Skip to main content

CROSS Safety Report

Plastic spacers in slabs

Report ID: 431 Published: 1 July 2015 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

A reporter has spotted plastic rails about 1.5 m long being used to support the bottom rebar mat of a slab. They are 'U' shaped with the open side being placed against the soffit. 

Key Learning Outcomes

For construction professionals:

  • Spacers for steel reinforcement should be in accordance with BS7973 which gives requirements for plastic spacers and requires an open area to allow for aggregate to pass through
  • These products should be installed in accordance with the manufacturers’ recommendations

Full Report

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

A reporter has spotted plastic rails about 1.5 m long being used to support the bottom rebar mat of a slab. They are 'U' shaped with the open side being placed against the soffit. They are quickly put down before the rebar is placed and avoid the need to fix on the traditional type of spacer. There are openings along the sides to allow concrete to fill the void. 

Having looked after the soffit was stripped, the reporter could not see where they were, which was encouraging. However, he is uncomfortable with how they may affect the slab strength near supports, where the slab is hogging and the concrete around the rail is in compression. 

He has heard that some such spacers have holes which are too small to allow aggregate to enter the void, just 'grout'. He has also heard that they may move around as the concrete is placed as they are not wired on, and presumably some may end up being loose. Are CROSS aware of these spacers being used and do others have any concerns?

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

Such spacers have been in use for many years. BS7973 gives requirements for plastic spacers and requires an open area to allow for aggregate to pass through. To prevent movement, they can be wired to the rebar. As with every product, they need to be used in accordance with manufacturers’ recommendations. Care does need to be taken where very heavy rebar cages are supported, as plastic spacers may not have the same capacity as concrete spacers.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.