It is advisable to maintain careful records about the
type of stone, name, and origin of the stone existing in your
building. If such records do not exist, you should
explore the following options before determining a
cleaning and maintenance program:

1. Consult with a professional stone supplier,
installer, or a restoration specialist to help identify
whe

ther your stone is siliceous or calcareous.

2. Conduct a visual identification of the stone.
While there are exceptions, the following
characteristics are common:

 

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Granites have a distinct crystal pattern
or small flecks; very little veining.

 

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Limestones are widely used as a building
stone. Colors are typically gray, tan, or
buff. A distinguishing characteristic of
many limestones is the presence of shell
and/or fossil impressions.

 

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Marbles are usually veined, fine-textured
materials that come in virtually unlimited
color selections.

 

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• Sandstones vary widely in color due to
different minerals and clays found in the
stone. Sandstone is light gray to yellow
or red.

 

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• Slates are dark green, black, gray, dark
red, or multi-colored. They are most
commonly used as a flooring material and
for roof tiles and are often distinguished
by distinct cleft texture. Some notable
cladding projects have also included slate.

3. Conduct a simple acid sensitivity test to
determine if your stone is siliceous or calcareous.
You will need:

• 4 ounces of a 10% solution of muriatic acid
or household vinegar

• Eyedropper

Because the test may permanently etch the stone,
select an out-of-the-way area (a corner or closet)
several inches away from any mortar joint. Apply a few
drops of the acid solution to the stone surface on an
area about the size of a quarter. Two possible reactions will occur:

1) Acid drops will bubble or fizz vigorously – a sign that
the stone is calcareous.

2) Little or no reaction occurs – stone can be
considered silicous. See note below.

Rinse the area thoroughly with clean water and wipe dry.

NOTE: This test may not be effective if surface sealers or
liquid polishes have been applied. If an old sealer is
present, chip a small piece of the stone away and
apply the acid solution to the fractured surface.

CAUTION: Muriatic acid is corrosive and is considered
to be a hazardous substance. Proper head and body
protection is necessary when acid is used. Again, it is
always wise to consult with a stone professional if you
are unable to visually identify the stone and/or are
uncomfortable using the acid test.