Concrete for kitchen bench-tops

Design and styling

The versatility of concrete opens the door to creativity, giving home owners, designers and builders the opportunity to create unique and personal designs. 

There are a range of finishes offered by the use of concrete, including:

• Embedding - Embedding objects in a concrete bench is one of the more personalised options. Examples of objects that people have embedded in their concrete bench-tops range from shells collected from a favourite beach holiday spot, to MTV’s countertops in its New York office being permeated with CD fragments
  
• Stamping - Stamping is a process whereby patterns and textures are pressed onto the concrete before it’s fully dry. Various effects and patterns can be created through stamping, especially when used in conjunction with colours

Polishing - There is nothing quite as elegant as a polished concrete finish. Polished concrete is a generic term that covers a range of finishing methods, such as steel trowelling, burnishing and honing. Trowelling will give the most basic flat, smooth finish. Burnishing is produced by steel trowelling the surface until the concrete surface takes on a polished or glossy appearance, and is usually specified where a surface free of trowelling marks is wanted. A honed finish is particularly good for exposing the aggregates within the concrete or any decorative inserts.

Comparison and maintenance

While concrete is a heat-resistant material, like granite it is subject to thermal shock. If a hot object such as a saucepan is placed directly onto the surface, it can cause flaking or chipping of the concrete. Excessive heat can also damage the concrete sealer. Using a trivet to protect bench-top surfaces, no matter the material it is made from, is always recommended.

Just like marble and granite, concrete should not be used as a cutting surface as it will probably result in scratches in the finish of your counter and a set of blunt knives. And like stone products, concrete corners can chip if struck by a hard object. Placing silicone in the inside corners of the mould will ease the edges and prevent chipping.

Concrete (again, like marble) has a certain amount of porosity. As such, it is vulnerable to acidic liquids such as red wine, lemon juice and balsamic vinegar, which can cause surface stains. In the case of severe staining, concrete surfaces can be repolished with a mechanical trowel to restore a bench-top to its original finish.

Construction mixes and techniques

Like many other materials concrete will experience a small change in volume as it dries out. This can result in hairline cracks in the concrete surface. These are not structural failures and in a lot of applications the hairline cracks work well with the characteristics of the concrete finish. But a concrete mix with maximum resistance to cracking is possible to achieve through admixtures such as super-plasticizers, water reducers, shrinkage-compensating agents and polymer resins. These are available from specialist manufacturers.

Concrete bench-tops should have a high-strength level, with the concrete mix having a compressive strength of 40Mpa minimum – therefore, the water-to-cement ratio should be kept to a minimum. It’s a good idea for builders to produce a test sample and a trial batch to finalise mix specifications.

You’ll find that most concrete benches and bench-tops are precast, giving the builder/designer more ability to fine-tune them and remove any imperfections. However, site access restrictions may mean that in-situ fabrication is the only practical option.

When it comes to sealing a concrete bench-top, it’s hard to have both perfect aesthetics and perfect stain protection. Topical sealers are an effective stain barrier, but can give an artificial look to the finish. Penetrating sealers will give off a low-sheen finish that will enhance the concrete finish, but several coats may be needed to make it effective against stains. When sealing a concrete kitchen bench-top, you should also take note of the toxicity of the sealer as it might not be suitable for food preparation areas.

Like all exposed surfaces, maintenance is key to ensuring the long aesthetic and functional life of your kitchen bench-top.

 References

• Carol Brzozowski (2006), The Personalized Countertop, published in Precast Solutions
• Cheng Concrete Concrete Benchtop Facts www.concreteexchange.com
• Freya Lombardo (2003) Specifying Concrete Benchtops, published in Cement & Concrete Aggregates Association Mix 11.

To find out more, contact HIA’s Building Services team.

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