Spillway Repair and Re-Pointing – NATCEM® 35
Following periods of heavy rainfall, reservoir levels rise rapidly, resulting in high-energy flows down the spillway. The force of the water began to lift and displace sections of the stone sets, creating a risk to the stability of the spillway structure. Stonbury were contracted to carry out the repairs to this spillway and used NATCEM® 35.
The project was carried out later in the year, when naturally low reservoir levels reduced water flow through the spillway and exposed the stone-lined channel. This timing allowed the team to safely access the work area and carry out repairs efficiently.
The team first raked out and pressure-washed the joints between the stone sets, removing loose mortar, built-up debris, and vegetation.
After fully cleaning the joints, the team re-pointed the stonework using NATCEM® 35, a rapid-setting, high-strength mortar. This product was selected for its exceptional durability, environmentally friendly properties, and it’s Regulation 31 approval for use in public water supplies.
In addition to the main repair works, further activities included re-forming the spillway steps, installing new concrete haunching along both sides of the spillway, and re-stabilising the stone spillway walls. Furthermore, repairs and re-grading were carried out on sections of the two-mile stone access track to improve overall access and durability.
As a result, the completed works successfully reinstated the integrity and stability of the spillway. Specifically, the works secured the stone sets, restored jointing, and enhanced both edge restraint and wall stability. Consequently, these improvements have significantly increased resistance to erosion and displacement during high-flow events. Ultimately, this ensures the spillway can safely accommodate rapid rises in reservoir levels while delivering reliable, long-term performance.
Date added: 27/01/2026