Membership Directory & Resource Guide - 2018 - 22

d micro-cracks. There is a special
TECHNICAL BULLETIN NO. 3 * 2016 * pg 2 of 4
sition Zone (ITZ). These ITZ's exist
nder and the aggregates; ITZ's also exist at the interface of the
und lights and/or PVC pipes and other dissimilar materials in the
different from the bulk cement paste
Inherent in cementitious coatings are
For swimming pools, water chemistry plays
nd have a higher water / cement
many
small
void
spaces
and
micro-cracks.
an important role in the life expectancy of a
34
There is a special region in cement/
cementitious coating. It is important that the
aggregate mixtures called the Interfacial
watersurface
chemistry
is maintained to proper industry
of the
Transition Zone (ITZ). These ITZ's exist atCarbonated upper
standards
to
maximize
the long-term durability
cementitious coating
the interface of the cement binder and the
and
aesthetics
of
the
pool's
interior finish.
Swimming Pool Interior Finishes
Chemical Etching Deterioration
Issue No. 3 / PG 3 of 5
(dark& area)
aggregates; ITZ's also exist at the interface
of the cement binder to the tile, around
However,
a cementitious
finish's
overall
For swimming pools,
water chemistry
plays an importantinterior
role in the life
expectancy
of a
lights and/or PVC pipes and other dissimilar
coating.
It is important
that
the water
chemistry is maintained
to proper industry
Small cementitious
micro cracks
filled with
lifemainly
expectancy
can
be severely
reduced
standards
to maximize the
long-term
durability and aesthetics of the pool's interior finish.
materials in the plaster. The chemical andcalcium
hydroxide
(lighter
areas)
whenever
water
is allowed to be in an aggressive
interior finish's overall life expectancy can be severely reduced whenever
physical properties in the ITZ's are different However, a cementitious
condition for extended periods of time. The
water is allowed to be in an aggressive condition for extended periods of time. The term
from the bulk cement paste in that they
term
water"
is considered
to be
"aggressive pool
water""aggressive
is considered to bepool
water that
is chemically
outside of established
contain significant amounts of calcium
balanced ranges.
This
aggressive
water
is
capable
of
removing,
dissolving,
or
otherwise
reacting
that is chemically outside of established
Sand /water
Aggregate
of the surfaceparticles
materials causing accelerated deterioration. This would include
hydroxide and have a higher water / cementwith components
ranges.
aggressive
water
is
water that has balanced
low calcium hardness,
low pH,This
low carbonate
alkalinity, and/or
a combined
of
ratio and greater porosity.3 4
these.5
capable of removing, dissolving, or otherwise

Swimming Pool Interior Finishes & Chemical Etching Deterioration

Issue No. 3 / PG 2 of 5

HAND
TROWELED
SURFACE
BULK MATRIX

Reactions with the soluble cementitious materials can take place whenever water, or moisture, is

allowed
permeate
through
a cementitious
surface coating.
Water
that is not maintained in the
Inherent in cementitious coatings are many small
voidtospaces
and
micro-cracks.
There
is a of
special
reacting
with
components
the surface
6
ranges," Transition
as defined by ANSI/APSP
to beThese
"balanced"
, can
deteriorate a cementitious surface
region in cement/aggregate mixtures called the "ideal
Interfacial
Zone
(ITZ).
ITZ's
exist
materials causing accelerated deterioration.
coating by dissolving components of the cement/aggregate matrix, resulting in the leaching of
at the interface of the cement binder and the aggregates;
ITZ's
exist
at the
interface
of
thehas
cement compounds.
Leaching
generally
appears
as etched
areas
on thelow
surface,
especially where
Thisalso
would
include
water
that
calcium
calcium
hydroxide
is
most
abundant.
Calcium
hydroxide
is
the
most soluble cement compound and
cement binder to the tile, around lights and/or PVC pipes and
other
dissimilar
materials
in
the
hardness, low pH, low carbonate alkalinity, and/
the first compound to be dissolved.
plaster. The chemical and physical properties inisthe
ITZ's are
from the
bulk cement
paste
5
or different
a combined
of these.
etched areasand
are around
inserts and other interfaces and often
that they contain significant
amounts of calcium
haveaggregate
a higherparticles,
watertile
/ cement
NPC online.org in
· mail@npconline.org
· ph: 847.416.7272
·These
fx: hydroxide
847.526.3993
appear as small spots. As with all chemical or physical action on a surface that is capable of
34
ratio and greater
porosity.
· 1000
N. Rand Road · Suite 214removing
· Wauconda,
60084
or dissolvingIllinois
away elements
or compounds of that surface, water chemistry will play a
key role in the etching process. Low calcium hardness, low carbonate alkalinity, and/or low pH
Carbonated
upperinsurface
thethe greatest solubility
create an aggressive environment that
will lead to etching
the areasof
with
and porosity such as in the ITZ's. Continued leaching
can cause complete
dissolution of the cement
cementitious
coating
paste over time in those regions of the coating.7
(dark area)

Technical Bulletins

Small micro cracks mainly filled with

NPC online.org · mail@npconline.org · ph: 847.416.7272 · fx: 847.526.3993
calcium· hydroxide
areas)
THE NATIONAL PLASTERERS COUNCIL
1000 N. Rand(lighter
Road · Suite
214 · Wauconda, Illinois 60084

Sand / Aggregate particles

NPC MEMBERSHIP DIRECTORY & RESOURCE GUIDE

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