Stainless Steel Weir Sealing, Norfolk

THE PROBLEM

The stainless steel weir had been installed to control flows into the storm tank. The original sealing arrangement using a butyl gasket had not performed as expected due to lack of compression, deflection in the concrete and the surface roughness of the substrate.

As a result when exposed to flows the butyl compound had pushed out from the interstitial space between the stainless steel and the concrete, meaning that waste water flows were not controlled as intended.

THE SOLUTION

We were contacted to see if we could develop a solution to seal the weir externally in order to avoid removing the weir with craneage.

The works had to be completed in December which presented challenges with regard to climatic conditions as required for most sealing and coating materials.

Sealing externally is always challenging as the negative pressure applies a load force against the applied sealant – meaning that any sealing solution must have sufficient adhesive, cohesive and tensile strength to resist this force.

We proposed a multi stage sealing solution, finishing with the application of PPG Raven 405. The reasons for proposing this material are as follows;

  • Excellent adhesion to damp substrates, with no dew point or humidity restrictions
  • High Tensile Strength
  • Designed and proven to withstand negative water pressures

Initially where possible any failed butyl sealant was removed. This was followed by the preparation of the steel and concrete by method of water entrained abrasive blasting.

The blast profile was tested and recorded using a surface profile needle gauge in order to ensure compliance with the manufacturers recommendations.

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Spent blast abrasive and arisings were removed and all surfaces to be coated vacuumed clean in order to ensure dust free surfaces for maximum adhesion.

Anchor rebates were cut at termination points using vacuum controlled diamond saws as per the manufacturers recommendations.

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Existing fittings were loosened and wet sealed using a polyurethane sealant. The interstitial space between the stainless steel and the concrete was first injected using Normet Tampur 125 hydrophilic polyurethane injection resin to form a primary pressure tight seal.

This was followed by the application of Remmers Stopaq Swellable sealant – which expands on contact with water. This was only possible to be used due to the high tensile strength of the coating to be finished with.

All areas not to be coated were masked with tapes.

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All surfaces were checked to be free from surface moisture and where necessary dried using 110V hot air guns.

Raven Lining 405 was then applied by trowel to a target thickness of 3mm. Because the material is applied in a single layer this significantly reduces the good weather window required – very useful for winter working.

Thicknesses were monitored during application using wet film thickness combs, to ensure that the required thickness was achieved.

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Following cure the weir was returned to service and the effectiveness of these sealing operations confirmed.