Top 5 Mistakes in Commercial Concrete (and How to Avoid Them)

Commercial concreting isn’t just about pouring and finishing — it’s a complex process of engineering, timing, and quality control. One incorrect assumption about the subgrade, one rushed pour, or one overlooked curing step can cost a business hundreds of thousands in rectification and lost time.

At OSM Concrete, we’ve spent years working on commercial and civil concrete projects across the Gold Coast — from high-traffic retail developments to heavy-load industrial slabs. Along the way, we’ve seen the same mistakes repeated time and time again.

Here are the five biggest commercial concrete mistakes we encounter — and exactly how we prevent them.

1. Skipping Proper Site Preparation and Subgrade Compaction

The foundation of every great slab isn’t the concrete — it’s the ground beneath it.

One of the most common causes of premature cracking or differential settlement in commercial slabs is insufficient compaction or poor subgrade preparation.

Common Failures:

• Failing to remove organic matter or unsuitable fill

• Inconsistent compaction density (especially near footings and services)

• Poor drainage causing trapped moisture under the slab

What We Do Differently: Before a single cubic metre of concrete is poured, our team performs density testing (using a nuclear densometer or plate load test where required) to verify uniform compaction to the specified 98% Modified Proctor. We laser-level the surface to tolerance and check fall direction for drainage compliance.

A stable, compacted, well-drained base ensures the concrete performs as designed — with minimal post-cure movement.

2. Using The Wrong Mix Design or Slump

No two commercial slabs are the same — a warehouse loading dock, for example, requires very different concrete properties from a decorative retail forecourt.

Typical Errors Include:

• Under-specifying compressive strength (MPa) for load-bearing applications

• Using excessive water to achieve workability, which reduces strength

• Choosing incorrect aggregate size for reinforcement spacing or pump line

• Not adjusting admixtures for temperature and humidity

Our Approach: OSM Concrete works directly with certified batching plants to tailor each mix. For industrial floors, we often specify a 32–40 MPa mix with a slump of 80–100 mm, incorporating micro-fibres or macro-synthetic fibres for added tensile control.On decorative or exposed aggregate jobs, we carefully select aggregate grading curves and oxide dosing to achieve consistent colour and texture.

We test on-site for slump, temperature, and air content, and always ensure delivery is within the 90-minute window to maintain workable hydration ratios.

3. Incorrect Reinforcement Placement and Cover

Reinforcement steel (mesh or bar) provides tensile strength, but only if it’s in the correct position.Many slabs fail because the steel has been pushed down during the pour or tied too close to the surface.

Problems Caused:

• Insufficient cover (less than 25–40 mm) → corrosion and spalling

• Overlapping mesh incorrectly or not securing tie wires

• Poor lap lengths, especially at column or joint transitions

OSM’s Quality Control: Our foremen check all steel placement before pour using bar chairs and spacers rated for load class, and we adhere strictly to the engineer’s reinforcement schedule.We maintain photographic QA records showing cover, lap, and alignment before concrete is placed.

In suspended slabs, we also check the deflection under wet load to ensure chairs maintain height during pumping.

4. Rushing the Finishing or Neglecting Proper Curing

Even with the perfect mix and placement, concrete strength can be ruined in the final stage. Improper curing or over-finishing are silent killers of slab integrity.

Frequent Mistakes:

• Trowelling too early, trapping bleed water

• Curing only for 24 hours instead of the full 7 days

• Exposing surfaces to wind and sun without membranes

• Not applying curing compounds or sealers uniformly

Professional Practices We Follow:

• Delay finishing until surface bleed water fully evaporates

• Use evaporation retardants in high-wind or hot weather (common on Gold Coast sites)

• Apply curing membranes immediately after final finish

• For structural elements, maintain curing with wet hessian or plastic sheeting for a minimum of 7 days

• Record ambient conditions during cure (temperature, humidity, wind speed)

Proper curing can increase compressive strength by up to 30% — and dramatically reduce cracking and dusting.

5. Poor Coordination between Contractors and Concrete Suppliers

Concrete is a perishable material — timing and communication are everything.When trucks queue without site access or the reinforcement team runs late, mix consistency, slump, and finish quality all suffer.

Typical Coordination Problems:

• Inaccurate delivery scheduling for large pours

• Inconsistent communication between site supervisors, batch plant, and pump operators

• No backup plan for weather interruptions or pump failure

OSM’s Project Coordination Standards:

• Detailed pour schedules shared with all trades at pre-start

• On-site supervisors in direct radio contact with batching and pump operators

• Contingency planning for temperature, traffic, and equipment delays

• Use of retarders when longer transport times are expected

• Continuous QA documentation during placement (time of batch, pour start/finish, temperature log)

This level of precision is why OSM consistently delivers commercial slabs that meet tolerance and finish specifications on time.

How to Avoid These Mistakes on Your Next Project

Avoiding concrete problems isn’t luck — it’s discipline. Choose a contractor who understands every variable from soil density to hydration curve. At OSM Concrete, our Gold Coast concrete experts have experience with civil and commercial projects of every scale and size.

Key Takeaways:

• Never underestimate site prep or compaction

• Choose the right mix and maintain delivery timing

• Verify reinforcement and curing procedures

• Prioritise communication between teams and suppliers

Want expert concreters on your next project?

Call OSM Concrete Gold Coast today or request a quote.