With this method, you'd still be at a loss on how to affix the tiles to the tub flange.

A better option will be to furr out the suds allowing the ceement board and poly to hang in front of the tub flange.

OR defeat the plastic behind the CBU and apply a surface membrane.

I think that is a common technique, where the tile spans/hangs over the flange, no? It is only about 1/2 an inch it would need to hang over. Than where the tile meets the tub deck gets it gets caulked too.

So the installation method is correct, although furring strips is another method? Still concerned where the caulk should go, and how will the water running down the poly sheet get out?

I would think location # 1 so the poly gives a surface to apply the caulk

Location # 2, I would think the caulk would fall behind the wall cavity unless it was at a stud location

What do you mean water "flows" behind the concrete board?

I would think location # 1 so the poly gives a surface to apply the caulk

Location # 2, I would think the caulk would fall behind the wall cavity unless it was at a stud location

What do you mean water "flows" behind the concrete board?

You are correct, I left a gap between the Durock and the top of the tub flange (instructions said to do this verus let it actually sit on top of the flange). When you pull up the plastic you can see the wall cavity. So am thinking if you put caulk on the # 2 side in the drawing, nothing will keep the caulk in place and it will fall into the wall cavity. But if on side # 1, the water cannot exit.

Agree...furring strips is another installation method, but the one shown is just as common if not more so. Not sure if caulk is needed there? But after tile is installed, you need to caulk bottom of tile along the tub.

I would say no caulk

I would say no caulk

Oh no. I am more confused now?

please clarify the water behind the concrete board flowing?

I think when they say caulk at this step, they may mean to cailk the poly to the tub flange? You may need to pull up the poly and put on side #2, then push it back down again?

When I mention water flowing, I read on this forum that water gets behind the durock and needs to flow down the poly vapor and back into the tub. Flowing may be the incorrect word?

Water does not flow per se. Water would need to go horizontal, through the grout joint, through the thinset, through the Durock to even get to the vapor barrier. I hardly believe it would be flowing behind your walls. I would not take apart your walls to add furring strips.

Sounds like the furring strips may prevent the water issue behind the backerboard. Did the contractor install the tile yet?

Not sure what is the most common method

Checked my literature, could not find any information. Also checked a book by Mike Byrne.

Try a post at John Bridge, you may get feedback on caulk from contractors

You should pull down the durock and redo. Many seem to being going away from cement board now.

fall, where did you get this info? What are they using instead?

Membranes and waterproof boards such as Kerdi and Kerdi Board. Read much literature that construction is mitrating away from traditional methods. Gone from mud and lath, to tar paper and concrete boards, to poly and concrete boards, to newer methods such as Kerdi. The last guy that did our bathroom said he has not used tar paper in years. Guess the advancement in technology will make other methods obsolete at some point? As the one poster mentioned, would eliminate the caulk issue.

Unless I am mistaken and I do not believe I am they still use Durock or Hardi most often as a substrate and use the membrane over the top. It is most definitely still an accepted substrate and even preferred by some. I would not be so quick to come on here and tell someone to rip out perfectly good Durock. I am not saying what the OP has is correct or incorrect by any means just stating that your advice is not correct.

Is caulk even needed at this point? My tub was built this way, the tile hangs over a bit, and the joint between the tile and tub is caulked.

Can I put caulk on each side to play it safe? Still not sure how the water behind the Durock drains into the tub if caulked. Plus after the tile is installed, the gap at the tub would be caulked too.

I think the poly plastic is too long and hanging too far over the tub flange. May want to cut that back.

Does this poly look like the correct length? Also shown is the 3rd location of the caulk. I added in how I thought the tile should be installed. Before I remove everything, still concerned about the water behind the Durock that cannot get out? Can I leave all the caulk out of these 3 spots so it flows back into the tub?

This post has a link that shows caulk should not be at location 3? If that is the case, no caulk at 1 and 2 also? Should I glue the poly to the flange to seal it to the flange?

http://ths.gardenweb.com/forums/load/bath/msg0722533830492.html?2

Overlap of poly was fine in your first drawing, too short in second. Caulking at 2 would do no harm and offers reassurance that the poly would remain in position. If you're a drop of water running down the poly you don't want caulk at 1 or 3. Argument for caulking at 3 is to protect the joint from water being injected through the bottom from splashing and ease in cleaning. But if water does get behind it may stay there.

Regardless, do not firmly attach the bottom tiles to the tub flange as one poster suggested, only to the Durock.

This post was edited by dadereni on Thu, Jul 10, 14 at 15:24

Found this, metal flashing may be an alternative. If you have water behind your Durock caulking would trap that, therefore black mold? That other post says to use grout...NOT caulk. Caulking at 1, 2, or 3 will trap the flow of water which needs to drain into the tub.

Forgot the text

Forgot the text

{{!gwi}}

How is water getting behind the Durock. Is this an urban myth? So water is essentially traveling horizontal and needs to go through grout, through thinset, than goes through Durock? If this is the case, maybe you should remove the Durock and remove the poly, than reinstall and use a membrane?? I have a basement shower and can see behind the wall being one side is unfinished. I never ever ever saw and water running down the vapor barrier. Cannot answer the caulk question and looked last night and cannot see if caulk exists at 1 or 2. But I do have caulk at location 3. Am thinking caulk at 1 or 2 would provide an additional barrier? But then again, urban myth...how is water spashing down going to get behind the # 3 caulk and go vertical, make a 90 degree turn and get behind the Durock?

So are we saying caulk at # 2 but not at # 3 ? So the tile to tub space should be left clear?

Appears so, but everything seems to conflict. Another post they put grout at # 3 so it can drain. A crack will form there over time letting water out. I should have not built my shower this way and used no poly barrier and used Kerdi. But it appears it is too late not because you cannot have the Durock between two vapor barriers.

Okay. My opinion?

First, about LIQUID water getting behind the tile. It can happen. It doesn't always happen, but it can happen. It's more prone to happen with a lousy tiling job or a lousy grout job, or with a failed installation where the grout is pitted or cracked. In those cases you literally have open paths for liquid water to get behind the tile.

What happens more often is that the grout can wet and you can get vapor drive. I'm not going to get into specifics, suffice it to say that the when moisture vapor gets into a wall via this mechanism...it usually comes out of the wall via the same mechanism during a drying cycle.

Typically, any moisture that gets behind the tile/grout is absorbed by the cement board. If there is no poly behind the cement board, the moisture can continue through the cement board and into the insulation or into the framing bay. But that'll only happen if the rate of moisture accumulation during a wetting cycle is greater than the rate of moisture evacuation during a drying cycle. It takes a broken installation for that to happen.

With poly behind the cement board, the cement board will hold the moisture until it can dry back out into the bathroom during the previously mentioned drying cycle. If, due to failed grout or cracked tile, more water gets behind the tile than can come back out during a drying cycle? Then yes, over time the moisture can travel down the poly/cement board wall and hit the tub's flange area.

If the joint between the bottom course of wall tile and the tub flange/poly is open, it can dry out through that opening.

If that area is caulked, you'll typically have problems with the caulk. The caulk might soften or re-emulsify. The caulk might be perpetually discolored. The grout may always appear damp at the bottom of the wall.

Some installers caulk that entire joint. Some don't caulk it at all. Some leave weep holes every few feet in the run of caulk.

To be honest, excess moisture behind cement board is usually not a problem in most installations, unless the installation itself is flawed.

Is a topical membrane on the face or cement board better than poly behind the cement board? Yes it is, as it limits how far moisture can penetrate into the wall.

But with proper detailing, there should be no negative issues with a cement board and poly installation, even with the bottom tile-to-flange joint sealed with caulk.

Again. My opinion.

Thanks Mongoct. If it was your bathroom, would you caulk the tile/tub flange or leave open? Do I need caulk behind the tile at 1 or 2? Assuming if the poly is in place, you would not apply a membrane like Kerdi or a liquid one to avoid the double membrane issue? Do you see many poly/cement board or tar paper/cement board installations or do you consider them "dated."

The poly gets sealed at #2. I'll run a bead along the top of the tub's flange. When the poly gets set into the sealant, some sealant can smoosh over the front face of the tub flange, sealing the poly to the face of the flange as well.

That overlap is part of the water proofing system for the shower, it is important to overlap it correctly.

The gap (#3) between the bottom course of tile and the tub deck is usually as wide as the grout lines on the wall. That gap usually gets caulked for decorative purposes. Most people want it caulked for a clean installation. I caulk it as well. Not caulking that gap does not affect the integrity of the waterproofing within the shower.

If I use poly, you are correct, I don't use a topical membrane on the face of the cement board in addition to the poly behind the cement board.

FWIW, in my own house I have both; a poly tub surround shower in the kids' bathroom and a Kerdi walk-in shower in the master bath. Both are roughly 15 years old.

With the proliferation of topical membranes, I suppose poly could be considered "dated". But it's still an appropriate way to build, especially for a tub surround with a flanged tub or for a shower with a manufactured flanged pan.

Were I to build a "fully tiled shower" with a tiled mud base and tiled walls? My first recommendation would be to use a flanged drain with topical membrane. Usually a Laticrete flanged drain with Hydroban (water proof but not vapor proof) on the floor and walls for a regular non-steam shower. If a steam shower, then a Kerdi flanged drain with Kerdi membrane (water and vapor proof) on the floor and walls.

Those are not hard recommendations, they are simply my personal preferences. I do feel that as the thermal envelopes of houses are built tighter and tighter, it becomes more and more important to control water. Thus the movement to topical membranes.

Still, in everyday construction, the attention to and execution of the installation details is more important than the materials used. I've seen impeccable poly showers. I've seen buggered up topical membrane showers.