Tagged ‘ natural breathing of stone ’

Your Natural Stone Is Breathing….

April 13th, 2009 by Ken Albrecht

Your stone is breathing…
Quite a statement, but in a way natural stone does breathe. Stone has an internal structure that is not totally solid. There are two physical properties found in stone: pores and capillary structures that are interconnected. The structure, size and orientation of these networks affect the degree which moisture can migrate by capillary action through the stone.
Moisture migrating through natural stone is called “moisture vapor transmission”
For example: Moisture present in the ground can be wicked or drawn up into the stone by capillary action. The porosity of the stone- that is the amount of voids in the stone and its permeability – a network of pores, move the moisture vapors like a sponge through the stone. The vapor is then released into the atmosphere.
Granite for example, during the formation process was under high pressure and temperature. This allows for very little open pore space the grain sizes of feldspar, quartz etc can increase porosity. During the cooling process of the stone after high temperature the quartz grains can contract more than half their size. This allows for extensive cracking around the quartz. So it’s more of a fracture than a pore throughout the stone.
Marble during the formation process takes place by an increase of temperature and pressure. The original minerals of the stone merge to form smaller crystals to larger crystals. These are then reformed into a new texture. It is during this process that micro-pores develop between the grains. Mineralogy and the degree of metamorphism of the stone cause the size and shape of pores in marble.
Sedimentary stone such as Limestone and Travertine consist mostly of fossilized material found in ancient sea, lake and river beds. Pores develop as a result of compaction of various minerals, organic material secondary older stone from the area and sediment. Due to the process an unlimited variety of pore sizes and shapes are prevalent in sedimentary stone.
Granite and marble are generally low in porosity while limestone is considered highly porous.
When the pores and capillary structures are interconnected, the result is permeability.
Liquids can be absorbed into the interior of the stone or move from the substrate by this capillary action of pores and fractures. Permeability may be greater in one direction or another depending on pore size, shape and the distribution of fractures within the stone. So in essence, the action is very much like breating.
So what happens if a stone can’t breathe? If natural vapor transmission is not allowed to take place the moisture gets trapped and can cause chemical and mineralogical changes within the stone. This action of decay in natural stone may take the form of pitting, spalling, flaking and oxidation.
Using a coating or polymer on your natural stone will essentially cause the problems of blocking the necessary vapor transmission process your stone needs. So when it’s time to restore your natural stone surface, think twice about the quick fix alternatives of just coating the surface. A natural stone restoration expert will be able to assess and recommend the correct procedure to keep your natural stone healthy and happy.

limestone

LIMESTONE
A sedimentary rock composed of calcium carbonate.

Marble

MARBLE: CHARACTERISTICS
This standard includes general information on the characteristics
and common uses of marble and identifies typical problems
associated with the material.
INTRODUCTION
Marble is an extremely hard, metamorphic stone composed of calcite
(CaCO3). It is formed as a result of the recrystallization of
limestone under the intense pressure and heat of geologic
processes. The effect of this process is the creation of a stone
with a very tight crystalline structure and small but definite
porosity. Because of its structure, marble can take a very high
polish and is a very popular decorative stone for architectural and
sculptural uses. The limited porosity of marble, especially
polished marble, makes it less vulnerable to the leaching effects
of water. Calcium carbonate, however, of which marble is composed,
is highly susceptible to attack by acidic agents. Marble is
readily dissolved by acids, even very dilute acids, however the
actual results of acidic exposure will vary with the nature of the
acid. Chlorides, nitrates, sulfates and other chemical compounds
react differently with marble and produce various by-products,
which have a wide range of solubility and impact on the durability
of marble. For this reason, it is always important to determine
the exact type of pollutants causing marble deterioration.
Marble itself can be of two types, one composed of calcite and the
other of dolomite. Dolomitic marble is much more resistant to acid
attack than calcite marble. The color of marble ranges from the
brilliant white of calcite to black, including blue-gray, red,
yellow and green, depending upon the mineral composition.
TYPICAL USES
Marble has many decorative and structural uses. It is used for
outdoor sculpture as well as for sculpture bases; in architecture
it is used in exterior walls and veneers, flooring, decorative
features, stairways and walkways. The way in which the stone is
used may be a factor in limiting or controlling the severity of
exposure. The use or function of the marble may also affect the
feasibility of applying certain treatments, but type of use is not
the primary factor in the major types of deterioration and damage
to which marble is susceptible.