A 4 inch thick concrete slab must be covered with 3 inches of gravel. The best gravel is gravel with a depth of 3 inches, but it is also ideal for a 4 slab floor. Most driveways require at least 6 inches of stone crushed or gravel.
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.
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.
Instead, use a layer of gravel underneath your concrete slab. Because concrete is porous, it absorbs water. If you place concrete directly onto dirt, water will collect under the concrete and slowly erode the bottom of the pad. Gravel prevents this erosion by allowing water to drain away from the concrete.
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. Razorback Concrete is always willing to work with you.
A 4 inch thick concrete slab must be covered with 3 inches of gravel. The best gravel is gravel with a depth of 3 inches, but it is also ideal for a 4 slab floor. Most driveways require at least 6 inches of stone crushed or gravel.
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.
Gravel adds a lot of strength to concrete but, if you use too much, it has the opposite effect and damages the integrity of the concrete mix. Therefore, it is important to know what type of concrete you need for a particular job.
Make sure the material under the slab is properly compacted. If you believe it needs more sand or gravel for better drainage or to level the area, then that added material has to be compacted before placing the concrete. Sand or road-gravel compacts better than loose stone.
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.
This strength is crucial for things like buildings, roads and driveways. 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.
Good quality concrete paving slabs laid on to a flat and level gravel base. A thick polythene sheet should be placed either under the slabs or alternatively on top of the slabs, which will help prevent moisture rising inside and possibly causing condensation.
A Level Surface
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. Pouring concrete over crushed stone, however, will eliminate these worries.
To manually calculate how much gravel you need, measure the length, width, and desired depth of the area in feet, then multiply those numbers to determine cubic feet. Next, divide your cubic feet value by 27 to determine cubic yards. Finally, to convert cubic yards to tons, multiply by 1.4.
How Much Gravel Do You Put Under a Concrete Slab? You will need 3 inches of gravel under a concrete slab that is 4 inches thick. More gravel is better, but 3 inches is the minimum amount of gravel you should have with a 4” slab. Use ¾” washed and screened gravel, then compact it to level.
Ideal construction aggregate should have a rough surface texture and should be clean, strong, and free from coating and other dirt particles. Coarse aggregates with a size of 20 mm or less are commonly used for the majority of concrete construction.
Snow and rain can cause the gravel to move around and even sink, causing ruts and sinkholes. Regular maintenance and top dressing the driveway may be required. Snow and ice removal can also be difficult unless supported by a porous paving system.
Ultimately, natural aggregate is nearly always the best choice as it provides the most strength, durability and longevity to any concrete mix, but if costs are a consideration then manufactured or bye-product aggregates are cheaper.
There are a variety of different materials that can be used for the sub base, but crushed stone, gravel, or sand are commonly used. Crushed stone or hardcore is usually the best option because it's easy to work with but is more durable than sand.
Below slab level, you'll lay a 100mm sub-base and a damp-proof membrane. Therefore, you need to dig a level-bottomed pit 100mm deep. Be sure to remove all grass and other vegetation, stones and debris, then compact the earth. A micro excavator will make light work of the digging.
You are not required to have a vapor or moisture retarding barrier for outside concrete pads or unheated buildings. Although a vapor or moisture retarder or barrier is not necessary beneath concrete floors used for unheated carports, driveways, and outbuildings, some DIY enthusiasts and builders recommend it.
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.
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.
The standard thickness for a concrete slab in residential construction is four inches. Five to six inches may be advantageous if the slab will receive heavy loads, such as a motor home.