Ensuring adequate support and stability is essential when building or renovating a structure with a slab foundation. The kind of pillow that is used to support the foundation is one crucial component that is frequently disregarded. These cushions, which are sometimes referred to as void forms or support cushions, are crucial in distributing the weight of the concrete slab and halting its gradual settling.
The type of soil, the necessary load-bearing capacity, and the particulars of the construction site all play a role in selecting the appropriate pillow. Expanded polystyrene (EPS), polyethylene foam, and even recycled materials are frequently used to make these pillows. Regarding moisture resistance, weight-bearing capacity, and installation ease, each material has special advantages.
You may find that making these support pillows yourself is a more affordable and personalized option. Usually, the procedure entails chopping the selected material into the proper sizes and shapes so that it fits snugly under the slab. Pillows positioned correctly aid in distributing the weight uniformly across the foundation, lowering the possibility of uneven settling and future structural problems.
The materials used to make these pillows vary in do-it-yourself methods. To get the right dimensions for EPS or foam pillows, careful cutting with a hot wire cutter or utility knife is necessary. It is imperative to adhere to the guidelines provided by the manufacturer or consult a professional to guarantee proper installation of the pillows and sufficient support for the duration of the building.
Choosing the Right Pillow for a Slab Foundation | Making Your Own Pillow for a Slab Foundation |
Consider pillows made of materials like foam or rubber for durability and moisture resistance. | Gather materials such as foam, rubber, or recycled materials. Cut to size and encase in a waterproof cover. |
- Needed or not?
- What are there and how to choose?
- Concrete
- Sand
- Other materials
- How to make it yourself – technology
- Sandy
- Concrete
- Alternative options
- Video on the topic
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Needed or not?
SP 22.13330.2016 (SNiP 2.02.01-83*) states that a specific cushion must be set up before a monolithic foundation slab is laid beneath the structure.
She plays the following role:
- forms a smooth and high-quality bottom of the base;
- is responsible for the uniform distribution of pressure on the ground due to resistance to soil compression;
- resists freezing of the foundation in winter;
- ensures the stability of the structure during operation;
- minimizes possible shrinkage of the structure;
- is an insulating layer against soil moisture entering the foundation of the house.
Considering the aforementioned factors, installing a damper substrate is an essential step in building a slab foundation. If not, there is still a chance that the soil will freeze and cause premature deformation and the structure’s total destruction.
What are there and how to choose?
In actual use, a damper gasket is actively installed beneath a monolithic slab using a variety of raw materials.
The selection of the content is supported by factors like:
- design conditions of construction;
- material capabilities of the customer;
- technical characteristics of raw materials.
The most common materials used to make the pillow are concrete, sand, crushed stone, sand, and gravel mixture. In multi-story construction, a cushion is arranged as a combination of multiple layers made of various materials, rather than sticking to just one layer.
It will be helpful for the owner to consult a specialist when designing a slab base themselves.
Concrete
In this instance, the concrete pad ought to be regarded as an independent structural component rather than a component of the foundation slab. Use high strength concrete when creating a substrate to give the load-bearing structure the necessary resistance against the forces of soil frost heaving.
To ensure that the structure has a level layout and doesn’t tilt while in use, the layer’s surface must be strictly leveled along the same level in the horizontal plane. Because the concrete itself is an expensive material, the device of the sandy substrate beneath it causes the height of such a layer to be reduced in order to save.
Sand
Backfilling with a layer of compacted sand is a cheap and simple solution that guarantees:
- the durability of the monolithic slab;
- protection from soil moisture;
- permissible load level on the load-bearing structure;
- reduces the likelihood of house subsidence.
If you are building something smaller than a single story, you can only have a sand cushion beneath a monolithic slab.
Sand with medium and large fractions is utilized when working with a slab foundation because of its notable resistance to compression and high absorption of moisture. Small amounts of loose material are not used in this instance since they may cause the structure to shrink unevenly.
Sand types used for backfilling the substrate include:
- river – with a minimum amount of impurities;
- quarry – after spilling and washing from clay particles;
- sea – after cleaning and hydromechanical processing.
Other materials
There are instances in which using extra materials is required:
- When construction is carried out on unstable soils with weak bearing capacity, then a sand cushion is not enough to strengthen the base. In this case, crushed stone backfill with a granule size of 20 mm or more is used. This material better resists shrinkage and heaving of the soil in winter, ensuring the integrity and stability of the foundation.
- On clay soil it is practiced to use a cushion of gravel-sand mixture. In this case, crushed stone can be replaced or diluted with broken bricks or small clastic stones. Such a layer will be a reliable protection against penetration of groundwater into the foundation.
The bottom of the pit still needs to have a thin layer (up to 20 cm) of coarse sand compacted before filling with crushed stone or a sand-gravel mixture.
How to make it yourself – technology
The width and height of this technological layer must be precisely calculated by designers for the pillow to perform as intended. Regulations state that the pillow’s width cannot be less than the width of the monolithic slab that will be placed on top.
The following considerations are made when determining the height:
- soil freezing depth;
- level of underground sources;
- design loads on the load-bearing structure;
- geological and seismic features of the site.
Giving the soil a condition where it can support the design loads is part of preparing a building site. Ultimately, the foundation base ought to be firmly positioned against the earthen base.
Thus, the following procedures are the first to be followed when laying the slab base:
- marking the field according to the dimensions of the structure;
- excavation of a pit inside the intended contour to a depth that will be slightly greater than the design value;
- surface leveling and bottom compaction.
Installing a sand cushion comes next once the pit is prepared.
Sandy
The following will be the sequence in which technology functions:
- Soil insulation. Inside the prepared pit, a layer of waterproofing material is lined, for example, geotextile sheets. At the same time, leave enough free material on all sides so that it is convenient for them to cover the surface and sides of the pillow. The event is aimed at eliminating the possibility of siltation of the base under the influence of groundwater during the service of the foundation.
- Backfilling with sand. The need for the amount of bulk material is determined by multiplying the base area by the height of the pillow. 15% is added to the resulting value, taking into account the reserve that will be needed during the compaction process.
- Sand compaction. The material is compacted using a vibrating plate until no traces of feet remain on the surface. To do this, the sand is periodically irrigated with purified water. It is impossible to achieve such a result with manual tamping. The surface is leveled horizontally using a laser level or a regular building level.
Concrete
In order to install a concrete pad, the prepared pit’s bottom is lined with a layer of geotextile, which is followed by crushed stone and compaction.
The concrete foundation may be:
- Slab. Here they use ready-made foundation blocks, which are placed on top of the bedding.
- Monolithic. Install the formwork around the perimeter so that the top plane of the finished slab is flush with the ground surface. Two layers of reinforcement cage are placed inside the formwork to give the structure rigidity and resistance to deformation loads. The prepared area is poured with concrete, then the concrete is compacted and leveled.
Alternative options
The same formula will be used to build a gravel-sand mixture and a crushed stone substrate:
- The bottom of the pit is leveled and compacted.
- Line with a layer of geotextile or rolled bitumen material. If the design loads are significant, the material can be laid in two layers.
- Coarse sand is poured on top and compacted, periodically irrigating the surface with clean water.
- The prepared sand surface is covered with crushed stone to ground level. The bulk material must also be properly compacted to eliminate any voids.
Builders proceed to the next technological step, laying the slab foundation, after installing the cushion.
For a slab foundation, selecting the proper kind of pillow is essential to guaranteeing stability and longevity. Depending on your unique requirements and the state of the soil, each type of pillow—whether it be compacted gravel, bags filled with concrete, or precast concrete—has advantages. Particularly for larger structures or in situations where ground settlement is an issue, precast concrete pillows provide consistent and long-lasting support.
Concrete-filled bags are ideal for smaller projects or locations with restricted access because of their flexibility and simplicity of installation. Due to their low cost and environmental friendliness, compacted gravel pillows minimize the possibility of soil movement beneath foundations and allow for drainage. For advice on which option best suits the particular needs of your building, think about speaking with an expert.
To guarantee stability and safety, if you choose to make your own pillow, make sure you follow the right instructions. Level and thoroughly compact the ground to prepare the site. Use premium materials, such as compactible gravel or concrete mix, that are appropriate for load-bearing applications. In order to avoid settling and guarantee even support throughout the foundation, properly compact each layer.
Recall that the performance and longevity of your slab foundation are directly impacted by the kind of pillow you select. You can reduce future maintenance costs and improve the structural integrity of your building by choosing the appropriate materials and installation technique. When building or remodeling your foundation, stability, toughness, and compliance to regional building codes should always come first.
This post discusses the kind of pillow that works best with a slab foundation and offers a straightforward tutorial on how to make one. A well-selected pillow can control soil moisture and provide structural support, which can greatly increase the stability and lifespan of a slab foundation. We’ll go over a variety of materials, including foam, sand, and gravel, and their advantages and disadvantages. In addition, we’ll walk you through the process of making your own pillow, with a focus on do-it-yourselfers and homeowners who want to increase the performance and longevity of their foundation at a reasonable cost.