This specification defined the requirements for quality assurance, construction materials, dimensional tolerance, jointing, testing, marking and workmanship of ferrocement linings intended for the renovation of gravity sewers where the lining is designed to act together with the existing sewer fabric and annulus grout to form a composite structure; Type I design, as defined in the Sewerage Rehabilitation Manual.

Caveats

The WUK Standards Board commissioned a review of WIS 4-12-06 Issue 1 that concluded in March 2023. Based on the review’s findings the Board determined that the document’s status should be changed from ‘current’ to ‘archived’ since:

• The WIS was published in 1990 and has not been revised since.
• The technique described has fallen out of favour within the UK water industry (see below).
• The materials and processes described are, for practical purposes, no longer used in the UK.
• A single dominant (though not exclusive) supplier of ferrocement in sewerage applications existed from the outset of this WIS. However the company was dissolved in 2020 having effectively ceased operation many years earlier.
• The WIS references 24 British Standards. Twenty three of these have subsequently been withdrawn – mostly because they have been replaced by later British, EN or ISO standards – and the updated version of the remaining one now has a different title.
• In its present form, with so many out of date reference standards for input materials and for compliance tests, the WIS is too poor to use for its intended purpose of product certification or site application.
• The “WRc Approved” website was checked for evidence of any manufacturer having any current approval and none were found.
• Even contractors consulted who are capable of implementing the technique were happy for it to be archived.
• No UK Water and Sewerage Company has expressed a wish to keep it (based upon absence of responses from the Water UK Sewer Renovation Group).

The WIS was produced in an era where there was rapid development of sewer renovation techniques and a need for specifications that could be applied across a fragmented client group (much of the wastewater system was still managed on behalf of the newly created Water Companies by relatively small local authorities who would otherwise be drafting individual specifications). It was written in a manner to facilitate third party approvals (certification) and avoid the need for individual approval by many different organizations.

In 1990 there remained many reservations around the use of plastics in sewer applications, but cement mortar was well established as a building product and relatively cheap. However, over time the acceptance of polymer/plastic products has increased. The range of pipe sizes that can be lined using Cured in Place Pipe has also increased. And occupational health and safety considerations now favour remote rather than insitu installation techniques. Consequently both ferrocement systems and the similar gunite lining technique have fallen out of favour.

There appears to be a gap in the alternative provision of specification and guidance for these types of work. However the existing WIS is so far out of date that it is not used in practice and the industry is functioning without reference to it – with little or no work of this type taking place for Water and Sewerage Companies in the UK at present.

Cement spray renovation systems have increased in use again in the UK recently, particularly in manholes but without reinforcement. The Review’s enquiries confirmed the ‘Hermes’ mortar spray system is sometimes used in conjunction with reinforcement in Germany and could easily get accepted for individual projects in the UK – thereby potentially falling within the scope of the WIS. However for such limited use it is more likely that the Water and Sewerage Company concerned would simply consider the manufacturers’ literature and not wish to spend time updating the WIS.

The technique has a wide overlap with IGN 4-12-05 Issue 1 Specification for precast gunite sewer linings which was published in 1986. Both are construction systems for combining fine aggregate concrete with steel reinforcement. If it is decided to revise WIS 4-12-06, consideration should be given to merging the two techniques and creating a new WIS as a materials and application specification for both ferrocement and gunite whilst creating new IGN covering them both.

One of the two principal materials used in ferrocement is cementitious mortar. Although there is no current sewer renovation standard in CEN or ISO for cementitious systems, work is currently underway in CEN/TC 165/WG13 Renovation of drains and sewers, to create a standard in three parts specifically for mortars for wastewater applications. Ferrocement, gunite and other cementitious spray coatings are within the scope of the work for Part 2 of that standard (Mortars for construction and rehabilitation of drains and sewers outside buildings — Part 2: Cement based mortars). It would therefore be sensible to review the need for a new WIS (materials and application) and a combined IGN (ferrocement and gunite) after the CEN standard is published.

It is currently unlikely that an economic case could be made (when comparing costs of oil based polymer/plastic products vs cementitious products) to revise the WIS. Nor is it currently likely that experts will come forward from Water and Sewerage Companies to participate in its revision.

However, in the event of a consensus on the need for preparation of a new WIS (and possibly an associated new IGN) the Standards Board would require the parties involved to form a Task & Finish Group to that end. For further information on how achieve this contact the Board’s Technical Secretary here.

One or more ‘Common Editorial Caveats’ apply – see ‘WIS & IGN Library / Navigation & Caveats’ for details.