Factors to Consider When Building a Concrete Slab

Concrete slabs Melbourne are an integral structural element in modern buildings, yet their construction involves numerous considerations – such as dirt work and grading, permitting, and choosing an aesthetic finish for it.

Slab foundations must be placed on undisturbed soil or on a surface which has been compacted to specific specifications, otherwise, the foundation can become settled over time and cause cracking or settlement issues.


Concrete is a highly resilient material and, with proper care and maintenance, it can last a lifetime. To extend its longevity even further, however, several basic rules must be observed; most importantly is to make sure all concrete is mixed, placed and finished according to specifications; after curing has taken place it must also be inspected, tested and approved as fit for use.

An effective way to reduce cracking is using an accelerating admixture that speeds the setting and drying times of concrete, helping it set more quickly so as to avoid crusting or excessive shrinkage cracking.

Control joints can either be tooled into plastic concrete, or saw cut later after it hardens, to release tension as your slab dries and shrinks; without them, tension begins building up inside it that eventually leads to visible cracks on its surface. Designing your home with carefully placed control joints will prevent this problem altogether and save you money in the long run.


Concrete is stronger in compression than tension, so floor slabs require reinforcing to resist bending loads. But the compressive strength can vary throughout its depth; depending on its design, some slabs may be more or less likely to unplanned cracking than others.

At last, concrete cracking can be prevented with contraction/control joints installed at predetermined locations. These joints create weak planes where concrete can crack straight instead of randomly distributed patterns. They should be tooled in when plastic, then saw cut after hardening has completed. When tested, composite slabs with hybrid fiber tension sides produced better results as their cracking load, ultimate load stiffness and toughness all increased significantly compared with single slab concretes.

Thermal Mass

Concrete slabs make an effective thermal mass, which stores and dissipates heat throughout a home. Unfortunately, however, concrete has a relatively high embodied energy factor; therefore, you should balance its use with other passive design principles appropriate to your climate zone.

Control joints in concrete slabs are vital. Whether tooled in while the concrete is plastic or saw cut after hardening, these releases tension that builds up during drying shrinkage and would otherwise result in unsightly random cracks.

If you opt for a concrete slab foundation, look for options with low embodied energy such as cement extenders, geopolymer cements and magnesium cements as well as hempcrete that have lower lifecycle environmental impacts. Eco-comparison websites can assist in selecting products with lower environmental footprints.


Concrete slabs make an ideal platform for radiant floor heating systems, provided they have sufficient insulation. Without insulation, heat easily escapes to the ground, leading to cold room temperatures, mold growth and pest problems.

To avoid such issues, it’s essential that a layer of rigid insulation be installed under slab. Optimally, this should have a high R-Value and be moisture resistant; rigid foam insulation like EPS or XPS provides superior energy efficiency and longevity.

Rigid insulation should also have a high compressive strength level, to maintain its shape and prevent it from collapsing under the weight of a building above. A vapor barrier must also be employed between concrete and insulation and the soil in order to stop moisture seepage into either component.


Even though slab foundations are relatively straightforward and cost-effective, void-filling may still become necessary from time to time. This involves drilling holes and filling them with an anti-crumbling compound that prevents concrete from cracking or settling over time.

If your concrete slab is on a grade, regular inspection and watering must take place to prevent too much moisture from reaching its surface. A saturated area could cause it to shift or crack over time.

Control joints are an inexpensive solution to avoid ugly slab cracks, and should be installed early during the placement process. They should be tooled into the slab while plastic or saw cut after hardening to release tension caused by drying shrinkage and tension build-up during drying shrinkage. Seams must also be constructed properly to protect termite infestation and ensure structural integrity.