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.
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.
Long story short, yes you can pour concrete over dirt.
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.
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.
The minuscule size of sand grains makes it possible to create a smooth concrete mix. If you were to use pebble-sized aggregate instead of sand, your concrete would be very bumpy. This would be fine for some situations, but most of the time, a finer consistency of concrete is preferred.
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.
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.
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.
Most driveways require at least 6 inches of stone crushed or gravel. 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.
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.
Fortunately, whether you plan to make a patio slab or a driveway, working in small areas divided by concrete forms and using bagged concrete mix can make the job easier for a DIYer.
A mixture of sand, cement and water is called mortar. Mortar mix is made by combining cement, sand, and water. Mortar doesn't have very much compressive strength because it contains no gravel. So its not used as a structural material. But it's still very strong and sticky.
As for thickness, non-reinforced pavement four inches thick is standard for passenger car driveways. For heavier vehicles, a thickness of five inches is recommended. To eliminate standing water, the driveway should be sloped towards the street a minimum of one percent, or 1/8 inch per foot, for proper drainage.
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.
Concrete will stick to some plastics, wood, metal, vinyl, cloth and other porous surfaces. But that's about it. Concrete won't stick to molds, smooth metal, glue, paint, oil, mortar, other concrete or most masonry products.
The only way to stop water from coming up through your foundation slab is by installing a drain tile system, vapor barrier, and sump pump. Installing a vapor barrier will counter moisture seepage – A vapor barrier is a thin (10 to 20-mil thick) sheet of polyethylene that's placed along your foundation walls.
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.
Gravel Beds Provide Natural Drainage
Water drains more quickly through gravel compared to most types of soil, so puddles form less-readily on gravel-covered pathways and borders than they do on soil surfaces.
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.
Unless your patio is going to be the size of your driveway, you can pour concrete you mix yourself. Buy your favorite brand and follow the instructions on how to mix. Once you have your concrete mixed, start pouring in the frame over the leveled and flattened ground.
Fast-setting concrete is ideal for setting posts because there's no mixing—you simply pour the dry concrete from the bag right into the hole, then add water.
Pouring concrete over existing concrete is possible as long as you do so properly. When the old concrete serves as the foundation for your new pour, it needs to be a solid one.