Membership Directory & Resource Guide - 2018 - 32

TECHNICAL BULLETIN NO.5, 2018 * pg 3 of 4

Plastering contractors and designers rely on careful selection of materials
and Plastering
attention tocontractors
mixing andand
placement
details
to achieve
eye-catching
finishes.
designers
rely on
careful selection
of materials
and attention to mixing and placement details to achieve eye-catching finishes.

Cement Hydration and Color
Cement
Hydration
As explained
above, and
whiteColor
cements are white because they have very low ferrite contents. In any cement the ferrite
As explained
white
cements
areinwhite
they have
very low
ferrite
any cement
the ferrite
phases
(C4 AF)above,
normally
become
lighter
colorbecause
as the cement
chemically
reacts
withcontents.
water, a In
process
called hydration.
phases
(C
AF)
normally
become
lighter
in
color
as
the
cement
chemically
reacts
with
water,
a
process
called
hydration.
Accelerators
are used to speed up hydration in concrete mixes placed during cold weather. One common accelerator,
4
Accelerators
are used
up hydration
concrete
mixes placed
during cold weather.
One common
accelerator,
calcium
chloride
(CaClto
), speed
has a retarding
effectinon
the hydration
of the ferrite-containing
compound
C4AF. When
CaCl2
2
calcium
(CaCl2),concrete
has a retarding
effecthydration
on the hydration
of thephases
ferrite-containing
compound
AF. When
CaCl2
is
addedchloride
to gray cement
it will retard
of the ferrite
which may remain
dark Ccolored
(Greening
4
is added
to gray
cement
it will retard
hydration
of the
may remain
dark There
coloredis (Greening
and
Landgren
1966).
Thisconcrete
effect associated
with
CaCl2 does
notferrite
applyphases
to whitewhich
cement-based
mixes.
very little
does not apply to white cement-based mixes. There is very little
and
1966). due
Thistoeffect
associated
CaClto
risk Landgren
of discoloration
adding
calcium with
chloride
2 white cement-based materials/mixtures because white cement
risk of discoloration
due toResearch
adding calcium
chloride
white
cement-based
materials/mixtures
whitehas
cement
contains
almost no ferrite.
associated
with Cto4AF
discoloration
by the
Portland Cementbecause
Association
been
contains
almost no
Research
C4AF discoloration
by the Portland Cement Association has been
done
exclusively
on ferrite.
gray cement
and associated
is discussedwith
in several
of their publications.
done exclusively on gray cement and is discussed in several of their publications.
Using white cement for various applications is the topic of PCA publications WC001, WC002, and WC003.
Using white cement for various applications is the topic of PCA publications WC001, WC002, and WC003.

NPC MEMBERSHIP DIRECTORY & RESOURCE GUIDE

Technical Bulletins

PRACTICE AND MATERIALS UNIQUE TO THE PLASTERING TRADE
PRACTICE AND MATERIALS UNIQUE TO THE PLASTERING TRADE
Supplementary Mix Water
Supplementary
Mix Water
The
process of adding
supplementary water above mix design water is used to combat substrate absorption and
The process Thicker
of adding
supplementary
water
above amix
designofwater
usedthin
to cementitious
combat substrate
absorption
and
evaporation.
materials
like concrete
maintain
reservoir
water,iswhile
coatings
do not. This
evaporation.
like concrete
maintain
reservoir
water,
thin from
cementitious
coatings
not. This
extra water isThicker
not partmaterials
of the design
water:cement
(w/c)aratio,
and isofused
up while
(removed
the system)
duringdoapplication
extra
watertoisfinal
not set.
part1 of the design water:cement (w/c) ratio, and is used up (removed from the system) during application
and prior
and prior to final set.1

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