How Thick Should a Concrete Worktop Be?

If you're planning to make your own concrete worktop, getting the thickness right is crucial. Go too thin and it could crack. Go too thick and you're wasting materials (and possibly throwing your back out trying to lift it). So let’s break it down.

🛠️ Precast Worktops: Slim but Strong

With precast worktops—where you pour the concrete into a mould and flip it out once cured—you have more control over the environment and reinforcement.

Recommended core thickness:

• 20mm for internal use

• 30mm for external use

Thanks to the strength of our Concrete Lab GFRC Mix, 20mm is more than enough indoors, especially when used with our glass fibre reinforcement and Superplasticizer. Outdoors, we recommend 30mm to handle thermal movement and exposure to the elements.

💡 Want a chunkier look? Just add a drop-down edge to the mould to create the illusion of a thick slab without all the extra weight or mix.

🧱 Cast-In-Place Worktops: 30mm Minimum

For cast-in-place worktops—poured directly onto cabinets or formwork on-site—you need a minimum core thickness of 30mm, regardless of where it’s used.

Why? Because there’s less control on-site. Any slight inconsistency in your shuttering or levelling introduces potential stress points. Going thinner, even with fibres, just isn’t worth the risk.

📏 Quick Guide

🔍 Final Thoughts

The thickness of your concrete worktop affects its strength, appearance, and ease of installation. Stick within these guidelines, use the right reinforcement, and make sure your base is sound—and you’ll have a durable, beautiful concrete top that lasts.

👉 Not sure how much material you need? Try our Concrete Worktop Calculators to get the perfect batch size for your project.