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Without proper backfill, your foundation could suffer serious damage sooner or later. Here’s what you need to know.

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The construction of any new home starts with the foundation, which, once built, will need to be backfilled. But what is backfilling exactly? 

After a construction crew pours the concrete for the foundation, there will be gaps and holes left around the substructure. You can’t leave them there like that. Therefore, the crew will need to fill up these voids by either using the previously dug-up soil or some other refill material. No matter what you choose, the material that will eventually occupy the space surrounding your foundation will be the backfill.

Here, we will explore different types of backfill and how they’re used during construction in more detail.


The Basics of Backfill

As we’ve said, any material you choose to occupy the gaps and holes next to your foundation will be the backfill. You can either go for the same soil the construction crew dug up during the prep work, a gravel and sand mixture, or any other commercial refill product. Nevertheless, each backfill will have a unique set of properties, so you’ll need to choose accordingly.

No matter which type you go for, the backfilling process will happen gradually, in layers. Once the construction crew finishes the floor joints that go above the foundation, they can begin backfilling your substructure. A proper backfill will provide your home with structural stability, support the foundation, and assist in exterior water drainage.

Backfill Types

Depending on the type of structure you’re looking to build and its drainage system, you can opt for the following types of backfill. We should point out that before you choose one, it’s best to consult professional contractors. With their knowledge and experience, there will be a much lower chance of you backfilling your foundation with inadequate material.

Coarse-grained soil: Your first option is coarse-grained soil. This is a mixture of gravel, sandy soil, and a negligible amount of fine materials. This is a high-quality backfill since it provides fine support for the foundation and is pretty easy to compact.

Limestone screenings: Limestone screenings are great when it comes to sewer and pipe backfilling. Like coarse-grained soil, this material also compacts pretty well. Some builders will use it even as a base for brick paving.

CA7 bedding stone: This third option is the most popular in construction nowadays. CA7 bedding stone is a grayish material that self-compacts and is perfect for bedding pipes, subbase work, and improving soil drainage.

CA6 base stone: Besides the CA7 bedding stone, its CA6 counterpart is another great option that you should consider. It’s used for both commercial and residential projects.

Trench backfill: Similar to CA6 base stone, trench backfill comes in the form of small aggregates and it drains and compacts quite well.

3” coarse stones: In case you’re dealing with large holes and trenches, it’s best to use 3” coarse stones. Just like all previous options, this backfilling material has great drainage properties as well. We always suggest that you use it as the first layer and then cover it up with another kind like CA6 base stone for compaction.

Commercial by-products: Depending on the quality of the soil on your property, you might need to use certain commercial by-products like fly ash to improve the quality of the soil on your property for backfilling. 

The Backfilling Process

Professionals backfill foundations in the following five steps:

  1. The crew will clean the area that they’re looking to backfill. While doing so, they will also pump out any stagnating water on the site.
  2. Afterward, it’s time to identify materials that they’ll use to fill out holes and trenches.
  3. Once they do that, they will pour the material into the space surrounding the foundation in consecutive layers of around 20 cm, beginning from the corners.
  4. Between refills, the crew will need to compact the layers by using a roller or another machine capable of such work.
  5. Lastly, they will need to further compact the layers by using steel or wooden log rammers and water them.

Compacting the Backfill

No matter how good of a job your construction team does, the backfill will always be a bit loose. This can cause numerous problems down the line. The most common of them is that such backfill will absorb heavy rain or melting snow. As such, the water will begin to push the walls of your foundation (crawl space or basement) in what’s called hydrostatic pressure.

This type of pressure will eventually cause cracks and fractures in the lower levels of your home. And if you don’t prevent it, this water and soil pressure will bow and could even take down your foundation walls completely. The best way to go about preventing any of this from happening is to properly backfill your substructure. You can do this with adequate compaction, using the right equipment and suitable rollers.

Why Risk Your Safety?

Are you worried about whether your foundation walls were properly backfilled during construction? Your best option is to schedule a free inspection and repair estimate with the experts at FSM. Our team serves the Detroit area, Grand Rapids, Traverse City, and surrounding areas in Michigan. With our help, you’ll easily repair any damage caused to your foundation during backfilling. Since these problems can cause serious safety issues, it’s best to eliminate them immediately before they become dangerous.

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