Applying a mortar bed
ting bed for wet and dry installations. It’s stable,
takes strength and a
unaffected by moisture, and easily cut and
lot of skill. After
attached. Backer board is also called cementi-
installing a curing
tious backer units (CBUs), HardieBacker®,
membrane and
Durock®, and WonderBoard—the last three being
attaching wire mesh,
you must carefully
popular brands. These products feature a
mix and trowel the
cement-based core, reinforced by fiberglass mesh
mortar on, level or
or integral fibers. Because there’s considerable
plumb float strips,
variation among brands, always consult product
and screed off excess
literature for details on installation.
mortar until the bed
is uniformly flat.
Glass-mat gypsum board. This board (one
Then, after it has set
brand is DensShield®) has a water-resistant core
a bit, use a wood float
and a heat-cured acrylic coating. It’s not as rug-
to roughen its surface
ged as backer board, but it’s an acceptable setting
slightly, which
bed in tub surrounds and other light-duty wet
improves the
areas. Don’t confuse this product with drywall.
adhesion for the
thinset to follow.
Glass-mat gypsum board is specifically designed
as a tile backer.
Unpainted drywall. Drywall is an acceptable
setting bed where walls stay dry. Caution: Never
bond tile directly to drywall in damp or wet instal-
lations. Moisture-resistant drywall is an accept-
able substrate in damp or wet installations only
when it is covered with a waterproofing mem-
brane and then a mortar bed or backer board.
Tile applied directly to drywall in wet installa-
tions invariably fails sooner or later, often
because people showering bump the walls, com-
pressing the drywall’s gypsum core. No longer
supported evenly by the core, the grout loosens,
water enters and soaks the paper, and—all too
often—the framing rots.
456 chapter 16
exterior-grade plywood. It’s usually a mistake
to use plywood, even exterior grade, as a setting
bed. Exposed to moisture, plywood tends to swell
and delaminate. If you must use it as a setting
bed for floor or countertop installations, be sure
to cover it with a continuous waterproofing
membrane; the base should be at least 11⁄8 in.
thick (for example, 1⁄2-in. plywood underlayment
laminated to a 5⁄8-in. plywood subfloor). On
walls, 5⁄8-in. plywood is the minimum. Never use
particleboard, OSB, or interior-grade plywood as
setting beds.
Self-leveling compounds. Self-leveling com-
pounds (SLCs), such as LevelQuik®, have many
of the virtues of a mortar bed but require few of
the skills needed to float one. Basically, SLCs are
fortified mortar powders mixed thin and poured
Here, a tiler uses a margin trowel to apply thinset to a trimmed slate tile. With
onto out-of-level floors. With a small amount of
the correct consistency, thinset spreads easily yet will adhere to a trowel
troweling, they spread across the floor and, with-
turned on edge. Because polymer-modified thinsets have great bonding
in minutes, start to set. Just two hours later,
strength, you’re safer wearing rubber gloves. Also, be sure to clean tools
you’ve got a hard, almost perfectly level mortar-
immediately.
setting bed ready to tile.
That’s the short list of common setting beds.
For other materials, see “Odd or Problematic
priate for virtually all setting-bed materials.
Setting Beds” on p. 465.
Thinsets also are used to laminate rigid setting
beds to substrates to create an inflexible sub-
adheSiVeS
structure for tiling. (Construction adhesive is
also used in such laminations, but it is flexible,
Once you’ve chosen a suitable setting bed for
so it doesn’t achieve the rigidity of a thinset
your wet or dry installation, choose a compatible lamination.)
adhesive. Adhesives vary greatly from brand to
Despite the cement ingredients they have in
brand, so again, always follow the manufacturer’s common, thinsets vary widely, depending on
mixing and application instructions exactly.
their additives. Water-based thinsets are the weak-
There are three major groups of adhesives: mas-
est of the group, although they are generally
tics, which come ready-mixed; thinset adhesives,
stronger than mastics. Latex- and acrylic-based
which are cementitious powders generally mixed thinsets (also known as polymer-modified thin-
on site just before setting the tile; and epoxy thin-
sets) are strong, somewhat water-resistant, and,
sets that, like most epoxies, require you to mix a
all in all, the best choice for bonding tile to backer
hardener and a resin.
board, mortar beds, SLCs, drywall, and concrete
Organic mastics are the least expensive of the
slabs. And they’re a close second for bonding
three adhesive options. Because they come pre-
almost everything else.
mixed, they’re the most convenient option, but
Most thinsets are mixed from powder. After
they’re also the weakest. They are OK for attach-
mixing, they have a “bucket life” of about two
ing tiles to dry counters or walls—over drywall,
hours. After being troweled onto a setting bed,
for example—but they’re inappropriate where
they start to set in 15 to 20 minutes.
there’s water, heavy use, or heat. Mastics just
epoxy thinsets have excellent compressive and
don’t have the strength of thinsets.
tensile strengths. They bond well and yet retain
Mastics require a nearly flat setting bed. That
flexibility when cured. After drying, they are
is, when they are applied thickly to fill voids, they unaffected by moisture, so they’re suitable for all
neither cure completely nor bond thoroughly.
situations and substrates. There’s a catch, of
Mastic cleans up well with water or solvent if you course: Epoxies are four or five times more
remove the excess material at once. Opened con-
expensive than other thinsets and quite tempera-
tainers don’t keep well, so throw away any left-
mental. You must mix the liquid resins and hard-
over mastic after you’ve set the tiles.
eners in exact proportions with the dry ingredi-
Thinsets have great bonding and compressive
ents. Setting times are similarly exacting. If
strength. Being cement based, they bond best
directions say 20 minutes, you can set your
with mortar beds or backer board but are appro-
watch by them. Above all, clean up epoxy before
&nbs
p; tiling
457
MeMbraneS
Tile, grout, and many setting beds are unaffected
zzzzzz Waterproofing a tub
Surround
by water. But they are porous, so water can
Water-resistant
migrate through them, potentially damaging ply-
(WR) drywall
wood substrates or wood framing. To prevent
or greenboard
damage in damp or wet areas, install a water-
proofing membrane first. Even areas that are nor-
1
mally dry, such as entryways, should have a mod-
/8-in.
gap
Waterproof
est building-paper membrane if the floors will be
membrane
subject to wet mopping and dripping umbrellas.
For walls above the water line in wet areas
and for countertops subjected to occasional
Fiberglass
mesh tape
water, a 15-lb. building-paper membrane is stan-
dard, but installing a 60-minute stucco paper
(which is impermeable for 60 minutes) makes
Thinset
sense. It’s stronger, less likely to tear, and more
water-resistant. When installing such mem-
branes, overlap the lower courses and vertical
4-in.
seams of paper by 4 in. Although some builders
overlap
recommend 4-mil polyethylene as a waterproof-
ing membrane, stucco paper has one big advan-
Backer
tage: Unlike plastic, it is semipermeable.
board
Tile
This tub surround would be sufficiently rigid
without the WR drywal . But instal ers frequently
add a drywal layer to build up the wal thickness
when they’ll be using bullnose edge trim.
it sets; some types sponge clean with water, oth-
P R O T I P
ers with solvents.
Manufacturers frequently change
grout
their grout colors, so buy 10%
more than you need for your cur-
Grout is a specialized mortar that seals the joints
rent installation. once the job is
between tiles. Most grouts contain sand, cement,
done, wrap the extra grout in a
and a coloring agent. Grout may also contain
plastic bag, label it as to where it
additives to stabilize color, increase water and
was used, and store it in a dry
stain resistance, and increase strength and
place. While you’re at it, buy
flexibility. Most grouts and premixed additives
caulking the same color as your
are sold as a powder, which is subsequently
grout; many tile stores carry
mixed with liquid and allowed to stand (or slake)
color-matched caulk, both
for 10 minutes before final stirring to the correct
sandless and sanded.
consistency.
Use sandless grout for joints narrower than
1⁄8 in. Use sanded grout for joints 1⁄8 in. and wider.
Most tile suppliers carry grout in hundreds of
colors. Whatever the color, remember that the
greater the contrast between grout and tile, the
more obvious the joints and workmanship.
All wet installations need a waterproofing membrane.
Here, a tub surround gets two layers of Fortifiber’s Super
Jumbo Tex 60 Minute stucco paper, which is a fiber-
reinforced barrier that’s tougher and more water-resistant
than regular building paper.
458 chapter 16
Therefore, it allows water to escape should any
When checking surfaces for plumb
get behind the barrier.
and level, take several readings with a
Below the water line, such as in a shower pan,
spirit level, especially in corners. If
you need to protect wood substructure with an
they’re out of plumb, tile joints won’t
align, and the mismatch will be
impervious membrane. Thus most shower pans
glaringly obvious. Correct the
are lined with sheet rubber, such as 30-mil, fiber-
condition or don’t tile.
reinforced chlorinated polyethylene (CPE),
whose seams are overlapped and chemically
bonded with a solvent. Of course, you don’t want
to puncture CPE shower-pan membranes with
screws or nails. Instead, roll the membrane onto
a fresh layer of latex thinset adhesive, and cover
it with a mortar bed.
Note: The comments in this section are gener-
alizations. Follow the manufacturer’s installation
instructions for specific adhesives, membranes,
and setting-bed materials.
Getting Ready to Tile
If the substructure beneath the tile isn’t sturdy
and stable, the job won’t last. Likewise, if walls
aren’t plumb or floors aren’t level, tiles may
adhere, but they may not look good. Start by
assessing the existing surfaces. And that will
inform your next steps, which can range from
merely sanding finish surfaces to tearing out and
zzzzzz corner out of Plumb
reframing with studs and joists. The condition of
existing floors, walls, and counters will also
determine which setting bed you choose—and
whether you should tile at all.
aSSeSSing areaS to be tiled
To check whether floors or countertops are level,
use a long spirit level or a shorter level atop a
perfectly straight board. Take several readings
and use a pencil to mark individual high spots
and dips. If variations from level exceed 1⁄8 in. in
10 ft., floating a mortar bed or pouring SLC may
be your best bet for establishing a flat setting
bed. If the surface irregularities are less than that
or the substrate just needs stiffening, adding a
single layer of backer board may be all you need.
If room corners aren’t square or facing walls
aren’t parallel, you may need to angle-cut floor
tiles around the room’s perimeter. This is not
ideal, especially in narrow alcoves or hallways,
but baseboard trim will partially cover those
angled cuts. Similarly, at the back of counters,
blacksplashes will cover angle-cut tiles.
To check walls for plumb, use a long spirit
level or a plumb bob; a taut string is also handy
to detect high and low spots. Begin by surveying
the entire wall. Unless the tiled corners are
plumb, you’ll have tapering cuts or mismatched
Corner wal s too far out of plumb can’t
grout lines where the planes converge. To correct
be tiled successfully. Their tile joints
out-of-plumb walls, your choices are floating a
won’t align, and the mismatch will be
mortar bed, reframing the walls, or not tiling at
glaringly obvious.
tiling
459
Removing the toilet lets you reinstall it on top
of the new tile. Some people mistakenly leave the
toilet in place and as a result are forced to make
a lot of unsightly tile cuts around its base, which
can also be troublesome to caulk an
d maintain.
Begin by turning off the shutoff valve to stop
incoming water, disconnect the supply line, flush
the toilet and remove the remaining water, and
disconnect the anchor bolts holding the base to
the floor.
Because toilets are heavy, find someone to
help you move the toilet out of the way. To block
septic gases and keep objects from falling
through the closet flange into the closet bend,
stuff a plastic bag filled with crumpled newspa-
per into the pipe (don’t forget to remove it before
reinstalling the toilet).
If you’re replacing tub/shower walls or installing backer board, protect chrome
With the waste pipe temporarily sealed, take a
gooseneck pipes or threaded spout stubs by replacing them with 6-in. pipe
look at the toilet’s closet flange atop the closet
nipples. The nipples are placeholders for the originals, ensuring that pipe stubs bend. Ideally, the top of the flange should be the line up to holes in the backer board. Here, Foilastic flashing reinforces the
same height as the finish floor. If your tiling
waterproofing membrane and later will serve as a dam for silicone caulking.
increases the height of the floor 1⁄2 in. or less, the
height of the flange shouldn’t be a problem. Just
run tiles to within 1⁄8 in. of the flange. When you
all. Note: A wall that’s plumb in the corner may
apply a new wax ring to the bottom of the toilet
have a twisted stud elsewhere that throws another horn, the wax will compress and seal the joint
section out of plumb.
Finally, survey surfaces for water damage,
P R O T I P
deflection, and other factors that could affect tile.
Examine the bases of bathroom and kitchen fix-
tures for discoloration, delamination, and spring-
the thick and thin
Weather-resistant barriers
and flashing designed for exteri-
iness, especially under toilets and tubs.
Crumbling grout atop a tub often means that
of Setting beds
ors often double as waterproof
membranes indoors, beneath
water has gotten behind the tile. Open kitchen
thin-bed installations such as latex thin-
tile. after all, a shower is just
and bath cabinets and examine the undersides of
set adhesive over backer board are, well, thin.
indoor rain. although sold pri-
sinks and countertops. If you see discoloration,
because they offer little depth for adjust-
marily as stucco paper,
probe it with an awl to determine whether mate-
Renovation 4th Edition Page 107