Insight To Help You Prepare The Foundation And Site For A Strong And Long-Lasting Garage Concrete Slab

Posted on: 17 August 2017

Completing most or all the work to prepare and complete installation of a concrete garage foundation can help save you a great deal on your construction budget. Whether you are preparing the site for the pouring of concrete for a commercial garage or a garage on your home's property, you want to make sure the slab is built well to last many years. Here are some tips to make sure you complete the appropriate quality of work to build a durable foundational concrete garage slab.

Excavate the Site

The first step of preparation for installing a concrete garage foundation is to excavate the soil on the site to make room for the slab's thickness. It is recommended to install an appropriate amount of gravel fill for drainage as the slab's base, then to pour the concrete at a required thickness, so you will need to remove soil to make space. Your concrete slab needs to be able to have proper drainage beneath its surface to prevent soil erosion, which can lead to settling and cracking of the slab. During winter's freeze-thaw cycles, moisture that does not drain from below the slab can expand and cause the concrete to crack.

You will want to remove the topsoil from the site, which you can use in landscaping on other areas of the property, or sell to a landscaping company for reuse in other landscaping projects. Use a Bobcat or skid steer with a bucket attachment, or similar earth-moving equipment to remove the soil and level the site. You may choose to hire an excavation company to complete this step properly if you do not have the skills to complete it. 

It is important to check the remaining subsoil for its drainage to determine if the soil has good or poor drainage quality, as this can affect the concrete slab. With poorly-draining soil you should increase the amount of base gravel from an average amount of 6 to 8 inches of gravel to a gravel layer that is twice the thickness of your slab. Make sure you remove enough soil to provide space for the gravel and the concrete above it. You don't want your slab to sit too high above the surrounding land, otherwise you will need to build up the landscaping to match the elevation of the slab.

Add Granular Fill

Once the soil has been excavated and leveled to remove any large boulders or other debris, it is a good idea to lay down a geotextile fabric barrier to further reinforce the gravel layer. This helps prevent the subsoil from coming up into the gravel layer and degrading its water-proof qualities. It is recommended to install a gravel that is a medium-sized gravel, with pieces measuring from 3/4-inch and larger.

When choosing the type and selection of gravel, it is best to use an angular gravel, which allows the gravel to be compacted together into an interlocking layer and makes the drainage layer more stable. But, you can also choose to use recycled concrete as a fill layer, which gives you the angular pieces required for the drainage just as traditional gravel and helps to reuse recycled products and prevents it from ending up in the landfills.

Pour the gravel into the site in 2-inch thick layers. With the use of a compacting machine, compact the gravel into place as you pour each layer. This helps the angular edges of the gravel grip one another and create the interlocking layer.

During this step, it is recommended to leave a 12-inch by 12-inch trench around the perimeter of the gravel within the concrete's forms. This trench will create a thickened edge around the concrete slab to give it more strength as it will be a garage foundation.

Use these tips to prepare the area for the pouring of your concrete foundation slab.