In order to protect a material belonging to Cultural Heritage (i.e., stone, wood)
from weathering, and in turn to preserve its beauty and historical value for the future
generations, the contact with external harmful agents, particularly water, must be
avoided, or at least limited. This task can be successfully obtained with the use
of a protective organic coating. The use of nano-metric reinforcing agents in conventional
polymeric coatings demonstrated to be a successful route in achieving better protective
performance of the films and improved physical properties, even in extreme environments.
The present paper would, therefore, review the more recent findings in this field.
Generally speaking, when a hydrophobic product is applied on its surface, the stone
material will absorb less water and consequently, less substances which may be harmful
to it. An efficient organic coating should also supply wear and abrasion resistance,
resistance to aggressive chemicals, excellent bond to the substrate; finally, it should
be also able to guarantee vapor exchange between the environment and the material
interior, i.e., the material should keep the same water vapor permeability as if it
was un-protected. To regard to the conservation of wood artifacts, protective treatments
for wood will preserve the material from environmental agents and biological attack.
Hence, potential advantages of hybrid (organic-inorganic) nano-composite coatings
for stone/wood have been found to be: Enhanced mechanical properties in comparison
to the pure polymeric matrix, due to the reinforcing effect of the nano-filler; superior
barrier properties (the presence of the nano-filler hinders the ingress of water and/or
potentially harmful chemicals); optical clarity and transparency. It has been found
that the efficacy of a nano-filled coating strongly depends on the effectiveness of
the method used to uniformly disperse the nano-filler in the polymeric matrix. Furthermore,
the presence of nano-particles should not impair the viscosity of the organic matrix,
in order to employ the conventional techniques of application for coatings.