Waterproofing of Georgian vaults at Roman Baths, Bath, United Kingdom, using Oldroyd Xv studded membrane

The vaults, which are thought to be of Georgian origin, had been out of use for many years. It is not known what their original use was, but they had been filled from floor to ceiling with earth. During phase 1 of the project approximately 1000 tonnes of earth had to be removed from the vaults by H Mealings, the main contractor. A large number of bones, both Roman and Victorian, were found in the excavated soil. Investigation of these bones meant that excavation had to be temporarily halted.

The contract was granted by Bath and Northeast Somerset Council, on behalf of the Roman Baths Museum, who wished to use the vaults for storage of papers, books, old bones, and other artefacts. This necessitated a design compliant with grade 4 of BS 8102. Because of the desire to build a grade 4 construction, and due to the fragile nature of the construction, it was decided to use Oldroyd Xv Clear studded waterproofing membrane to carry out the waterproofing, rather than a cementitious system.

Work Carried Out

Oldroyd Xv Clear membrane was fixed to the vault structure using Oldroyd Brick Plugs. This was followed by a galvanised metal frame system to receive rigid boarding. A drainage gully system was fitted at the floor-wall junction to facilitate ingress of moisture at the worst case scenario.

The principle problem encountered during construction was the abnormally high levels of relative humidity encountered in the vaults – caused by the hot water springs that the baths were built on. This caused problems with sealing the pieces of membrane together using the Oldroyd butyl rubber tape. The problem was resolved by using heat guns and vapour wipes to dry the surfaces to be sealed. A temporary dehumidification system was also installed to help reduce the relative humidity. Relative Humidity levels had been as high as 92% with a normal range of 82-88% prior to the installation of this system.

Maintenance

The drainage channels must be examined regularly to ensue that they remain free of silt.

Although the installation of the Oldroyd Xv system will prevent moisture entering the vaults from the ground, condensation remains a risk due to the abnormally high levels of relative humidity. The relative humidity should be regularly monitored to ensure that it remains below 35% (CIRIA recommendation for book storage).