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Backfill is used to fill foundation holes. Find out what backfilling entails and which materials are suitable for the process.

Anytime you build a home, you’ll have to dig the ground and install the foundation. This will leave gaps or holes around your foundation walls. Such holes need to be filled five to seven days after the foundation slab cures. Otherwise, you will experience water problems. Most builders pour the excavated soil right back into the holes while others use alternative refill materials. 

Let’s explore what backfill is and why it’s necessary after construction. Then, we will look at some common backfill materials. We’ll finish off by taking you through the steps of backfilling the foundation hole. 

What Is Backfill? 

Backfill is any material that’s used to refill an excavated hole or trench in your yard. It can be the soil that’s been dug out of the ground, a mixture of gravel and sand, or commercial products.  

Backfilling, which is the process of refilling the trench or holes in excavated areas, is done in layers. Foundation builders usually wait for the floor joists to be built above the foundation before they start filling the holes. 

Backfilling serves these four purposes: 

  • Increases the foundation’s strength to withstand the load from your home or building 
  • Supports a building’s foundation 
  • Increases the overall performance and stability of the structure 
  • Promotes exterior water drainage 

You have to choose a suitable backfill material, the best way to compact it, and the duration of backfilling. 

Types of Backfill 

Depending on your project and drainage needs, your contractor may recommend and use any of these materials. 

Coarse-grained soil: It’s a mixture of gravel, sandy soil, and a negligible amount of fine materials. This material provides good foundation support and is easy to compact.  

Limestone screenings: If you’re looking for a backfill material that compacts well, consider limestone screenings. They’re mostly used for sewer and pipe backfills and a base for brick paving. 

Trench backfill: Similar to CA6 base stone, trench backfill is made up of small aggregate that drains and compacts well. 

CA7 bedding stone: One of the most popular backfill materials, the CA7 or ¾” limestone is white/gray stone that self-compacts. Builders use it for pipe bedding, subbase, and improving soil drainage. 

CA6 base stone: This is a subbase granular backfill that’s used along roadway shoulders. Some builders also use it as backfill for residential projects. 

3” coarse stones: We recommend that you use the 3” stones to fill large holes in your yard because of their good drainage properties. These stones will form the first layer of the backfill. Once the trench is filled, a layer of CA6 base stone can be added for compaction. 

Commercial by-products: Where suitable natural fills don’t exist, fly ash or furnace slag can act as backfill. The choice of commercial backfill depends on the site’s condition and engineering properties. 

How to Backfill Your Foundation 

Backfilling the foundation is a five-step process that goes like this: 

  • The area that needs backfilling is first cleaned and any stagnant water pumped out; 
  • A suitable backfill material for the foundation is identified;  
  • The contractor refills the trenches with backfill material in consecutive layers of 6” to 8”, starting from the corners; 
  • Each layer is compacted using a roller or any machine that’s available before the next refill; and 
  • Finally, all the layers are watered and compacted further using steel rammers or wooden log rammers. 

Note: Wait for the foundation to cure before backfilling. 

Compacting the Backfill 

Regardless of how well you backfill the soil along your home’s perimeter, some of it will still be loose. This isn’t good as the backfill can get saturated by rainwater or melting snow. With nowhere to go, the standing water will start pushing against your basement or crawl space walls. This can lead to cracks and bowing walls. To prevent this scenario, compact your backfill properly. You can use a roller or any suitable compaction equipment to tamp down the soil. 

If you’d like to waterproof your foundation after backfilling it or inspect your drainage systems, contact JES Foundation Repair for a free foundation repair inspection and quote. We’ll come over and assess the foundation and make recommendations that’ll keep water out. 

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