What do you put under concrete?
Medium gravel, which is 1.8 cm (3/4 inch) in diameter, is the best material for a concrete base. To cover a 4 inch thick concrete slab, you'll need 3 inches of gravel. Because gravel surface is level, you can easily estimate the number of yards of concrete required.
Adding crushed stone under your concrete slab will provide a level surface for your foundation. Simply pouring concrete onto the ground will expose it to elemental erosion that will cause cracking and sinking. Similarly, if there are roots or plants under your slab, they may rot and cause unevenness.
A base of gravel will help prevent erosion and keep the slab from settling. Pour concrete sand to fill the gaps in the gravel base. Use a tamper or plate compactor to flatten the gravel base. If needed, add more gravel and compact until you have a 4-inch base.
As a general rule, stay away from using sand as a subbase. You're better off using gravel. Your concrete will last longer and have less of a chance of cracking over time.
Paint – Paint is another material that has no natural bonding agents, so concrete generally won't stick to it very well. Oil – Oil or oiled surfaces are often used to make the surface resistant to concrete bonding.
Most concrete contractors want a mix of coarse and fine aggregate to create a compactable base that is going to be safe for settlement and drainage. Crusher run (a mix of crushed stone and stone dust) and #57 coarse aggregate are two of the best base materials for concrete slabs.
Long story short, yes you can pour concrete over dirt. However, you need to follow the process outlined in this article for the best results. If this all seems a bit overwhelming, we suggest reaching out to a professional concrete contractor.
Pouring your own concrete is a relatively simple process and a great way of saving money, but you want to do it correctly. Pouring the concrete is a critical step, but can you pour concrete on unprepared ground? You should not pour concrete directly on the ground before preparing a proper concrete base.
Standard concrete floor slab thickness in residential construction is 4 inches. Five to six inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks. To prepare the base, cut the ground level to the proper depth to allow for the slab thickness.
To prevent cracking and crumbling, concrete patios need to be built on solid, well-drained soil. If you live in a region with lots of clay in the soil, you will need to dig down further and backfill with layers of compacted sand and gravel.
How much sand do I need under concrete slab?
For gravel, you'll need 4–6” of ¾ minus crushed gravel. One yard of gravel covers approximately 80 square feet. For the sand, you'll need 1” of concrete sand. One yard of sand covers about 200 square feet.
No, you cannot make concrete without gravel. The ingredient mix of 1 part cement, 2 parts sand, and 3 parts gravel (stone) is what makes up concrete. Without gravel, concrete would not be strong or be able to be used as a foundation or base that could withstand heavy loads.
As a rule of thumb, concrete slabs supporting lighter weights such as paths, patios and shed bases will need to be 75-100mm thick, while driveways and garages need to be at least 100mm thick. Slabs intended for commercial use should be at least 175mm thick and reinforced.
Mudjacking. A type of sand-cement slurry (called “mud” in the industry) can be used to fill voids under concrete slabs. This mixture of sand, cement, and water is pumped through holes drilled in a slab foundation to fill voids underneath.
If the ambient temperature is too low, the hydration of the cement will drastically slow down or completely stop. Cold weather slows down the setting process or stops it completely, negatively impacting the concrete's strength gain.
Water facilitates the curing and hardening processes. Without it, the chemical reactions needed to form the hard crystals that give the concrete its strength can't take place. Too little water leads to structurally weak concrete, and too much will disrupt effective curing and cause flaking, shrinking, divots or cracks.
The recommended thickness is 4″ to 6″ inches for residential driveways that only lightweight vehicles pass through. For commercial concrete driveways that deal with heavy traffic by garbage trucks, heavy trucks, moving vans, and other heavy vehicles, the recommended thickness is 6″ to 8″.
Working With Ready-Mix Concrete
And, if you mix it yourself, it's the cheapest way to make your slab. For most do-it-yourselfers, the best material for building a concrete slab is a ready-mix, crack-resistant concrete product. The wet mix is poured into a prepared wood form, then left to cure.
Technically you can, but you really shouldn't pour concrete over grass. To maintain its tensile strength, concrete needs to be laid on a firm, even, and dry foundation. Grass and soil will naturally channel moisture into the concrete from below, which will likely result in it cracking over time.
When temperatures dip below 40 °F, the chemical reactions that strengthen concrete slow down and can lead to weaker concrete. If concrete curing temperatures are below freezing, the water inside the concrete can freeze and expand, resulting in cracks in your surface.
Why do you wet the ground before pouring concrete?
As noted before, concrete doesn't dry out to harden, it cures through a chemical reaction that needs water to facilitate the reaction. If the ground is dry, the ground will absorb moisture from the concrete and it won't cure properly. The ground should be very moist and compacted as well as you can manage.
Even if the concrete foundation is enough to keep water away from the building, water vapor can easily rise to the surface and damage a building's foundation, subfloor, and main floor. A vapor barrier is crucial to protect a building from the many negative effects of water vapor on building materials.
If it loses too much moisture through evaporation, it will not cure properly and will become prone to cracks. Many construction specialists recommend watering it down five to ten times per day, for the first week, starting 2-4 hours after it has been poured.
Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.
In residential concrete, 4 inches is the minimum thickness for walkways and patios. Garage slabs and driveways should be 5 to 6 inches thick if any heavy truck traffic is anticipated, otherwise 4 inches is adequate.
To be effective, a concrete patio should be approximately 1 inch (2.54 cm) higher than the ground surrounding it. This difference in height serves both functional and aesthetically pleasing purposes.
The minimum thickness for a residential concrete driveway is 4 inches. However, 5 or 6 inches is recommended if you live in an area with heavy traffic or large vehicles. For extra strength and durability, you can go up to 8 inches.
Because concrete slabs “float” on the soil, soft ground or voids underneath may cause unsupported areas to crack under heavy weight like vehicles. Pack about 4 in. of sand or gravel over clay and other poorly draining soils to provide even support.
Typically a naturally occurring material that has a high clay/fine silt content to ensure the material can hold its shape when used under concrete slabs, base for pipe laying.
Play Sand contains much finer, smaller particles that feel softer to the touch and stick together better for building sandcastles and best for playing with toy trucks. Construction Sand typically contains larger particles that are better for improving drainage and adding strength to concrete.
What is the correct sand for concrete?
Concrete Sand, often referred to as sharp sand or grit sand, is typically used in applications that require greater strength and solidity, such as concrete mixes, less flexible mortar mixes, and paving and floor screeds.
Reinforcement should also be placed low enough so saw cutting does not cut the reinforcement. For welded wire reinforcement, the Wire Reinforcement Institute recommends steel placement 2 inches below the surface or within the upper third of the slab thickness, whichever is closer to the surface.
Each ton covers approximately 60 square feet at 4" deep, 80 square feet at 3" deep, 120 square feet at 2" deep, or 240 square feet at 1" deep. Concrete Sand does not compact and should not be used in between the cracks of paver or natural stone.
All concrete slabs used in heated structures must have a vapor barrier installed. A minimum of at least 6-mil polyethylene vapor retarder must be installed between the concrete and prepped ground, according to the 2018 IRC.
What is Vapor Barrier? A plastic sheet that is placed between the base and the concrete slab. Always placed beneath the rebar or wire mesh and on top of the gravel base. The sole purpose of the vapor barrier is to prevent moisture from penetrating through the concrete.
The short answer is no, vapor barrier plastic underneath concrete slabs is required by ASTM compliance standards for many reasons. Vapor barriers protect not only the building project itself but the people inside.
Plastic should be placed under a concrete slab to protect it from moisture damage. Moisture from soil can penetrate the concrete causing it to crack with time and potentially risking lots of structural damage. A vapour barrier put under a concrete slab such as plastic sheets can protect it from this.
Rigid insulation under a concrete slab is an essential part of home construction as it improves the energy efficiency of the building, controls moisture, and reduces energy costs.
Without a vapor barrier in place, a slab that dries from its top surface will be exposed to disproportionate moisture levels in the slab for its entire lifetime. This can be a far greater curling threat to the foundation, long-term.
Covering your concrete basem*nt floor with a different material can be detrimental to its longevity and condition. This is because the concrete needs exposure to air in order for it to breathe properly.
Will concrete dry under plastic?
The most efficient way to cure concrete is to use a plastic cover. The covers are placed on freshly poured concrete until the concrete has a chance to dry. Plastic concrete curing covers seal off concrete and prevents water from evaporating.
Using synthetics like plastic in concrete generally weakens the material because they do not bond to the cement mix as well as sand. Properties such as the type of plastic, particle size and shape, and the rheology of the wet mix all have an influence on the strength of the finished concrete.
The most common types of under slab or concrete insulation include rigid foam insulations, such as expanded polystyrene (EPS), extruded polystyrene (XPS) and radiant insulation, such as Prodex.
How do you install vapour barrier under a slab? To install a vapour barrier, roll out the roll of black plastic on top of the compacted sand subbase and before placing your slab on ground reinforcement. A vapour barrier must be installed as follows: lap not less than 200mm at all joints.
The first step in keeping moisture out of a concrete floor is using a waterproofing barrier such as polyethylene sheeting or other waterproof membranes. There are also some sealants that you can spread on the concrete floor and wait for it to dry. Water will then bead off the floor instead of absorbing in it.
According to a school press release, the researchers say that exposing plastic flakes to small doses of gamma radiation, pulverizing the flakes into a fine powder, and mixing it with cement paste and fly ash results in a concrete up to 15 percent stronger than conventional concrete.
Sealer prevents moisture and other elements from seeping below the surface and negatively affecting your concrete surface.
The best base for under a concrete driveway is a gravel base. There are a few reasons why this is the case. In any concrete construction gravel generally is considered the best prep and base layer. The soil subgrade needs to be prepped before you can put concrete on it.
Expansion material is placed between sections of concrete. It's that black stuff you see between concrete slabs sometimes if a contractor doesn't put a sealant on top of it. If they do seal it, you're likely going to see a grey sealant between sections of concrete.
