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8.3.3 Additives imparting a charge to the pore surface to
repel water particles i.e. hydrophobic.
There are a variety of additives which may
be used as an integral part of the cast Metal stearates have been used as an
stone mix. The two main uses of additives integral water proofer for over 50 years.
are to improve the plasticity of the mix These stearates are hydrophobic and are
and to reduce permeability of the finished typically blended with other materials to
product. Self compacting admixtures can obtain good dispersion within the cement
be used in the wet cast process. matrix.
Plasticisers tend to be chemicals based Calcium stearates are used primarily as
on compounds of Formaldehyde or damp proofers, where an electrostatic
Lignosulphate and improve the workability charge is imparted into the walls of the
of the mix and aid compaction. Water capillaries of the cast stone mix. By the
proofers can either be a surface treatment very way in which these stearates are
or an integral part of the mix. produced, they also have the added
advantage that they act as water proofers
Surface treatment water proofers tend to by sealing the voids within the macro
be based on acrylics, silicones, silanes texture of the material.
or siloxanes that can either penetrate the
surface to form a chemical bond within 8.3.4 Pigments
the substrate imparting hydrophobic/
hydrophilic properties or form a water Metallic Oxide pigments used in the
impervious surface. manufacturing process should conform
to BS EN 12878: 2005 Specification for
Integral water proofers work by either Pigments for the colouring of building
filling the pore structure to block the further materials based on cement and/or lime.
penetration of water i.e. hydrophilic or
8.4 Requirements for Units
The declaration of the properties of the • The information on which the
units called for in this Standard will assist relationship is based is available for
the designer in correctly designing the inspection.
construction works.
8.4.1 Two Part Mixes
All requirements for testing of products
detailed within this section are further When cast stone is made from separate
defined in Appendix 1 & 2. facing and backing mixes the facing shall
have a minimum thickness of 20mm at
For Internal Quality Control, other test any point. A bond between the facing and
methods may be used provided that: backing mixes shall be made either by a
mechanical key or by inter-diffusion.
• A relationship can be shown to exist
between the results from the standard 8.4.2 Surface Finish
test and those from the alternative test,
and Surface finishing techniques may be
employed in the manufacture of cast
