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What do you put under a concrete slab?
You do need gravel under a concrete slab, footing, or patio. Gravel provides a solid foundation for your concrete as it can be compacted. It also improves drainage, preventing water from pooling beneath the concrete.
Should I put sand under concrete slab?
Pour concrete over a solid, well-drained base 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.
How much base is needed for a concrete slab?
Excavate the slab area to a depth of about 7 inches, allowing 3 inches for a gravel base and 4 inches for concrete.
What is the base under concrete?
The base in concrete construction is usually a form of crushed stone. 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.
What type of sand should be used under concrete slab?
The base course material, according to ACI 302, “Concrete Floor and Slab Construction,” should be “compactible, easy to trim, granular fill that will remain stable and support construction traffic.” ACI 302 recommends material with 10 to 30% fines (passing the No. 100 sieve) with no clay, silt, or organic materials.
Why is sand placed under slabs?
A layer of packing sand is placed between the stiffening beam locations. This allows a firm level base for the slab and takes up any irregularities in the level of the site. The sand is screeded level and provides a good base for the plastic membrane.
Can I pour concrete directly on dirt?
Long story short, yes you can pour concrete over dirt.
How do I work out how much sub base I need?
Steps: Measure the length and width in metres of the area you wish to fill with a sub base aggregate e.g. 20m x 10m. Multiply the length and width to find the area in square metres. Multiply by the depth e.g. 150mm. Multiply by 2 to get the tonnage required.
Can you pour a 2 inch concrete slab?
The minimum thickness for pouring concrete over concrete is 1.5 inches. In most cases, I don’t like to pouring the new concrete less than 2 inches thick. Two inches of concrete (or more) that’s bonded, gives you adequate strength for a wear surface, especially if you’re driving over it.
Do you need a subbase for concrete?
Subbase for Concrete Slab The subbase placement is optional and it serves as a work platform for construction of the slab and provide more uniform support for the slab. As the thickness of subbase increases, the ultimate load carrying capacity of slab increases.
Do you have to remove grass to pour concrete?
Conclusion. Although certain projects allow a little wiggle room by leaving grass underneath your concrete, it is best to remove all grass and loose debris before pouring. This will ensure you have an even, smooth, crack-free look for many years without needing to deal with any expensive or time-consuming maintenance.
How long should ground settle before pouring concrete?
An hour at most would be sufficient to let dirt and dust settle before you start pouring. If you have used a combination of water and rollers (or stompers) to compress the dirt, it is usually a good idea to wait for at least 4-6 hours. This is so that excess water gets drained or rises to the top.
Is sand a good base for concrete?
Simply put, sand isn’t sturdy enough to work well as a subbase for something like a driveway. It is also difficult to maintain a level sand surface when pouring concrete, and therefore difficult to maintain a uniform thickness of the concrete slab.
What is the best base for concrete driveway?
The best sub-base for a concrete slab is gravel. The soil has to be prepped first before the gravel can be laid down; pouring concrete directly onto rock is not considered a best practice. You can use different kinds of gravel for the subbase as long as it is clean and uniform in shape and size.
Can I pour concrete over gravel?
Laying a concrete driveway over an existing gravel one is possible, but it is not generally recommended. However, if the gravel in your driveway is small enough, it is possible to create a cement driveway over the existing one.
What happens if you don’t put gravel under concrete?
Because concrete is a very porous material, it will absorb any moisture that it contacts. This can cause pooling. Without crushed stone, pooling water will settle under it and erode your slab.
Can I lay concrete on sand?
Whilst you may get away with it in some instances, the vast majority of slabs won’t stay put when laid straight onto sand. We’d recommend bedding the slabs down with a simple mortar mix each and every time. Avoid laying straight on to sand as whilst it may be convenient, the headaches are simply not worth it.
How do you fill a dirt slab under concrete?
A sand-cement grout can be used to fill voids under concrete slabs. This mix of sand, cement, and water is pumped through holes drilled to fill up the voids.
What is the best sub base for a patio?
‘ The most common granular aggregate sub-base is DoT (Department of Transport) Type 1 and Type 3 Limestone. They are both crushed stone: Type 1 has a maximum permitted top size of 63mm, graded down to dust; and Type 3 is an open-graded 40mm unbound mixture with a reduced amount of fines.
What is the purpose of the subbase?
The subbase layer is typically used to protect the pavement from the effects of frost heave and/or used to improve the constructability of the pavement layers above the subbase.
Can you pour concrete without rebar?
Rebar is not necessary for every concrete project. The general rule of thumb is that if you are pouring concrete that is more than 5 inches in depth, you are probably going to want to add in some rebar to help reinforce the entire structure. Wire mesh use is becoming much more common for projects like a home driveway.
