How to Prep Subfloor for Tile Installation

We’re working on renovating this bathroom
and right now it’s time to start on the new tile floor. It’s definitely one of the more
advanced projects, but you can do it. In this video we’ll show you how to prep the floor.
After you’ve prepped, watch How to Install a Tile Floor at Getting the subfloor ready is THE most important
part of the job because if you don’t do it right the floor could crack. Now a tile floor
can be installed several ways. Whatever you do, just be sure to follow your local codes
and your manufacturer’s directions. To give you an idea of our installation, here’s
what we’ll do: After we take out the old floor, we’ll apply
unmodified mortar to the existing concrete mortar bed. Then we’ll put down this Schluter
DITRA uncoupling membrane; a layer of unmodified thinset; our tile; grout; and sealer. Now keep in mind that this install is not
the same as tiling a shower or tub. Before you get started, figure out how much
new tile you’ll need. Multiply the length times the width and add 10% for extra. If
you special order your tile, you can schedule your project for when your tile order will
be ready. Now it’s time to remove the old flooring.
Start by taking out the toilet, vanity, and any trim that might be in the way. Oh, and
plug the sewer pipe with a rag to keep sewer gas from leaking into the room. If you’re removing tile like we are, it’s
a really good idea to mask off the doorway and open a window. I’m not going to lie—removing
tile gets really dusty. Ok, take a hammer and give the old tile a whack. After you’ve
broken some up, use a hammer and chisel to remove the tile. Once the tile is gone, use a floor scraper
to remove the old thinset. As you can see, our bathroom has a mortar
bed. This is common in homes built before 1950, like ours. You can repair minor cracks
and tile over it like we are, but if it has major damage you’ll have to remove it. Your
subfloor has to be in good condition, uniform, proper thickness, dry, clear of any residue,
and level. If it isn’t level, just fill the low spots with a leveling compound. There’s been a big change in this room. As
you can see we’re also working on replacing our tile walls. You can find the video for
this process at our website. All right, well now it’s time to put down the Schluter DITRA.
This stuff is pretty cool. It’s a flexible membrane that allows for expansion under the
tile, but it also gives us a strong foundation and helps protect the subfloor underneath. So to begin installing this membrane, start
in a corner and roll it out across the floor. Cut it at the wall and that’s the first piece.
Go ahead and cut all your pieces. If you have to cut around pipes, just use
a utility knife. It’s also a good idea to mark the edges of
each run to know where to spread your thinset. Once all the pieces are cut and in place,
be sure to mark numbers on each piece as well as corresponding numbers on the floor. If you have doorjambs and doors, stack a floor
tile on a piece of the membrane against the trim. Use a jamb saw to cut it about 1/16
of an inch above the stack, and cut doors about 1/8 of an inch above the stack. Next, you’ll need to mix unmodified thinset
mortar. Mix it fairly loose, but not so thin that the ridges fall down when it’s applied
with a trowel. Use a 14-in by 3/16-in V-notched trowel. Apply a thin layer of mortar to the
substrate with the flat side to produce solid contact with the surface. Then comb the mortar
using the notched side. Roll the membrane over the floor, fleece side
down, and solidly embed it in the mortar using a wood float. Pull back a corner of the membrane
to check that you’re getting full coverage. You should see half of the mortar on the floor
and half on the fleece. Continue laying the DITRA, keeping the pieces tight against each
other. To make the floor completely waterproof, install
KERDI-BAND on the seams and corners. Use unmodified thinset mortar with the same trowel, making
sure there’s at least a 2-in overlap at all seams. We’re really making progress on this bathroom
and we’re almost done with prepping the floor. We just need to make some reference lines
for the new tile. Mark the center of two opposite walls and
snap a chalkline. Spraying hairspray works well to hold the chalk on the membrane. Do
the same on the other two walls to form a cross, and check that it’s square. Loose lay
the tile along the lines, using the spacers for accuracy. Leave about 1/4-in between the
perimeter tiles and walls for expansion. If the layout gives you thin cuts on the sides,
adjust it to get a wider cut, and mark new reference lines. Now you can pick up the tiles. Well, our lines are set so now it’s time to
start laying some tile. Check out the rest of this project at

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