Summary: No, gravel is not mandatory in all cases; but it can be very important in others. It depends what you need: gravel can provide a capillary break (preventing water from wicking upwards), can facilitate drainage, and can facilitate gas movement (like radon).
Do I need gravel for 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.
How much gravel do I need under concrete?
Determine the depth of the excavation. Let’s say it’s d = 2 yd . Multiply the area and depth of the excavation to obtain its volume in cubic yards: 18 * 2 = 36 yd³ . The volume of gravel required is equal to the volume of excavation.
Can I pour concrete directly on dirt?
Long story short, yes you can pour concrete over dirt.
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. Adding a layer of crushed stone will add proper drainage, as well as create a barrier between your slab and the ground.
What is the best base for concrete slab?
What Material is Used for a Slab Base? 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.
Does a 4 inch slab need rebar?
No, rebar is not required for a 4-inch slab of concrete on grade. A 4-inch-thick slab cast on the ground and in constant touch with it will float, with no need for rebar. For concrete that is 5–6 inches thick, rebar is suggested.
Do you need sand under concrete?
Just as every home needs a good foundation, your property’s concrete slab needs a good subbase to function properly. Contractors sometimes use sand as a subbase when pouring concrete, but it all depends on the slab’s function as well as your region’s climate.
Is 3 inches of concrete enough?
A concrete patio slab should be at least 4 inches thick and have a compressive strength of 3,000 PSI. You’re free to make it thicker or stronger, but unless specifically required for your patio build, it’s likely overkill to surpass 4 inches in thickness.
Do I need a sub-base for a concrete slab?
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.
Can I pour concrete over gravel?
Cement mix might work in some cases over an existing gravel driveway. Laying a concrete driveway over an existing gravel one is possible, but it is not generally recommended. The kind of gravel that is intended to go under cement is typically a smaller grade than what is used for gravel driveways.
How do you prepare the ground before pouring a concrete slab?
Quote from the video:
Quote from Youtube video: The first thing you want to do is bring in a backhoe or a skip loader and scrape off any organic material or topsoil from the area where the slab will be poured topsoil.
What is the purpose of gravel being poured under the concrete before it is poured?
Whether you pour concrete for a walkway or patio, a strong gravel base is required to prevent the concrete from cracking and shifting. Gravel is especially important in clay soil because it doesn’t drain well, which results in water pooling under the concrete slab and slowly eroding the soil as it finally drains.
Do I need to compact soil before pouring concrete?
Concrete slabs require a hard and compact soil for a foundation to hold it in place! If the slab was poured on the native ground then Mother Nature has done the contacting with the rain and gravity over a long period of time. But there is a higher probability that the slab was poured on push fill or backfill dirt.
What is the purpose of plastic sheeting under a concrete slab?
Quote from the video:
Quote from Youtube video: And if you don't have this moisture barrier then what's going to happen is you're gonna end up having a wet slab wet slab means you can't put down any.
Do you need a membrane under concrete?
These days, damp proof membranes are required in the construction of all new buildings to prevent rising damp. These strong and highly durable Polyethylene 1200 Gauge DPMs are sandwiched between the hard core and concrete slab to form an impermeable layer.
Do you need a vapor barrier under a concrete slab?
If you have a concrete floor that’s in continuous contact with a source of moisture, you’re going to have problems. This is why a vapor barrier under concrete is essential. Vapor barriers are a way to keep moisture from getting into the concrete. Note: A vapor barrier is not the same as an underlayment.
