In-situ characterization of efflorescence and other
saline compounds in walls
José Miguel Rodrigues Tuna
Extended Abstract
INTEGRATED MASTERS IN CIVIL ENGINEERING
Supervisors:
Doutora Inês dos Santos Flores Barbosa Colen
Doutor Jorge Manuel Caliço Lopes de Brito
Lisbon, October 2011
In-situ characterization of efflorescence and other compounds in saline walls
1. Introduction
The presence of soluble minerals (salt) is one of the most common anomalies on buildings.
When disregarded, they can produce a negative impact, either esthetical, on the living
conditions or, in the worst case scenario, in the structural performance.
The rehabilitation of walls affected by the presence of salt is frequently problematic. Experience
indicates that interventions only have a temporary effect, as the symptoms of the phenomenon
often reappear after some time.
This thesis aims to improve the understanding of the efflorescence phenomena, as well as
contributing to enrich the knowledge about inspection methodologies used in this type of
anomalies and other saline compounds.
A diagnosis methodology suitable for the various studied cases was defined. The utilization of
different techniques is also considered, in order to increase the quality of the results.
These techniques can be divided in three groups: sensorial analysis, which uses the human
body senses, in-situ assessment techniques, and laboratorial tests. The applicability of the
techniques used and their sensitivity to various factors involved are also studied.
Another goal that this thesis aims to achieve is the association of different types of
efflorescence with the corresponding causes, which may lead to more efficient inspections and
rehabilitation methodologies.
2. Efflorescence characterization
There are two distinct groups of anomalies due to the presence of salt: efflorescences and
subflorescences. The first group is usually related to the constant presence of humidity and
esthetic problems on the walls (Rodrigues and Gonçalves, 2005).
The subflorescences originate peeling and detachment of plaster fragments, leading to its
rupture. In some cases, where the anomaly reached an advanced stage, and especially in old
buildings, the degradation leads to structural problems. This fact is due to the construction
process and materials used in it: these buildings are usually erected by solid walls of great
thickness, with porous and hydrophilic materials that enable the rise of capillarity water from the
ground. In most of the cases these two types of phenomena occur simultaneously (Gonçalves
and Rodrigues, 2005).
The degradation process associated with subflorescences is often related to the increase and
decrease of salt´s volume within the pores. This increase is due to the stages of hydration /
dehydration and crystallization / re-crystallization of those minerals.
There are several types of mechanisms that enable the development of efflorescences.
According to the authors’ experience, the presence of a specific type of salt is related to its
origin. It is, therefore, easier to determine the efflorescence’s origin and immediately act on the
1
Extend Abstract
source of contamination, instead of resorting to more accurate methods.
3. Experimental work’s methodology
Experimental tests were carried out in 10 different case studies. The diagnosis methodology
proposed in the beginning of the thesis was adapted to the cases throughout the work, when
necessary (Figure 1).
The referred methodology consists of distinct stages.
Initially, an assessment of the building’s general properties is performed: type of utilization,
number of floors (elevated and underground) and type of structure. Then, the building’s
configuration in plan is sketch, as well as its orientation. It is also important to register the
building’s distance from the sea, the environment to which it is exposed, the type of soil, the
presence of vegetation and the groundwater level near the building.
To understand the evolution of the anomalies associated with the efflorescence phenomenon, it
is necessary to inquire the users of these divisions, in order to establish whether the
efflorescence’s size increases or decreases depending on the weather, and when its presence
was detected for the first time.
The next step consists of a sensorial analysis of the anomaly, where all of its aspects are
described and several photos of the phenomenon and its localization are taken. It is important
to visualize the anomaly and its surroundings first, and then register
the type of coating, the
substrate and the area of the wall where the efflorescence is located. The color, size, flavour,
texture, wall’s humidity, and in some cases, the smell, are properties that should also be
registered.
Two or three different samples of the affected areas should be collected, using independent
laboratorial tagged bags. The samples are afterwards analyzed with the field kit and colorimetric
strips. These tests measure the concentration of chloride, nitrate and sulfate ions present in the
different samples, providing the results in milligrams of ion per liter (mg/L). If these tests
manage to determine the types of efflorescence and the causes for its appearance, a report is
prepared and an intervention methodology is proposed.
The last step of the diagnosis methodology consists of the execution of laboratorial tests that
present high reliability, when necessary, despite their elevated costs when compared to the insitu techniques.
Parallel to the experimental work, standard solutions with the desired concentration of chloride,
nitrate and sulfate ions were prepared, in order to assess the quality of the results of the tests
performed with the field kit and the colorimetric strips. These solutions were produced using salt
samples, which were afterwards dissolved in pure water, resulting in solutions with known
concentrations. Six solutions were prepared (two for each type of ion) with different
concentrations.
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In-situ characterization of efflorescence and other compounds in saline walls
Choose the place to
inspect
Record all the information about the
anomaly, including its evolution and
possible causes identified by the user
Photographic record
Sensorial analysis:

sight

touch

smell

taste

hearing
Sample collection
In-situ analysis:
Conclusion about the type of efflorescence

colorimetric strips

field kit
No
Yes
Laboratorial Techniques:
Report

XRD

XRF (confirms in-situ
analysis results)

FTIR (if XRD is not possible)
Conclusion about the type of efflorescence
Yes
No
Report and intervention
New analysis
proposal
Figure 1 – Flowchart illustrating the diagnosis methodology applied on the efflorescence’s assessment
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Extend Abstract
4. Results
The experimental tests enabled the gathering of enough information on the use of the various
techniques proposed in the diagnosis methodology, thus helping to deepen the existing
knowledge in this area. In several case studies, in addition to the sensorial analysis of
anomalies, 17 different samples were collected. The total of walls analyzed presented obvious
signs of degradation associated with the presence of salts. During the assessment based on the
in-situ techniques (using the field kit and colorimetric strips), 116 samples were analyzed.
Laboratorial tests were performed on another 35 samples, adding to a total of 151 analyses.
4.1. Case study example
This case study is located in Torres Novas, on a multi-storey building of two floors (Figure 2).
The anomaly is located on the first floor, next to a window (Figure 3).
Figure 2 – Exterior photograph of the building (the
anomaly is identified by the red circumference)
Figure 3 – Interior Photograph of the Anomaly
Being built around the 1960’s, the structure had to suffer some repairs to ensure a desirable
service performance. The initial structure featured thick stone walls, which proved to be very
porous and permeable.
According to the owner, the building was subjected to some repairs in 2002. Approximately 3
years after this intervention, the presence of efflorescence was noticed. This anomaly was only
visible in one of the interior walls, which indicates that it is a localized anomaly.
During the repair of the building, the walls’ thickness was reduced, and some openings were
created to build windows. This situation may have enabled the beginning of the phenomenon.
After the detection of the anomaly, an inspection form was completed with the owner’s help,
where the general condition of the building and the anomaly itself were carefully examined.
Several pictures were taken and two samples were collected: one picture featuring the fluffy
efflorescence (Figure 4) and the other illustrating the plaster affected by the presence of salts
(Figure 5).
A sensorial analysis was carried out on site, where a characteristic smell was not detected. It
was verified that the efflorescence had a fluffy texture and white color. This aspect is enhanced
by the fact that the salt was on its hydrated phase, which implies bigger volume. The presence
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In-situ characterization of efflorescence and other compounds in saline walls
of moisture was not detected by touching, although, given the rotten of the skirting board, it was
reasonable to assume the existence of moisture where the anomaly was first detected.
Figure 4 – Sample 1 (fluffy efflorescence)
Figure 5 – Sample 2 (salt affected plaster)
The samples were analyzed applying the colorimetric strips and the field kit, in order to quantify
the presence of chloride, nitrate and sulfate ions. The results are presented in Table 1.
Table 1 – Results of the analysis carried out on the two samples, using colorimetric strips and the field kit
Chloride
Sample 1 – fluffy
colorimetric strips
(mg/kg)
efflorescence
field kit
(mg/kg)
colorimetric strips
(mg/kg)
0
267,5
0
Sulfate
> 40 000
Nitrate
12 500
7300
3475
> 80 000
10 000
12 700
830
Sample 2 - plaster
field kit
(mg/kg)
2500
After the sensorial analysis, it was not possible to distinguish the type of salt present in the wall,
so further tests were needed. The tests using the kit and strips, as exposed on table 1, showed
a high amount of sulfate ions, followed by a smaller amount of nitrate ions and an even smaller
quantity of chloride ions.
Even though there was no complete convergence between the results of the tests carried out
with the strips and the kit, it was concluded that sulfate and nitrate ions, in the first sample, and
the sulfate and chloride ions, in the second, were the main problem.
Flores-Colen (2009) established concentration limits for nitrate, sulfate and chloride ions for
samples of plaster. It is only possible to compare these values with the results of sample 2,
because sample 1 is composed only by pure efflorescence, resulting in higher concentrations.
For sulfate ions, all values superior to 5 000 mg of ion per kg of mortar are defined as an
unfavorable concentration. For chloride ions, the same limit is defined as 300 mg / kg, and 500
mg / kg for nitrate ions. A careful analysis of the results for sample 2 revealed that they were in
the unfavorable interval. The situation was expected, since the wall presented high degradation,
according to visual observation.
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Extend Abstract
In order to confirm the results obtained using the field kit and the colorimetric strips,
complementary tests were performed using the X-Ray Fluorescence (XRF), the Fourrier
Tansform InfraRed (FTIR) and the X-Ray diffraction (XRD) tests. The results are presented in
Table 2.
Table 2 - XRF, FTIR and XRD test results for samples 1 and 2 results (fluffy efflorescence and plaster
respectively)
Results
XRF
Sample 1 efflorescence
Sample 2 plaster
FTIR
Potassium (K) ++
Polyhalite
K2 Ca2 Mg [SO4]4 . 2H2O
Calcium (Ca) +
Calcite CaCO3
Syngenite
Calcite
K2 Ca [SO4]2 . 2H2O
CaCO3
XRF
Potassium (K) -
Magnesium (Mg) +
Gypsum
Ca SO4 . 2H2O
Sulfur (S) ++
Sodium (Na) -
Niter KNO3
Polyhalite
Niter KNO3
XRD
Sulfur (S) ++
K2 Ca2 Mg [SO4]4 . 2H2O
XRD
FTIR
Magnesium (Mg) +
Chloride (Cl) -
Calcite CaCO3
Gypsum
Ca SO4 . 2H2O
Aphthitalite
K3 Na (SO4)2
Calcium (Ca) ++
Niter KNO3
Calcite CaCO3
Caption: ++ very high concentration; + high concentration; - low concentration.
In what concerns the results obtained with XRF, the table presents only the atoms that may be
related to the presence of efflorescence, excluding therefore atoms that appeared on the
sample, such as titanium. This atom was found in most samples, but was excluded as it is one
of the constituents of ordinary ink.
XRF analysis of sample 1 detected a high level of potassium atoms. This technique does not
identify the atoms of nitrogen (N), which correspond to the nitrate ions found in the field kit’s
results. It was also detected a high level of sulfur atoms in both the kit and the strips’ analysis.
In sample 1, various substances were detected, both by XRD and FTIR analysis, in which the
sulfate group was present. This fact reflects the ease with which the sulfate ions are grouped to
others, when in an aqueous solution. The substances present in the samples show a very
complex composition. It is difficult to determine the genesis of these compounds, but it is known
that the presence of sulfate ions in those is often related to the use of Portland cement used in
the mortar, as stated by Bianchin (1999), citing Uemoto (1984).
The XRF analysis of sample 2 confirmed the results of the tests carried out using the kit and
strips. In this case, the high intensity of the reflection of the sulfur corresponds to the highest
concentration of sulfate ions. On the other hand, the lower intensity of the chlorine atoms
matches the lowest quantity of chloride ions, as confirmed by the in-situ analysis (Figure 6).
In sample 2 the substances found using the XRD analysis were potassium nitrate, calcite and
gypsum (Figure 7). The latter compound was the only one that wasn’t found in sample 1, due to
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In-situ characterization of efflorescence and other compounds in saline walls
the fact that it is mainly composed by pure efflorescence, contrary to sample 2, which features a
considerable percentage of plaster.
Figure 6 - Graph representing intensity peaks of calcium, magnesium, chlorine, potassium and sulfur
atoms of a plaster’s sample analyzed by XRF
The intensity peaks are indicators of the concentration of each mineral in the sample. However,
it is not possible to obtain absolute indicators, because each mineral responds differently to the
XRD. Therefore, it is concluded that getting a higher percentage of a mineral does not mean
that the sample has more quantity of that mineral, but only that it presents a more intense
reflection than the other when subjected to X-Ray diffraction.
Figure 7 - Graph representing intensity peaks of compounds in plaster sample analyzed by XRD
In many cases, the origin of the substances with high concentration of nitrate ions is due to the
rise of capillary water derived from soil contaminated by animal’s droppings or manure’s
fertilizers (Freitas, 1992). In this case, the referred situation is not likely to happen, as the
efflorescence is located on the first floor wall, and no kind of contamination was found below the
place where the samples were collected.
Analyzing the in-situ analysis’ results, it is concluded that the detected efflorescence is mainly
composed of sulfate and nitrate ions. Laboratorial tests verified that potassium nitrate, hydrated
potassium calcium magnesium sulfate, syngenite, calcite and potassium sodium sulfate are the
efflorescence´s compounds. All of the substances, except potassium nitrate and calcite, are
7
Extend Abstract
composed by the sulfate group that, by linking with other groups, presents itself in various forms
of salt.

Causes for the anomaly
The appearance of efflorescence with high concentration of sulfate ions may be related to a
high quantity of Portland cement in the mortar’s composition, used in the plaster. It is also
plausible that the mortar applied to the plaster had sand contaminated with animals’ droppings
in its composition. However, the main cause for the appearance of the efflorescence is,
probably, the infiltration of water from the outside wall.

Eliminate the causes and repair
All of the visibly affected plaster and surrounding area must be removed. It is also necessary to
verify if the masonry is affected by the presence of salt. If so, it must be replaced. An insulating
layer should be placed on the wall, eliminating any kind of moisture’s leakage. A fresh coat of
plaster should also be applied, with a lower percentage of Portland cement. Special caution is
required when choosing the materials used in the new mortar’s preparation.
The plaster used on the repair of the walls should allow the accumulation of salts in its interior,
and be composed of at least two layers: an interior layer, featuring a large number of macro
pores, and an exterior layer, which prevents the passage of water in liquid phase, but enables
the passage of steam. The wall should be painted with paint that allows the passage of steam.
5. Conclusions
When performing the analysis to the different cases, it was verified that the inquiry made to the
user was of great relevance. The approach must be meticulous and accurate, as the information
gathered might lead to a more rigorous analysis of the anomalies and its causes.
The sensorial analysis performed to different anomalies showed that certain characteristics
occur in all of the cases that featured the same type of compounds. For instance, the cases in
which the efflorescence is composed of sodium sulfate, the wall evidenced a salty taste, a white
fluffy texture and a high volume, if the inspection was performed during its hydrated phase.
This analysis depends deeply on the user’s experience, and lacks in precision, and therefore
must serve only as an accessory to diagnosis. However, when combined with other techniques,
it may contribute strongly to a correct analysis.
The efflorescence’s texture was checked using vision and touch. This is an important aspect in
the saline compounds’ assessment, particularly in the treatment and cleaning of the anomalies.
Touch and hearing are the senses commonly used to confirm the presence of hollow walls.
These senses are, therefore, used to diagnose presence of subflorescences.
The olfactory assessment performed in the various cases only revealed useful in one. A strong
odor of sewage was detected at the entrance of the building, and confirmed later using other
test methods.
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In-situ characterization of efflorescence and other compounds in saline walls
When applying the colorimetric strips to analyze the presence of chloride ions, only in one
sample that presence was detected. This fact is due to the wide range presented by the first
scale of concentration.
High concentrations of sulfate ions were found on all of the samples analyzed. That fact relates
to the use of cement based mortar in the plaster’s composition, as well as in the majority of
mortars used in construction.
Relatively to nitrate ions, there is a wide variation on the concentration of these ions in different
samples. In most of the samples tested, only residual presence of that ion was identified.
However, in cases I and X, it was confirmed that the presence of efflorescence was related to
the presence of that ion.
It can be concluded that the in-situ inspection methodologies are reliable in characterizing the
type of ion that is found in greater quantity in a sample. However, when quantifying the ions’
concentration, these tests don’t provide accurate results. This inaccuracy becomes more
evident in low and high concentrations. The first is due to the low solubility, and the second is
due to the fact that it is necessary to perform various dilutions of the solutions, affecting the
results’ quality by increasing the errors.
Tables 3 and 4 summarize the results provided by the most relevant sensorial analysis, the
colorimetric strips and field kit tests, and the XRF, XRD and FTIR.
The results of the tests performed on the mortar samples using field kit and colorimetric strips
were compared with the concentration limits suggested by Flores-Colen (2009), being tagged
with green, orange and red colors, according to the concentration of each ion.
The laboratorial techniques XRF, XRD and FTIR proved to be relevant when assessing the salt
compounds. The XRF analysis was used in order to confirm the results of the colorimetric strips
and field kit tests, since this technique evaluates qualitatively the atoms present in the sample.
This laboratorial test should only be used if it proves to be necessary to confirm the results
given by the in-situ assessment techniques.
When comparing the XRD to the FTIR analysis, it is confirmed that the first one is more effective,
as it identifies a wider range of compounds. Consequently, FTIR analysis was only performed
when the other equipment was unavailable. These tests enable the assessment of the type of
compounds present in a sample. Identifying the samples that are taken for evaluation through
sensorial analysis, it is possible, through laboratorial experiments, to understand which
substances are in excess and which cause degradation of the walls. These tests are particularly
relevant when the in-situ tests prove to be inconclusive about the kind of efflorescence that is
present on the wall.
9
Extend Abstract
Table 3 - Summary of the results provided by sensorial analysis, and in-situ and laboratorial tests
Colorimetric strips (mg/kg)
Field kit (mg/kg)
Sensorial analysis
XRF
-
SO4-
0
> 40 000
Cl
Case I sample 1
efflorescence
Case I sample 2 plaster
Case II sample 1 brick
Case II
White color, salty taste, fluffy
NO3-
12 500
Cl
-
267,5
SO4-
NO3-
7300
3475
texture , rotting wood, peeling paint,
deteriorated plaster
Salty taste, plaster and brick in an
advanced state of degradation
sample 2 plaster
Case III sample 1
efflorescence
Case III sample 2
White color, salty taste, presence of
plaster
moisture in the wall, inflated paint
Case III sample 3
and plaster, fluffy texture
plaster and other
0
> 80 000
10 000
2 500
37 500
< 5 000
2 500
0
> 10 000
500
> 7000
> 9 750
0
> 160 000
0
< 200
0
> 60 000
1 250
0
> 30 000
0
> 20 000
14 250;
12700
2 900;
Na
K; Mg; S; Cl;
Ca
K2 Ca2 Mg [SO4]4 . 2H2O; CaCO3;
KNO3; K2 Ca [SO4]2 . 2H2O; K3 Na
(SO4)2
Ca SO4 . 2H2O; CaCO3; KNO3
Cl; Na
Na Cl; CaCO3
550
Cl; Na; S; Ca
CaCO3; Ca SO4 . 2H2O; Na Cl
> 500 000
250
Na; S; Ca; Mg
Na2SO4; Na2SO4.10(H2O)
< 100
< 2 000
95
Na; S; Ca; Mg Na2SO4; Na2SO4.10(H2O); CaCO3
1 250
875
> 12 500
< 12,5
Na; S; Ca; Mg
CaCO3; Ca SO4 . 2H2O
0
-
40
Na; Ca; S; K
Na2SO4.10 (H2O); Na2SO4
14 500
< 1 000
830
K; Mg; S; Ca;
XRD and FTIR
2 950
compounds
White color, salty taste, presence of
Case IV efflorescence
moisture in the wall, inflated paint
and plaster, fluffy texture
17 000;
23 350
Caption:
favorable concentration
10
moderate concentration
unfavorable concentration
In-situ characterization of efflorescence and other compounds in saline walls
Table 4 - Summary of the results provided by sensorial analysis, and in-situ and laboratorial tests, continuation
Colorimetric strips (mg/kg)
Sensorial analysis
-
SO4-
Case V efflorescence
Case VI efflorescence
White color, encrusted salt
0
> 80 000
0
White color, salty taste, inflated
paint and plaster
0
> 80 000
Case VII efflorescence
White powder, inflated paint
Case VIII concrete,
Inflated paint and white powder
0
paint and efflorescence
encrusted in column
Case IX degraded rock
Disaggregated rock and mortar
Field kit (mg/kg)
190
> 250 000
205
K; Ca; S; Mg
500
-
141 500
125
S; Na; K
Na2SO4
> 5 000
25
-
-
-
S; Na; Ca
Na2SO4; Na2SO4.10 (H2O)
0
> 30 000
0
185; 190
32 500
97,5; 102,5
S; Ca
Ca SO4. 2H2O; CaCO3
0
> 30 000
250
2 225
105; 122,5
Cl; Na; S; Ca
Ca SO4. 2H2O; CaCO3
0
> 40 000
6 250
190; 205
0
> 40 000
5 000
475; 465
0
-
500
-
-
33 000;
30 500
Case X sample 1
plaster, building
entrance
Case X sample 2
White powder encrusted to mortar,
sewage
Case X sample 4 dust,
9 500;
9 750
62 250;
7 450;
65 000
7 500
259; 255
> 25 000
-
-
entrance
room
> 125 000
-
Ca SO4 . 2H2O; MgSO4·7H2O;
K2Ca2Mg (SO4)4·2(H2O); CaCO3
CaCO3; Ca SO4. 2H2O; Na2SO4;
Na3(NO3)(SO4).H2O;
peeling paint and plaster, smell of
efflorescence, building
Case X sample 3 salt,
XRD and FTIR
NO3-
Cl
-
XRF
SO4-
Cl
NO3-
Presence of moisture in the interior
-
CaCO3; Ca SO4. 2H2O; KNO3
690; 695
-
NaCl; Ca SO4. 2H2O; NaNO3
-
-
CaCO3; SiO2; KAlSi3O8
wall, peeling paint, presence of
blisters on the exterior wall
exterior wall
-
Caption:
favorable concentration
moderate concentration
unfavorable concentration
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Extend Abstract
During the experimental tests, a variety of compounds were identified through laboratorial
analysis, being the sodium sulfate one of the substances most commonly found. This
compound, being hygroscopic, represents a high danger to the walls’ integrity.
Collecting different samples for the same anomaly proved to be very advantageous, especially
in laboratorial tests. That fact is reflected in the results for the several case studies.
The inspection methodology, applied to several cases, provided the information to characterize
the type of efflorescence present in the existing samples. However, in some cases, finding the
causes for the occurrence of the anomalies was difficult.
In the future, when planning the repair of salt affected walls, this thesis may be useful. If the
proposed diagnosis methodology is followed, it will be easier to determine certain types of
efflorescence present in walls, as well as their causes. It may also contribute to a more effective
approach to existing anomalies.
The work carried out through this dissertation achieved its initial goals, as it provides useful
guidelines to be applied in the diagnosis methodology used to characterize the saline
efflorescence and other compounds in various types of walls. It also mentions the aspects that
should be considered in every test performed.
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