Drossbach Task Force

Ah, the elusive drossbach. Drossbachs are a common construction system widely used across New Zealand. CSI know the system well, […]

December 1st, 2020

Category: News

Ah, the elusive drossbach. Drossbachs are a common construction system widely used across New Zealand. CSI know the system well, and we regularly identify faulty drossbach installations to ensure everything is fully grouted through Non-destructive testing techniques (such as Ultrasonic Testing). This testing is crucial to ensure structural resilience and to prevent compromised construction.

CSI is very proud to be part of a Drossbach Compliance Task Group.  This group is made up of Engineer’s, Non-destructive Testing technicians and others in the Construction and Grouting industries. The two main elements the task group are looking at are Drossbach and Grout Sleeves

Here is a quick description of both:

Grout Sleeves

Grout Sleeves offer a splicing solution for reinforcing bars, and achieve a full-strength structural connection in critical hinge zones.  The internal surfaces are ribbed to ensure full bar break after the sleeve has been filled with high performance cementitious grout.

Grout Sleeves are used for connecting Reinforcing bar lengths where a connection cannot be spun, as well as for converting standard reinforcing bar (rebar) or for vertical connections where continuity of steel reinforcement is required.

The internal surfaces are ribbed to ensure full bar break after sleeve has been filled with high-performance cementitious grout (65 MPa, 28-day compressive strength)”. ReidBar


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


The semi-rigid metal duct is strong and durable for casting into concrete and is easily tied into position adjacent to reinforcing steel. Standard grout injection tubes, grout vents or blanked ends can be supplied on request.


Key features of Drossbach:

  • Duct sizes from 33mm to 130mm ID as standard.
  • Fabricated from 0.30mm thick galvanised strip steel
  • Cutting service provided (charges applicable).
  • Grout and vent tubes”  BBR Contech

The role of the Task Group is to look at the practice of inserting and grouting both Grout Sleeves and Drossbachs; and if the application methods ‘in practice’ are sufficient.  Equally as important is that the Drossbach and Grout Sleeves operate as intended for the life and performance of the structure.

Looking for an estimate? Fill out our Estimate Form here.


That’s it for this week! If you would like to contact the CSI team, feel free to email or drop us a line at 0800 33 7767.

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