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Masonry
Stone, Brick, Concrete,
Terracotta, Adobe,
Tabby
[Plaster & Stucco]
STONE
Oldest building material
 Simplest building technique — stacked stone
 Most expensive

– Traditionally, large public buildings built of stone
– Less often used for residential buildings, except
for facing or decoration.

The high cost of transporting stone meant
that it was advisable to use local stone
Egypt’s first
pyramids ca. 3000
BCE. Built mostly
from limestone;
other stones used
on interior.
Sphinx, ca. 2500 BCE.
Carved out of limestone
outcrop. Granite facing
applied later.
Great Wall of China, 7th6th Centuries, BCE
Sandstone, rammed
earth, brick
Longest human-made
structure, approx.
3,948 miles
Parthenon, Athens,
Greece, 447-432 BCE.
Marble and limestone
Colosseum, Rome
Vespasian, 70-82 CE
Concrete and tufa faced
with travertine
Taj Mahal
Agra, India
1630-1653
Marble
How to Distinguish Rocks
Lightness / Darkness
 Coarseness / Fineness

– Are the grains visible?
Rhyolite
Gabbro
Basalt
Granite
“Granite” Countertops?
Marketing claims aside,
these countertops are
andesite
How not to Distinguish Rocks

Not by color: color often comes from
impurities in the rock
– Greens — chlorites, magnesium
– Reds — iron oxides, esp. hematite (iron ore)
– Yellows/tans — hydrated iron oxides
Chlorite
Iron Ore
Limonite
Igneous — rock deposited in a molten
state
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Plutonic — formed deep beneath earth’s surface,
when magma cools & hardens
– Granite (light); diorite (dark); gabbro (very dark,
mistakenly called black granite)
– Granite: “grain”-y, non-porous, light colored (gray to
pink), hard, durable, scratch- and chemical-resistant,
takes a variety of finishes, low thermal expansion, can be
used in contact with the ground or exposed to severe
weathering

Volcanic — formed close to the earth’s surface when
lava cools & hardens
– Rhyolite, andesite, basalt, pumice, tuff
– Not often used for building in U.S. — few volcanoes
Boston Public Library
Pink granite; 1888-1895;
McKim, Mead & White
Rhodes Hall — 1516 Peachtree Street NW;
Stone Mtn. granite and Lithonia gneiss;
1904; W. F. Denny, II
Stone Mountain, GA, ca. 1916
Sedimentary — rock deposited
on the earth’s surface by the
action of wind and water

Anisotropic – directionally dependent
– Specific bedding planes
– Sandstone and limestone are examples
Sandstone Crossbeds
1st Sedimentary Rock Type

Carbonates: CaCO3 and Mg(CO3)2
– Composed of carbonate minerals which
precipitate out of supersaturated waters, or
are formed when the water evaporates
– Limestone, travertine, tufa are precipitates
– Oolitic limestone, gypsum are evaporates
– Porous; will not accept a high polish; soluble
in acid; very absorbent and susceptible to
staining  not usually in contact with soil
Tufa — Ostia, 1st
century BCE
Travertine — LA,
1984-1997
Tufa
Towers,
Mono
Lake, CA
“Tufa” – a
sedimentary rock...
Not to be
confused with
“Tuff” – an
igneous rock
Tuff buildings, Kirkland, AZ,
ca. early 1900s
Tuff columns, Pompeii forum,
pre-79 CE
Georgia Capitol — Atlanta; Indiana oolitic
limestone; 1889; Edbrooke & Burnham
Manufacturer and Builder, XIX, 11 (Nov. 1887), 253.
Georgia Capitol, West Exterior Stairs
2nd Sedimentary Rock Type

Silicates: SiO2 (quartz) + Fe2O3 or CaCO3
– Composed primarily of silicate minerals
transported by moving fluids, and were
deposited when the fluids came to rest
– Sandstone (brownstone & bluestone are
colored sandstones)
– Highly stratified, durable  good for paving,
sills, hearths, mantels, copings
Mount Airy, Warsaw, Virginia, 1758; dark brown
sandstone, trimmed in light-colored sandstone,
projecting limestone pavilion; John Ariss (?)
Connecticut
brownstone used
to build the New
York Brownstones
Bluestone —
used for
coping and
flagging
Metamorphic Rock — formerly igneous
or sedimentary rock, transformed by
heat and/or pressure
Three Main Types: Gneiss, Slate, Marble
Types of Metamorphic Rocks
–Gneiss: formed from igneous or
sedimentary rocks
 Very hard
 Good for foundations, walls, & other loadbearing applications
–Slate
–Marble
Peachtree Center MARTA Station —
carved out of solid gneiss
Granite vs. Gneiss
Granite is a plutonic igneous rock. Its crystals
form differentially upon cooling deep in the
earth's crust. Granite’s visible crystals are
randomly arranged.
 Gneiss is a metamorphic rock that shows
obvious banding of light and dark minerals
resulting from recrystallization of the original
material due to high heat and pressure.
 If you can discern a pattern, it's not granite!

Arabia Mtn. gneiss among the
granite
Arabia Mountain Migmatitic Gneiss
“Tidal Gray”
Atlanta Area Rock Outcrops
georgiarocks.us
Distribution of Granites & Gneisses in
Georgia from quarriesandbeyond.org
Types of Metamorphic Rocks
–Gneiss
–Slate: formed from shale (sedimentary
rock)
 Very dense and hard
 Good for paving stones, roof shingles,
water courses, and countertops
–Marble
Slate
Pentagon,
Arlington, VA,
ca. 1943,
George
Bergstrom
September 11,
2001 attack
destroyed more
than an acre of
the slate roof.
Slatebearing
formations
in Georgia
Types of Metamorphic Rocks
– Gneiss
– Slate
– Marble: recrystallized limestones
(sedimentary), easily carved and polished
 Carrera and Vermont marble — grains are
smaller, more porous, metamorphic process did
not go as far, chisel can go through it cleanly 
finely detailed carving, more susceptible to
deterioration, especially granular disintegration
 Georgia marble — larger grained, stronger, used
as foundation stone
Candler
Building
127 Peachtree
Street NE; 1906;
George E.
Murphy, architect;
F. B. Miles,
sculptor; Georgia
marble from the
Amicalola quarries
in Pickens County
Distribution of Marble in Northwest Georgia
Igneous or Sedimentary Rock Type
 Metamorphic Rock Type
Almost any rock subjected to high-grade
(high heat and pressure) regional
metamorphism  Gneiss
 Sandstone (Sedimentary)  Quartzite
 Limestone (Sedimentary)  Marble
 Shale (Sedimentary)  Slate
 Basalt (Igneous)  Greenstone

Forms of Stone
Naturally occurring or human-made
Fieldstone — from riverbeds or fields
 Flagstone — thin slabs used for flooring,
paving (stones split on a bedding plane)
 Rubble — irregular quarried fragments,
unsquared
 Dimension stone — quarried and cut into
rectangles

– Cut stone: large slabs
– Ashlar: smaller, rectangular blocks
Fieldstone
Flagstone
Bluestone — a colored sandstone popular
for flagging
Rubble (unsquared)
Coursed = continuous horizontal lines
Uncoursed = discontinuous; no horizontal lines
Ashlar (squared)
Courses and Wythes
Load-bearing
Weight of upper floors
supported by walls of
lower floors
 Interior spaces smaller
on lower floors
 Arches, vaults, domes
opened up space,
reduced weight
 Limited height due to
volume and mass
necessary to support
the building

Veneer
Skeletal framing system
supports building
– Wood
– Metal (steel)
– Reinforced concrete
 Masonry veneer
 Taller buildings possible
 By early 1900s, most
stone and brick
buildings in the U.S.
were veneer

Monadnock Building; Chicago; unreinforced
brick; 16 stories; 1891, Burnham & Root
18”
6 ft.
Expensive ashlar face (veneer) over
inexpensive brick or rubble wall
(wall section diagrams)
More veneer examples
Dressed stone over
poured concrete
Concrete block
over steel I-beam
Modern
ties
Stone over
concrete masonry
units (CMUs)
Thin stone veneer over wood
framing
What is the error in the labelling?
Thin stone veneer over wood
framing
Stone Finishes
Tooth chiseled
Point chiseled
Rock faced
Broached
Drove
Crandalled
More Stone Finishes
Vermiculated
Rusticated
Bush
hammer
Bush hammered
Wire sawn
Washington Hall,
U.S. Military
Academy, West
Point, NY; gneiss
Modes of Deterioration
Solution Weathering
 Acid Rain
 Salt Weathering
 Dry Deposition
 Freeze-Thaw Cycle
 Hygric Swelling
 Thermal Effects
 Biological Effects

Solution Weathering
Occurs when soluble chemicals in stones
dissolve in rainwater and get washed off
and re-deposited elsewhere
 Occurs naturally when rain falls

– Rainwater is a weak carbonic acid formed by
the reaction of CO2 with atmospheric moisture
– Carbonic acid can dissolve calcium carbonate
(primary component of limestones and
marbles)

In polluted environment, rainfall acidity is
increased & solutional activity intensifies
Solution Weathering, cont.
Marble headstone with lead
lettering, 130 years old.
Rainwater (carbonic acid)
washes unevenly over the
surface, causing pitting and
wave-like deterioration
patterns in the marble. The
lead letters, originally even
with the stone surface, now
are “raised”, indicating how
much stone surface has been
lost.
Acid Rain
Mostly sulfur dioxides and
nitrous oxides
 Creates gypsum (hydrated
calcium sulfate) on
building surfaces
 Loss of material—gets
washed off and redeposited somewhere else

Acid Rain & Solution Weathering
Processes
1. Rainwater - naturally
composed of carbonic
acid formed by Rx of
CO2 with atmospheric
moisture
2. Calcium carbonate is
soluble in carbonic acid
3. Sulfur oxides in
atmospheric pollution +
water in the air form
sulfuric acid. When it
“rains” on stone
containing CaCO3, it
forms gypsum
Salt Weathering
Every salt has its own relative
humidity equilibrium point.
Depending on the surrounding
RH, the solution of salt can give
up its water, forming salt
crystals, which can split rock.
 Marine environments
 De-icing salts
 Salt contained in Portland
cement—alkalis can migrate
into the surrounding stone

Dry Deposition
Occurs on carbonate rocks (e.g.,
limestone, marble) constantly
 Fly ash and sulfur dioxide in the air
captured by the moisture that is
always present in the stone 
formation of a crust
 Occurs more often in winter

– More particulates in the air
– Greater temperature differential 
more condensation, so the wet stone
captures more particulates
Freeze-Thaw
Cycle
More porous stones
are more affected
(e.g., limestone more
susceptible than
granite)
 Water experiences
10% volume increase
when it goes from
liquid to solid (freezes)

Stonework should be
laid on the quarry
bed (grain running
horizontally) because
stone is stronger and
more weatherresistant in that
orientation.
Photo
courtesy of
Ben Sutton,
2014
Hygric Swelling
Clay swells when it gets wet; differential strain
between wet and dry areas causes deformation,
stress, cracking
 Sedimentary rocks more susceptible: weaker
mechanically, more porous, have layers, contain clay

Bio-deterioration
Physical and chemical processes
Bacteria, algae, and fungi — cause mostly
chemical effects; have a specialist identify
these
 Lichens — chemical and physical effects;
can tear away surface of rock; hard to
clean
 Mosses — mostly physical effects; easier
to remove than lichens
 Higher Plants — can damage surface and
retain moisture

Algae growth on sandstone
Lichen
growth on
stone wall
Plant-covered brick building
Thermal Effects

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Coefficient of linear thermal expansion = rate at
which mineral expands with increasing
temperature
Stone temperature can vary between 30%-50%
higher than air temperature
Darker stones absorb more heat and give it up
more readily
Daily and seasonal heating cause stress and
micro-fractures in and along mineral grains,
eventually producing flaking
Mable is particularly susceptive to thermal
effects
Creep or drift — building expands during day but
does not fully contract at night
Before cleaning or repairing stone:
Know what the stone is, and its source
 Understand the nature of the stone:
grain, chemical composition, crystal
structure, water solubility
 Understand the structure: number of
wythes, type of fasteners or dowels
 Analyze the mortar (composition, color,
texture, type of joint)
 Know the chemical composition of
pollution/salts

Cleaning Masonry
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Water wash – fine spray directly onto element
(removes gypsum crust)
Chemical cleaners – acidic, alkaline – use
extreme care; watch dwell time; rinse
thoroughly. Environmental hazard, containment
is essential.
Hot water, steam – degreasing
Particulate cleaning – more easily localized; can
perform partial cleaning; can be used on
different stones in juxtaposition; containment
problems; requires trained operators
Lasers – can clean extremely fragile surfaces;
can only clean light surface with dark soiling;
primary risk is yellowing
Cleaning Dry Deposition — Reconversion of
gypsum films into calcite on the surfaces of
monuments & statues
Gypsum on marble forms crust that preserves
underlying design details
 Gypsum crust itself is fragile
 Washing gypsum off stone surface causes loss
of historic material, esp. carving relief details
 Inversion of marble sulfation — chemically
return gypsum to calcite (CaCO3) by spraying
K2CO3 (potassium carbonate) on stone

– Consolidates layers of stone, preserving design details
– Calcite is five times harder than gypsum
– Calcite is 29,000 times less soluble in water than
gypsum
Traditional
Sandblasting
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Larger particulates,
diameter = one mm
Delivered at hundreds to
thousands psi (pounds
per square inch)
Particulate used
– True sand (quartz)
Modern Particulate
Cleaning

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Smaller particulates,
diameter = tens of microns
Delivered at tens of psi
Particulates used:
–
–
–
–
–
Walnut shells
Sodium bicarbonate (Armex)
Dry ice
Calcite or dolomite particles
Façade grommage
 Glass beads
 Aluminum oxide
Power Washing / Sandblasting
Sandblasting
Historic Brick
Repairs to Stonework
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Re-tool mortar joint
Re-dress surface of the stone
Re-attach using adhesives and pins, dowels,
or staples
Patching (Dutchman or composite)
Use consolidants (alkaoxysilane monomers)
Remove and replace stone
Dismantle and rebuild wall
Remove and replace corroded metal elements
Do all work in accordance with the Secretary’s
standards
Inappropriate
& Appropriate
Repairs
Washington
Park,
Charleston, SC
Preservation Briefs
#1: Assessing Cleaning and WaterRepellent Treatments for Historic Masonry
Buildings
 #2: Repointing Mortar Joints in Historic
Masonry Buildings
 #6: Dangers of Abrasive Cleaning to
Historic Buildings
 #38: Removing Graffiti from Historic
Masonry
