Filling voids under concrete is usually done to reduce settling and improve the longevity of the concrete. It’s important to be aware of the dangers and best practices associated with filling voids.
The most common method for filling voids under concrete is grouting. This involves mixing an appropriate material such as cement with water to create a slurry that is then poured into the void. The material needs to be mixed so that it has enough body and density to fill the void completely and be on the same plane as the existing concrete.
When grouting, you should avoid using too much water in the mix or else you could end up with air pockets in the void. You also need to ensure the void is as dry as possible. For larger voids, a layer of packing material such as pea gravel may also be used to hold the grout in place.
Other materials that may be used to fill voids include polyurethane foam, cementitious grouts, polyurethane sealers, and other epoxy mixtures. These materials are typically injected into the void, so you may need a specialist to do this for you.
Finally, it is important to properly prepare the area before filling the voids. This includes removing any dirt and debris, ensuring that the surface is free of cracks and divots, ensuring there is proper drainage, and ensuring the void is deep enough for the material you’re using.
When in doubt, contact a professional for assistance.
What is the fill under concrete?
The fill under concrete is the material that is placed into the excavation prior to the placement of concrete. This fill material can be composed of a variety of materials such as sand, gravel, soil, crushed rock, insulation, or any combination of these items.
The fill layer helps to provide stability for the slab, dispersing the weight of the concrete more evenly and helping to prevent settlement, cracking, or other issues. It also helps to equalize temperatures both in the slab and in the climate, preventing snow and ice from penetrating the concrete and also helping to insulate it against extreme summer temperatures.
The fill under the concrete should be compacted, to ensure that it won’t compact over time and cause different areas of the slab to settle; it should also be free of organic materials such as peat, algae, wood, or wood byproducts.
As a rule of thumb, the fill should be at least 4” below the top of the slab, in order to provide the proper coverage and protection.
Can you put dirt under concrete?
Yes, it is possible to put dirt underneath concrete. The dirt will act as a base for the concrete and will help to support it. This is commonly done for sidewalks, patios, driveways, and other areas of concrete.
However, when covering the dirt with concrete, it is important to make sure that the dirt below is level and compacted to provide good support for the concrete above. Any soft or loose soils need to be removed and replaced with more stable, compacted fill material.
In addition, it is also important to ensure that any drainage issues are addressed before pouring the concrete, as standing water beneath the concrete can increase the risk of damage.
What kind of foam do you use under concrete slab?
When installing a concrete slab, a layer of foam is used in order to provide additional strength, reduce cracking, insulation, and water protection. The most common type of foam used for this purpose is polystyrene foam.
Polystyrene foam is lightweight, yet insulates better than other types of foam and can be used as the base of the concrete’s vapor retarder. When installing a concrete slab, the foam should be laid in a single continuous layer to provide an even surface and guarantee that the slab is anchored to the underlying surface.
The foam should also extend slightly up the sides of the subfloor and be taped down securely to reduce movement and ensure it is fully compressed. In addition to polystyrene foam, there are also other foam materials available for use in concrete slab installation, such as foam boards, expanded polystyrene (EPS) foam, and extruded polystyrene (XPS) foam.
The type of foam used will depend on project requirements, including cost, installation ease, R-values, and the intended application of the concrete slab.
Why do you put crushed rock under concrete mixture?
Crushed rock is commonly used as a base material for concrete mixtures. It provides a stable foundation for the concrete, ensuring that it does not sink into the ground. The rock also provides drainage for the concrete, allowing for water run-off instead of pooling.
In addition, crushed rock can serve as an anchoring agent, preventing the concrete from shifting.
Without the supporting layer of crushed rock, the concrete could develop cracks and wear unevenly, resulting in costly repairs or replacement of the foundation. By utilizing crushed rock as a base material, the concrete is more stable and less likely to require frequent repairs.
What happens if you don’t put gravel under concrete?
If you don’t put gravel under concrete, it can lead to a number of problems. Without the gravel bed, there is nothing for the concrete to rest on and a possibility of shifting or settling can occur. This can lead to uneven surfaces, cracks, and other issues.
Additionally, without the gravel, moisture and water vapor can move more freely, weakening the concrete foundation and leading to additional problems, including crumbling and cracking. Additionally, the gravel serves an important role in allowing for drainage to prevent flooding, water retention, and other related issues.
Lastly, the gravel helps prevent weeds and other plants from growing beneath the concrete and destabilizing the surface. As such, not putting gravel underneath a concrete slab is essentially asking for trouble.
How long should ground settle before pouring concrete?
The amount of time you should allow for soil to settle before pouring concrete depends on several factors including the type and amount of soil, the level of compaction and drainage, weather conditions, and the types of loads your foundation will bear.
In general, it is best to wait a minimum of two weeks before pouring concrete over the ground. During this time, the soil should be closely monitored to ensure that it is adequately stable and dry. If the soil is well-compacted, a shorter timeframe may be possible.
If the soil is dry and loose still longer settling times should be allowed.
If the subgrade soil is of a clay type, it is especially important to ensure adequate settling time has been allowed. Clay soils behave differently than looser soils, and can take a long time to settle.
The time should be determined by expert soil engineers and will likely differ from the settling times for sand or loam soils.
Additionally, if the foundation will bear heavier loads such as multi-story buildings, special attention should be paid to the settling time. This is due to heavier loads bearing on the foundation, and typically longer waiting times will be required before pouring the concrete.
Again, expert care should be taken to ensure that the soil has settled sufficiently before pouring.
Ultimately, the amount of settlement time should be determined by expert soil engineers, who will take into account the types of soil, past weather conditions, future weather conditions, and the types of loads that the foundation will bear.
It is best to err on the side of caution and allow a minimum of two weeks before pouring the concrete.
What is slab on void?
Slab on void is a design technique that involves the placement of a slab or slab-like structure over a void or discontinued area. This method is often used to ensure that the structure is kept in contact with the ground, as the slab is typically heavier and more stable than the base.
The slab may also serve to separate the void from the rest of a structure, such as a building. Slab on void is often used to bridge gaps between two structures, like a bridge across a river or valley.
It is also used to create a platform over a pool, particularly in outdoor spaces that do not lend themselves to traditional pool construction, such as large bodies of water. Ultimately, slab on void is an effective solution for creating stable, durable structures while not overburdening the area with additional weight.
Why does my concrete sound hollow?
Concrete can sound hollow if it has not been properly compacted. During concrete installation, it is important to ensure that the concrete is thoroughly compacted and vibration is used to settle particles in the concrete mix.
This helps create a strong and consistent bond between the particles in the concrete. When this does not happen, pockets of air or a weak foundation can be created resulting in a hollow sound when walked on or a lower density in the area.
Additionally, if the surface has been improperly sealed or covered in some way, it can also cause an area to sound hollow. Ultimately, a professional should be consulted to inspect the area and make any necessary repairs.