Cast stone items are manufactured with natural products and colour variations are inevitable and should not be a cause for rejection.
Cast stone is trying to replicate the appearance and character of quarried stone with it’s inherent variations in both colour and texture.
Initial colour variations can often be down to the age of the products. There could be 6-8 weeks differences in the age of the products when initially installed, leading to colour differences due to inherent moisture content, weathering etc. These will all equalise in time when the pieces are installed and subject to the same water content, weathering and sunlight conditions.
Colour differences can also arise due to the water content of individual castings. This may simply be due to the position on the building which allows one piece to get wetter than another during normal weather conditions, or may be due to problems with the waterproofer in the castings. In the latter case, this should be dealt with as a failure of the stone to comply with the British/UKCSA Standard, rather than a colour acceptability issue.
Colour Variations (due to Efflorescence)
Lime bloom, or efflorescence is a temporary, naturally occurring phenomenon that occurs to varying extents on all items containing cementitious binders. It will, with time, disappear as a result of normal weathering. The length of time will depend on many factors such as rainfall, atmospheric pollution etc. The bloom can also be removed by the judicious use of a mild brick cleaner.