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?
| 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.
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.
| 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.
| If you use the plastic, it will trap the small amount of moisture that
| through the grout, resulting in possible mildew problems. Better to use a
| coats of Redgard or a similar product on the concrete board before tiling.
| Without any coating, moisture can evaporate after going through the
| 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.
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,
| 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
"The TYPAR Weather Protection System. It provides
exceptional air and water holdout, optimal moisture
(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.
| 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".
No stock in the company, and this "cutting edge technology" is about
30 years old.
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
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
| The coating is over the board, board tape, and thinset applied at those
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
| through the grout, or find a path, hopefully back into the tub area,
| 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
| wall/floor space below the plastic, or the same potential water issue at
| 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.
Grout has ALWAYS been considered a non-watertite material.
It's your job and your choice. You will do it your way regardless.
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
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.
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