What Gravel to Use Under Concrete [2021]

Table of Contents

What type of gravel can be used? | What kind of gravel can be put under concrete? | What is the best base for a concrete slab? | What size gravel is best for concrete? | Why is a concrete slab base necessary? | What material is used for a slab base? |

Even though you can pour concrete over dirt it’s not recommended. You should use any type of gravel and this really comes down to the homeowner and the subgrades. It’s recommended to use something compatible and easy to trim, which in turn will keep everything stable and will properly support the slab.

Having a gravel layer helps keep the slabs even, prevents cracks, helps with water drains and helps avoid low spots within the subgrade. The subbase is literally the foundation and with it, you don’t have to worry about the subgrade material. It can be clay soil, dirt, none of it will matter when you have a proper layer under the concrete. Although it is recommended to have a good subgrade preparation in place before putting in the gravel.

What Type of Gravel Can Be Used?

Depending on what you’re looking to do, there are a few gravel options you can choose from:

–         Crushed Stone

–         Washed Clean Stones

–         Pea Gravel

–         Quarry Process

–         White Marble Chips

These are the most common types you can use for a gravel base with crushed stone being the most popular.

What Kind of Gravel Can Be Put Under Concrete?

First off, the gravel base should be around 10cm (4 inches ) deep and 10cm more for the slabs themselves. Most people use a plate compactor to get a proper subsurface but it depends on the project itself and the soils themselves. Having a good foundation will be key to keeping moisture content, water amount and any elements in check. Depending on the bearing capacity the most common type of gravel used is crushed stone or washed clean stones. It all comes down to what you are actually making, how much weight would be on top of it and what the ground underneath is like.

What is the Best Base for a Concrete Slab?

Most people build a driveway or a patio so in that case, a good choice would be a mix of coarse and fine aggregate which will create a compactable base. Overall, a mix of crushed stone and stone dust is the best base material for any concrete flatwork. It all comes down to the ground and soil you will be working with.

What Size Gravel is Best for Concrete?

The aggregates for concrete are divided into two distinct categories, one is coarse and the other being fine. These are both great options to use for concrete. The coarse aggregate is usually around 9.5mm up to 38mm and on the other hand, the fine aggregate is usually anything less than 9.5mm. In order to have a good concrete mix (and use less water and cement) people tend to mix larger aggregates that go above the 20mm diameter. Most of them are a mix of crushed stone and sand and this is our best advice for what to use for your concrete mix. Sometimes rebar can be used in order to add increase the strength of the mix.

Why is a Concrete Slab Base Necessary?

It’s very important to have a proper base in order to avoid a lot of problems such as cracking, movement of the area, improper drainage or form. Placement of the slab without the right material or any vapour barrier will result in a lot of headaches so it’s important to know what you’re doing way ahead of time. Having a concrete slab base layer properly setup can be one of the reasons why your many driveways look amazing and last a long time.

What Material is Used for a Slab Base?

Contractors usually use a form of crushed stone of various sizes, the largest being around 37mm. Any material that can help with drainage and has an easy application will work. The best choice for an easy application is a mix of crushed stone and stone dust. The concrete slab must have a good foundation in order for you to avoid problems.

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