7 Common Concrete Formwork Mistakes and How to Avoid Them

When pouring concrete, good preparation makes all the difference. And one of the most important parts of that preparation is getting your concrete formwork right.

Formwork provides the temporary structure that holds freshly poured concrete in place until it gains sufficient strength. That might be laying a concrete slab, constructing foundations, or working on a larger building project,

Get it right, and you’ll have a solid foundation for a successful pour. Get it wrong, and you could face concrete leaks, uneven surfaces, wasted materials, or costly remedial work.

Here are seven common concrete formwork mistakes and how to avoid them.

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What Is Concrete Formwork?

Concrete formwork, also known as shuttering, is a temporary or permanent mould that shapes and supports concrete as it hardens.

It’s commonly used for foundations, floors, walls, columns and concrete slabs. Formwork can be made from timber, plywood, steel, aluminium or plastic, depending on the project.

Whatever material you choose, the purpose remains the same: to hold the concrete in the correct position, shape and dimensions while it develops sufficient strength.

Because freshly poured concrete puts considerable pressure on its surroundings, formwork must be properly designed, installed, and secured before pouring begins.

#1: Using the Wrong Formwork Materials

Not all formwork materials suit every concrete project.

Using timber that’s too thin, damaged plywood, or materials that aren’t strong enough to withstand the pressure of wet concrete can cause bending, bulging, or even formwork failure.

This can affect the concrete’s dimensions and finish, potentially resulting in expensive repairs.

How to Avoid It

Choose formwork materials that are appropriate for the size, shape and requirements of your project.

For smaller domestic slabs, suitable timber boards may be sufficient. Larger or more complex structures may require engineered steel, aluminium or proprietary formwork systems.

Always inspect materials before installation, and avoid using anything warped, split, or damaged.

Remember that formwork needs to withstand the pressure of fresh concrete, not just hold its shape when empty.

#2: Failing to Secure and Brace the Formwork Properly

Fresh concrete is heavy, and it can put substantial pressure on formwork. If the formwork isn’t adequately supported, it can shift, bow outwards or fail during pouring.

Even relatively small movements can affect the finished dimensions and alignment of your concrete.

How to Avoid It

Make sure your concrete formwork has adequate bracing, supports, stakes or ties to resist the expected loads.

Check that all fixings are secure and that supports are positioned on stable ground.

The amount and type of bracing required will depend on the formwork design, concrete depth and placement method.

For larger or more demanding pours, use a properly designed formwork system and follow the manufacturer’s instructions.

#3: Getting the Measurements and Levels Wrong

A few millimetres might not seem important when you’re setting up formwork, but inaccuracies can quickly become noticeable once the concrete has been poured.

Incorrect measurements can result in slabs that are too thick or thin, uneven edges or surfaces that don’t line up with adjoining structures.

And once the concrete has hardened, correcting those mistakes can be difficult and expensive.

How to Avoid It

Take your time when setting out the formwork.

Use a tape measure, string lines, a spirit level, or a laser level to check dimensions, alignment, and finished height.

Measure diagonally across rectangular formwork to help confirm that the corners are square and check levels at several points rather than relying on a single measurement.

Top Tip: Check everything twice before ordering your concrete. Adjusting formwork is much easier before the concrete arrives!

Need Expert Advice?

Speak to the team at Flowmix Tewkesbury, Gloucestershire or Aldridge, Walsall. We are happy to help with all your concrete requirements. Contact us by email or telephone.

Flowmix Tewkesbury: Tel: 01684 217888 Flowmix Walsall: Tel: 01922 741731

#4: Leaving Gaps and Poorly Sealed Joints

Gaps between formwork boards or poorly fitted joints can allow cement paste to escape during pouring.

This can leave surface defects, rough edges, and areas of poorly consolidated concrete, and leakage can also affect the finished structure’s quality.

How to Avoid It

Formwork boards and panels should fit together correctly, with properly secured joints and sealed where needed. Common leakage points are corners, connections, and areas around penetrations.

Use suitable sealing materials where required, ensuring they’re compatible with the formwork system, and keep the inside of the formwork clean and free of loose debris before pouring.

#5: Failing to Prepare the Ground Properly

Even well-constructed concrete formwork can cause problems if the ground beneath it hasn’t been properly prepared.

Soft, uneven or unstable ground can allow formwork supports to move or settle under the weight of fresh concrete.

For ground-bearing slabs, poor sub-base preparation can also cause settlement and cracking after the concrete hardens.

How to Avoid It

Check that the ground is suitable for the proposed work before installing the formwork.

For concrete slabs, this may involve removing unsuitable material, preparing the formation and installing a properly compacted sub-base in accordance with the project specification.

Make sure stakes, props and other formwork supports have adequate bearing.

Where ground conditions are uncertain, seek appropriate professional advice rather than assuming the surface is stable.

#6: Overlooking Checks Before the Concrete Arrives

You’ve built your formwork, booked your concrete delivery, and you’re ready to get started. Or are you?

Discovering a loose support, incorrect level or access problem when the concrete arrives can cause unnecessary delays and disruption.

Once delivery is underway, you may have limited time to make corrections.

How to Avoid It

Carry out a thorough inspection before your scheduled concrete delivery.

Check that:

• Joints are properly sealed.
• The formwork is clean and free from debris.
• Dimensions and levels match the project requirements.
• The site is accessible for concrete delivery and placement.
• All formwork is secure, adequately braced and correctly aligned.
• Reinforcement and spacers, where required, are correctly positioned.
• Suitable equipment and enough people are available to place and finish the concrete safely.

Also confirm that you’ve ordered the correct quantity and specification of concrete.

A little extra preparation can make the difference between a straightforward pour and a stressful one.

#7: Removing the Formwork Too Early

It’s tempting to remove the formwork as soon as the concrete looks hard, particularly when you’re keen to move on to the next stage of your project.

However, concrete needs time to develop sufficient strength. Removing formwork too early can damage edges, cause cracking, or, with load-bearing formwork, create serious structural risks.

How to Avoid It

Don’t judge whether concrete is ready for formwork removal by appearance alone.

The right time to remove formwork depends on the concrete specification, temperature, structural design, and the loads the concrete must support.

Non-load-bearing side forms may be removable sooner than formwork supporting beams, slabs or other structural elements.

Always follow the project specification and obtain appropriate confirmation before removing load-bearing formwork or temporary supports.

How Flowmix Can Help with Your Project

Flowmix has two plants, Gloucester and Walsall. We provide the following services (with time slots):

✅ Ready-mix concrete, mix on-site (volumetric concrete)
✅ Traditional and liquid screed.
✅ Concrete line pump Hire to reduce manual labour and associated costs, increase efficiency, reduce wastage and clean up.
✅ Interlocking concrete blocks for temporary or permanent barriers.
✅ Mini-Mix loads up to 4 cubic metres.

Flowmix holds the BSA-approved Ready Mix Concrete Kitemark KM683844, a certification that “confirms a product or service’s claim has been independently and repeatedly tested by experts” (source BSI).

Flowmix Tewkesbury: Tel: 01684 217888 Flowmix Walsall: Tel: 01922 741731

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