I understand that the layers under bathroom tile go (from bottom to
What is the purpose of the chicken wire?
Also, I know that Thinset is used to hold the tile to the hardboard.
But where else is Thinset (or other compounds) used in between the
You're using the membrane as a cheap replacement
for a copper pan? It's not needed in a normal bathroom
floor application. I'd be leery of using something like
that in a shower. It seems to be advertised for "constant
steam" applications, like for walls in steam rooms, to
reduce the migration of moisture through the wall.
Chicken wire might serve as structure in a sandmix
bed, like rebars in concrete, though I've never heard
of it being used.
For bath floors I normally screw concrete board to
plywood subfloor and use thinset on top of that.
I know a lot of people use the hardboard. I'm hesitant
to trust it because it seems to be some kind of glue-
based composite. Like using flakeboard for sheathing:
It might work fine, but what if the glue breaks down
in 20 years? There's nothing else holding it together.
|I understand that the layers under bathroom tile go (from bottom to
| Kerdi membrane
| Chicken wire
| What is the purpose of the chicken wire?
| Also, I know that Thinset is used to hold the tile to the hardboard.
| But where else is Thinset (or other compounds) used in between the
| lower layers?
Copper pan? You mean inside a shower, right? (I've always heard
'lead pan', not copper). Anyway, this is just regular floor tile
outside the shower, but still prone to getting wet sometimes.
Re concrete board: I thought that was the same has hardboard.
From what I could make of it, the chicken wire is intended as a sort
of cushion to keep the tile from cracking under uneven pressure. But I
don't deal with this stuff.
| Anyway, this is just regular floor tile
| outside the shower, but still prone to getting wet sometimes.
There's no reason for a vapor barrier under that.
But if you have large tiles there is reason to make
sure the subfloor is strong and stable -- that it
doesn't flex enough to possibly cause cracking tiles
down the road.
| Re concrete board: I thought that was the same has hardboard.
It may depend on where you live. What's available to
me are two things. One is called something like HardiBacker.
It's a composite fiber board. The other is actually a sheet of
concrete, usually made lighter by the addition of stryrofoam
pellets, and reinforced with fiberglass mesh. With the
concrete board and thinset you end up with something
that's like a solid sheet of mortar. The backer board may
be fine. I just avoid it because it's a fairly new product
and I don't want to trust the long term integrity of
whatever bonding agent they're using.
| From what I could make of it, the chicken wire is intended as a sort
| of cushion to keep the tile from cracking under uneven pressure. But I
| don't deal with this stuff.
I've never heard of that. It wouldn't make sense with
thinset. There isn't enough depth. The only way it might
make sense that I can think of is "for good measure" when
pouring a bed of sandmix. That's what you might do for
something like brittle marble tile, but not normally for floor
> ;3214176']I understand that the layers under bathroom tile go (from
> bottom to
I don't know what that chicken wire is all about.
And, from what I understand, Kerdi is primarily used on walls to prevent
humidity from accumulating inside the walls with the result that mold
grows in there.
For a wall, Kerdi serves much the same purpose as Red Gard; it's a
moisture barrier to prevent humidity accumulating in the walls.
For floors, I think you want to use a different Schluter product called
Ditra is a plastic mat.
You see, wood is a natural material that swells and shrinks with changes
in it's moisture content. Ceramic tile and the thin sets used to set
ceramic tile simply don't have the elasticity to accomodate that
movement in the substrate. So, it's never a good idea to set ceramic
tile directly over wood of any kind, including plywood.
This is why Mayayana says he screws a dimensionally stable tile backer
board down to the wood floor first, and then tiles over that
dimensionally stable tile backer. The effect is exactly the same as
standing on the fault line the day before the quake. There can be
tremendous stresses in the rock a mile below your feet, but if the
ground under your feet isn't moving, then you're completely unaware of
any tension or compression in the ground down there.
So, if you were a grout line, you'd have no reason to crack.
I exagerate when I say there can be tremendous stress between the wood
bathroom underlayment and the dimensionally stable tile backer board.
Wood used in construction is relatively soft and compresses easily.
Also, the movement of the wood is small and the screws will bend a
The important thing to remember is that the tile gets set on a
dimensionally stable tile backer board like Hardibacker board,
Wonderboard, Durarock, Aquaboard, DenShield, etc. so that there's no
tensile or compressive forces put on the tiling because of swelling or
shrinking of the wood below.
Schluter Ditra accomplishes the same thing without using a dimensionally
stable tile backer board. It's a plastic mat that allows movement of
the wood below the mat without causing stress in the tiling above the
And, because Ditra is a PLASTIC mat, it prevents to accumulation of
humidity in the floor just like Kerdi does in the walls.
If I were you, I would use Ditra under your floor tiles, Red Gard or
Kerdi under your wall tiles, and leave the chicken wire out.
Agreed. Don't try to complicate it by mixing different incompatible
processes and using materials that are not intended to be used as you are
planning. Go the entire Schluter system and you cannot go wrong. It may cost
a little more but will give you an iron clad installation. Check the
Schluter.com website for detailed instructions on using their materials.
Shop around as prices do vary with the big box stores being the most
expensive and with a limited selection of components. Large tile
shops/warehouses can have the lowest prices and the best selection.
Checking back: I just spoke to someone at Thinset (asking about max
thickness) and described the general layout without mentioning the
chickenwire. The lowest layer is oak floorboards, so that may have
something to do with this. Granted, the guy at their help desk was not
an installer, but he thought that oak may present a problem in
dimensional stability. But he also thought that Hardibacker and
concrete board are the same, which in this case, is not true.
If there is a problem with dimensional stability of oak, it should not
be of much consequence within the small 1 foot by 2.5 feet rectangle
that I'm working with. But I would think that any dimensional problems
would relate to ply or other types of wood as well. Perhaps that's
where the chickenwire was supposed to come into play.
I ended up using hardibacker for spacing, under concrete board, then
the large slate tile.
I think you need to forget about the chicken wire. :)
You're only tiling 1' x 2.5'? That's a very small space.
Oak boards would be less stable than plywood, which
has plies alternating in opposite directions for stability.
Also, if the oak ever gets wet it might swell up. If it were
me I'd either take up the oak or at least go over it first
with something like 1/2" plywood. But if it's good and
flat you're probably fine. As long as you seal around the
edges (in case there's ever a flood) you'll probably
never have to worry about it.
| >|I understand that the layers under bathroom tile go (from bottom to
| >| top):
| >| Kerdi membrane
| >| Chicken wire
| >| Hardboard
| >| Tile
| >| What is the purpose of the chicken wire?
| >| Also, I know that Thinset is used to hold the tile to the hardboard.
| >| But where else is Thinset (or other compounds) used in between the
| >| lower layers?
Chicken wire is used as a reinforcement in a custom mud bed shower pan.
Expanded metal lath, or metal hardware cloth would be better choices if
you can get them.
If you're just tiling a bathroom floor, you can skip the Kerdi and
chicken wire. Just install the backerboard, then tile directly over that.
If you're building a custom shower pan with a mud bed, you would normally
install a layer of roofing felt or rosin paper on the subfloor. This acts
as an isolation membrane, and prevents the subfloor from sucking the
moisture out of the mortar before it cures.
Then you would install your reinforcing wire, and build up your mud bed.
Hardibacker board is used on the walls.
Then you can install your Kerdi waterproofing membrane on the shower pan
and up the walls.
Finally, you can install your tile, and grout it once the thinset has
Of course, this is just a basic overview. There are a lot of details you
should research first. I recommend you visit the John Bridge tile forum
and study Kerdi shower pan installations:
You can also see how I handled the different situations in our two
| Then you can install your Kerdi waterproofing membrane on the shower pan
| and up the walls.
I'm curious why you'd recommend that. This forum
is the first I've heard of plastic backer films. I've
used concrete board for many years. Companies like
Durock have never recommended moisture barrier. I
put plastic sheet behind the lower section of concrete
board on walls, in case there's ever a long, slow leak,
but I'm careful not to seal the board entirely.
The idea is that water shouldn't be getting through in
the first place. If it does, sometime down the road, the
concrete board can diffuse it without breaking down.
By putting a sheet of plastic between tile and board,
or between tile and sandmix base, you're breaking the
continuity of the mortar, for no apparent reason that
I can see. If the tile were not, in itself, waterproof there
would be little point in going to the trouble of using it.
Are there some kind of studies somewhere -- not paid
for by the plastic membrane companies -- showing
that the polyethylene layer is somehow an improvement?
I could see the possible logic of using such a membrane
in places like low-end condo conversions, to float a floor
on the subfloor without needing some kind of mortar
base or board, though even that seems hokey to me.
I can't see the logic of what you're describing.
Before Kerdi was available, the traditional way to make a waterproof
shower pan was to have a custom copper pan manufactured, or to use a
vinyl pan liner embedded in the mortar bed. In those cases, the tile
backer board usually overlapped the shower pan, so any water that found
it's way behind the tile "should" eventually work it's way down to where
it would drip inside the pan liner. (I believe you're supposed to keep
the bottom of the backerboard up off the pan so it doesn't wick moisture
up into the wall) Of course, it's always better to keep the water out of
the wall in the first place.
Kerdi is applied to the mortar bed AFTER the pan is built-up. It is
installed directly under the tile. In this case, the kerdi waterproofer
laps up the walls, and the manufacturer recommends it extend up above the
water source (shower head or tub spout, whichever is highest). It makes
sense as you wouldn't want any water getting behind the kerdi membrane
and into the structure. Basically the entire shower area becomes a
unified waterproof barrier.
Tile is waterproof. Grout is not.
Also, Kerdi isn't just a sheet of plastic. It's some kind of fabric
material and you use regular thinset to install it.
I am not aware of any studies, but I seem to recall several topics on the
John Bridge forum talking about moisture problems in traditional vinyl
lined mud beds. It has been about 10 years since I really researched tile
work, but I believe the moisture soaks through the grout and into the
mortar above the liner. Mold, mildew, and probably other problems. You
might search the tile forum if you need details.
I used Kerdi on our entire master bathroom, even the flat areas of the
floor that didn't need to be waterproofed. Zero problems in the last 10
years. Compared to all the other costs of building a bathroom, the cost
of Kerdi was insignificant. Certainly cheaper than a copper pan.
While it still has seams, epoxy grout is far superior to sand grout.
I used a one piece Swanstone base for my shower and I'm going to do the
same in the other bathroom soon too. Tile on the walls and floor.
| I used Kerdi on our entire master bathroom, even the flat areas of the
| floor that didn't need to be waterproofed. Zero problems in the last 10
| years. Compared to all the other costs of building a bathroom, the cost
| of Kerdi was insignificant. Certainly cheaper than a copper pan.
It's good to know that it's held up. I'd be
wary of the interrupt it's causing between
the two layers of thinset. They claim that
hairs on one side, and insets on the other,
solve that problem. Maybe so. I still find
it hard to justify using it, though. In a copper
pan it makes no sense, and a shower should
not be built without a copper pan.
On a wall inside a shower, using concrete
board, I could see how it might seem to make
sense, but water simply doesn't get behind the
concrete board normally. Grout *is* waterproof.
If it were not then people would have to rebuild
showers every couple of years. The only problems
I normally see are where there's a gap between
a tub and wall, and people don't keep it caulked.
On a wall or floor outside the shower I can't
see any possible justification. As you say, it's
creating a "unified water barrier". But that would
only be relevant in the case of something like a
tub overflow. In that case, the water will not be
going through the tile floor, anyway, in all likelihood.
It will go down through the gap around a radiator
pipe, perhaps, or under the door and through the
floor in the hall. It would never be held in the
bathroom long enough to test the resistance of the
I have never used a copper pan, so I can't really say much about them. I
suppose they would work fine in a traditional square or rectangular
shower, but irregular shapes might be tricky. Copper pans aren't really
DIY friendly either. Kerdi is.
Our master shower is 6'x6'. It would have been very expensive to have a
copper pan made for that size of shower.
A quick Google search ("is grout waterproof") shows numerous sites that
If grout and tile were waterproof, there would be no need for a shower
pan or waterproofing membrane beneath the tile.
Walls are less likely to have leaks because the water mostly just
splashes on and runs off. Floors are a different matter where water can
stand and soak in.
For the most part, I agree with this. In my case, I had extra Kerdi
leftover with no other use, so I went ahead and waterproofed the entire
bathroom floor. If there's a major spill or the bathroom sink develops a
leak, it's just an extra layer of protection.
Also, we have a "curbless" shower, so in effect the entire bathroom
becomes part of the shower pan. I had to cover most of the floor anyway,
so an extra three feet was insignificant. I had it, why not use it.
I was very skeptical of Kerdi when we built our house, since I had never
seen it used before. Now that I've used it, I can't imagine doing a
shower any other way. It's waterproof, easy to install, and relatively
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.