How To Pour A Concrete Slab

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NOTE:  If you would like to obtain a quote from a reliable, licensed, bonded, local contractor to pour your slab, access:  Local Contractors

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 building permits. 

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, nail additional support stakes every four feet; backfill around the exterior of the forms and remove the guide strings and four guide posts.

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 structure.

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 metal mesh.

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

NOTE:  If you would like to obtain a quote from a reliable, licensed, bonded, local contractor to pour your slab, access:  Local Contractors


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