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

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

Extend Abstract

2

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 in-

situ 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.

In-situ characterization of efflorescence and other compounds in saline walls

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Figure 1 – Flowchart illustrating the diagnosis methodology applied on the efflorescence’s assessment

In-situ analysis:

colorimetric strips

field kit

Sample collection

New analysis

Conclusion about the type of efflorescence

Yes No

Report and intervention

proposal

Sensorial analysis:

sight

touch

smell

taste

hearing

Choose the place to

inspect

Record all the information about the

anomaly, including its evolution and

possible causes identified by the user

Photographic record

Laboratorial Techniques:

XRD

XRF (confirms in-situ

analysis results)

FTIR (if XRD is not possible)

Conclusion about the type of efflorescence

Yes

No

Report

Extend Abstract

4

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

In-situ characterization of efflorescence and other compounds in saline walls

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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 Sulfate Nitrate

Sample 1 – fluffy

efflorescence

colorimetric strips (mg/kg)

0 > 40 000 12 500

field kit (mg/kg)

267,5 7300 3475

Sample 2 - plaster

colorimetric strips (mg/kg)

0 > 80 000 10 000

field kit (mg/kg)

2500 12 700 830

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.

Extend Abstract

6

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

Sample 1 -

efflorescence

XRF Potassium (K) ++ Magnesium (Mg) + Sulfur (S) ++ Calcium (Ca) + Sodium (Na) -

FTIR Polyhalite

K2 Ca2 Mg [SO4]4 . 2H2O Calcite CaCO3 Niter KNO3

XRD Niter KNO3 Polyhalite

K2 Ca2 Mg [SO4]4 . 2H2O

Syngenite K2 Ca [SO4]2 . 2H2O

Calcite

CaCO3

Aphthitalite K3 Na (SO4)2

Sample 2 -

plaster

XRF Potassium (K) - Magnesium (Mg) + Sulfur (S) ++ Chloride (Cl) - Calcium (Ca) ++

FTIR Gypsum

Ca SO4 . 2H2O Calcite CaCO3 Niter KNO3

XRD Gypsum

Ca SO4 . 2H2O 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

In-situ characterization of efflorescence and other compounds in saline walls

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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

Extend Abstract

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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.

In-situ characterization of efflorescence and other compounds in saline walls

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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.

Extend Abstract

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Table 3 - Summary of the results provided by sensorial analysis, and in-situ and laboratorial tests

Sensorial analysis

Colorimetric strips (mg/kg) Field kit (mg/kg)

XRF XRD and FTIR

Cl- SO4

- NO3

- Cl

- SO4

- NO3

-

Case I sample 1

efflorescence White color, salty taste, fluffy

texture , rotting wood, peeling paint,

deteriorated plaster

0 > 40 000 12 500 267,5 7300 3475 K; Mg; S; Ca;

Na

K2 Ca2 Mg [SO4]4 . 2H2O; CaCO3;

KNO3; K2 Ca [SO4]2 . 2H2O; K3 Na

(SO4)2

Case I sample 2 plaster 0 > 80 000 10 000 2 500 12700 830 K; Mg; S; Cl;

Ca Ca SO4 . 2H2O; CaCO3; KNO3

Case II sample 1 brick Salty taste, plaster and brick in an

advanced state of degradation

37 500 < 5 000 2 500 14 250;

14 500 < 1 000

2 900;

2 950 Cl; Na Na Cl; CaCO3

Case II

sample 2 plaster 0 > 10 000 500 > 7000 > 9 750 550 Cl; Na; S; Ca CaCO3; Ca SO4 . 2H2O; Na Cl

Case III sample 1

efflorescence

White color, salty taste, presence of

moisture in the wall, inflated paint

and plaster, fluffy texture

0 > 160 000 0 < 200 > 500 000 250 Na; S; Ca; Mg Na2SO4; Na2SO4.10(H2O)

Case III sample 2

plaster 0 > 60 000 1 250 < 100 < 2 000 95 Na; S; Ca; Mg Na2SO4; Na2SO4.10(H2O); CaCO3

Case III sample 3

plaster and other

compounds

0 > 30 000 1 250 875 > 12 500 < 12,5 Na; S; Ca; Mg CaCO3; Ca SO4 . 2H2O

Case IV efflorescence

White color, salty taste, presence of

moisture in the wall, inflated paint

and plaster, fluffy texture

0 > 20 000 0 - 17 000;

23 350 40 Na; Ca; S; K Na2SO4.10 (H2O); Na2SO4

Caption:

favorable concentration moderate concentration unfavorable concentration

In-situ characterization of efflorescence and other compounds in saline walls

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Table 4 - Summary of the results provided by sensorial analysis, and in-situ and laboratorial tests, continuation

Sensorial analysis Colorimetric strips (mg/kg) Field kit (mg/kg)

XRF XRD and FTIR Cl

- SO4

- NO3

- Cl

- SO4

- NO3

-

Case V efflorescence White color, encrusted salt 0 > 80 000 0 190 > 250 000 205 K; Ca; S; Mg Ca SO4 . 2H2O; MgSO4·7H2O;

K2Ca2Mg (SO4)4·2(H2O); CaCO3

Case VI efflorescence White color, salty taste, inflated

paint and plaster 0 > 80 000 500 - 141 500 125 S; Na; K Na2SO4

Case VII efflorescence White powder, inflated paint 0 > 5 000 25 - - - S; Na; Ca Na2SO4; Na2SO4.10 (H2O)

Case VIII concrete,

paint and efflorescence

Inflated paint and white powder

encrusted in column 0 > 30 000 0 185; 190 32 500 97,5; 102,5 S; Ca Ca SO4. 2H2O; CaCO3

Case IX degraded rock Disaggregated rock and mortar 0 > 30 000 250 2 225 33 000;

30 500 105; 122,5 Cl; Na; S; Ca Ca SO4. 2H2O; CaCO3

Case X sample 1

plaster, building

entrance White powder encrusted to mortar,

peeling paint and plaster, smell of

sewage

0 > 40 000 6 250 190; 205 > 125 000 9 500;

9 750 -

CaCO3; Ca SO4. 2H2O; Na2SO4;

Na3(NO3)(SO4).H2O;

Case X sample 2

efflorescence, building

entrance

0 > 40 000 5 000 475; 465 62 250;

65 000

7 450;

7 500 - CaCO3; Ca SO4. 2H2O; KNO3

Case X sample 3 salt,

room Presence of moisture in the interior

wall, peeling paint, presence of

blisters on the exterior wall

0 - 500 259; 255 > 25 000 690; 695 - NaCl; Ca SO4. 2H2O; NaNO3

Case X sample 4 dust,

exterior wall - - - - - - - CaCO3; SiO2; KAlSi3O8

Caption:

favorable concentration moderate concentration unfavorable concentration

Extend Abstract

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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.

Bibliography

Bianchin, A. (1999) - Influência do proporcionalmente dos materiais constituintes no

desempenho de argamassas para reboco de recuperação de alvenarias contaminadas

por umidade e sais, Dissertação de Mestrado em Engenharia Civil, Porto Alegre,

Universidade Federal do Rio Grande do Sul, 153 p.

Flores-Colen, I. (2009) - Metodologia de avaliação do desempenho em serviço de fachadas

rebocadas na óptica da manutenção predictiva, Dissertação de Doutoramento em

Engenharia Civil, IST, Lisboa, 487 p.

Freitas, V. (1992) - Transferência de humidades em paredes de edifícios, Dissertação de

Doutoramento em Engenharia Civil, FEUP, Porto, 200 p.

Gonçalves, T.; Rodrigues, J. (2005) - Rebocos para paredes antigas afectadas por sais

solúveis, patologia, princípios de funcionalidade e adequabilidade, Seminário sobre sais

solúveis em argamassas de edifícios antigos, LNEC, Lisboa, pp. 4.1-4.14.

Rodrigues, J.; Gonçalves, T. (2005) - Sais solúveis nas construções históricas introdução e

relatório sumário, Seminário sobre sais solúveis em argamassas de edifícios antigos,

LNEC, Lisboa, pp. 1.1-1.14.

Uemoto, L. (1984) - Patologia: Danos causados por eflorescências, Tecnologia de edificações,

São Paulo pp. 95 - 98.