Concrete Tabby Plaster Stucco

Concrete

Tabby

Plaster

Stucco

Concrete

 Raw materials easily available  Does not rot or burn

 Relatively low cost

 Used for every building purpose —

foundations, walls, pavement, interior finishes

 Has no form of its own

 Has no useful tensile strength, but

Roman Concrete

 Invented by Romans

– Volcanic rock and ash from Pozzuoli (near Naples), called “pozzolan”

– Ground it up

– Mixed Pozzolana cement (naturally-hydraulic) with lime

– Burned the mixture

– Added sand

– When mixed with water, it hardened under water better than in the air

Roman Concrete, cont.

 Changed the way Romans built

– Masonry of stone and brick used for surface layers

– Hollow interiors were filled with concrete

Pantheon, Rome, 118-128

Pantheon

 Current version built by Hadrian, 118-128  Original built by Marcus Agrippa in 27

BCE; destroyed by fire in 80 CE

 Largest unreinforced concrete dome in the world

 Weight 5000 tons

 Thickness varies from 21 feet at base to 4 feet at the oculus

 Height = Diameter = 142 feet

 Coffering decorative but also reduced the weight of the ceiling

 Knowledge of concrete construction

virtually lost during Middle Ages

 Late 18th - early 19th century, British

and French inventors experimented with cements

 1824 Joseph Aspdin invented

Portland cement

 1853 – 1st modern poured

Sidney Root-Joseph E. Brown house; 159 Washington Street, Atlanta; unreinforced concrete (?); 1858 “Sebastopol;” West Court Street, Seguin, Texas; unreinforced concrete, 1854

 1867 Joseph Monier (France)

patented iron reinforcing bars (re-bar)

– Added the tensile strength of the metal to the compressive strength of the concrete

 1886 Rotary kiln introduced — made

production of cement more practical

 1900 1st ASTM tests for cement

(American Society of Testing and Materials)

Re-bar in CMUs (concrete masonry

units)

Unity Temple; Oak Park, Illinois; pre-cast,

reinforced concrete; 1906; Frank Lloyd Wright

Terminal Building, Dulles International Airport; Washington, DC; 1958-1962;Eero

Deterioration of Concrete

– Freeze/thaw problems

– Corrosion of iron reinforcing bar or ties

 Absorbs CO₂ from atmosphere — deteriorates

 Poor materials — impure aggregates (e.g., beach

sand); seawater

 Not poured property

– Historic: tamping, rolling left voids

– Modern: vibrated as poured

– Joints between pours

 Cracking Fill cracks  Spalling Patch

 Deflection Call engineer  Erosion Replace

 Corrosion of re-bar Remove & replace

Problems Solutions

All fills, patches, replacements should be compatible with the original for appearance and durability.

Iron re-bar should be replaced with galvanized (steel coated with zinc) or epoxy-coated re-bar.

Water penetrating through concrete

leaches out calcium oxide, forming

TABBY – Coastal Concrete

 From Spanish word

tapia

“

 First used in North America by the

Spanish in the 1500s

 English began using “tabby” or

Tabby Composition

 Lime — the binder (glue)  Shells — the aggregate

 Sand — prevented shrinkage and cracking

of the tabby mixture. Channel (river) sand was used; beach and dune sand contained too much salt

 Water — had to be fresh

 Ash — by-product from burning the shells;

increased hydraulicity (ability of a binder to harden in contact with water);

Making Tabby

 Ingredients: Equal parts lime, sand,

water, and shells, plus small amounts of wood ash

 Mix into a slurry  Pour into a mold

 Let set until hardened

Advantages of Tabby



Used inexpensive local materials

No skilled labor required



Versatility of form and application

– Poured into a mold, blocks, bricks, floors, ceilings, columns, arches



Durability in a humid climate.

Can be re-used

Disadvantages of Tabby

 Extremely labor intensive; a cheap

source of labor was necessary to

make tabby construction practicable (

i.e.,

 Susceptible to water damage, unless

a finish coat of stucco or whitewash is applied

Four Types of Tabby



Oglethorpe tabby – 1733-1795

Spalding tabby – 1795-1875



Tabby Revival – 1875-1930



Pseudo-Tabby (faux tabby) –

Oglethorpe Tabby

Spalding Tabby slave quarters;

Spalding

Tabby

Tabby Revival

Hollybourne Cottage, 1890, James Day, Jekyll Island, GA

Coquina

 Spanish word for “little shells”

 A sedimentary rock composed of the

shells of invertebrates

 Particles must be 2mm or larger in

size

 Quarried and used as a building stone

PLASTER

 Generic term for cementitious substances

applied to a surface in paste form that harden to a solid material

 Prehistoric plaster — mud smeared over

masonry walls or over a mesh of woven sticks and vines (wattle & daub)

 Egyptians and Mesopotamians developed fine plasters based on gypsum and lime

 Portland cement added in late 1800s

 Chosen wall surface until ca. World War II, replaced by drywall (gypsum board)

 Quarried, crushed, dried, ground to fine

powder, heated to 350° F to remove most of the moisture (calcining)

 Calcined gypsum ground to fine powder is

Plaster of Paris (discovered by Egyptians)

 When mixed with water, rehydrates and

recrystallizes rapidly, giving off heat as it hardens, and expands

Early Plaster

 Clay and water

 Sand added to reduce shrinkage

Lime Plaster

 Composed of non-hydraulic lime,

sand, fiber or hair, and water

 Can be applied directly to masonry or

over wood or metal lath

 More water resistant than early

plaster

Gypsum Plaster

 More rigid than lime plaster

 Requires furring strips against

masonry

 More vulnerable to water damage  Has more sculptural potential than

Characteristics of Plaster

 Major disadvantage — water soluble  Durable

 Lightweight

 Somewhat soundproof  Easy to work, wet or dry

– Fashioned into a variety of shapes and textures

 Inexpensive

Historically, plaster applied by hand using hawk and trowel; now

Plaster Application

 Can be applied directly to masonry

surface

 Most often applied to lath

– Wood strips nailed to wood framing with small spaces in between allowing keying of the plaster

 Hand split lath, accordion lath, sawn lath

– Metal lath, must be attached with furring strips

Three-coat application

SCRATCH BROWN

FINISH

1. 2.

The scratch coat forms “keys” when it oozes between the lath. These help hold the plaster

Ornamental Cast Plaster

 Poured into molds

 “Running” with a template to make

Problems with Plaster

 It is rigid, will crack

– Structural movement, settling, vibrations

– Lath movement

 Poor workmanship; e.g., too much sand

 crumbling

 Improper application  Improper curing

 Lath set too closely, keys cannot form  Water - softens plaster, rots wood lath,

Solutions

 Filling cracks  Patching

 Re-plastering

 Veneer plaster replacement system All fills, patches, replacements should

be compatible with the original for appearance and durability.

STUCCO

 Before 1870s: slaked lime, water, sand,

straw or hair

 Old stucco was usually whitewashed

annually for protection

 1870s-present: Portland cement added,

straw/hair can be omitted

– Harder, more like modern masonry mortar

– Used on surfaces exposed to moisture

 Widely used on residences in U.S. in 17th

and 18th _centuries

 A. J. Downing advocated its use in 1850  Renewed use in 1890s-early 20th century

— Prairie, Art Deco, Streamline Moderne, Spanish Colonial Revival, Mission Revival, Tudor Revival

 Modern stucco – gypsum instead of lime  Color depends on sand used, or from

“Cliveden;” Philadelphia; stone main façade; stucco over rubble, scored to resemble ashlar on side; 1764

Richardson-Owens-Thomas House;

Savannah, GA; stucco over tabby, scored to resemble ashlar; 1817; William Jay

Swan House; Atlanta; stucco over terracotta

block with cast stone trim and reinforced

concrete fountain; 1928; Philip T. Shutze

Characteristics of Stucco

 Provides weather protection  Somewhat fire resistant

 Can be worked to simulate stonework  Used over less-costly substrate

 Can be applied directly to masonry or

on lath over wood

 Same three-coat application as

plaster

Modern stucco being sprayed

over expandable metal lath

Stucco Repairs

 Identify the type of stucco before

attempting repair

 Patch rather than replace when

possible

 Repair/replacement should be

compatible to the historic stucco in durability, color, and texture

 Repairs should be applied with similar

Staff

 Invented in France ca. 1876

 Plaster of Paris, cement, glycerin, dextrine mixed with water

 Cast in molds lined with hemp or jute fiber  Usually ½” thick, off-white in color

 Casting to resemble cut stone, rock, faced stone, any masonry

 Can be bent, sawed, bored, nailed  Impervious to water

Columbian Exhibition;

Chicago; 1892-93

Most buildings in the “White City” were temporary structures