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Can You Pour Concrete Over Dirt?

You want to build a driveway but aren't sure if it's okay to pour concrete directly on the dirt below. We have researched this topic in depth to find out if you can do this or not.

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Yes, you can pour concrete over dirt. However, you may need to do some extra work, like compacting the surface if the dirt is composed of loose particles like sand, silt, or small rocks. If it's mostly clay, you may need to put gravel as a sub-base.

The key to using concrete as a foundation material is to make sure you do it correctly. After all, you don't want the foundation to crack when you put some load or walk on it, right? Keep reading as we provide more information on how to pour concrete over dirt the right way!

Is Dirt the Same As Soil?

Soil is earth and is composed of various minerals and organic materials such as decaying plant and animal matter. Dirt is usually a mixture of clay, sand, and other particles (soil included). 

Before you pour concrete, you need to know what kind of dirt composition you are dealing with. Dirt is mostly composed of clay, sand, silt, and small rocks.

What Prep Work You Need To Do If You Have Dirt As Subgrade?

Knowing how much percentage of each component you have in your dirt will help you decide the kind of prep work you need to do.

If the majority of the dirt is made up of clay, then it is usually easier to deal with than if you had dirt that is made up of loose particles. The clay's plasticity makes your job of compacting the dirt faster. 

On the other hand, if the dirt composition is mostly made up of loose particles such as sand, silt, and small rocks, then you need to compact the surface with a plate compactor. It may take you a little longer to finish the compacting than if you had dirt with mostly clay in it.

A plate compactor looks like a lawn mower with a vibrating plate instead of a cutter which forces the aggregate (sand, gravel, silt, soil, and crushed stones) to pack more tightly, making the surface even and compact. 

pouring readymixed concrete after placing steel

Why Is It Important To Compact The Subgrade Before Pouring In The Concrete?

A properly compacted subgrade is necessary for your foundation to have sufficient strength and load resistance. You don't want your subgrade to be loose or have a large volume of air space. 

A subgrade that has too much air space will cause settlement and deformation of the foundation, which in turn can lead to cracks in the foundation. 

Is Too Much Clay Content In Your Subgrade Bad?

natural clay piece hands isolated on white

You may not want a subgrade with high clay content if you're living in a region where winter temperatures are below freezing for extended periods of time. This is because clay and water freeze at the same freezing point.

To offset the effect of the clay freezing in winter, you can add gravel on top of it. The gravel will now act as the sub-base of your subgrade.

Foundation problems are usually caused by faulty subgrade conditions. A subgrade is a layer below the concrete slab. It is a crucial part of your home's foundation. If it is not done properly, it can lead to a weak foundation. 

Imagine if you have a frozen clay subgrade and you're standing on it. Since your weight is concentrated on that spot, it will become weaker and weaker over time until the frozen clay underneath cracks.

This causes the concrete on that spot to lose support and will eventually follow suit. It may not be immediate, but it will certainly happen. 

How To Use A Plate Compactor

builder worker sand ground compaction vibration, Can You Pour Concrete Over Dirt?

1. Clean the surface

If the ground has weeds, it is important to rake it first before using the machine. Any organic matter needs to be removed. You don't want them in your subgrade because they release moisture when they start to decompose. Moisture in your subgrade can affect the life expectancy of your foundation. 

2. Start your plate compactor

Locate the switch which is usually found on the right-hand side of the compactor and turn it to the on position. 

3. Pull the cord like you would a lawn mower

Once you get the plate compactor up and running, flip the choke switch to the close position. 

4. Adjust the throttle

A plate compactor basically has two speed settings: fast and slow. Adjust the speed according to your surface conditions and begin compressing the ground.

The plate compactor will push the aggregates into the area where you want to compact it. Continue to drive your machine around the area until the ground is completely compacted.

If you need a visual demonstration of this, you may find the video below helpful.

Check out this plate compactor on Amazon.

Can You Pour Concrete On Mud?

Subgrading is a process that involves creating a base to support your concrete. A good subgrade will keep your concrete from cracking. It also reduces the possibility of the concrete moving due to uneven ground.

You can find a wide variety of materials for subgrading, including dirt, crushed rock, clay, and more.

But do you really know what works best? You can use any of the mentioned materials above for subgrade, even mud, as long as you do the necessary prep work like putting gravel as a sub-base.

Gravel allows water to drain from the concrete mix gradually and this is important if you want a strong concrete foundation.

This is what makes compacting the subgrade important. The water in your concrete mix will eventually be expelled, but you don't want any of it on your subgrade. The gravel will act like a filter in this case.

A fast-drying and very fine cement in your concrete mix will also help your concrete mix retain water better. A cement with good water retention properties helps expel water slowly before it gets to the subgrade.

What Happens If You Don't Have Gravel Under Your Concrete?

constuction details worker laying cement concrete

Before pouring concrete, you have to lay a gravel sub-base on your subgrade that will allow moisture to drain from the concrete. If you don't have a gravel sub-base, then you will have moisture seeping in directly into the subgrade and this will make the concrete weak.

Gravel helps prevent concrete from cracking by absorbing its moisture and providing a layer of reinforcement or support between the concrete slab and the subgrade.

pile gravel on white background

Can You Use Sand Instead Of Gravel As a Sub-base?

If you're looking to build a solid foundation that's strong enough to support heavy loads, you should have a gravel sub-base on your concrete. Gravel is usually used to make foundations in high-traffic areas that require a decent load-bearing capacity. You can use sand though, but it just doesn't do the job as well.

How Much Gravel For A Concrete Driveway?

If you are about to install a new driveway, it's crucial to know how much gravel you'll need to complete the job. You'll need to consider the size of the driveway, the length, the width, the slope, the depth, the grade, and more.

While all these factors play a part in the amount of gravel you'll need, the general rule is that you should have at least 6 inches of gravel as a sub-base.

How Thick Should My Concrete Be For A Driveway?

If you're thinking of building a new driveway, you're probably wondering how much concrete is enough.

According to the Portland Cement Association, a driveway should be at least 4 to 5 inches thick. This will give the driveway enough strength to resist the constant traffic from vehicles.

Why Should I Pour My Own Concrete?

As a homeowner, it is best to know how much you will pay for concrete. This will help you budget and plan your project properly. However, the price depends on a number of factors. 

These factors include the size of the area, how deep it is, and how much concrete is required. The other things that you need to take into consideration include the cost of cement, sand, gravel, and aggregates.

Regardless of how much you'll pay, Forbes magazine says that you'll save up to 40% if you do it yourself.

You don't really need a professional contractor who has experience in maximizing the output of the concrete. Just remember the ideal ratio for a concrete mix which is 4:2:1 (crushed rock, sand, and cement).

man pour concrete bucket out cement

3 Most Common Concrete Pouring Mistakes

1. Getting the wrong type of cement

When it comes to cement, you may think that the type of cement used matters less than it actually does. However using the wrong cement makes your job more complicated and frustrating. It is best to know the right kinds of cement for the job you're about to do so that you can avoid wasting time and money.

2. Miscalculating the amount of concrete for your project

The most common mistake DIYers make is that they underestimate the amount of concrete they will need. As a general rule of thumb, you should estimate the project you will be working on and consider the area and its specifications.

You need to be aware of this fact because if you get the wrong amount, it might not harden in time or might not give you the strength needed for your foundation.

3. Wrong concrete mix ratio

Paying attention to the ratios of your mixture is a critical factor in the quality of the concrete. Off ratios will result in poor workmanship, uneven texture, and weak structure. 

When you mix concrete, you need to know the right ratios for each part of the mixture. For instance, you can mix cement with water, sand, and gravel and add different types of additives for different purposes.

In Closing

builder worker sand ground compaction vibration

If you're going to pour concrete over a dirt subgrade, you should also add a gravel sub-base for a stronger and more stable foundation. Otherwise, you might run into some troubles when it comes to retaining moisture in your concrete mixture which will cause a weak foundation.

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