Applying Self-Leveling Underlayment
In the following set of pictures, we will be flashing what will soon be two bathrooms. All the drain lines have been
changed to a new location and it was obviously necessary to break up parts of the original slab. There are very rough patches
of concrete left in the floor by the plumbers (Fig. 1). There are also places where the thinset from an old tile floor will
not come up without considerable effort. Self-leveling compound is a very effective way to prepare a rough surface for
tile, carpet, vinyl and even hardwood. Remember that this stuff does not add any structural strength. If you put it on
an unsound surface (a bouncy floor), it will break up.
In order to achieve successful adhesion, the surface must be clean. A thorough sweep, hopefully assisted by a
vacuum, followed by a light "spongedown" is essential.
The next step is to prime the surface. The primer is a special latex primer that is applied like normal paint. An old
paint brush, small broom or roller may be used. The primer should be applied in pure form unless the surface is very
porous like concrete. In this case, it is mixed with one part water to make it stretch out and better cover the area (check
the directions on the container). Use your paint roller or small broom or paint brush to make sure the primer penetrates all
of the little pits, cracks, bumps, etc. Let the primer dry thoroughly.
This step is the most crucial: Mixing. Consult the directions on the package for mixing directions. Use a mixer hooked to
a power drill (Fig. 2). Our experience shows that the best way to get it right is to start with about 1 1/4 gallons of water in
a clean bucket. Add about half the bag of powder and start mixing (check the bag for any health warnings about
breathing dust). Keep adding powder until you reach a milkshake-like consistency. Milkshake or split pea soup are good
consistencies. If you get to "pancake batter", it's already too thick: add a little water. Remember, the compound needs to pour
out onto the floor with great ease so that it can flow to the low spots. It will not do its job if it is too thick or lumpy. Mix for
at least two minutes while trying to scrape the sides of the bucket with your mixer.
Pour the compound out onto the lowest spot on the floor (Fig. 3). If there are two or three different low spots pour
a puddle into each one. You do not have much time if you need to mix another batch so get going!!! This is no time to
sit around and watch it ooze. Your working time is about ten minutes, fifteen is pushing it and will likely lead to poor
results. Use the flat trowel to feather the edges once the puddle has stopped moving.
Clean your buckets and tools with regular old water as this stuff will dry up quickly and it's not so easy to clean up
later. Drying time will vary depending on temperature and humidity. You should be able to walk on it within two hours but 12
are recommended for full curing before application of a carpet adhesive or other.
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