How to Pour a
Floating Concrete Slab
Preparation is everything in getting your
site ready to pour a floating concrete slab.
1. Determine the location and size of your
site; install four, temporary 3' metal stakes to mark the four
corners of the footprint of the
structure (assuming it is square or rectangle in shape; procedure
applies to any shape); add two feet laterally in all four directions beyond the
footprint of the finished structure; this added two feet is for
drainage. Ensure that you comply with
local building codes for site placement and apply for proper
2. Determine the height of the top surface of your concrete slab; using your temporary stakes apply string
around the perimeter at the elevation to indicate the top surface of
the concrete slab; use a transit, laser level, or string level to
keep your strings level and square.
3. Measure down from your perimeter strings
the following distances:
a. Six inches for the concrete slab.
b. Two inches for solid foam insulation.
c. Two or three feet of sand.
d. Three inches of 3" rock as a base.
e. Add all the above figures together to a
total of 3'11" (2'11" if 2' of sand used). This is the depth
required from the top surface of the planned cement slab downward to
the base ground before the 3" rock is applied.
2. Pick a site that has good drainage to
avoid flooding. Bring in fill or remove excess soil to acquire the
desired height of the finished top surface of the slab.
3. Add a minimum of two feet of sand on top
of the fill and/or 3" rock, to include the additional, lateral two feet
beyond the footprint of the finished structure.
4. Using a compactor, compact the sand so
that it is eight inches below the marker strings; use a transit and
make measurements at multiple locations within the footprint to
confirm the surface is level; add or subtract sand as necessary.
5. Dismantle the four temporary stakes and
reset them to represent the footprint of the finished slab. Ensure
the four stakes are placed with accuracy; pound them in straight;
ensure the slab dimensions are accurate; confirm that the diagonal
measurements are equal to confirm the string will represent an
accurate footprint of the finished slab. Do not be concerned with
the height of the string to the ground; the strings should be
approximately six inches above the ground. When finished with this
step, the strings should represent the footprint of the finished
slab; the cement forms will be placed around the outside edge of the
stakes and strings.
5. Install the cement forms (2 x 10's).
Begin with a corner; set two forms on edge and butt join the two at
the corner using dual-headed spikes. Use a transit to
determine the top edge of the two corner forms; the top of the forms
will equal the top surface of the slab. Remove as much sand as
necessary to set the two corner forms in place at the proper height.
The guide strings will be used to keep the form placement straight.
Ensure the top edge of the forms are at the proper height; use
support stakes (there are two foot metal posts with nail holes
available for this specific purpose; if not available, use 2 x 4's x
24" long with a pointed end) on the exterior side of the forms at
each end of the forms (the top of the stakes need to be hammered
into the ground lower than the top edge of the forms); the forms
should be nailed to the support stakes. It may be necessary to dig down into the sand to place the
forms, depending on the size of the forms used (2 x 10's are
recommended). With all forms in place, confirm that the forms are level
(use transit), straight (use perimeter strings), and the corners
square (distance across the corners are equal). The space within the forms will determine the size and
depth of the cement slab. With all measurements confirmed,
additional support stakes every four feet; backfill around the
exterior of the forms and remove the guide strings and four guide
6. Install any drain pipes and other utility
pipes, wires that may be required within the concrete slab. Compress
any sand that was disturbed in this operation.
7. Using a shovel, dig a trench 16" wide and
18" deep around the perimeter of the forms (inside the forms).
This will provide a footer, added strength and depth, to the perimeter of the
cement slab to support the weight of the exterior walls of your
8. Lay two inch insulating foam on top of
the sand; ensure that all sand within the forms is covered including
the perimeter/footer trench; you will need to cut the foam to fit the
bottom and sides of the trench.
9. Lay 6 mil plastic vapor barrier over the
top of all foam; tape any seams.
10. Lay the narrow, 3/8" rebar in a crisscross
pattern (18" squares) using rebar supports to lift the rebar two
inches above the plastic; use connecting wire to connect the rebar
at the junction of each crossing point. As an option, use
11. Lay the thicker, 5/8" rebar in a cage pattern
into the trenches around the perimeter. Following this step, all
should be ready to pour the cement.
12. Contact your local cement finishing
contractor to schedule the finishing team and the cement delivery.
By providing accurate measurements, they will assist in determining
the amount of cement required and delivered.
How to Pour a Cement Slab
If you would like
to obtain a quote from a reliable, licensed, bonded, local contractor to
pour your slab, access: Local
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