Ceramic or stone floor tile is typically
applied over a sturdy, continuous cement surface. Years ago,
a tile layer would build up a thick bed of mortar, perhaps 1 to 2
inches thick, before laying floor tiles.
Today there are cement-based tile
backerboard products that take the place of a mortarbed. These
tile backer materials are cement-based sheets that are mortared to
the floor and fastened with nails or screws. Durock® and Wonderboard®
are two products that are made from cement and glass fibers.
HardieBacker® from James Hardie Corporation is made from cement and
wood fibers, similar to fiber-cement siding. HardiBacker is easier
to cut and fasten than the cement-and-glass materials.
I used 1/4" thick HardieBacker, which
is available at Lowe's and Home Depot. Half-inch thick HardiBacker
is also available, which is called HardieBacker 500.
| The bath room
subfloor in this 110-year-old house was replaced
during remodeling. The old subfloor was heavy
OSB, which had begun to rot because of a small
leak around the toilet. We replaced the
subfloor with pressure-treated 3/4" plywood in
the areas that could get wet, and regular
plywood elsewhere. |
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I laid the first sheet of HardieBacker on the
floor and used a straightedge to mark the cut
line. |
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| This is a
scoring tool for fiber-cement backerboard.
There are 2 sharp tungsten-carbide cutting teeth
on the end. |
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I just held the straight-edge in place and ran
the scoring tool along the edge, pressing
firmly. I made about 5 or 6 passes with the
scoring tool, which cut about halfway through
the cement board.
After the first two passes, I didn't need the
straight-edge because the groove was deep enough
to guide the tool. |
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| Then I simply
lifted the edge of the HardieBacker board, and
the material snapped along the scored line.
This is different from scoring and snapping
drywall, where you fold the board away
from the scored side. With HardieBacker, you can
fold the board towards the scored
side... as long as the scored line is deep
enough. |
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For a smoother edge, it's possible
to score both sides before snapping the board. Just
make sure the score lines are aligned perfectly.
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Cutting The Hole For The
Toilet
Drain Flange:
I laid out the location of the circle (7˝
inches diameter, in my case), based on the
location of the centerline from the edges of the
panel.
To cut the hole, I first
drilled several small holes with a 3/8"
carbide-tipped masonry drill bit. |
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| Then I used a
jig saw to cut along the circle. I was going
to use a tungsten carbide jig saw blade, but it
would not fit in this newer Bosch jig saw. Bosch
has their own style of jig saw blades, with a
sort of "T" shape at the end.
So I had to use an ordinary wood-cutting jig
saw blade, figuring the blade would be destroyed
after just a few cuts in this cement board.
Actually, the teeth didn't get dull as fast as I
expected. |
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Warning:
The instructions for cutting
HardieBacker say to do any power tool cutting outdoors
to keep dust out of the home. Obviously I did not follow
those instructions, but I did have a large fan in the
window nearby to extract dust.
The instructions warn about breathing the dust from
cutting HardieBacker, which contains silica. If
too much silica is breathed in, it can cause
silicosis, a serious lung disease.
I strongly urge you to follow the instructions: wear an
N95 dust mask, keep the room well ventilated if cutting
with power tools, and use a HEPA-filter vacuum up any
dust or shavings instead of sweeping. |
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The first two pieces of HardiBacker set in place
after being cut. I cut all the pieces of
HardiBacker and made sure they fit properly
before fastening them to the subfloor. |
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| Also, before
fastening the HardieBacker, I pre-drilled some
shallow dimples (countersinks) for the screw heads.
I used a 3/8" carbide-tipped masonry drill for
this. |
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These special screws are sold for fastening
cement tile-backer panels. Note the serrations
on the underside of the screw head... these are
supposed to dig a counter-sunk hole for the
head, but it doesn't really work perfectly,
which is why I drilled my own countersink holes
earlier. |
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| At this
point, all of the HardieBacker panels have been
cut and fitted, and the countersink holes have
been drilled. I spaced these hole 8 inches
apart, wherever there were shallow marks molded
into the backerboard. |
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I mixed some thinset mortar in an empty 5-gallon drywall
bucket. I used a paddle-type mixer with my
heavy-duty 1/2" drill... although a "cage-type"
mixer may be faster.
Mixing mortar requires a serious, powerful
drill... preferably a drill with a low top speed. |
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| I used a
clean garden trowel to scoop out the thinset
mortar from the bucket... |
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...then I used the smooth edge of a notched
trowel to spread the thinset mortar around. |
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| After the
mortar was completely spread over the target
area, I used the notched side of the trowel to
"comb" the mortar. |
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The instructions say to use a 1/4"
square-notched trowel to comb the mortar, but I used a 3/16"
V-notched trowel instead. Why? Because I needed to keep the
overall thickness of the tile floor to a minimum, to avoid a
problem where the bathroom tile meets the hardwood floor at
the doorway.
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I only applied thinset mortar to the area
beneath the first piece of HardiBacker...
otherwise I'd step in the mortar. |
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| I laid the
first piece of HardieBacker in the mortar. |
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Then I used an impact driver to drive those
special cement-board screws through the
HardieBacker into the plywood subfloor. |
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Drill-Driver Vs. Impact
Driver:
I started driving screws with an
ordinary drill-driver, because both of the
batteries for my impact driver had become
discharged. I found that my 14.4 volt drill-driver would
leave the screw head slightly above the
surface, in spite of the countersunk holes I
pre-drilled.
After an hour of recharging, I
tried setting screws with the impact driver. I was able
to drive the screw heads below the board surface with no
problem. It seems that the hammering action makes a big
difference in helping those serrations under the head do
their cutting action. Maybe a
more powerful drill would sink the screws deeper, but I
think this is a good example of the benefits of an
impact driver: a drill-driver just uses a simple motor
to turn the screw, while an impact driver uses a
rotating hammer to pound the screw through the material
with minimal effort and no kickback. |
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| After the
first piece of HardieBacker (against the
windows), I laid the next large piece towards
the door. Then I installed a couple of narrow
strips: at the door way, and on the left-hand
side next to the wall. |
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Then I installed two more pieces of HardieBacker
in this L-shaped bath room to complete the
project. |
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| The dark
patch is where I filled in this gap with mortar,
because my Hardibacker panels shifted slightly
from the intended position. The instructions
say to stagger the joints and avoid a
"4-way corner", where 3 or 4 panels meet at one
point, as they almost do here. This wasn't
practical in my situation... unless I cut that
first panel narrower and made a wider final
strip at the doorway. We'll see if any cracks
appear at this point. |
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Note that fiberglass mesh tape (red
arrow) must be applied over the joints between
panels of HardiBacker. Normally this can be
done right after installing the backerboard
panels, or right before laying the floor tile.
In my case, I had to install floor warming
cables before doing the tile, so initially I
applied the mesh tape only where it would be
covered by the metal anchor straps. |
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I figured the mesh would be peeled
up from walking on it, so I waited as long as possible
before placing tape on all joints.
