Glossary Of Terms - Plastering
Accelerator - A material that shortens the setting time of gypsum plasters and other cementitious materials.
Acoustical Plaster - Sound-absorbing plaster formulated for application where reduction in sound reverberation or intensity is required.
Admixture - Any substance added to a plaster component
or plaster mortar for the purpose of modifying
its properties.
Aggregate -
An inert granular material, usually silica sand,
limestone, perlite or vermiculite, which may
be added to gypsum plaster on the job, or is
present in mill-prepared plaster. Fiber may be
considered to be an aggregate.
Aggregate Fallout -
A condition associated with machine gypsum
plaster application, where the sand (usually)
aggregate segregates, or “falls out of,” the
cementitious slurry during pumping; the
plaster or stucco is therefore referred to as
having poor sand “carrying” capacity or
quality.
Air-Entrainment - The process by which air in the form of small
isolated bubbles is introduced into a mortar
while in a liquid or plastic state.
Alabaster -
A massive, dense, crystalline, softly textured
form of nearly pure gypsum.
Alligator Cracks - See: Craze Cracks.
Alpha Gypsum - A classification of specially processed
calcined gypsums of low consistency and
high strength.
Angle Float - A plaster finishing tool having a surface bent
to form a right angle; used to finish interior
angles.
Anhydrous Calcium Sulfate - (“Anhydrite” or “dead-burned”); Anhydrite is
a naturally occurring impurity (CaSO4), usually
found in gypsum (CaSO4 • 2H2O) deposits.
Dead-burned gypsum is a calcined anhydrous
gypsum that, unlike anhydrite, is very slowly
converted with addition of water to
CaSO4 • 2H2O.
Background - This refers to the surface to which is to be plastered, weather this is a brick wall or plasterboard ceiling etc.
Basecoat - Any plaster coat applied over lath or other
substrate prior to application of the finish coat
of plaster. See also Scratch Coat and Brown
Coat.
Base Screed -
A preformed metal screed with perforated or
expanded flanges to provide a ground for
plaster, and to separate areas of dissimilar
materials.
Bead - A strip of sheet metal, usually formed with a
projecting nosing and one or two perforated
or expanded flanges. Nosing provides the
plaster base; e.g., corner bead, casing bead,
base bead, etc.
Beading - See: Joint Deformation.
Bedding Coat - A coat of plaster (usually portland cement
exterior stucco) to receive lump aggregate or
other coarse decorative material. This
aggregate is embedded into the soft plaster
prior to set.
Bleeding - See: Watering Out.
Blistering - A condition characterized by bulging of the
finish coat layer as it separates and draws
away from the basecoat.
Body - A subjective and often misused term relating
to the working properties of a plastic
cementitious mass such as gypsum or
portland cement plaster, generally referring to
the relative stiffness or resistance to
movement under the trowel.
Bonding Agent - A material applied to a surface to improve the
quality of bond between it and succeeding
plaster application.
Bond Failure - See: Delamination.
Bond Plaster - A specially formulated gypsum plaster applied
over monolithic concrete as a bonding coat
for subsequent plaster application.
Brown Coat - The second layer in three-coat plaster
application.
Brown Out:
1. To apply the second layer or brown coat ofBucking - A condition associated with lime putty, veneer and other plastering materials characterized by poor workability or stiffness well before normal setting. This condition may be related to exposure of the dry material (open bag) prior to wet mixing; use of material beyond published shelf life; or rapid dispersion of particles within the plaster when mixed in water.
a three-coat plaster application.
2. The visual darkening of a plaster surface
which indicates the completed setting
(hydration) of the plaster.
Bulk Density - The weight of a material per unit volume expressed as pounds per cubic foot (lb./ft.3) or kilograms per cubic meter (kg/m3).
Bull Nose - A special formed rounded external angle with a radius of 1/29 (12.5 mm) or more; usually associated with Tudor or Spanish architecture.
Butterflies or Butterfly:
1. Color imperfections in a lime putty finish
coat that smear out under trowel pressure.
2. An interior corner angle trowel (see Corner
Tool).
Cage-Type Mixing Paddle - A special configuration mixing tool designed
to provide high-shear mixing action with
minimum air-entrainment in veneer plaster
mixing. Provides quick and efficient
dispersion of plaster additives to achieve
optimum mortar plasticity.
Calcine - To drive off chemically combined water or
carbon dioxide (CO2) by heating. With
gypsum, combined water is driven off in
calcination to yield stucco (CaSO4 • 1/2H2O)
or dead-burned gypsum (CaSO4). In limestone
calcination, carbon dioxide is lost to form
quicklime (CaO) or dolomitic quicklime
(CaO • MgO).
Calcined Gypsum - Partially or fully dehydrated gypsum used as a
cementitious base for gypsum plaster.
Casing Bead -
A single-flange bead used as a plaster stop
and as exposed trim around windows and
door openings; also used at junction or
intersection of plaster and other wall or ceiling
finishes.
Casting Plaster - See: Moulding Plaster.
Catface - Blemish or rough depression in the finish coat
caused by variation in basecoat thickness,
poor finish coat mixing, and/or poor
application technique.
Cement - A material or mixture of materials that, when
in a plastic state, possesses adhesive and
cohesive properties and which will set in
place.
Cementitious Material - A component of plaster (gypsum, portland
cement, etc.) that, when mixed with water,
provides plasticity required for placement. On
setting, it serves to bind aggregate and filler
particles together, forming a rigid
heterogeneous mass.
Cement Plaster - Variously defined as plaster containing
portland cement.
Check Cracks - See: Craze Cracks.
Checking - See: Craze Cracks.
Chip Cracks - Fine cracks in a finish plaster coat similar to
craze cracks except that bond is partially
destroyed, producing concave fragments of
the finish.
Coat - A thickness or layer of plaster applied in a
single operation.
Cold Joining - The line at which, or the method by which,
two separate plaster applications are jointed
to provide a continuous plane surface. The
first application (set, but not dry) is terminated
at a sharp line using the trowel edge. The
second application is brought up to the line of
set material and finished to provide a smooth
continuous surface. This method is used
where termination of a plaster application at
an edge, angle, control joint or bead is
impractical.
Colored Finish - A plaster finish coat containing integrally
mixed color pigments or colored aggregates.
Combined Water - Water chemically retained as water of
crystallization; e.g., in calcium sulfate
dihydrate (gypsum) or calcium sulfate
hemihydrate.
Compressive Strength - Maximum load sustained by a material when
subjected to a crushing force expressed as
pounds per square inch (lb./in.2) or kilograms
per square centimeter kg/cm2).
Consistency - A term denoting the fluidity or viscosity of a
plaster or cementitious paste; also refers to
the amount of water required to bring a given
quantity of dry cementitious material and
aggregate to a given fluidity.
Control Joint - See: Expansion Joint.
Cool - A term referring to relative workability of a
plaster application resulting from water
absorption of the substrate (usually basecoat),
or of a plaster’s tendency to relinquish water
to the substrate. A cool basecoat contains
substantial free water (either freshly installed
and not dried, or rewet prior to finish
application); the finish applied to this
basecoat will be cool working, or have little
tendency to lose its water to the basecoat,
thereby maintaining sufficient water to provide
easy working and finishing characteristics.
Corner Reinforcement -
Material used at reentrant or interior angles to
provide continuity between two intersecting
plaster surfaces.
Corner Tool - A tool consisting of a right angle (90°) metal
form with a handle used for application of
plaster and finishing of interior angles.
Cove - A concave molding or curved surface used at
the junction between a ceiling and a wall.
Craze Cracks - Fine, random fissures or cracks of the finish
plaster surface caused by plaster shrinkage.
These are generally associated with lime
finish coat improperly gauged or troweled, or
with veneer plasters subjected to rapid-drying
job conditions.
Cure - In gypsum plastering, to provide environmental
conditions conducive to complete gypsum
hydration (low air movement and moderate
temperatures); in portland cement plastering, to
maintain sufficient quantity of water to complete
hydration.
D
Darby - A flat wooden or metal tool about 49 wide and
429 long with handles; used to smooth or
float the brown coat; also used on finish coat
to give a preliminary true and even surface.
Dead-Burned Gypsum - See: Anhydrous Calcium Sulfate.
Delamination - The physical separation of plaster coats, or of
a plaster coat from the substrate, that results
from chemical or physical impairment of
plaster bond to previous coats or other
substrates.
Devil Float - A terms used to describe a tool that scratches the surface of plaster to create a key, a Devil Float is normally a Poly Float with a few nails driven through it.
Dew Point - The point at which air becomes saturated with
water vapor and condenses to form dew.
Diamond Mesh - Types of metal lath having small diamond
pattern produced by slitting and expanding of
metal sheets. See Expanded Metal Lath.
Dolomitic - A type of limestone containing calcium
carbonate, with up to 50% magnesium
carbonate. Also refers to the quicklime or
hydrated lime derivatives of this type of
limestone.
Dope - A term used by plasterers for additives of any
type that adjust setting, workability or bond
characteristics.
Dot - A small lump of plaster placed on a surface
(usually scarified basecoat) between grounds
to assist the plasterer in obtaining the proper
plaster thickness and aid in aligning the
surface.
Dot n Dab (dot and dab) - A technique used to attach plasterboard to walls using small lumps of adhesive.
Double Hydrated Lime - Calcium magnesium hydroxide Ca (OH)2 • Mg
(OH)2, the product obtained from reaction of
water with dolomitic quicklime (CaO • MgO).
When mixed with water, forms a plastic paste
(lime putty) which may be mixed with gauging
plaster and applied as a finish plaster coat.
Double-Up - Successive plaster coat application with no
setting or drying time allowed between coats,
usually associated with veneer plastering. The
double-up coat is applied (from the same mix)
to a scratch coat over gypsum base.
Drag - A workability problem encountered during
knockdown or finish troweling, where
excessive pressure is required to draw the
trowel across the surface to smooth it. This
occurs when the material has not retained
sufficient surface moisture to lubricate the
trowel; in the extreme, the trowel may skip or
“chatter” across the surface, creating ripples.
Dry-Out - A condition caused by excessive evaporation
or substrate water absorption, when the
plaster loses some or all of the water required
for hydration (setting). Appears as a ightcolored
soft area.
E
Early Stiffening - Low plasticity (hard or poor workability) of
plaster occurring substantially prior to actual
setting (hydration) reaction; see also Bucking.
Efflorescence - A white, powdery surface deposit sometimes
found on plaster or masonry. Results from
migration of soluble salts to the surface; also
called “whiskering” or “saltpetering.”
Eggshelling - See: Chip Cracks.
Electric Radiant Heat - A heating system comprised of an electric
resistance heating cable attached to radiant
heat plaster base, and covered in two coats
with a specially formulated heat-resistant plaster.
Ettringite - Ca2A12(SO4) • XH2O, where X = 0-30;
a dimensionally unstable material formed
when gypsum plasters or gypsum-containing
materials intimately contact portland cements
in the presence of excess moisture. As
additional moisture is made available, the
ettringite crystal (and bulk material) expands,
creating bulges, cracks, and delamination at
the portland cement/gypsum interface.
Expanded Metal Lath - A general term to denote slit and drawn sheet
metal forming openings of various
configurations; used as a plaster base.
Expansion Joint - A product formed from sheet metal having
“W” shaped cross section; provides controlled
discontinuity at locations in a plaster
membrane to relieve stress.
False Set - Rapid stiffening (not setting) of portland
cement plaster, which can be counteracted
through additional mixing. Similar reactions
with lime and gypsum plaster are described
as bucking or early stiffening.
Fat - A mixture of fine lime and/or gypsum particles
and water accumulated on the trowel during
the finishing operation, which is used to fill in
small surface imperfections.
Feather Edge - A metal or wood tool having a beveled edge.
Used in finish coat work to straighten
reentrant angles.
Fibatape - See Scrim: But Self Adhesive
Fibered Plaster - Usually a basecoat plaster containing animal
(hair), vegetable or glass fibers, which
promote cohesiveness in the mix.
Finish Coat - The last layer of plaster applied in a multilayer
application.
Finishing Brushes - Brushes used to apply water to a smooth lime
finish coat during final troweling; may be fiber
or felt type.
Fish Eyes - A term describing small blemishes (about 1⁄49
in diameter) found in lime/gauging finish
coats, caused by insufficient finish-coat
mixing.
Flashing - A “photographing” or “see-through” effect
observed with plaster finishes applied over
block or tile mortar joints, plaster base joints,
and beads and trims, where nonuniform
water absorption can occur.
Flash Set - See: Quick Set.
Float - A tool or procedure used to straighten and
level the finish coat, to correct surface
irregularities produced by other tools, and to
impart a distinctive surface texture.
Float Finish - Finish-coat texture that is rougher than a
smooth trowel finish, and which is derived
from aggregate in the mortar.
Fresco - An artistic or decorative medium consisting of
a water-soluble paint applied to freshly
applied plaster.
Furring - A term applied to spacer elements (channels,
rods or strips) used to maintain a space
between a plaster application and the
structural elements behind it.
G
Gauging - A cementitious material, such as gypsum
plaster, Keene’s cement or portland cement,
added to lime putty to provide and control set;
also the act of adding gauging material.
Glass Fiber Tape - Glass fiber mesh material of various widths
used to reinforce joints in veneer plaster
applications over gypsum base. Attached with
stapes or pressure-sensitive adhesive.
Green - A term to describe freshly applied plaster that
has set, but has not dried.
Ground - Piece of wood or metal attached to the plaster
base so that its exposed surface acts as a
gauge to define the thickness of plaster to be
applied. Also a term used to denote plaster
thickness.
Grout - Gypsum or portland cement plaster used to fill
crevices or to fill hollow metal door and
window frames.
Gypsite - A surface gypsum deposit containing loam,
clay, sand and humus impurities; gypsum
content ranges from 60% to more than 90%.
Gypsum - Hydrated Calcium Sulfate (CaSO4 • 2H2O);
a naturally occurring mineral that, when
calcined, serves as the base to formulate
plastering materials and other building
products.
Gypsum Lath - A plaster base manufactured in sheets of
various dimensions. Composed of special
gypsum core surfaced with multilayered
absorptive face paper suitable to receive
gypsum plasters.
Gypsum Partition Tile (Block) - A cast gypsum building unit of various
dimensions for use in nonloadbearing interior
construction for protection of columns,
elevator shafts, etc., against fire.
Gypsum Plaster - Ground calcined gypsum combined with
various additives to achieve specific
application, working and set characteristics.
H
Hand Tool - A term referring to a method of application of
plastering materials using a hawk and trowel.
Hard Wall - A generic term referring to conventional gypsum
basecoat plaster.
Hawk - A tool used by plasterers to hold and carry
plaster; consists of a flat wood or metal piece
from 109 to 149 square, with a wooden
handle centered and attached to the
underside.
Hemihydrate - CASO4 • 1/2 2H2O; a calcined gypsum used
for plaster formulation.
High Calcium Lime - A type of lime containing mainly calcium oxide
or hydroxide and not more than 5%
magnesium oxide or hydroxide.
Hoddability - A term describing the ease with which a
plaster may be handled with a hod or hawk;
depends on plaster flow characteristics and
angle of repose.
Hold-Out - The water retention characteristic or property
of a plaster.
Hot - Opposite of cool; refers to plaster working
characteristics, where reduced spread and
plasticity result from excessive basecoat
absorption of available water from the plaster,
or plaster has an increased tendency to
relinquish available water to the basecoat.
Hydrate - To chemically combine water as in the
hydration of calcined gypsum: CaSo4 •
1/2H2O + 3/2H2O Õ CaSO4 • 2H2O, or
slaking of quicklime: CaO + H2O Õ Ca (OH)2.
Also the product resulting from this
combination.
Hydrated Lime - Ca (OH)2 or Ca (OH)2 • MgO; produced by
slaking, or adding water to, calcium quicklime
(CaO) or dolomitic quicklime (CaO • MgO).
Hygrometric Movement - The dimensional response (expansion or
contraction) of gypsum laths and set
cementitious materials due to a variation in
relative humidity.
Inhibitor - See: Retarder.
J
Joint - The junction of two masonry, gypsum lath or
other plastering bases, in a plane surface.
Joint Deformation - Deviation of the formed joint from a plane
surface; may be referred to as “ridging,”
“beading,” “lipping” or “stepping” of the joint.
Condition may be caused by improper lath
attachment; improper joint treatment to
achieve reinforcement; irregular water
absorption over the joint; abnormal substrate
movement in response to thermal,
hygrometric (humidity), structural and other
construction influences.
Journeyman - A plasterer or lather who, through training
and experience, has become thoroughly
skilled in the trade.
Keenes Cement - An anhydrous gypsum plaster of low
consistency that, when mixed with lime putty,
provides a dense, hard finished surface. This
material is unique in that it may be
retempered using water and reworked with a
trowel to resume the plastic, workable state.
Knock-Down - An intermediate plaster finishing step where
sizable surface imperfections of the partially
stiffened plaster application are removed prior
to final finish troweling.
Land Plaster - Coarse-ground natural gypsum that is
calcined for the manufacture of gypsum
plasters.
Latex Modifiers - Dry powder or emulsified admixtures that
improve plaster plasticity, surface hardnessand compressive strength of the set material,
and that improve bond between the plaster and base.
Lath - A metal or gypsum material applied
separately to a structure that serves as a base
for plaster.
Lean Mixture - Any plaster which has a high ratio of
aggregate to cementitious material. Usually
exhibits poor or hard working characteristics.
Lightweight Aggregate - Low-density, inert aggregates such as
vermiculite and perlite (as opposed to silica
sand and pumice).
Lime - The principal product derived from calcining
various types of limestone consisting of
oxides or hydroxides of calcium or
magnesium.
Lime Plaster - A basecoat plaster consisting of lime and
aggregate.
Lime Putty - A finishing material resulting from slaking of
quicklime or soaking and mixing hydrated
lime with water to form a plastic mass;
usually mixed with a gauging plaster or
gauging and aggregate as a finish over
basecoat.
L
Machine Application - Plaster application by mechanical means;
generally by pumping and spraying.
Mason’s Lime
See: Type “N” Hydrated Lime.
Mechanical Bond - The physical kerfing of one plaster coat to
another, or to a plaster base; e.g., clinching
of plaster keys to expanded metal lath, and
the bond obtained between adjacent plaster
coats by brooming or crossraking the first
coat prior to set.
Metal Lath - A metallic plaster base manufactured from
sheet metal by slitting and expanding, or by
punching and forming.
Mortar - A plastic mixture composed of water and a cementitious material, which may be machine or hand applied, and which hardens in place.
M
Moulding Plaster - A fine-grind, high-consistency hemihydrate
gypsum that, when mixed with water, yields a
pourable slurry for casting ornamental trim
units or decorative plaster runwork.
N
Neat - A basecoat gypsum plaster product produced
and supplied without aggregate. It is intended
to be job mixed with aggregate, such as sand,
perlite or vermiculite.
O
One-Coat System - Veneer plastering; the veneer finish is applied
to veneer gypsum base or other approved
substrate in a scratch and double-up method
(both “coats” from the same batch), to a full
thickness of 1/169 (1.6 mm) to 3/329
(2.4 mm).
Open Time - The amount of time, from the point of mixing, during which a plaster retains a plastic workable consistency, until it becomes too stiff to be applied.
P
Parge - To coat with plaster; usually refers to
application to foundation walls and rough
masonry.
Pencil Rods - Mild steel rods of 3/169 (4.8 mm), 1/49
(6.4 mm), or 3/89 (9.5 mm) diameter, used to
provide rigid internal reinforcement of the
base for plaster application.
Perlite - A siliceous volcanic glass that, when
expanded by heat, is used as a lightweight
plaster aggregate.
Plaster - A cementitious material or combination of
cementitious materials and aggregate that,
when mixed with water, forms a plastic mass.
When applied to a surface, plaster adheres to
it and subsequently sets or hardens,
preserving in a rigid state the form or texture
imposed during the period of plasticity.
Plaster of Paris - CaSO4 • 1/2H2O or hemihydrate gypsum
without set control additives, used in casting
and industrial applications.
Plasticity - The property of plaster that permits
continuous and permanent deformation in any
direction. As opposed to fluidity, a plastic
material requires a measurable force (yield
value) to initiate flow. A material of low
plasticity is usually described as being “poor”
or hard working; high plasticity is described
as “rich” or easy working.
Plasticizer - An admixture to improve plasticity,
workability, and spread under the trowel.
Popping - See: Chip Cracks. Usually refers to gauged
lime putty finish where the unhydrated
magnesium oxide (MgO) in the hydrated lime
hydrates over a long period of time when
exposed to free moisture. Results in local
areas of high expansion in the finish surface
that may crack and “pop” off, leaving small
craters or blemishes in the surface.
Portland Cement - A cementitious material made by heating a
mixture of limestone and clay containing
oxides of calcium, aluminum, iron and silicon
in a kiln, and pulverizing the resultant clinker.
This material is usually mixed with lime and
aggregate for exterior plastering (stucco
work), or in interior construction in areas
where high resistance to moisture is required.
Potassium Aluminum Sulfate - Alum; a generally recognized accelerator of
gypsum plaster. Usually spray applied as a
solution to dry basecoat plaster or faded
veneer gypsum base to promote bond of
subsequent layers of plaster.
Pressure-Sensitive Tape - An open-weave, glass-fiber joint
reinforcement tape used in veneer finishing,
coated with a pressure-sensitive adhesive for
easy application to base without need for
staple attachment.
Putty Coat - A smooth-troweled finish plaster coat
containing lime putty and a gauging plaster.
PVA - PolyVinyl Acetate, Glue, when mixed with water and applied to high suction background forms a great key. Also used to bond together loose material.
Quicklime - CaO or CaO • MgO; materials produced by
burning or calcining limestone. For plastering,
quicklime is slaked with water to hydrate the
material to form Ca(OH)2 or Ca(OH)2 MgO.
The resulting lime putty is gauged for use as
a finish coat.
Quick Set - Premature hardening (setting) of a plaster.
This condition may be attributed to improper
job use of accelerator, damp plaster prior to
mixing, contamination of the mix (rusty or
dirty mixing water, equipment or tools), or
other factors.
R
Rake - A plastering tool with tines (teeth) that is used
to roughen or scarify basecoat plaster
application prior to set. Promotes mechanical
bond with the finish-coat plaster layer.
Rapid Drying Conditions - Job environmental conditions that cause
premature removal of water from the plaster
(prior to set), which results in incomplete
hydration of the gypsum plaster; e.g., high
temperature, low relative humidity and high
air movement. These conditions promote dryout
and a variety of shrinkage cracking
problems as a result of rapid and excessive
evaporation.
Rapid Plaster - Gypsum neat plaster “Type R”; calcined
hemihydrate gypsum mill-mixed with
materials to control set and working
properties; sand aggregated on the job for
application over gypsum lath to a maximum
thickness of 1/49 (6.4 mm).
Relative Humidity - The ratio of the amount of water vapor
actually present in the air to the greatest
amount possible at the same temperature,
expressed as a percentage.
Retarder - An admixture used to delay the setting action
of plasters or other cementitious materials.
Retempering - A procedure whereby plaster (usually Keenes
cement or portland cement) is remixed to a
workable consistency using water and/or
mechanical action.
Rich - See: Plasticity.
Ridging - See: Joint Deformation.
Rod - A straightedge tool of various lengths used to
straighten the surface of wall and ceiling
plaster applications.
Runwork - A plaster installation where the material is
applied in a continuous formed method
using a metal or wood template; usually
done as a decorative application at
wall/ceiling junctions.
S
Sag - A warping condition in ceiling construction
where the lath and plaster bow down from the
framing members; can result from a variety of
causes, such as improper framing, spacing,
long-setting plaster, slow drying conditions,
excessive weight of insulation, and improper
placement of vapor barrier.
Salamander - A portable gas or oil-burning heater used at a
jobsite to provide minimum comfortable
working conditions and prevent freezing of
plaster.
Sand - Loose granular aggregate resulting from
natural disintegration of siliceous rock or from
crushing of friable sandstone; serves as an
inert filler and provides internal expansion and
contraction stress relief in plaster mix,
minimizing cracking problems.
Sand Coat - See: Scratch Coat.
Sand Float:
1. A method of texturing a sanded finish coat
that raises sand particles to the plaster
surface through use of a dampened
sponge or sponge rubber float.
2. Refers to the type of finish texture
obtained through use of a sponge or
sponge rubber float.
Scaffold -
A temporary platform or network of support
members erected at a jobsite to permit safe
and convenient construction, repair or
cleaning of a structure.
Scarifier - See: Rake.
Scratch Coat - Where the plaster is stracted with a tool (rake) that makes grooves where the next coat of plaster can key to (Grip to).
Screed - Noun, See: Grounds; Verb, to level or
straighten a plaster coat application with a
rod, darby or other similar tool (e.g., a
“screed” bar).
Scrim - Woven natural or artificial fiber material
coated with a binder or binder and adhesive;
used to provide joint reinforcement.
Scrim Tape - See: Scrim.
Setting Time - The elapsed time required for a cementitious
material to attain a specified hardness after
mixing with water. The set time is a physical
indicator for the chemical reaction of
hydration in gypsum plasters.
Sheet Lath - Metal lath formed by punching perforations in
steel sheets; made from heavier gauge steel
than expanded metal lath; has greater
stiffness.
Shelf Life - See: Storage Life.
Silica Sand - See: Sand.
Single Hydrate Lime -
See: Hydrated Lime.
Skim Coat - A thin finish plaster coat troweled smooth.
Slaked Lime - See: Hydrated Lime.
Slicker - A beveled device four feet (1.2 m) long and 69
to 89 (15.2-20.3 mm) wide, sometimes used
by a plasterer in place of a darby to level and
smooth a plaster coat.
Slip - A plaster workability characteristic relating to
the relative ease with which the trowel is drawn over the plaster surface both during
application and after the coat has stiffened or
“taken up.”
Spalling - See: Chip Cracks.
Spread - A term referring to the extendibility or
coverage obtained with a plaster; sometimes
used incorrectly to refer to plaster workability.
Staff
Fiber-reinforced ornamental plaster casts.
Also used in trades to refer to a person that is a plasterer.
Stilts - Devices employed by plasterers which are
strapped to the feet, providing an elevated
footrest to permit ceiling and high wall
application without use of cumbersome
scaffolding. Stilts have extension capability of
up to three feet (0.91 m).
Storage Life - The time during which packaged material can
be stored under specified temperature and
humidity conditions and remain suitable for
use.
Stucco
1. A cementitious material used in exposed
exterior building construction.
2. A plaster manufacturing term referring to
freshly calcined gypsum not yet formulated
or processed into a finished plaster product.
Suction - The absorptive quality of a surface, such as
concrete masonry, gypsum lath, previous
plaster coat, etc., which is to be plastered.
Sweatout - A defective gypsum plaster condition
characterized by a soft, damp area remaining
after the surrounding area has set. This is
usually caused by insufficient ventilation,
which inhibits normal drying.
T
Take-Up - The loss of water of a plaster into the
absorptive substrate during application, as
evidenced by a moderate stiffening of the
plaster coat.
Template - A gauge or pattern used as a guide to
produce arches, curves and other shapes or
forms of a repetitive nature (see: Runwork).
Texture - A patterned plaster finish as contrasted to a
smooth finish.
Thermal Shock - A stress created by an extreme or sudden change in temperature that may result in
cracking of plaster after application.
Thin-Coat Plaster - See: Rapid Plaster or Veneer Plaster.
Thixotropy - The property of a plastic mass that enables
the material to achieve higher fluidity on
agitation, and to thicken on subsequent rest.
Three-Coat Plastering - The application of plaster in three successive
coats—scratch, brown, finish—leaving time
between coats for setting and/or drying of the
plaster.
Tie Wire - Soft annealed steel wire used to joint lath
supports, attach metal lath to supports, and
reinforce metal lath joints.
Torpedo Sand - A natural, well graded plastering sand
obtained from pits along the Fox River, west
of Chicago, Illinois.
Trowel - A tool used by a plasterer to apply, spread,
shape and smooth plaster.
Troweling - Refers to a technique where you use a trowel to spread the material on with.
Turtle Back - See: Blistering.
Two-Coat Plastering - See: Double-Up.
Two-Coat System - A veneer plaster installation consisting of a
veneer basecoat and finish coat. Each coat is
applied using the scratch and double-up
method, with the basecoat allowed to set
prior to finish coat application. Each coat is
applied to a nominal 1/169 (1.6 mm)
thickness, for a total installation thickness of
1/169 (3.2 mm) to 3/169 (4.8 mm).
Type “N” Hydrated Lime - See: Type “S” Hydrated Lime.
Type “R” Hydrated Lime - See: Rapid Plaster.
Type “S” Hydrated Lime - A special hydrated finishing lime, distinguished
from type “N” (normal or mason’s hydrated
finishing lime) by restrictions on the amount of
unhydrated oxides.
Type “X” Base - A gypsum lath with specially formulated core
to increase fire retardent properties and
improve system fire-resistance rating.
Ultraviolet Radiation -
UV light; the component of sunlight that can
degrade gypsum-lath face paper to produce
organic acids. These acids react with an
alkaline veneer plaster, forming a potent
retarder at the plaster/gypsum base interface,
and destroying the mechanical bond of the
plaster to the gypsum base.
Undercoat - See: Basecoat.
Unsound - A term referring to the condition of a plaster
installation whereby the hardened mass has
lost internal strength, exhibiting cracking,
spalling, delamination, etc. This general state
may be contributed to by excessive aggregate
addition, water damage, poor drying
conditions, overwatering and other factors.
V
Veneer Gypsum Base - A special lath four feet (1.22 m) wide and in
various lengths, having blue-tinted face
paper; used as a plaster base for one- and
two-coat veneer plaster application.
Veneer Plaster - A calcined gypsum plaster specially
formulated to provide specific workability,
strength, hardness and abrasion-resistance
characteristics when applied in thin coats
(1/169 nominal) over veneer gypsum base or
other approved base. The term thin-coat
plaster is sometimes used in reference to
veneer plaster.
Vermiculite - See: Aggregate. A micaceous mineral
expanded by heat and used as a lightweight
plastering aggregate.
W
Water of Crystallization - See: Combined Water.
Water-Out - A plaster condition indicative of a poor waterretention
characteristic. When at rest on a
mortar board, the plaster loses or “weeps”
free water in puddles or depressions in the
mass.
Water Retention - The ability or characteristic of a plaster to
retain sufficient water, when applied to an
absorptive surface, to maintain a plastic
workable state under the trowel for ease of
application.
Weeping - See: Water-Out.
White Coat - A gauged lime putty finish plaster or, more
generally, any white finish plaster coat.
Wood Fiber - See: Aggregate.
Wood Fiber Plaster - A mill-prepared gypsum plaster formulated
with shredded or ground-wood fiber; usually
used as a scratch coat over expanded metal
lath.
Workability - A general term encompassing the
performance of a plaster mortar under the
trowel in terms of spread, plasticity and slip.
Working Life - See: Open Time.
X
X-Ray Plaster - A gypsum plaster specially formulated for use
in construction wherever x-ray equipment is
installed
Are we missing any terms?