This specification defined the requirements for construction, materials, dimensional tolerances, joints, testing, workmanship and inspection of precast gunite segmental linings for the renovation of sewers where the lining is designed to act with the existing sewer fabric and annulus grout to form a composite structure (i.e. Type I design).

Caveats

The WUK Standards Board commissioned a review of IGN 4-12-05 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 technique described has fallen out of favour within the UK water industry (see below).
• Hence the materials and processes described are, for practical purposes, no longer used in the UK.
• The IGN was published in 1986 and has not been revised since that time.
• It references 22 British Standards. Eighteen of these have subsequently been withdrawn – mostly because they have been replaced by later British, EN or ISO standards.
• In its present form, with so many out of date reference standards for input materials, and for compliance tests, the IGN is too poor to use for its intended purpose of product certification.
• 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).
• Until recently the IGN was not listed on the WUK website. This unavailability has not prevented spray mortar systems of any type from being used.

In 1986 there were 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 gunite lining and the similar ferrocement systems have fallen out of favour.

Although written with the title IGN (information and guidance note) not WIS (water industry specification), the content is much more like a specification. The limited content that is useful information or guidance is contained in an Appendix and lists the items to be agreed between the contracting parties.

The technique (in the context of how it is described in the IGN) has a wide overlap with WIS 4-12-06 Specification for Precast and In-situ Ferrocement which was published in 1990. Both are construction systems for combining fine aggregate concrete with steel reinforcement. If it is decided to revise IGN 4-12-05, consideration should be given to merging the two techniques and making the IGN a guidance note covering both gunite and ferrocement whilst creating a new WIS as a materials and application specification for them both.

One of the two principal materials used in gunite 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. 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 revised IGN (gunite & ferrocement) and a new WIS (materials and application) 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 IGN. 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 IGN (and possibly an associated new WIS) 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.