Sand or Gravel Under Concrete Slab? Let’s End the Debate! 

Concrete in your area broke over time due to exposure to the environment and strain? 

It’s normal to think about what to put under a slab of concrete that will extend the life of your investment.

So, wondering about sand or gravel under concrete slab?

Gravel is required beneath a concrete slab. Gravel, which may be compacted, provides a solid base for your concrete. The driveway’s base may need to be 4 to 12 inches deep, depending on its purpose. Most driveways should have a minimum of 6 inches of crushed stone or gravel.

Let’s dive into the discussion to clear all of your doubts 

What Should You Use as a Sub-Base for Concrete?

To prevent concrete from cracking, the concrete slab needs a quality sub-base. Professionals like to use sand as a sub-base while laying concrete. However, this depends on the slab’s function as well as the environment in your area.

A professional would be aware of your region and can assist you in making the best option, but there are a few things to consider.  

Sand is great as a sub-base for patios that don’t require a lot of load-bearing, but it’s not as reliable as gravel. When pouring concrete, it’s also difficult to have a level sand surface, which makes maintaining a regular thickness of the slab challenging. 

A gravel layer under concrete slabs helps to level the slabs, eliminate cracks, and improve water drainage. It doesn’t matter if it’s clay soil or dirt, as long as you have an appropriate layer under the concrete. Although for good subgrade preparation, you need to first caulk or grout to install the gravel.

What Type of Gravel Can be Used?

Most driveways should have a minimum of 6 inches of crushed stone or gravel. The driveway’s base may need to be 4 to 12 inches deep, depending on its intended purpose. In colder climates, the foundation must be strong and sturdy.

The two levels beneath driveways are a subgrade of native soil covered with a gravel sub-base beneath the concrete slab. Gravel is the greatest sub-base for a concrete slab. Before the gravel can be set down, the soil must first be prepared; pouring concrete directly onto rock is not recommended.

There are a couple of gravel options available depending on what you’re seeking to do:

  • Crushed stone
  • Stones that have been washed and dried
  • Gravel from peas
  • White marble chips 

These are the most used gravel base materials, but crushed stone is the most common one.

What is the Best Size of Gravel for Concrete?

The coarse and fine aggregates for concrete are separated into two categories. Both of them are excellent concrete possibilities.

Multiply the length, breadth, and depth of the driveway in yards to calculate how much gravel you’ll need. Different types of gravel can be used for the sub-base as long as they are clean and equal in size. You’ll need roughly 3/4 inch of depth, and order ahead of time to avoid delays.

Soil Compaction for a Concrete Slab

A vibrating plate compactor is recommended by Family Handyman since they are built for distinct tasks. For every 2 inches of material you lay down, make three or four passes with it. Each layer must be compacted thoroughly. These machines look like push mowers and are simple to use.

Grab a handful of soil and see if it crumbles. Make sure it’s not too wet. Muddy soil can damage the drainage under the pipe. 

For pipes, choose between sdr 35 and schedule 40 as they have the most success rate to prevent drainage leaks. For best results, the gravel should be compacted to roughly 95%. It ought to be even, firm, and well-drained.

This extra effort put in before laying the concrete will ensure that your driveway lasts longer. Water collection and settling around the foundation of a property can be caused by low-quality subgrades and sub-bases. This can actually make it weaker.

How Can we Improve the Sub-Base?

Soil stabilization can be employed in extreme instances, such as when the soil is exceptionally bad or the loads are really high. The dirt is blended with portland cement, calcium chloride, or lime, and then compacted in this procedure. To improve the sub-base we can try the below methods. 

Method 1: Reduce the Soil Compresses  

To keep the soil healthy, it’s critical to till it as gently as possible. Conservation-oriented tilling, which preserves the soil structure, is now widely used. Tire pressure, wheel load, wheel slip, and the number of trips over the fields are all aspects to consider when driving on the soil.

You need to keep in mind the wiring structure underground as tire pressure and weight of the car can easily destroy them. In the market, 14/2 and 14/3 wires are eye-catching right now. They can be used without fear.

The soil is most affected by the first pass. When the soil is wet or damp, you should avoid driving on it. Furthermore, routes that lead downhill increase the likelihood of water erosion. To help with this difficulty, a significant number of radial tires are already available on the market. Here are a few suggestions. 

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You can drive on the field with low tire pressure using these. They provide for a high load capacity at a low speed while maintaining a broad surface contact area. A tire pressure control system may be useful if you regularly drive between the field and the road.

Method 2: Determine Soil Compaction by Proctor Test

The Proctor compaction test is usually a laboratory procedure for evaluating the optimal moisture content. It will tell at which point a particular soil type will become most dense and its maximum dry density.

The dry unit weight of the soil can be used to determine its degree of compaction. When water is added to the soil, it softens the soil particles, allowing them to move more easily between one another. 

After the water content percentage is exceeded, any additional water will result in a drop in dry unit weight because the pressure of water in-between each soil particle will beThe dirt particles are being pushed apart, reducing friction between them.

This is all we have regarding the topic.


Can I use pea gravel under concrete?

A base will provide a solid underpinning for the slab if the earth is disturbed and packed, or if the soil is unstable, such as some clays. It will need to be packed if you use crushed rock and dust. Pea gravel, on the other hand, is a non-packing material.

What is self-compacting gravel?

Clean gravel and crushed rock are often referred to as self-compacting, implying that dumping them next to a pipe will result in a dense substance.

Does 3/4 minus gravel drain?

A 3/4″ rock with particles down to 0″ helps gravel pack in tight. It also prevents it from draining. The most common one is basalt as it packs the tightest. But if you want to choose lighter color, 3/4″ minus is also available. 


We hope we have ended the debate of sand or gravel under concrete slab. Gravel is a better choice as your concrete will endure longer and be less likely to crack over time.

If you still have any doubts, don’t fret. Ask us without feeling hesitate.   

Till next time, adios!