One of the team’s recent project involved the investigation of failures to external render and internal bathroom wall tiling at a high-end residential unit in London, UK. The building had retained a Victorian rendered brick masonry façade behind and beneath which a complete rebuild had occurred. A few years after work completion, sporadic coating failures and cracking were reported in the external render along with some debonding of the natural stone tiles used on walls in the bathrooms.
For the render investigation, RSK took core samples through the render and associated masonry and sent them to its UKAS-accredited materials testing laboratory for various chemical analyses of the render, mortar and concrete materials, and petrographic examination of the paint, render and masonry materials. Dr David Crofts’, an RSK expert on construction materials chemistry, commentary on the performance of the external paint coatings concluded that the failures in the recently applied coatings related to cracking of the earlier coating layers and subsequent preferential water egress from the masonry through these cracks.
Dr Ian Sims, an RSK materials and structures director and a specialist in cementitious materials, assessed the render and concluded that as render failures rarely relate to defects with its material, other than some inevitable drying-shrinkage cracking, the render cracking reflected cracking of the background brick masonry. Some of this was possibly historic, including some perhaps caused by World War II bombing nearby, but most was likely caused by unloading and reloading of the façade and foundations during the demolition and rebuilding behind the retained façade.
The investigation of the failures of bathroom wall tiling, including loss of grout and debonding of the large-format stone tiles, noted that these units were only fixed with adhesive; there were no mechanical fixings. More importantly, the tiling was installed directly onto plywood backing, in many places without suitable waterproofing. Some modern plywood materials are incompatible with cement-based wall tile adhesives and can be dimensionally unstable when exposed to moisture. Dr Ian Blanchard, an RSK materials and structures associate director, assessed the tiling and adhesive, and Dr John Williams, an RSK materials and structures timber specialist, assessed the timber.
In one location, a visible wet mould had developed behind the tiling, which was identified at RSK’s ADAS laboratory.