Shepley Engineers undertook the restoration of the Grade 2 Listed Triplets Gas Holders, constructed from a combination of cast and wrought iron. The combined structures contained 123 cast iron columns each in excess of 10m long and weighing on average 10t each, this, coupled with all the connecting lattice works presented a large-scale restoration & painting project, works were carried out off site in the workshop.
All components were placed in a strictly controlled area with specifically built racking to ensure historic component protection and maximum efficiency of space. All components were subjected to an initial pre-blast where historic lead-based paint was removed to expose the base material, all blasting operations and exposure to lead based paint remnants were carried out in a controlled environment and to strict H&S guidelines and RAMS.
All structural cast columns required major structural repair works, in one case a full column repair sleeve was applied to re-build the columns structural integrity. A large majority of the wrought iron lattice beams had suffered over years from lack of maintenance, the endplates were badly corroded and needed replacements along with repairs to the interconnecting lattice beam outer angle structure. All repair types were of a mechanically fixed over-plate design as instructed by the engineering team.
Following repair of each component the goods were final blast cleaned prior to applying the corrosion protection system; the system was a 3-part coating system made up of a primer base coat zinc phosphate primer, a mid-coat of micaceous iron oxide and a top coat of high performance acrylic urethane gloss finish.
All paints, along with wet and dry film thicknesses, were specified by the client team coatings advisors and paint manufacturers.
On completion of the coating system application and curing period, the components were transported back to the yard-based racking systems for storage until requested for delivery to site by client team. The storage racking at this stage was wrapped using ‘Envirowrap’ to protect the batch of components from weathering for up to 18 months.
The components processed were up to 8 tonnes in weight and up to 10mtrs in length, each component required strategic handling and movements to both protect the workforce and the heritage material.
Columns required lifting cradles and strict 7-point lifts for structural integrity protection. All lifting, handling and movements of products were controlled via training and strict method statements and risk assessments.
Each weekly delivery was met, Shepley further assisted in the extraction of goods from racking systems and loading to the sub-contractor appointed transport, working heavily throughout each week in preparation for trailer hitching for multiple despatches. All components prior to despatch were checked and signed for as handover to the re-erection team appointed by the client team.