Drossbach Investigation

CSI has developed the knowledge to use NDT methods to single out compromised Drossbachs without the need to drill each one as it is the current practice.


Drossbachs are a common construction system widely used in NZ. Unfortunately, they are often not installed with the required attention to detail, causing many issues throughout the structure. If Drossbachs are not fully grouted, the strength of the structure is severely compromised, endangering people’s lives.

A Drossbach Duct is used as a duct former for a variety of precast and cast – insitu concrete works including:

– Precast connectors
– Service penetrations
– Formers for starter bars
– Post-tensioning ducts

In large investigation projects where CSI was involved, there were up to 70% of faulty drossbach installations, leading us to believe there is a correlation between badly installed Drossbachs and New Zealand’s well-known leaky building problem.

CSI has developed the knowledge to use NDT methods to single out compromised Drossbachs without the need to drill each one as it is the current practice.

By using Ultrasonic Testing of the latest generation, CSI can sketch up and report to which level a Drossbach is filled or distinguish whether a Drossbach has problems (not only on the top but also on the bottom).

Our highly trained technicians can analyse the wave propagation results on the spot, mark out the Drossbach with problems and work alongside a repair crew. The data can also be taken back to CSI for thorough analysis and reporting. The Drossachs can be analyzed in increments to build up a full picture of their state.

Ultrasonic Testing

Ultrasonic Testing is the only technology providing answers for several applications; while it is, in general, complementing our toolkit.

The technology is based on the principle of acoustic wave propagation. By transducer emitted sound waves reflected from objects of different density. Their return signals enable a specialized analyst to make conclusions about the quantity and quality of the objects and structures. It is possible to perform localised testing as well as area analysis.

Some of the many tests Ultrasonic is used for include:

  • Delamination and voids
  • Thickness and thickness variation, e.g. for slabs or tunnel linings up to 1000mm
  • Objects and inclusions
  • Quality Assurance (QA)
  • Grouting defects in Drossbachs and tendon ducts

We’re pretty excited by this leading-edge development. . We’d love to hear from you with any questions you have, leave us a message on this blog post or feel free to drop us a line either via email or phone 0800 33 77 67.

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Kurtis and his team showed highly skilled reading of scan results. These allowed them to be the only ones who successfully located the defects (random voids) in Polystyrene blocks filled with concrete and lined with Gib in a prepared area...

Maynard Marks

Engaging CSI to conduct the Pile Integrity Testing on the large 1.8m diameter piles was a wise choice. Their technicians were knowledgeable, approachable, punctual, health and safety conscious and flexible when we encountered late changes to the works programme. Results...

Fulton Hogan

As requested, the workers from CSI ltd contacted this office on arrival at the site and invited me (Kevin J Heays) to site visit and get an understanding of the intended works. I was impressed with the workers knowledge of...

Kevin Heays (ECANZ)

The CSI team were great and they did a good job for us. They were employed to complete QA on a Wellington Apartment Development using Pile Integrity Testing. We would recommend CSI to others in the future.

Richardson Drilling

CSI did a good job for us at an Auckland Apartment building; saving our team from drilling through services which would have caused considerable delays. We would recommend CSI to others for scanning

Allendale Electrical

CSI provided a great service. We could not advise them on areas of improvement as their service was highly professional.

Wilson Building

We found CSI via their website and were grateful that we had. Their service was highly professional.

Artisan Developments Ltd

CSI have completed several jobs for us. They are highly skilled operators.

Tracer Construction

CSI was recommended by a health board, and they did a great job for Q Interiors. We are already looking at employing them for future work.

Q Interiors

The service and follow-up of CSI Ltd was excellent. We would definitely use them again.

Grayburn Property Service

CSI Ltd did a great job for us. When we were asked what improvements could be made, we could think of no gaps in their professional service.

Trademark Building Services

CSI Ltd were recommended to us and did a great job. We would be happy to recommend them to others.

Stanley Construction

We were recommended CSI by an Engineer and he was absolutely correct; their GM particularly communicated well and was highly professional.

MSC Consulting Group

CSI has completed some exciting projects with Novare Design “I am very impressed at the responsiveness, relevance and accuracy of the testing and data supplied to Novare for some recent strengthening projects. We have worked with CSI on several projects...

Novare Design

Darren, Ali and the team at CSI have been a great help at the Oaks Shores refurbishment project. CSI was willing to work through the difficulties of travel under various Covid-19 levels, ensuring they could be of assistance in Queenstown...

Brosnan Construction