Q. A white 'bloom' has appeared on my concrete roofing tiles. What is it, and will it harm the tiles?
A. Efflorescence is a naturally occurring phenomenon caused by water in the form of rain, condensation or dew penetrating into the pores of the concrete and dissolving lime. The solution diffuses to the surface of the product, the water then evaporates and leaves behind a white film of lime. The lime naturally occurs in the cement which is used in the manufacture of all concrete products. Since the lime content of the concrete can vary and the weather conditions obviously differ, the level of efflorescence can also fluctuate considerably.
The same chemical process which brings the lime to the surface of a tile carries on, enabling it to be degraded and washed away by the rain, so that eventually the efflorescence disappears by itself - usually in a matter of months. Once the lime has disappeared from the surface of the tiles it rarely re-occurs. Unlike some manufacturers, Sandtoft treat the surface of all their concrete tiles with acrylic polymer coatings to not only minimise the formation of efflorescence, but to give stronger and longer lasting colours If efflorescence does appear, it has no detrimental effect on the long-term performance of the tile.
Q. My roofer has laid Calderdale Concrete Slates on my roof 'straight bonded'. As all the photos and other roofs I have seen have the tiles laid 'broken-bonded', will I have problems with my roof?
A. Although it is recommended that Calderdale Slates are laid 'broken bond', this is mainly for aesthetic purposes - they are a flat tile emulating the appearance of a double lapped slate. But as Calderdale Slates are a single lapped, interlocking tile there is no technical reason why they cannot be laid 'straight bond' in the same way as other single lapped tiles such as, for example, Double Roman tiles. However, it should be noted that all Sandtoft specifications for Calderdale Slates are based on the tiles being laid broken bond. Also, technical data such as the minimum recommended roof pitch are based on wind-driven rain testing carried out on tiling arrays laid broken bond.
Q. My concrete tiles have a painted finish. Why is this and will it weather off?
A. All concrete tiles are coloured to give them the appropriate appearance. Unlike clay tiles this colour will eventually fade away over time. However Wienerberger, unlike some other concrete tile manufacturers, colour the tile body, the tile surface and then add an acrylic coating, which gives the Sandtoft tiles the following benefits: -
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The Roof tiles Technical Hub provides easy access to useful advice, documentation and technical tools.
Advice on finding the perfect product which works for your project
Useful answers to the most popular questions about clay tiles
The importance of roof design and its relationship with the external envelope and environment.
An explanation of roof design and terminology