Float Slab

Floating Slab | Float Slab Foundation | Floating Concrete Slabs9 min read

What Is a Floating Slab?

Floating Slabs are concrete slabs that are laid on the ground without any anchoring, such that it simply sits and floats on them. The floating slab, as the name suggests, looks like a plate, which is only placed on top of the water, with no connection between them.


Why Use a Floating Slab?

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Floating Slab

Floating slab construction is one of the most economical methods of foundation construction. Traditional foundations include a strip foundation using a frosted wall above.

Strip footing is installed below frost level, typically 4′-0″ below grade. The cost of strip footing and frost wall is very high as it requires more excavation, concrete, and labor.

Read More: Floating Slab Vs Monolithic Slab | What Is Monolithic Slab | What Is Floating Slab


Construction of Floating Slab

Construction of Floating Slabs requires details. The proposed building requires a solid foundation to fully support the entire weight of the superstructure. As mentioned they are more commonly used in garages, extensions to a house or shed do not necessarily require a large foundation. These buildings are light in structure.

Hence Floating Slabs are found to be most suitable and economical as compared to conventional slab construction. The main construction layers in a floating slab are shown in Figure-1. The construction includes the following steps:


1. Site Excavation for Floating Slab Construction

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Site Excavation For Floating Slab

The primary stage of the construction of the floating slab is to clean the land and excavate the area as per the plan. This is the preliminary preparation for construction.

The step also includes creating drainage in the sides to drain water through the gravel base as shown below. The constructed trench is sealed with geotextiles and gravel as shown below, which will drain water from the concrete slab foundation.


2. Laying Gravel Base for Drainage

Install a gravel grid before pouring gravel. Add an 8- to 12-inch gravel base of various rock sizes, compacting each layer for durability.


3. Reinforcement for Slabs

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Reinforcement Of Floating Slab

A slab mold is placed for the casting process. For reinforcing slabs, reinforcing bars are provided as per the dimensions and code.


4. Casted Floating Slab

Concrete is poured into the slab formwork. This compresses either my labor or a mechanical vibrator, depending on the area and workmanship. Proper compaction has to be done to make the slab fully productive. Appropriate treatment has to be taken for about 2 to 3 days.

Read More: What Is Floating Foundation | Suitability of the Floating Foundation | Advantages & Disadvantage of Floating Foundation | How to Build a Floating House Foundation


How to Build a Floating Slab?

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Floating Slab Components

STEP 1: Decide the area for the floating slab and mark all four corners with 3-foot metal stakes.

STEP 2: Calculate the height of the top surface of your concrete slab. Once you have completed this determination, use a cord for marking the height by covering it around the metal stake. Use a level to make sure the string is straight and that the height is consistent.

STEP 3: Measure two feet (the rafter) from the circumference and mark this area for drainage.

STEP 4: Measure 2 feet and 11 inches down from the circumference wire. This is the initial point of the base for the slab. Dig the entire interior area of the foundation to this depth. Also, excavate a 2-foot drainage section.

STEP 5: Fill the excavated area 3 inches deep with crushed stone to create a drainage area for the foundation.

STEP 6: Cover a 3-inch rock with 2 feet of sand.

STEP 7: Compact the sand with a compactor (sand compactor) until it is 8 inches below the perimeter lines. Check the area in several places to make sure the entire area is level.

STEP 8: Place 2-by-10-inch lumber approximately the edge of the proposed slab to create the slab form. Connect the corners to the butt joints and secure them with framing nails. Make sure the forms are level.

STEP 9: Add support stakes [2-foot metal stakes with nail holes] every four feet outside the slab form. Secure them with framing nails as well.

STEP 10: Remove the starting guidepost and perimeter string. At this point, it is time to install any drainage lines or electrical conduit needed to run through the foundation.

STEP 11: Dig a 16’’ x18’’ trench inside the slab form to provide additional support on the exterior of the slab to support the walls.

STEP 12: Install 2-inch foam insulation on top of the sand. Cut pieces to seal in the sides and base of the trench as well.

STEP 13: Install a vapor barrier over the entire foam. Overlap the pieces by 2 to 4 inches and secure with tape.

STEP 14: Lay three-eighths of an inch of rebar over the vapor barrier in a criss-cross pattern. Be sure to use 2-inch rebar supports to lift the rebar off the ground so that the liquid concrete can flow around it.

STEP 15: Add five-eighths of an inch of rebar to the trench area. Build a cage with bars to add extra support.

STEP 16: Mix and pour your cement. If you are dealing with a cement delivery service they will determine the amount of concrete needed to be poured, otherwise, you will need to follow the calculation on your cement bag to decide how much to pour.

NOTE- Remember that the size of your cement slab will be length x width x 6 inches (the depth of the concrete slab) plus an additional 16’’x18’’ length of the perimeter for the trenches.


Advantages of Floating Slabs

Floating Slabs have the following advantages,

Floating Slab | Float Slab Foundation | Floating Concrete Slabs
Floating Slab Track
  • Floating slab construction can be employed in site areas with low load-bearing capacity and where it is futile to invest big money on soil treatment. This system lets us use it in loose soil or soil with different compressibility.
  • Floating slabs have the property of spreading the vertical load or the stress on it to be distributed over a large area.
  • Floating slab foundation is a good solution when it comes to the extension of houses. There are situations when we need a building extension without affecting the already existing foundation. It will not interfere with already constructed building structures.
  • The floating slabs act as a barrier to the entry of moisture coming from the ground. It acts as a barrier between the superstructure and the ground.
  • It protects against water seepage and frost. For this purpose, the slab can be insulating for frost or moisture. This led to their widespread use in cold field construction.
  • Floating slabs do not need the use of footer trench. They can be pouring with the help of trenching or digging which is economical.
  • The layer of soil lying below the floating slab does not disturb nor will it interfere with the quality.
  • In areas where the soil layer has the potential to move, mainly because of the high moisture content, floating slabs are best suited.

Disadvantages of Floating Slabs

Along with advantages Floating Slab also has some disadvantages as listed below,

  • The floating slab does not provide underground access for the connection lines facing the utilities.
  • It’s a primitive technology.
  • Floating slab foundations have low design resonance.

Read More: Monolithic Definition | Monolithic Slab | Monolithic Footing | Monolithic Foundation | Advantages & Disadvantages of Monolithic Slab Foundation


Uses of Floating Slab

Floating Slab can be used for the following conditions,

  • The primary use of floating slabs is as a base for industrial workshops, sheds and garages.
  • It is very cost effective in areas where need foundation is not required.

FAQs

What Is a Floating Slab?

Floating Slabs are the one which is created through two-stage slab construction, where footings are individually poured, and then the center floor of the slab is poured after footings had cured.

Floating Concrete Slabs

Floating Concrete Slabs are slabs made of concrete that is laid on the ground without any anchoring, such that it simply sits and floats on them. The floating slab, as the name suggests, looks like a plate, which is only placed on top of the water, with no connection between them.

Why Use a Floating Slab?

Use or Construction of Floating Slab is recommended because it is one of the most economical methods for construction. Also, it behaves as a barrier for the entry of moisture hence act as a barrier between the superstructure and the ground.

Advantages of Floating Slabs

Floating Slab Advantages,
1. Floating slabs have the property of spreading the vertical load or the stress on it to be distributed over a large area.
2. A floating slab foundation is a good solution when it comes to the extension of houses.
3. The layer of soil lying below the floating slab does not disturb nor will it interfere with the quality.
4. This system lets us use it in loose soil or soil with different compressibility.

Disadvantages of Floating Slabs

Floating Slab Disadvantages,
1. The floating slab does not provide underground access for the connection lines facing the utilities.
2. It’s a primitive technology.
3. Floating slab foundations have low design resonance.

Float Slab

The terminology Float Slab is usually used to refer to the floating slab which is two-stage slab construction where footings are individually poured and the pouring of the center floor of the slab is done after footings have cured.

Floated Concrete Floor

Floated Concrete Floor is a technique used in subsidiaries with a power trowel, a finishing machine essential to smooth and even the surface of the concrete to make it exceptionally high tolerance.


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1 thought on “Floating Slab | Float Slab Foundation | Floating Concrete Slabs”

  1. Nice Article, Well described Floating Slabs, Basically, I saw using these Floating slabs in a variety of structures, garages, cottages, and sheds.

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