Home' Inclean : INCLEAN Jul-Aug 2016 Contents 38 INCLEAN July/August 2016
In my last article
I explained how
different types of
stone are formed;
but how is that
characteristics of the stone, we can choose
the most effective products to use on it. This
is particularly important when choosing
sealers and coatings.
Sealers and coatings offer a level of
protection to a stone or tiled surface by
helping prevent water and/or contaminants
from entering the surface. This means that
the stone is less likely to stain, discolour, or
Even cheap sealers work on most surfaces;
however some sealers perform better than
others. As the saying goes, you get what you
pay for, and it’s highly likely that a more
expensive sealer will actually be cheaper in
the long run.
Using the wrong sealer – or using the
right sealer in the wrong way – is not only
ineffective; it’s also a waste of time and
money. However by the time this becomes
apparent (either by ongoing staining or
visible sealer residue) the time and money
has already been spent.
Choosing the right sealer is the first vital
step to a well-protected surface. The better-
performing sealers tend to suit specific
stone or tile types, and provide targeted
protection against either mineral or non-
mineral contaminants. It’s important that
the sealer suits the pore size of the stone.
There is little value in sealing sandstone
with a sealer suited to granite as the active
ingredient penetrates far too deeply, and
similarly a sandstone sealer will not penetrate
far enough into granite to be effective.
The carrier (water or solvent based) is
important to get the active ingredient to the
correct depth in the stone, and wetting agents
are crucial to reduce the surface tension of
the stone. Appropriate sealers act quicker,
perform their duty better and will often
have a longer guarantee. With the research
undertaken by well-known companies and
their use of high quality ingredients it is little
wonder that, although more expensive, they
will save money in the long run.
Let’s review the characteristics of the 3
different kinds of stone, and what that means
in terms of sealer or coating selection:
Choosing sealers and coatings for natural stone
Sedimentary stone is formed as particles
are pressed together by gravity and the
weight of the layers of earth above.
Sedimentary stone types include sandstone,
limestone and travertine.
• Water-based sealers will easily penetrate deep
into the porous stone for best protection.
• A solvent-based sealer can be used, but it’s
unnecessary and generally more expensive.
• Limestone will also require additional
protection from acids, as it is primarily
calcium-based (which can be etched
away by contact with anything acidic).
Usually this can only be achieved with a
• Generally colour-enhancing sealers won’t
provide much benefit on sedimentary
stones and should always be tested
carefully before use.
• Coatings (or polishing sealers) won’t work
on less dense sedimentary stone such as
coarse sandstone – they can be applied but
they won’t polish up evenly, and will look
patchy and duller than intended. Limestone
and travertine are the occasional exception
to this rule, however it depends on the
density of the stone.
Igneous stone occurs from volcanic
eruption, and is generally quite hard. It
can be coarse- or fine-grained, with coarse
graining being more porous. Igneous stone
types include bluestone (or basalt), granite,
• Fine-grained igneous stone such as granite
and quartz may not even require a sealer –
it depends how dense the grain structure.
Denser = naturally more impervious.
• Bluestone (basalt) can often benefit from a
sealer as its coarser-grained structure allows
more water penetration, and it is particularly
vulnerable to oil and grease staining.
• Solvent-based sealers will penetrate deeper
into igneous surfaces to ensure optimum
protection. Water-based sealers won’t be
effective on fine-grained igneous stones,
and while they may work on coarser-
grained stone, they still won’t work as
well as a solvent-based sealer would.
• Darker coloured igneous stone can also
benefit from a colour-enhancing sealer to
bring out the natural deep colours, giving
the surface a permanent ‘wet look’.
• Surface coatings can be applied to igneous
stone to provide an extra level of shine,
and the gloss level that is achievable will be
determined by the smoothness of the surface.
Metamorphic stone started out as either
a sedimentary or igneous stone that is
transformed into something else by a
combination of heat and pressure. The most
common metamorphic stone types are slate
It is worth noting that while slate and
marble are both metamorphic, the way they
are formed is quite different and affects
their characteristics. Slate is formed from
layers of shale, mudstone or sometimes
basalt under relatively low pressures, and
it is foliated (formed in layers). Marble
is formed from limestone under intense
pressure and heat where it is essentially
‘cooked’, turning the limestone’s individual
particles into a single piece of stone.
• Marble (like its main ingredient limestone)
is very acid-sensitive, so any sealer needs
to provide excellent acid-protection.
• Marble can often benefit from a polishing
coating. This provides the highest level of
protection possible, while also allowing a
beautiful glossy finish to be maintained.
Coatings should definitely be considered
in high traffic areas, or areas where
exposure to acidic contaminants is more
frequent (e.g. kitchens).
• Slate is highly absorbent, and is often used
outside, so it needs to be protected from
water. Quite often slate is polished or
‘waxed’ to ensure no water can enter.
• When applying sealers or coatings to
slate it’s important to completely remove
any waxes or coatings that may have
previously been applied.
• Both marble and limestone are very dense,
and so any sealer should be solvent-based
as it is able to penetrate much further into
the surface. This gives highest levels of
protection and also prevents visible sealer
marks sitting on the surface.
The second step to a well-protected
Continue page 41...
Sandstone: sealing can make porous surfaces
such as sandstone water-repellent. You can
clearly see on this sandstone surface the section
that has been sealed vs the natural stone
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