Page 47 - Haddonstone

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Appendix 5 – Acceptability Guidance

The following minor blemishes to cast stone on structures are considered acceptable by
UKCSA:

Chips, Scuffs, Blemishes, Hairline Cracks, Crazing.

Shall not be obvious under direct daylight illumination from a distance of 6m.

Cracking

Minor hairline cracking can seal itself through the action of autogenous healing and as
such is unlikely to be a major problem.

However, a live crack, one that is continuing to move due to external forces, is unlikely to
heal quickly as the walls of the crack will be moving and the crack width changing.

The cause of the cracking may be a more important factor than the crack itself. For
instance, cracked cills are usually caused by incorrect installation, eg fully bedding the cills
instead of just bedding under stools, the cills not being able to move independently to the
brickwork around and being pulled apart by the brickwork movement at the opening. In this
instance the incorrect installation should be dealt with rather than the result ie the cracked
cill, and a replacement cill should be correctly installed.

Colour Variation

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.

Surface Texture Variations

All surfaces intended to be exposed to view shall exhibit a texture approximately equal to
the approved sample when viewed under direct daylight illumination from a distance of 3m.