durock or green rock for shower

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Hello NG,
I'm tiling a very small quarter bath (shower) in the wet part of Oregon. In other places, I've thought that the expense of Durock wasn't worth it, but I'm leaning toward recommending it for this job.
Floor is concrete, bottom floor of 2 stories.
What say you?
--
Cal

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| I'm tiling a very small quarter bath (shower) in the wet part of Oregon. | In other places, I've thought that the expense of Durock wasn't worth | it, but I'm leaning toward recommending it for this job. |
I wouldn't tile on drywall even in a dry room. It's just stuck to paper. In the 80s, before concrete board and after metal lath was common, most tiling was either on plywood or drywall. The former would pop off due to expansion/contraction, while the latter had a short life expectancy - often less than 10 years, depending on how carefully one caulked to keep water out of the wall.
I only tile on concrete board with thinset. It's more work than using tile mastic and/or drywall, but the result is a mortar wall that will last.
Side note: I've noticed that greenboard is no longer grayish inside, and sometimes comes as "purpleboard". I'm curious whether anyone knows the story there. I thought greenboard probably had tar to make it water-resistant, and that maybe that was banned, but I don't know.
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On 11/1/2015 5:19 AM, Mayayana wrote:

Thx for your comment, Maya, I didn't read closely enough. Do you plywood behind joints (between studs) as backer?
Can we use ordinary drywall mesh for the seam?
--
Cal

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Hardibacker comes in 3'x5' sheets (Durock can be bought in 4'x8' sheets). In most showers a single sheet will span wall to wall so you shouldn't have any seams. However, if you need to have a joint cut the sheets as needed so the seam ends up over a stud.
Adding blocking behind horizontal seams would add a little extra strength, but it is not a necessity if you tape and mortar the joints (similar to taping drywall joints).

I used the mesh specifically sold for taping backerboard seams, but I don't think there's any real difference from the regular fiberglass tape used with drywall. Still, a roll is only $4 so it seems pointless to guess on something so inexpensive.
Anthony Watson www.mountainsoftware.com www.watsondiy.com
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| Thx for your comment, Maya, I didn't read closely enough. Do you plywood | behind joints (between studs) as backer? |
I usually just try to leave such joints high up. As Anthony said, it come 1/2"x3'x5'. (I've never seen 4x8 where I am.) So it's basically one sheet on each end and two in the middle. The joint where they meet should be a stud.
Staple plastic on the studs first and cut it at the bottom after boarding. If you then caulk that joint before tiling you'll have 2 caulk joints at the end to keep water out of the wall. (The concrete board companies at least used to recommend no plastic, in order to let it air out behind if it gets wet. That doesn't make sense to me. First, it shouldn't get wet. Second, if it ever does the concrete board can tolerate being damp for far longer than the studs can.)
I had one job where the customer apparently fell against the wall and a crack in the tile resulted. I assumed it must have been on a joint and offered to replace that tile. It turned out not to be on a joint. It was in the middle of the board. As far as I could tell, the cause seemed to be a combination of flex in the concrete board and cheap tile that was soft. I don't actually know, though, what they did to cause the cracks. But the moral of that story for me is to avoid large spans. Some horizontal blocking is not a bad idea if that's practical.
Personally I don't trust hardibacker, but I've never actually used it. I'm just wary of a composite product. Like using chipboard for house sheathing. It's legal. It seems to work. But what if the glue breaks down in 20 years? 30 years? 40 years? Or even 10 years. There's a lot of technology out there that hasn't been around long enough to be time-tested.
| Can we use ordinary drywall mesh for the seam? | I'd double it if you do that. The concrete board mesh tape is stronger, though.
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| If you use the plastic, it will trap the small amount of moisture that WILL go | through the grout, resulting in possible mildew problems. Better to use a few | coats of Redgard or a similar product on the concrete board before tiling. | Without any coating, moisture can evaporate after going through the backerboard | so that moisture does not build up to cause problems. |
That's the theory, but it doesn't make sense to me. Moisture can migrate through the top if it gets through. But if there's a break, and lack of plastic is letting moisture reach a stud, then eventually the whole thing will have to be redone. I've always used plastic and never had a problem.
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On 11/02/2015 06:30 AM, Mayayana wrote:

The idea is that you only want one moisture barrier, and with so many houses now using housewrap, if you put plastic on the studs you are creating an area in which any trapped moisture has no where to go. As the dewpoint changes, this trapped moisture will, at times, condense, leading to mold problems.
In my shower I just put the hardibacker right on the studs, then slathered it with redgard before I began tiling (using thinset mortar, of course).
Jon
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| The idea is that you only want one moisture barrier, and with so many | houses now using housewrap, if you put plastic on the studs you are | creating an area in which any trapped moisture has no where to go. As | the dewpoint changes, this trapped moisture will, at times, condense, | leading to mold problems. |
That's not actually how it works. The housewrap should be a wind barrier that allows moisture to migrate through.
"The TYPAR Weather Protection System. It provides exceptional air and water holdout, optimal moisture vapor transmission"
(I wouldn't trust housewrap to stop liquid water, but that's another debate. :)
The inside walls can then be covered in plastic as a moisture barrier. So moisture is never getting into the walls from the inside in the first place. That's also a nice bonus where winters result in very dry indoor air.
Though in most of the places I work houses are not wrapped. They may have tar paper, but the walls are usually leaky in terms of air flow. Old houses are not wrapped unless they're wood and have been completely redone on the outside, with all the old siding stripped off. Where I live that's not at all common. In fact, I'm often dealing with houses that have incomplete or no insulation.
| In my shower I just put the hardibacker right on the studs, then | slathered it with redgard before I began tiling (using thinset mortar, | of course). |
I'd consider that an unnecessary experiment. Hopefully it works out OK. But your thinset is now not bonded to the hardibacker. It's bonded to the Redgard plastic coating. You've lost the advantage of producing a composite mortar wall. With concrete board, thinset and tile you'd end up with essentially a single mortar panel.
We've discussed this issue before. People have different opinions. To my mind there are an awfully lot of new inventions that are not time-tested and for which there's really no standards system to decide whether they actually make sense. I'd consider hardibacker, Redgard and waffle sheet underlayment all to be in that category -- claiming to solve a non-existent problem. Though I would be interested if someone came up with an easier- to-use version of concrete board that's also stronger. It's too easy to cause cracks in the concrete filler by bending and hitting.
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On Mon, 02 Nov 2015 07:00:02 -0800, Jon Danniken

Except housewrap is water repellant and not moisture proof. It is designed to breathe and pass moisture freely.

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On Mon, 2 Nov 2015 09:30:20 -0500, "Mayayana"

moisture proof. No second guessing.
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| Just use the shluter system and be done with it. 100% water and | moisture proof. No second guessing.
I'm about convinced that you have stock in that company. I see no reason or even logic for it, other than to make lots of money selling the allure of "cutting edge technology".
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Mayayana posted for all of us...

-1 He resoning is: because it works.
--
Tekkie

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On Mon, 2 Nov 2015 12:48:11 -0500, "Mayayana"

30 years old.
It works Period. It is a small part of the cost when you consider the labour and everything - and it GUARANTEES you don't need to redo it in 5 years because you guessed wrong and used the wrong stuff trying to save $50.
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On 11/2/2015 12:48 PM, Mayayana wrote:

It works, a very important part of the job. We opted to use Swanstone bases rather than tile on the base, but if not, Schluter would have been used.
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snipped-for-privacy@snyder.on.ca posted for all of us...

+1
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I just looked up Redgard. Personally I'd be very dubious about such a product. You'll end up not with a mortar wall but with tile stuck to a plastic coating, that's in turn stuck to the concrete board. Will that hold up? Who knows? Another product that's not necessary and not time-tested.
Also, if you waterproof the concrete board you haven't done anything to stop water getting through. Leaks won't happen in the middle of the sheet. They'll happen at the bottom, corners, or around fixtures. In those areas a coating on the concrete board won't help.
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| The coating is over the board, board tape, and thinset applied at those | locations.
Yes, I understand that, which is why I said you're losing the mortar integrity. You're gluing your tile to a plastic coating rather than getting a thinset -> concrete bond.
| The redgard keeps any moisture that gets through the grout from | getting through the concrete board. Then it either has to find its way back out | through the grout, or find a path, hopefully back into the tub area, through the | caulk at the bottom of the tile. |
That sounds like Redgard marketing hocus pocus to me. Tiling on mortar has been done for thousands of years. Why, all of a sudden, is grout considered to be a non-waterproof material? Even if tiny bits of moisture can go through some grout, the concrete board is designed to let it migrate out. The top of the concrete board is not plastic wrapped.
I've been doing the same for years and never had a problem. I also built a steam room about 12-15 years ago. It's been heavily used with no sign of problems. Just as nearly every other steam room ever built has been some version of tile on mortar and has worked just fine. If moisture were getting through then even steam rooms built with concrete wall on metal lath would eventually break down.
The Shluter system is, in theory, similar to the Redgard approach, except that it would provide full waterproofing where Redgard probably won't. But it's also similar in that it's a plastic sheet glued to the wall. So the tile is only as stong as the bond between the thinset and that plastic sheet. The Shluter people even show their sheet being used over drywall! In that case the bond depends on tile -> plastic and also plastic -> paper. That seems idiotic to me. And why do they claim it makes sense? Just to keep the moisture barrier on the front side of the wall, with the theory that otherwise the concrete board will somehow get wet due to water leaking through the grout. The reasoning just doesn't hold water, so to speak. :)
| The plastic you suggest would likely create a problem with condensation into the | wall/floor space below the plastic, or the same potential water issue at the | caulking at the bottom of the tile. |
No, because the plastic is sealing it out. The plastic comes down behind the concrete board and the gap gets caulked before tiling. It's always possible that water can get through -- at the top of a porrly caulked tub or around a poorly sealed mixing valve, for instance. But in general a plastic sheet is going to provide a good seal.
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On Mon, 2 Nov 2015 14:53:39 -0500, "Mayayana"

Grout has ALWAYS been considered a non-watertite material.

If it works for you, that's all that counts. I'm just saying if someone who has not done it many times your way wants to do the job and be SURE the job is done right, Shluter is his best friend.
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On 11/01/2015 12:50 AM, Cal Dershowitz wrote:

IMHO the only choice you have available is between durock or hardibacker.
Jon
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I used Hardibacker for our showers. It's thinner and easier to cut.
The backerboard is a minimal cost compared to the rest of a tiling project.
Do it once, do it right.
Anthony Watson www.mountainsoftware.com www.watsondiy.com
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