavy 12" tiles on the wall and I was worried about them sagging and drooping while setting. I have Laticrete 255 which is supposedly best for non-sag. As for removing the tiles in the future, won't the backerboard just come off the studs along with the tile and whatever thinset was used?

You can see pictures of my progress at:

http://picasaweb.google.com/russellblaine/Soffit?authkey=m9PQ7PmaRjE


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## Nestor_Kelebay (Jun 17, 2008)

I'd be really concerned about using 12 inch tiles. The problem is that the larger the tile, the less well it will conform to any curvature in the wall. If you don't have a flat wall, large tiles like that aren't going to meet well at their corners.

Or, are you confident that your wall is flat enough that large tiles will still lay flat?

Instead of using Laticrete to avoid sagging, just put up a straight wooden molding 11 1/2 inches above your tub, set your bottom row of full tiles so they rest on the molding and allow the thin set time to fully set up. Then you can tile above them with no concern about sagging.

Also, I'm kinda leery about how well silicone will stick to asphalt impregnated roofing felt. If it wuz me, I'd be more inclined to caulk roofing felt to the tub lip using plastic cement (the black stuff used for repairing roofs). That's totally waterproof and will stick to roofing felt well. It'll certainly stick well to the tub, too.


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## rblaine (Jun 5, 2008)

I like the idea of 6x8 tiles set horizontally, so I'm going to do that. I want to minimize the amount of grout on the finished job, so what's the smallest grout lines I can get away with? 1/8"?

Are 6x8 glazed white tiles a standard item? A couple tile shops I visited today didn't have them.

As for the flatness of the walls, I'm putting CBU up against the studs - doesn't that create an extremely flat surface to tile over?


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## Nestor_Kelebay (Jun 17, 2008)

rblaine said:


> I like the idea of 6x8 tiles set horizontally, so I'm going to do that. I want to minimize the amount of grout on the finished job, so what's the smallest grout lines I can get away with? 1/8"??


I always use 1/8 inch wide grout joints. Get yourself some 1/8 inch tile spacers and put them in PERPENDICULAR to the wall so you can pull them out after the thin set hardens. (Some people are still telling people to put them in flat against the wall and fish them out later when the thin set hardens or grout right over them, and if there were a Nobel Prize for Stupid Ways to do Things, I'd nominate that idea.)



> Are 6x8 glazed white tiles a standard item? A couple tile shops I visited today didn't have them.


6 inch wide X 8 inch tall wall tiles are a VERY standard tile size, along with 6X6 and 8X8. My guess is that the people you talked to didn't realize that you could use a 6" wide X 8" tall tile as a 6" tall X 8" wide tile. The only problem I can see is finding them in plain white. You won't have trouble finding them in any colour except white. That's cuz most tubs are white, and few people are going to want to accent their white tub with white tiles. The main reason why I use 6X8 tiles is that it's the largest standard tile size that I can hold with one hand. That way, I can hold the tile in one hand and back butter it with the other hand before setting it. Maybe handle a 6X8 tile to make sure you can do that comfortably.

[/quote] As for the flatness of the walls, I'm putting CBU up against the studs - doesn't that create an extremely flat surface to tile over?[/quote]

NO. Take a bright light and hold it against your wall to exagerate the roughness. You'll find that none of the walls or ceilngs in your house is really flat. The drywall on them is smooth, so the eyes tell the brain that the walls and ceilings are flat for lack of evidence to the contrary. But they're not flat, at least they're not in the building I live in. Nor are they plumb. After they put the studs in the wall, they'll dry, and when they do they can twist, bend, split, you name it, with the result that one corner, or one end or one piece is sticking out in front of the rest of the stud, and the rest of the studs. 6X8 tiles are small enough to conform to my walls well, so I think you should be OK with them too.

Also, if you're going to have the front of your CBU's flush with the tub lip, I'd put extra thin set on the back of your bottom tiles (the ones you cut). That's cuz there's be a radius of curvature of about 1/16 of an inch where the lip meets the tub.

Also, after setting all your tiles, use some narrow masking tape to mask off the gap between the tiles and the tub. You don't want grout in that joint because it'll always crack in that joint. Mask off that joint and caulk it with silicone afterwards.

And, finally, when I set tile, I use a "V" notched trowel to trowel the thin set on. I run my trowel vertically to make a bunch of VVVVVVVVVV ridges on the wall. And, when I back butter my tiles, I make a final trowel pass in one direction too so that the ridges on the back of the tile and the wall are both vertical. That way, when I set the tiles on the wall I get a consistant thickness mortar bed between the two. When you set your tiles, they may look like a mouthful of crooked teeth before you grout, but grouting makes all the difference.

You should decide on what kind of grout sealer you want to use now; penetrating or film forming. On a shower wall, you're better off with penetrating in my view. On a kitchen floor or counter top, I'd use a film forming grout sealer so that soft food like cheeze or jello or whatever didn't get mooshed into the porous grout and provide a food supply for the bacteria.


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