Bidston Moss Viaduct Refurbishment

Client: Costain

Location: Bidston Moss, The Wirral

Project: Strengthening and refurbishment of Bidston Moss viaduct

Service: Metal surface preparation

 

Background

Denholm Industrial Services secured the contract to provide multi-discipline services in support of the refurbishment of the Bidston Moss viaduct.

The viaduct was owned by three different public authorities and there were three different paint systems to remove. In total this complex project lasted three years.

 

The Challenge

The existing coatings all required different approaches for correct removal prior to the application of the new protective coatings. The coating types involved were:

  • Conventional epoxy coatings
  • Lead-based primers
  • Thermal metal sprayed zinc coatings
  • Wax coatings
  • Chlorinated rubber coatings

 

The Solution

Due to the lead content of the primers, stringent health and safety control measures were deployed to protect our employees from unnecessary exposure to this toxic material and to comply with the “Control of Lead at Work Regulations”.

Thermally sprayed metal coatings are hard and tenacious and full removal requires considerable time and materials. The areas where the existing coating was good were left in place and only the failing areas of metal coatings were removed. After checking that the specified protective coatings to be re-applied were compatible with this approach, the solution was agreed and written into the project specification.

Wax coatings had been applied by one of the viaduct owners to lengthen the life span of the existing coatings some years beforehand. This presented a surface preparation problem as attempting to blast wax coatings is mostly unsuccessful. The soft waxy nature of these coatings prevents the removal abrasive from working as it should, as it simply becomes embedded in the wax. To overcome this challenge the wax coatings were first removed by hand-scraping and solvent-washing prior to conventional blasting.

In certain circumstances chlorinated rubber coatings can present similar problems to wax coatings. Trials were conducted and it was found that the chlorinated rubber coatings had degraded and become brittle so that they could be removed using conventional methods.

Summary

Being involved in the project from an early stage enabled effective project planning, with Denholm Industrial Services ensuring that risks were mitigated as much as possible.

The project was delivered successfully, with zero reportable accidents (AFR = 0.00), ahead of programme and under budget.