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How to Avoid Concrete Blowholes

Posted on by EKA Concrete

concrete blowholes

Whatever concrete project you’re working on, it can be frustrating to find that, after all your hard work, the surface is riddled with small blowholes. These blemishes can ruin the decorative quality of your concrete, and it’s always best to prevent them entirely instead of trying to repair them at a later date.

In this article, we’re looking at what causes concrete blowholes, as well as what can be done to prevent them from forming in the first place.

What are concrete blowholes?

You’ve probably seen concrete blowholes on many concrete structures over the years. They are small, typically round cavities which form on the surface of the concrete. Blowholes generally appear towards the top of the structure, and mainly pose an aesthetic problem – however, they can pose a structural issue if the blowholes grow too large or are concentrated heavily in one area.

How do blowholes form?

Blowholes are created by entrapped air against the concrete formwork. The severity of blowholes is influenced by a number of factors, usually depending on the kind of formworks used, as well as the concrete mix itself.

Entrapped air is forced upwards and to the surface during compaction, resulting in identifiable cavities which pockmark the hardened concrete. Blowholes usually form at around 5-10mm, and aren’t considered a structural issue unless they are 25mm in diameter. 

How to prevent blowholes

Repairing blowholes can be tricky, especially if you want to avoid any further inconsistencies in the surface itself, such as discolouration. The best thing to do is try to eliminate the chance of blowholes forming from the start, and there are a number of things that can be done to help achieve this.

As we said earlier, the formwork used on the pour site will have a big say in the creation of blowholes. Using impermeable formwork will make blowholes much more likely, as entrapped air won’t be able to escape as easily as they would with permeable forms.

A concrete mix which is too sticky, or has poor workability all round, will also encourage blowholes, while self-consolidating mixes will help reduce the chance of blowholes appearing.

The consolidation process is a key factor in the formation of blowholes. The proper use of a concrete vibrator will help eliminate most cases of entrapped air, so speak with your concrete supplier for advice on the size of concrete vibrator needed, as well as the best insertion points and the most suitable techniques to use.

Professional contractors will be able to employ different preventative measures throughout the project, including the use of release agents on the formwork to encourage entrapped air to escape and not become trapped against the face of the formwork itself.

professional concrete suppliers

Experienced professionals

The experience of your supplier will play a significant role in the finish of your concrete structure. Heading into the project with the aim of mitigating, or even eliminating, blowholes allows greater opportunity for your supplier to create a fully suitable mix, as well as advising on formwork and consolidation to ensure entrapped air doesn’t become a problem. So if you’re looking to create a concrete wall, pillar or any other project, make sure to seek out a reliable, professional and experienced supplier to give you the best chance possible of a beautiful, unblemished finish.

EKA Concrete have over 20 years of experience in the industry, and are proud to be leading suppliers of high quality concrete to commercial and domestic customers alike. Our friendly team are on hand to provide knowledgeable advice every step of the way, to ensure you end up with the ideal concrete mix for your needs, and a finish you can be proud of. To find out more about all of our services, dont hesitate to get in touch with us today.

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