Page 11 - Haddonstone

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2.2 Wet Cast Production

This process uses a higher water content Wet casting requires significant work
mix than semi dry production resulting in a before a satisfactory stone like finish is
dense product with a typical cube strength achieved. This is due to the formation of
of 35-50 MPa. This is generally a through a layer of cement laitance typically 0.5-
mix of the finished face material which can 1.0mm thick against the mould face. This
be produced in a wide range of shades. laitance requires removal if a consistent
stone like finish is to be achieved. It is
The mix generally will have a slump of up normally removed by chemical etching
to 100mm and compaction is achieved although other mechanical methods are
using conventional wet-casting techniques used such as hand-rubbing, grinding
i.e. table-vibrator, poker or in some cases and polishing. Its removal reveals the
vacuum casting. Many UKCSA members constituents of the mix and therefore
use sustainable self-compacting concrete, quality of aggregate and control of
requiring no additional energy as the need batching is essential if uniformity is to be
to vibrate the mix is obviated. Vacuum achieved throughout a particular project.
casting is only suitable for relatively small
elements (up to 250kgs) and is extremely The product requires a controlled initial
effective in producing high quality surface cure protected from direct sunlight and
finishes, although this is mainly a function drying winds. As with all cast stone the
of correct mix design. product should normally be cured for a
minimum of 14 days prior to despatch.
The wet-cast process generally only yields
one cast per mould per day. This is an
aspect of wet-casting that both user and
specifier should be aware.

2.3 Fibre Reinforced Cast Stone Production

This process incorporates fibre reinforcement into a higher water content mix that can be
either poured or sprayed into moulds, from which the product is demoulded the following
day. A dense product with a close face texture is achieved which can be varied by the
use of secondary surface treatments. Often the units are produced in thin sections which
reduces the weight and associated manual handling issues, and offers the opportunity –
through careful design and use of fixings – for retrofitting to the structure.