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  • Writer's pictureGabrielle Glasson

Site Preparation for laying your home's slab

Site Excavation

Any old structures have been demolished and you are ready to excavate your site in preparation for the slab! ⁠

Clay is prone to contracting and expanding with the weather, so to ensure your slab can’t shift or crack over time, it's critical to prepare the land with deep piers to pin your slab into the ground. You know all those sayings about laying a strong foundation? Yep, this is it!⁠

Digging the piers can often result in the discovery of more asbestos in old underground sewer pipes or septic tanks, so be prepared that some additional contaminated waste removal expenses may come about during this stage. ⁠

Once we’ve dug the piers, we need to remove all the newly excavated earth. There are a few different options here depending on the site: ⁠

⛏️ The most cost-effective option is to try to use the earth somewhere else on your site – like building up sloped areas to make them flat and packing excess landfill behind retaining walls. ⁠

⛏️ The easiest option is to bobcat the waste into a truck for removal. ⁠

⛏️ If site access makes this impractical, our final option is to use skip bins. This option is a bit more expensive, so we only go this route if necessary. ⁠

Formwork and slab preparation

There's quite a bit of detail that goes into the pre-slab preparation. Our approach is guided by the requirements set out by the Engineer based on the structure we're building and the type of ground it rests on. ⁠

To maintain structural integrity, we need to have footings spread across the entire slab that fix the slab firmly and deeply into the ground to prevent it from shifting or cracking over time. ⁠

The depth and type of footings are specified by the Engineer. Often-times this specification is 'until we reach bedrock.' Hence the piers are generally only covered by a cost allowance or 'Provisional Sum (PS) allowance in your quote, as it's not possible to know how deep they will need to go to reach bedrock at the time of quoting. ⁠

We run plumbing and electrical provisions through the footings, then steel reinforcement (REO) to further prevent cracking, then we're ready to pour concrete. ⁠

Sometimes, when the ground allows, we can pour a 'Raft Slab' which is an all-in-one with the footings. That makes it nice and easy!⁠

Other times the Engineer decides that won't cut the mustard and they determine that each component need to be poured separately. ⁠

Once the footings are poured, we install any additional services, lay plastic to control moisture, then cover with steel reo to strengthen the slab and prevent cracking. Finally, we add termite barriers, and then ta-da! We are READY FOR THE SLAB!!! ⁠

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