Politecnico di Torino
Porto Institutional Repository
[Proceeding] Conservation of earthen constructions
Original Citation:
Manuela Mattone; Elena Bignamini (2013). Conservation of earthen constructions. In: Terra 2012XI
conferencia Internacionale sobre el Estudio y Conservacion del Patrimonio Arquitectonico de Tierra,
Lima, 22-27 aprile 2012.
Availability:
This version is available at : http://porto.polito.it/2522361/ since: December 2013
Publisher:
Pontificia Universidad Catolica del Perù
Terms of use:
This article is made available under terms and conditions applicable to Open Access Policy Article
("Public - All rights reserved") , as described at http://porto.polito.it/terms_and_conditions.
html
Porto, the institutional repository of the Politecnico di Torino, is provided by the University Library
and the IT-Services. The aim is to enable open access to all the world. Please share with us how
this access benefits you. Your story matters.
(Article begins on next page)
CONSERVATION OF EARTHEN CONSTRUCTIONS
Manuela Mattone
Politecnico di Torino, II Facoltà di Architettura
Dipartimento Casa-città
Viale Mattioli 39 – 10125 Torino – Italy
Phone 0039/0110906441
[email protected]
Elena Bignamini
Politecnico di Torino, Alta Scuola Politecnica, Torino, Italy
[email protected]
Theme 6: Research in Materials and Technology for Conservation and Contemporary
Architecture
Keywords: earthen construction, plaster, gypsum.
Abstract
Earthen constructions, built in many European, American, Asian and African countries,
represent an interesting and important architectural heritage, whose conservation is necessary
in order to make possible the transmission of a technological culture which keeps values of the
uniqueness of the landscape as well as of their history. A study of the conditions of preservation
of many unplastered earthen buildings revealed the need to set-up and test out treatments for
the protection of the walls of such kind of buildings, which are still in good conditions, in order to
improve their resistance against the aggressive action of external agents. The preservation of
this heritage calls for the definition of effective techniques able to mitigate and, if possible, to
prevent processes of alteration and ruin in order to guarantee their long-term conservation.
Accordingly, it was deemed worthwhile to carry out activities designed to assess the
effectiveness of different surface protection methods whose intent is to prevent the arising of
defects. The application of plasters on earthen constructions, even if it makes it difficult to
appreciate their real material consistence, it can guarantee their adequate safeguard. Used
since ancient times, it certainly is the protection method more diffused worldwide. A testing
campaign was conducted on different plasters prepared mixing earth and gypsum (the so-called
plaster of Paris) or earth, gypsum and additives, real sacrifice surfaces which, trying to
guarantee the readability of the actual aspect of the walls, intend to offer an effective way of
protection against the atmospheric agents characterising the environment in which the
constructions to be protected are located. The testing campaign, including chemical and
mineralogical characterization (XRD and FTIR), colour evaluation (spectrophotometry) and
performance tests as capillary absorption, erosion spray tests and Geelong tests made it
possible to assess effectiveness and performances of the different plasters.
1. INTRODUCTION
Earthen architecture has not been until now, except in few cases, subject of
appropriate measures to ensure its effective preservation over the time. The
preservation of this complex of technology and knowledge, evidence of either tangible
and intagible culture, is particularly important since “the earth is the most common
material used for the construction of historic villages [but not only, ndr.], whose
conservation ensures the transmission of a technological culture that welcomes the
landscape's values of uniqueness and not only its history" (Mattone, 2010, p. 19).
In particular, if not adequately protected, earthen buildings are affected by degradation
due to the aggressive action of the weather, as, for example, the damages caused by
the pouring water during the rain and the erosion caused by the wind.
To preserve this heritage is necessary to design operational methods able to mitigate
and, if possible, to prevent alteration and/or degradation processes, allowing a better
and lasting conservation during time.
The observation of the actual situation of many earthen buildings has highlighted the
need to develop interventions aiming at the protection of earthen masonry.
2. EARTHEN BULDINGS PROTECTION: THE PLASTERS
It is a very widespread practice to apply on an earthen contruction a layer of plaster, or
at least of a “sacrifical” coating. In certain cases this type of intervention could hide and
make it difficult to understand the real material consistency of these structures, but in
any case it seems to be an effective protection against the weather. During the last
years experimental tests have been conducted to identify suitable coatings for this type
of surface. For example, mortars containing earth in their mixture have been designed
with the dual aim of improving the performance of traditional lime-based plasters
(Maspero, Mattone, 1998; Uviña Contreras, Guerrero Baca, 2007; Guerrero Baca,
2011) and to verify the possibility of facilitate the perception of the material consistency
of earthen buildings, prevented by a plaster made of lime and sand. In certain cases
different tests have been carried out proposing, as a stabilizer, the use of gypsum
which, thanks to its phisical and chemical properties, allows to control the clay typical
shrinkage (Mattone et al., 2005).
All this considered, an experimental campaign has been started at the Laboratory
“Prove Materiali e Componenti” of the Politecnico of Torino and the Laboratory
“MaMeCH” of the Politecnico of Milano, aiming at identifying and evaluating the
performances of the protective systems that, ensuring resistance against aggressive
action exerted by the weather (and, expecially, water), are intended to prevent the
occurrence of defects. In particular, plasters of earth and gypsum have been tested,
adding different additives both of natural and syntetical origin. They represent a real
“sacrifical” coating that, paying particular attention to the need to allow the “readibility”
of the real materical texture of the masonry on which they are applied, aim to
guarantee their protection.
3. MATERIALS AND TESTING TECHNIQUES
The experimental activity aimed to evaluate the performance characteristics and
physical and chemical properties of earthen plasters, stabilized with gypsum (calcium
sulfate hemihydrate). The mortars have been admixed with both synthetic products
already on the market and others of natural origin traditionally used in different
contexts, interesting in terms of reduced or none environmental impact and complying
with sustainability requirements.
Fig. 1 – Grain size curve of the earth used for the research.
The plasters samples have been first of all observed with a stereomicroscope and their
colours variations has been quantified by spectrophotometry, then they have been
characterized chemically and mineralogically using X-ray diffraction (XRD) and Fourier
transformed infrared spectroscopy (FTIR). Datas about their performance
characteristics have been obtained after tests of capillary absorption and surface
erosion following the directions of New Zealand Standard NZD 4298.
All the plasters have been made using earth from the Vallendona Natural Park in the
Asti area in Piedmont, Italy. Its particle size analysis is shown in Figure 1. Here below
is shown the composition of the different plaster mixtures tested, the additives
percentages refer to the weight of the dry earth (Fig. 2).
A
B
C
D
E
F
G
H
Mixture composition
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
earth
gypsum 20%
Additive
linseed oil 6%
wheat gluten 2%
casein 9,6%
beeswax 3%+linseed oil 3%
cactus mucilage
acrylic emulsion 4,8%
vinyl powder 1,8%
Fig. 2 – Table of the plasters produced.
Three different samples have been made for each type of mortar, their performances
have been compared with those resulting from tests conducted on the samples of the
plaster made of only earth and gypsum (A), without additives.
The amount of gypsum used, 20% of the weight of the dry earth, was determined on
the basis of the literature examined, in relation to experimental tests carried out on
clay-based plasters and buildings, all stabilized with gypsum (Kafesçïoğlu et al., 1983;
Mattone et al., 2005).
For the cactus mucilage, it has been obtaind by soaking for 18 days 1400 gr of Opuntia
ficus indica pulp in 2 liters of water (Hoyle, 1990, Vargas Neumann et al., 1986) and
has been added to the earth and gypsum mixture instead of the water. For the plaster
admixed with casein, the numerous cracks that have occurred on its surface indicate
the need to perform additional experiments to understend which components have to
be used for its correct realization and their dosage. However, despite of the widespread
cracks, it was decided to carry on the tests on those samples in order to evaluate their
performances.
3.1 Spectrophotometry
This analysis permitted to define in form of absolute numbers the colour of the various
samples and then the color differences between them. In particular, it has been
possible to observe the color variation caused by the use of additives, by comparing
the values of the samples from B to H (plasters with additives) with those obtained from
the sample A made with earth and gypsum, used as a standard. The color
measurements have been made with a reflectance spectrophotometer in VIS light
Minolta CM2500D, with colour space CIE L*a*b*, where L* is the brightness and a* and
b* the chromaticity coordinates. For each specimen have been conducted ten
measurements, from which the average value has been obtained.
The values of chromaticity variations ΔL*, Δa* e Δb* have been calculated for each
plaster in relation to plaster A (Fig. 4), used as standard, and then the value of total
color difference ΔE* was mathematically obtained (Fig. 3).
Fig. 3 – Chart of the total color difference ΔE* of the plasters B-H compared to
plaster A (credits: E.Bignamini, 2011).
Fig. 4 – Chart of the average variation of brightness ΔL* and chromaticity coordinates
Δa* and Δb* of the plasters B-H compared to plaster A (credits: E.Bignamini, 2011).
By analysing the results of the test is possible to observe that the component that has
undergone the most consistent variation is the brightness ΔL*, lower that the standard
A for all the plasters, indicating thus a general darkening of the plasters containing
additives. It can also be generally noted a positive increase for the values of Δb*,
indicating an increase of the yellow component's saturation, highlighting a widespread
phenomenon of yellowing of the admixed plasters surface.
3.2 X-ray diffraction (XRD)
The analysis was performed on powder of the samples by using a X-ray diffractometer
Philips PW1830. The main raw materials used for the realization of the plaster mixtures
have been thus characterized from the mineralogical point of view, as the XRD analysis
allowed to identify all the crystalline mineral phases contained in the earth and in the
gypsum.
Especially for what concerns the earth, this analysis was essential to define the
minerals composing its clayey, silty and sandy parts, until now distinguished only by
the size of the grains by the particle size distribution analysis. The montmorillonite has
been recognized as component of the clay contained in the sample, while the presence
of albite, muscovite and, must of all, quartz has been attributed to the sandy
component.
For what concerns the gypsum, the XRD exam has established the purity of the
calcium sulfate hemihydrated, totally composed by bassanite.
3.3 Fourier transformed infrared (FTIR)
Thanks to the FTIR analysis it has been possible to complete the characterization of all
the raw materials in their compositional and chemical aspects and, subsequently, also
to identify the individual compounds in the mixtures of dry plasters. It has been used a
FTIR spectroscopy Thermo Nicolet 6700 with detector DTGS between 4000 and 400
cm-1. The samples of both raw materials and plasters have been grounded,
homogenized and analyzed in KBr pellet. The samples of raw materials in liquid form
were applied directly on KBr pellet and then analyzed. The quantitative proportions
between the main components of the mixtures (earth and gypsum) and those in smaller
quantities (additives) have influenced in many cases the possibility to identify correctly
all the compounds present. In particular, in the case of plasters C, F and H,
respectively admixed with wheat gluten, cactus mucilage and vinyl powder, the
presence of the additives has not been detected in the FTIR analysis. It can be
assumed that this outcome is due to the low percentage of the additive introduced, but
in all of the three cases futher tests are required.
3.4 Water capillary absorption test
The capillary absorption tests have been carried out using a Karsten pipe (Karsten,
1983) and by measuring, for a maximum of 15 minutes and at regular intervals of one
minute, the rate of water absorption introduced in the graduated pipe (Fig. 5).
The values obtained, as it is clear from the diagram in Figure 5, show that while
products as wheat gluten (C), cactus mucilage (F) and vynil powder (H) have not
effectively reduced the water capillary absorption, other products as linseed oil (B),
beeswax (E) and acrylic emulsion (G) have instead led to its decrease. Very significant
results have been obtained from the samples of the plaster admixed with casein (D).
Fig. 5 – Diagram illustrating the results of capillary absorption tests. (credits: M. Mattone, 2011).
3.5 Geelong test
The erosion tests have been conducted, as required by New Zealand Standards NZD
4298, with two differents procedures: the Geelong test (1) and the spray test.
The Geelong test is based on the measurement of a sample's erosion caused by the
repeated impact of a water drop – from an height of 400 mm and for a total of 100 ml of
water – on the tested surface, placed at an angle of 30° to the horizontal.
All the tested samples have reported an erodibility index of 2, since the erosion was
none or extremely low.
3.6 Spray test
The erosion spray test involves the measurement of a sample's erosion after it has
been exposed to a water jet projected from a distance of 470 mm and with a pressure
of 0.5 bar (2). The test lasts up to one hour, or until complete erosion of the sample,
and is interrupted at regular intervals of 15 minutes to assess the entity, in term of
depth, of the erosion caused by the water jet.
Fig. 6 - Diagram illustrating the results of erosion spray tests (credits: M. Mattone, 2011).
The diagram of the results obtained (Fig. 6) shows how, except the plasters admixed
with cactus mucilage (F) and wheat gluten (C), all the other mortars have an increased
capacity of erosion resistance.
The erodibility level was extremely low for the samples admixed with linseed oil (B) and
none for those containing casein (D).
4. CONCLUSIONS
The research made so far, although in need of further study, allows however to
formulate some preliminary considerations.
From the exam of the results obtained, it is possible to notice that products such as
linseed oil (B) and, especially, casein (D) are able to ensure to the plasters a good
resistance to the water erosive action.
The plasters admixed with beeswax (E), vynil powder (H) and acrylic emulsion (G)
have given also good performances. Regarding the water absorption tests, all the
products have led to a more or less consistent reduction of the phenomenon; the only
exception has been the casein, which has enhanced a significant decrease in the
amount of water absorbed.
It is important to stress out that the results of the research, when compared with those
obtained during other previous testing campaigns, highlight the existence of numerous
variables (as the earth specific properties and characteristics, methods of preparation
and typology of the mixture components) that may affect the results achieved.
Therefore, it is absolutely necessary to study for each case what type of plaster seems
to provide the best performances considering all the possible variables and making, if
possible, direct in situ tests, with the materials and labour available. The influence of
the additive on the colour changes, moreover, is an important parameter to consider,
especially in the case on intervention on historical structures.
In the future developments of the research it is intended to study the use and role of
casein used as an additive for plasters, in order to avoid the occurrence of cracks,
defining the optimal casein percentage to be added to the mixture and the most
suitable way to realize the plaster.
Bibliography
Guerrero Baca, L. (2011). Revestimientos. Neves, C., Obede Borges, F., Tècnicas de
construcción con tierra. Bauru: FEB-UNESP/PROTERRA, pp. 72-77.
Hoyle, A. M. (1990). Chan Chan: aportes para la conservacion del la arquitectura de
tierra. 6th International Conference of the Conservation of Earthen Architecture, (Las
Cruces, 1990), pp. 225-229.
Kafesçïoğlu R. (et alii) (1983). Adobe blocks stabilized with gypsum. Proceedings of a
Symposium Appropriate Building MATERIALS FOR Low-cost Housing, (Nairobi, 1983),
Nairobi, pp. 3-11.
Karsten, R. (1983). Bauchemie für Studium und Praxis, Heidelberg.
Maspero, M., Mattone, M. (1998). La protezione degli edifici in terra: l’intonaco.
Mattone, R., Gilbert, A (a cura di). Terra: incipit vita nova. Torino: Politecnico di Torino,
pp. 61-68.
Mattone, R. (et alii) (2005). Uso de productos naturals para mejorar el comportamiento
al agua de revoques a base de tierra. Terra en seminário 2005, Lisbona: Argumentum,
pp. 266-269.
Mattone, R. (2010). Il paesaggio delle case in terra cruda. Savigliano: L’Artistica.
Uviña Contreras, F., Guerrero Baca, L. (2007). El uso de la cal en la conservación de
estructuras de tierra. Fourth International Adobe Conference of the Adobe Association
of the Southwest, AdobeUSA 2007 (El Rito, 2007), El Rito, pp. 40-45.
Vargas Neumann, J. (et alii) (1986). Preservation of Adobe Constructions in Rainy
Areas, CIB. 86 Advancing Building Technology, Washington, pp. 1457-1465.
Notes
(1) Cfr. NZD 4298, appendix E.
(2) Cfr. NZD 4298, appendix D.
Curriculum: Manuela Mattone, architect, PHD, university researcher at Turin Politecnico. She is
interested in studying architectural restauration problems. In particolary, she studies the
following subjects: wooden structures, concerning both the evaluation of their conditions of
preservations, and the study of the consolidation technics; earthen architecture, concerning the
problems connected to the conservation of this architectural heritage; iron architecture,
especially concerning the study of past building technics.
Curriculum: Elena Bignamini, graduated in Architecture at Turin Politecnico. She completed also
the ASP (Alta Scuola Politecnica, www.asp-poli.it) program during the master. She studied one
year at the KTH in Stockholm, Sweden. She experienced the earthen plaster during her master
thesis work and various workshop.
© Copyright 2024 Paperzz
