 |
 |
| Workers combine a ready-mix
topping product with water (top). It's also possible to
buy liquid polymer and add it to conventional dry materials.
The overlay is then poured over a wood-frame floor (above).
Note the diamond lath nailed over the blue CIS crack isolation
membrane. |
Many polymer overlays are designed specifically
for producing decorative concrete floors. Some products can
be stamped or textured; others should be finished smooth.
All can be colored with stain or dye. Most overlays are designed
to be used on slabs, but some of them can be applied to plywood
subfloors, which is how we create decorative floors in structures
that won't support a thick layer of concrete. For example,
a 2-inch slab weighs 24 pounds per square foot, while a 1/2-inch
overlay weighs only 6 psf and can be installed flush to the
existing floors in adjacent rooms.
Substrate
Prep
Polymer overlays are tough, but they're only as good as the
substrates they're applied to. The toppings will crack or
delaminate if you put them on floors that are dirty, overly
flexible, or structurally unsound. Good prep work is a must,
so if you attempt an ' overlay job, be sure to carefully read
the instructions for the material you are using.
Slabs.
Some manufacturers recommend that you acidetch concrete substrates,
while others specifically prohibit it. The concern there is
that you won't properly neutralize all the acid and some will
remain to off-gas and break the bond between topping and slab.
We neutralize acid by flooding the surface with a solution
of baking soda and water or ammonia and water. We remove the
solution with a wet vac or mop and then repeat the process
with clean water. Another way to remove contaminants is to
use a stiff broom to scrub the surface with a cleaning agent
or cleaner degreaser.
We are frequently asked to apply decorative
overlays on slabs that are covered with linoleum tile. Typically,
the tile is attached with cutback adhesive. We start by manually
scraping the tile and as much mastic as possible off the slab.
If the slab is in good shape, we'll attempt to remove every
bit of mastic. Sometimes we can get it all off by scraping
alone; other times we have to use chemical strippers. Occasionally,
we'll pay a sub to bring in a shotblasting machine, which
shoots a large number of small steel balls into the surface
of the slab. It's like sandblasting, but removes more material
- from 1/16 to 1/8 inch off the top. The bottom of the machine
is enclosed to prevent the balls from escaping; an internal
vacuum collects the dust. Shotblasting is one of the best
ways to create a good bonding surface.
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