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Proceedmgs
PRO 78
Historic Mortars and
RILEM
TC
203-RHM
Final
Workshop
HMC2010
Proceedings
of the
2"'^
Conference
and
of
the
Final
Workshop
of
RILEM
TC 203-RHM
Edited by J.
Valek.
C. Groot. J. J.
Hughes
RILEM
Publications
S.A.R
L.
2"
Historic Mortars Conference and
RILEM
TC
203-RHM
Final
Workshop
HMC2010
22-24
September
2010
Prague, Czech Republic
Historic
Mortars Conference
HMC2010
and
RILEM
TC
203-RHM
Final
Workshop
22-24 September
2010,
Prague,
Czech Republic
IV.18
Two
Views to
Deal
with
Rain
Penetration
Problems
in
Historic
Fired
Clay
Brick
Masonry
Caspar
Groot'
and Jos
Gunneweg'
'
Delft
University
ofTechnology,
The Netherlands,
c.j.w.p.groot@tudelft.nl,
j
.gunneweg@hetnet.nl
Abstract
In this
paper
a comparison is
made
between two views to solve
rain
penetration problems in
solid
historic
fired
clay
brick
inasonry.
The
first
one aims
at protecting the masonry against
rain
penetration ("rain coat" concept). In the
second approach the penetration of
rain
in the masonry is accepted and the
measures
taken are focused on
improving
the
capillary
moistine
transport in the
masonry and on the application of materials
with
favourable
drying
characteristics
and/or the
enhancement
of the
drying
conditions ("breathing" concept). It is
shown
that the
often
preferred protection approach may result
into
deterioration of
the
rain
penetration problem instead of
diminishing
it.
Also
is shown that the
second approach generally
leads
to a significant
drying
of the
walls,
thus
providing
a sound
solution
for
rain
penetration problems in
solid
historic
fired
clay
brick
masonry.
1
Introduction
Water
leakage in historic
solid
masonry walls regularly occurs and is a major
somce
of
damage:
in masonry it
causes
frost and salt
damage;
in timber it may
lead
to rot. Moreover,
humidity
may
have
negative effects on the
living
conditions
in
historic
buildings.
From
practical experience and
from
the
literatine
[1-3] various
causes
for
moisture
problems
like
leaking can be deduced:
•
inadequate material properties of the apphed
fired
clay
brick
and masonry
mortar;
incompatibility
between
brick
and mortar properties
•
cracks in masonry
•
inadequate design
•
poor
ventilation
•
negative effects of a
nmnber
of inadequate restoration
measmes
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•
poor workmanship
ofthe
builders during construction and/or restoration
This
paper
is
based
on a study of
rain
leakage
problems studied in particular in
historic
masonry of wmd
mills
in the west of the Netherlands.
These
are ideal
objects for such a study as
wind
mills
are intentionally exposed to
wind
and
rain
(to
opthnize
their
flinctionality)
and often show
leakage
problems. The problems
observed in this study are
also
applicable to historic
solid
masomy of towers,
chinches,
castles
etc.
Before
discussing the different
measines
that may be taken to solve
leakage
problems
some
flnther
thought is given to
different
types of moisture transport in
solid
masonry.
2
Rain penetration and porosity
Brick
and mortar are porous media,
which
means
that
moistirre
absorption in
these
materials is governed by capillary action and
drying
by evaporation. For the
separate
materials moisture transport is
easy
to understand, for the composite
material
masonry
this is more complicated.
Capillary
water transport
Optimal
contact between mortar and
brick
is the result of
(i)
the correct choice
of
brick
and mortar
(compatibility)
allowing
the
formation
of a
dense
mortar-brick
interface and (ii) the
skill
of the mason: the
brick
should be
fiilly
surroimded
by
mortar (no cavities). Under
these
conditions, the two capillary
systems
of
brick
and mortar are smoothly connected.
Moisture
transport
from
mortar to
brick
and vice
versa
are
dependent
on
differences in pore dimensions and pore distributions of the two
separate
materials. The transport of moisture
from
brick
to mortar may be hindered if the
porosity
of the mortar is much
finer
than that of the
brick:
in that
case
the mortar
acts
as a barrier and slows down or even
stops
moisture transport through the
masonry.
Liquid
moistine
transport may take place in the
case
of
coimected
capillary
pore
systems
as a result of
pressure
differences (e.g.
wind
pressme,
drying,
ventilation)
if
the moisture content in
brick
and mortar are higher than the
critical
moisture content (at the
critical
moisture content the capillaries are covered by a
thin
layer
of
water).
This may lead to leakage.
"Free
water transport"
Apart
from
capillary action (in fact moistme transport through capillary
pores
of
porous materials) moisture transport can as
well
occm as a
form
of
"free"
water
transport.
With
this is meant water that travels through a
wall
along
"canals"
formed
by interconnected fissures, hollows, cavities, cracks etc. ("canal" porosity
more than 100pm in diameter).
Pressme
differences, especially
wind
pressure
do
1006
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have
a significant effect on the
moistine
transport
velocity
for this type of
porosity:
water may pour out
ofthe
wall
as
a
jet of water.
This
is a far more
imfavorable
condition for leakage than capillary
moistine
transport: as the capillary water transport
velocity
is much slower than the "free"
water transport
velocity
It
seems
obvious that creating or reinstating conditions of capillary water
transport (by
filling
up the cavities) may
significantly
improve the water tightness
behavior of the
wall.
Grout
injection
may be the proper way to realize this
change
in water transport
behavior in a
wall.
3
Two
views to solve water leakage problems
Basically
to solve leakage problems in sohd masonry two different ways of
approach are applied. The
fnrst
one
ahns
at protecting the masonry against
rain
penetration ("rain
coaf
concept). In the second approach the penetration of
rain
in
the masonry is accepted and the
measmes
taken are focused on (i) if
necessary,
improving
the
capillary
moisture transport in the masonry (ii) the application of
materials
with
favourable
drying
characterisfics
and/or
(iii)
the
enhancement
of
the
drying
conditions, e.g. improvement
ventilation
("breathing" concept).
The potential and
limitations
ofboth
views are discussed hereafter.
3.1 Protection against rain penetration
In
case
of leakage the
inost
logical
and promising way to solve this problem
seems
to be, the protection of the masonry
from
the penetration of
raui
(rain
coat
solution).
In practice a number of solutions are applied in
which
this approach is
chosen, such as the application of
•
render
•
tar
•
thatch on masonry
•
tiles
•
ivy
•
etc
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tiles
ferrocement
Fig.
1 Examples
of
protection
measures
against
rain
water leakage
Apart
from
protecting the underlying masonry agamst
rain
penetration
these
solutions
have the disadvantage that they
significantly
alter the visual
appearance
of
the object. This is often unacceptable if the structure has a
cultural
heritage
value.
Water
repellent
In
that
case
protection against
rain
penetration is often headed for by the
application
of
water repellents, as they are transparent. The assumption then is that
the application
of
water repellent
causes
(i)
rain
water to be warded
off
and
(ii)
the
wall
to be dryer and dryer in the
comse
of
time.
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before after
Fig.
2 Idealized graphic presentation
of
the
effect
of
a
water repellent [5]
Fig.
2 shows that the water repellent
coats
the
pores
and
penetrates
for
some
mms in the
wall
and allows vapor transport after application
of
the water repellent.
The graph idealizes
drying
as
only
vapor transport,
which
is not hindered by the
water repellent. In most
cases
also
liquid
transport plays a role. Water is then
stopped by the water repellent and
only
can evaporate
from
the
pores
some
mm's
withm
the
wall:
a slow
process
(see Figs. 2 and 3).
Influence
water
repellent
on
drying
1S50-I
,
1650
I
. ,
1
0 1 00 200
300
400
Time
(h)
Fig.
3 The application of
a
water repellent
significantly
slows down the
drying
of
a
wall.
Inspection
of more than 25 masonry
wind
mills,
where water repellents were
applied,
showed that the leaking problems in
stead
of diminishing always
increased. An important
reason
is that
wind
mills
may develop micro-cracks in the
masonry as a result of the heavy dynamic oscillations of the sails.
So
rain
water may enter through
these
micro-cracks in the
wall
instead
of
being
warded off.
Also
other moisture
soturces
like
occasional
floodmg,
continuous
rising
damp, recurrent inside condensation and hygroscopic
moistiire
uptake may
be
causes
of moisture absorption into the
wall.
With
moisture
niside
the
wall
the
1009
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2010,
Prague, Czech Republic
applied
water repellent turns out to be a disadvantage as
aheady
shown:
drying
is
significantly
slowed down.
There is as
well
another strong motive to
refi-ain
from
the application of water
repellents in the
case
of historic masonry. The reason is fhat very often historic
masonry contains salts.
Drying
leading to salt crystallization just under the
repellent
layer may
cause
substantial
damage
(see
Fig.
4)
Fig.
4 Salt
damage
as a result
of
the
application
of
a
water repellent
It
can be concluded that protection against
rain
penetration ("rain coat"
concept) may be rather
tricky:
one should be
well
aware
of
possible other moisture
sources
(which
may be
imavoidable)
and as
weU
take
into
account possible side
effects.
3.2 Accept rain penetration and focus
on the
realisation
of
capillary moisture transport
in the
masonry
and
enhance
drying
Intuitively
this
view
("breathing" concept)
seems
to be
less
promising as the
promotion
of
drying
is normally aimed at through materials
which
as
well
significantly
absorb moisture.
However
as
well
the
following
should be considered:
•
if the water leaking is
caused
by "free water tiansport"
measures
taken (e.g.
injection)
to
create
or reinstate
capillary
moishure
transport have the
effect
that
the moisture transport
significantly
slows down. Experience has learned that
well-made
solid
masonry, having capillary moisture transport, generaUy is
water
tight.
•
in sound masonry the mortar
acts
as a barrier; and as been shown in [6], the
penetration of
rain
water in the
wall
dming
a shower is
limited
to a depth of 1.5
brick
length; more water
will
drain
from
the outer face of the
wall;
so, the
amoimt
of absorbed water is
limited.
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•
In the Netherlands 1 hour of
rain
shower is counter balanced by
15
hours of
drying.
Case:
rain
penetration problems in the
Windmill
at Maassluis
In
a number of
consulting
projects this
view
has
been
chosen as a guidance to
solve
rain
penetration problems; this
appeared
to be successful. One of the
cases
the
windmill
at Maassluis showing serious
rain
penetration problems.
Will
be
elaborated.
Starting
conditions
The starting conditions of the masonry were as indicated in Fig. 5. From this
figure
can be deduced that an attempt was
made
to protect the
wall
against
moisture
penetration: at the outside face of the
wind
mill
a water repellent was
applied;
the repointing consisted of a
dense
cement mortar, showing interface
micro-cracks
as a result of shrinkage, at the inner face a
dense
cement plaster.
water
repellent
dense
cement
plaster
outside
J
^'—~
inside
Fig.
5
Cross
section
ofthe
v/ind
mill
wall
before
intervention:
at the outside face a water
repellent
was applied, at the inside a
dense
cement plaster, the
pointing
consisted
ofa
dense
cement mortar.
It
is clear that if the
wall
absorbs
through e.g. micro-cracks moisture, this
moisbne
is more or
less
entrapped as
drying
is hindered at the inside face and is
very
slow at the outside face.
In
order to obtain
data
on the
moishire
content situation in the
wall
moisture
profiles
were determined at two
places
in the
wind
mill
waU,
using powder
samples.
Fig.
6 shows that the moisture content in the
wall,
in spite of the protecting
measures
(water repellent,
dense
plaster layer) is very
high.
1011
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Moisture
Profiles
Maassluis
30
T
O-I
^ ^ : .
1
2,5 7,5 12,5 17,5 22,5
wall
depth
(cm)
from
interior
to
exterior
Fig.
6
Moisture
content
profdes
at the south-west side
(rain
side) and the north-east
of
the
wind
mill
wall
[7].
Drying
measures
In
a
process
of more than 2
years
measures
were taken to
change
the situation
from
moistiue
absorbing to
drying;
to this end the
following
was done:
•
removal
of
the plaster
•
2
years
of
drying
•
meanwhile,
o application
ofa
simple
ventilation
system inside de
wind
mill
o removal of
pointing
mortar and replacement by an open good
drying
mortar, compatible to the
substrate
•
After
2 years: apphcation of a new restoration plaster
with
high
porosity and
good
drying
properties.
Monitoring
moisture content over the years in
wall
of wind
mill
wall
at
Maassluis
In
order to
verify
the effectiveness of r the
measures
taken were moisture
content
measurements
were performed over the years. To this end a
TRIME
sensor
was used
[8].
The
TRIME
technique
(Time
Domaine Reflectometry
with
Intelligent
Micromodule
Elements)
enables
the measurement of a
reflection
of a pulse that
travels in a
material.
Instrumental to the
introduction
of the pulse
into
the material
are two
antennas
at the side of the probe
(Fig.
7).
These
anteimas
are by
means
of
expansion
sprhigs
in contact
with
a tube that is glued to the material.
The
travelling
time of the pulse up and down the conduction rods and
into
the
material
provides
information
about the
presence
of water in the material, as the
travelling
time is a
fiinction
of
dielectric
properties
of
the material.
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The tube
remahis
m the
wall;
the
moistiure
content in the
wall
is monitored by
taking
measurements
from
time to time in the course
ofthe
years.
^
DhinetGi
specimen
12
cm
^
22.5
mm
Fig.
7
Left:
graphic presentation
of
TRIME
sensor
The
measurements
showed that a significant
drying
of the
wall
took place in
the
cotuse
of a period of several years.
Monitoring
moisture
content
wall
windmill
at
Maassluis
25
I
O-I
^ , ,
1
2002 2004 2006 2008 2010
time
[in
years]
Fig.
8
Drying
over the period
2002-2010,
monitored
using a
TRIME
sensor.
1013
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4
Conclusions
From
study
of
field
cases
and the
execution
of
several
test
cases
the following
could be
concluded:
Protection
against
rain
penetration
("rain
coat"
concept)
Many
meastues
(render,
tar,
thatch,
tiles, ivy etc) to
realize
the "rain
coat"
concept
are not
suitable
in
cases
of historic
masonry
where
change
of visual
appearance
is not
acceptable.
Protection
of the
outside
face
of the
masomy
by a
transparent
water
repeUent
and a
dense
plaster
on the
inside
has often
unexpectedly
resulted
in a significant
increase
of
moistme
in the wall.
Specifically in historic
masonry
possible
salt
damage
as a
result
of the
application of
water
repellent
should
be
considered.
Accepting
rain
penetration,
promoting
drying
("breathing"
concept)
In
the
"breathing"
concept
rain
penetration
is
accepted
and drying is
aimed
at
through
the
skilflil
application of
materials
with
good
drying
characteristics
and
improving drying
conditions
(ventilation). A
basic
condition is
that
there
is
capillary
moisture
transport
(preliminary injection may be
needed).
It
was
proven
in
test
cases
that
this
approach
resulted
in a significant drying of
walls;
even
in
case
the
outside
face
of the
wall
still
contained
water
repellent
and
only the pointing was
replaced
by
adequate
good
drying repointing
material
and
at the
inside
of the
wall
the
dense
plaster
was
replaced
by high
porous
restoration
plaster.
5
References
1.
Grimm
CT (1982) Water
permeance
of
Masonry
Walls:
A Review
of
the Literature, in
Masonry: Materials,
Properties
and Performance,
ASTM
STP 778, J.G. Borchelt ed.,
American
Society for testing and Materials, pp.
178-199
2.
Ramamurthy
K,
Anand
KB
(2001) Classification of Water Permeation
Studies
on Masonry,
Masonry Intemational,
Vol.
14, No 3, pp.74-79
3. Thomas K (1996) Masonry
Walls,
Butterworth-Heinemann
Ltd,
Oxford,
Chapter
: Rain
penetration,
dampness
and remedial
measures,
pp.
144-159
4.
Sass
O,
Viles
HA (2010) 'Wetting and drying of Masonry walls', Joumal
of
Applied
Geophysics,
Vol70,
Issue
1, Jan 2010,
pp.72-83
5. http://www.ervas.nl/?id=254)
6. Groot C, Gunneweg J
(2010)
The Influence of Materials Characteristics and Workmanship
on
Rain Penetration in Historic Fired Clay
Brick
Masonry,Heron,
in prep.
7. Groot C, Gunneweg J (2002) Wochtproblematiek
stenen
molens' -
TU
Detó
faculteit
CiTG,
Delft
8. Groot CJWP, van
Gaanderen
HJ, Heme S (2001) 'Potential
ofthe
TRIME
Probe
for
the
determination of moisture content
changes
in monuments',
Proceedings
Intemational
Millennium
Congress,
Icomos, Unesco,
Vol.
1-lb,
No. 18
1014