Basic construction of a slab on foundation?
If you live in a colder climate, your foundation will be a “Pier and Beam” or “Basement” foundation due to the depth of the frost. In warmer climates, “slab-on-grade” or “monolithic” concrete foundations are more popular, since the surface freezes for only short periods. The cost of a slab on grade foundation is much less expensive and, if built correctly, has the same longevity.
A slab-on-grade or monolithic foundation is a continuous concrete slab. The slope beams and the slab surface are one unit. If there is a fear of foundation failure or a history of foundation failure in the area due to poor ground conditions, bell bottom piers drilled down to stable ground would be an excellent precaution.
First, you need to prepare the substrate to provide a stable platform on which the concrete pad will rest. Determine the perimeter of the house and raze a six to eight inch layer of grass and unstable top soil to what is called 98% stable soil. If an unknown girl has been brought in over the years, she may want to remove up to twelve inches.
Next, you want to set the height of your finished floor. If you have a fairly level lot, the finished floor level will usually be eighteen inches higher than the crown of the street in front of your house. If you are building on a hillside, make sure that during heavy rains the water drains quickly from your slab.
Your backfill should be what is called “sandy loam” or, in construction terminology, “select backfill.” This is very stable soil that does not expand or contract from a wet season to a dry season. It will compact and support a base slab with very little uplift. Make sure all the fill is consistent as you don’t want a difference in movement from one end of your slab to the other.
Sandy loam soil (selected backfill) will compact very easily and the best way to achieve this is to have a bulldozer spread the soil as it is unloaded and let the pneumatic tires of two-axle trucks roll over it as it is unloaded. lift each lift. applied, however, you must use a compactor to ensure complete compaction. If the soil is extremely dry, while spreading the soil, apply a small amount of water to help compaction.
The normal thickness of a residential slab is four inches; therefore, you want to bring the selected fill to within six inches of the final level, then bring in a two-inch layer of sand for a cushion between the deck and the concrete slab.
Wood forms are built to the desired grade and grade beams are excavated. These beams are normally eighteen to twenty-four inches deep and twelve to fourteen inches wide. Whether your foundation plans were designed correctly; the size of the beams, how many and their placement will be specified. A vapor barrier using 6m or similar polyethylene film should be placed over the prepared substrate. Reinforcing steel will also be specified by the engineer and must be strictly adhered to.
In case of heavy rain, be sure to remove the water from the leveling beams and let them dry for a couple of days. A light rain shower is not a cause for concern and will not damage your pad.
The final stage is pouring the concrete into the beams and forms. Don’t let concrete finishers thin the concrete; so that it is as dry as possible but leaving enough water to allow slow curing and proper finishing. On a hot summer day, once the surface has hardened enough, install a water sprinkler to cool the hot concrete and retard curing. If the surface cures much faster than the rest of the slab, you will have some surface cracks.