Natural Stone Tiles – The Confusion Surrounding
Sealing
David Andrew Smith
There would seem based my own experience that there is a lot of
confusion amongst the general public and some builders as to
what sealing natural stone actually means.
When we talk about sealing a surface we normally mean that an
impenetrable barrier is painted on or applied in some way. For
example tiled floors are often sealed to give them added
protection and make them shine. To do this a series of coats of
emulsion polish are applied to the surface and allowed to dry.
This seals the floor and gives it protection. Other surfaces
such as wood are often sealed with a coating of a polyurethane
product. This adds strength to the surface and protects it.
Many other normally porous surfaces can be sealed with a layer
that sits on the surface acting as a barrier to penetrative
agents and gives protection also.
The sealing of natural stone such as marble, granite, limestone
and slate is very different. Natural stone is made up of
crystals that interlock together. The actual minerals that are
present as crystals in the stone give it its colour and
striations. However there are spaces between the crystal and
the smaller these spaces are and the more the crystals have
been compacted together the less porous the stone is. So these
spaces will determine the porosity of the stone. A combination
of pore size and mineral content of the stone will also
determine its hardness and thus its durability. These spaces in
the stone are air filled when the stone is dry and water filled
when the stone is wet. Bacteria inhabit these spaces and these
are often vital for the maintenance of the stone. Very little
research has been carried out into these bacteria but what has
been done would suggest that they are essential in maintaining
the integrity of the stone.
Consequently we have the picture of stone as quite a complex
mix of minerals, bacteria and spaces. You must imagine the
stone to be something akin to a very hard sponge! If you drop a
liquid onto the stone it will be absorbed and spread through the
spaces. This is why what initially looked like a small spillage
can end up as quite a large stain in the stone. To remove the
stain it has to be flushed out of these spaces. All a stone
sealer does it fill up these spaces. Many of the stone sealants
in use are based on fatty acids rather than synthetic sealants.
These natural sealants are better because they do not destroy
the bacteria but often enhance them. Synthetic sealants will
destroy these bacteria that has longer-term consequences on the
stones makeup. Sealants based on fat however have a shorter
lifespan and must be renewed periodically.
Whatever sealant is used it simply fills up the spaces between
the crystals it does not cover the surface of the stone. Its
purpose is simply to delay the penetration of liquids into the
stone. So if corrosive materials get onto the stone then it
will be damaged. Stone sealants do not form a protective ‘seal’
on the surface of the stone. Consequently stone is only
protected from absorbing liquids. It is not protected from
surface damage.
About The Author: David Andrew Smith is the owner of
http://wesparkle.co.uk a commercial
and domestic cleaning
services company. One of their specialist fields is in the care
and maintenance of natural stone surfaces.
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