STUDY AND CONSOLIDATION OF SANDSTONE: TEMPLE OF KARNAK, LUXOR,
EGYPT
Saleh A. Saleh, Fatma M. Helmi, Monir M. Kamal and Abdel-Fattah E. El-Banna
Abstract—Sandstone samples from the Temple of Karnak, Luxor, Egypt, were studied by Xray diffraction (XRD), thin-section analysis and scanning electron microscopy (SEM).
Physical, mechanical and thermal properties were determined before and after treatment with
six different consolidants. The data were confirmed by SEM examination. Methyl tri-methoxy
silane (MTMOS) gave the best results in the consolidation of the Karnak sandstone.
1 Introduction
The temples of Karnak in Luxor are a record of the history and civilization of Egypt from the
Middle Kingdom to the reign of the Ptolemies. The Temple of Amun-Ra is one of the most
important of the temples at Karnak. It was constructed by Rameses III (New Kingdom). The
deterioration of this temple takes the form of loss of the surface layers of sandstone which
carry mural paintings. This phenomenon is considered to be due to the dissolution of the
binding materials between the grains of quartz. Humidity combined with air pollution
produces acidic water which is a deteriorating factor. Water combined with salts dispersed in
the surrounding environment or accumulated in the core of the monument itself produces
crystallization pressures which weaken bonding between the grains in the stone [1-3].
The aim of the present work is to study the deterioration of the sandstone of the temples of
Karnak; then to study the effect of different consolidants on the physical, mechanical and
thermal properties of the sandstone, to see how they compensate for the loss of the natural
binding materials from the stone [4-8].
2
Experimental and results
2.1 Material studied
Sandstone fragments and samples of salts were taken from the Temple of Amun-Ra, Karnak,
Luxor, Egypt. The stone samples were treated with seven consolidating materials. Physical,
mechanical and thermal properties were determined for the treated and untreated samples,
which were examined by scanning electron microscopy (SEM). The sandstone was yellow in
colour with some dark brown areas. Salt crystals were found at the surface of the sandstone in
some areas in the Temple. The sandstone is similar to the Nubian sandstone quarried at
Quseir, dating from the period between Upper Cretaceous and Lower Tertiary [9]. Seventyrive samples were used. Each measurement was repeated at least three times and the average
value is quoted in each case.
2.2 X-ray diffraction analysis The samples were ground to a fine powder in an agate mortar
and pressed into the specimen holder, then mounted in a Philips X-ray diffractometer.
The operating conditions were: Generator: CuKα radiation (1-5418Å) with Ni-filter, 40kV,
20mA current, speed: 0.1, chart: 5, range: 1 x 103, time constant: 1, and slit: 0.1.
XRD data of sandstone samples (Figure 1, Table 1) showed that it consists essentially of
quartz α-SiO2 (JCPDS 5-0490), with trace amounts of the following minerals: kaolinite
Al2Si305(0H)4 (14-146), haematite a-Fe2O3 (13-534), albite NaAlSi3O8 (9-466) and oligo-clase
0.71 NaAlSi3O8, 0-29 CaAl2Si208 (9-456). Samples of iron nodules from the sandstone were
examined (Figure 2, Table 2) and found to contain goethite α-FeO(OH) (17-0536) and haematite α-Fe2O3 (13-534) in addition to quartz, the main constituent mineral. The crystalline
salts from the temple walls (Figure 3, Table 3) were found to consist of halite NaCl (5-0628)
with a small amount of sylvite KC1 (4-0578), in addition to trace amounts of nitre KNO3 (1130), nitratite NaNO3 (7-271) and haematite α-Fe2O3 (13-534).
Table 1
Luxor
X-ray diffraction data for shaly sandstone sample from the Temple of Karnak,
Figure I X-ray diffraction pattern of sandstone sample from the Temple of Karnak, Luxor.
Major: quartz (Q). Traces: kaolinite (Kal), haematite (Hem), albite (Alb) and oligoclase
(Olig).
2.3 Thin-section analysis A sandstone sample was sectioned and mounted on a microscope
slide. Different materials were identified using a Leitz polarizing microscope (Figure 4). A
large number of quartz grains had fine cracks showing strain shadows near the extinction
position. The presence of potassium feldspars, orthoclase and plagioclases was
Table 2 X-ray dijfraction pattern of iron nodules in sandstone, Temple of Karnak, Luxor
Figure 2 X-ray diffraction pattern of iron nodules in sandstone sample from the Temple of
Karnak, Luxor. Major: quartz (Q). Traces: goethite (Geo) and haematite (Hem).
Figure 3 X-ray diffraction pattern of salt sample, Temple of Karnak, Luxor. Major: halite
(Hal) and sylvite (Sylv). Traces: nitre (Nit), nitratite (Nitr) and haematite (Hem).
detected. Decomposition of potassium feldspars into sencite and kaolinite minerals was
inferred from the presence of blurred dispersed points and strong interference colours between
the quartz grains. The section also showed inclusions of muscovite and rutile crystals.
2.4
Consolidation
The sandstone was cut into cubes (5cm3) and dried in an oven at 105°C for 24 hours to constant weight, left to cool at room temperature and 55% RH for half an hour, then weighed
again. Table 4 lists the consolidants used. Aral-
dite was applied in one coat. All the other consolidants were applied perpendicular to the
bedding plane in two applications. A six-month interval separated the first from the second
application to allow the polymerizationprocess to take place. The second treatment increased
Figure 4 In thin-section, the sandstone shows quartz, feldspar plagioclase grains, and binding
material containing kaolinite and seriate minerals dispersed between the quartz granules; x
63, crossed nicols.
Figure 5
The effect of consolidants on the colour of the treated sandstone samples.
Figure 6 The difference between the water absorption of the treated and untreated
deteriorated sandstone samples.
the amount of precipitated polymer coating the grains in the stone without sealing the pores,
so that the stone could still breathe [8, 9].
2.5 Physical properties
Some sandstone samples were cut into sheets (1 x 4 x 12cm) and consolidated as given above.
The effect of the consolidant treatments was evaluated according to ASTM D 1729 [10]:
visual evaluation of the colour difference between the treated and untreated samples. Figure 5
shows that Araldite failed this test as a consolidant, both in its pure state and in dilute solution
[11]. Therefore it was excluded from the rest of the tests. In comparison, sample no.4 treated
with 2.5% w/v Paraloid B-72 dissolved in MTMOS (methyl trimethoxy silane) gave little
colour change and sample no.3 treated with MTMOS showed a very small colour change.
The depth of penetration of the applied consolidants was tested by capillary rise through the
5cm3 cubes. It was found that the time taken to penetrate right through the cubes was four
times greater for Paraloid B-72 dissolved in toluene or mixed with either HEY'DI M.S.
Siloxane or MTMOS than for HEY'DI M.S. Siloxane, MTMOS or Wacker OH used alone.
Water absorption of the treated and untreated samples was determined according to ASTM C
97 [12]. Figure 6 shows the difference between the water absorption of treated and untreated
samples.
2.6 Mechanical properties
Compressive strength was determined according to ASTM C 170 [13, 14] with the load
applied perpendicular to the bedding plane. Figure 7 gives the average values of compressive
strength for treated and untreated samples. The untreated samples had an average value of
98kgcm'2 whereas those treated both with TEOS and 5% Paraloid B-72 in toluene gave the
highest value, 242kgcm-2.
Indirect tensile strength was measured by a split test [15]. Figure 8 shows the average values
for the indirect tensile strength of the treated and untreated samples. The value for the
untreated sample was 6kgcm-2, whereas those for the treated pieces lay between 6.5 and 79kgcm-2.
2.7 Thermal properties
Linear thermal expansion factors were deter mined for the treated and untreated samples.
Figure 9 shows these values. The sample treated with Wacker OH was the only one that had
an increase in linear thermal expansion (6.6 x lO-6m°C-1), whereas all the other treated
samples gave values lower than that of the untreated sample (6 x lO-6m°C-1).
2.8 Scanning electron microscopy (SEM) A Jeol SEM was used for examination of the
untreated sample and evaluation of the consolidants used in the treatment of sandstone. The
samples were coated with gold to a thickness of lOnm. The SEM micrographs of the untreated
sample (Figure 10) show the homogeneous structure of the fine-grained quartz mineral, the
volume and distribution of the pores, and the binding material which contains salt and
kaolinite crystals. SEM micrographs of samples treated with different consolidants are shown
in Figure 11. The sample treated with 5% Paraloid dissolved in toluene (a) had a network of
polymer and a fine membrane coating of spongy appearance on the sandstone grains. The
sample
Figure 8
samples.
The average tensile strength values of the treated and untreated sandstone
Figure 7 The average values for compressive strengzth of the treated and untreated sandstone
samples.
Figure 9 The thermal expansion coefficients of the treated and untreated sandstone samples.
Figure 10 SEM micrographs of the untreated sandstone sample, (a) The homogeneous, finegrained quartz pores showing volume, distribution, binding materials and a columnar crystal
of some impurity on the right-hand side ( x 200). (b) Detail of (a) showing the binding
materials containing salt crystals and kaolinite ( x 1000).
treated with MTMOS (b) shows that the polymer has precipitated in the form of nodules and
that the consolidating material has penetrated inside pores and around grains in a condensed
form. The sample treated with 2.5% Paraloid B-72 dissolved in MTMOS (c) shows the
coating of the consolidant material on sandstone grains obscuring the boundaries between
them. The network structure of consolidant can be seen dispersed between the grains and
through the pores. The sample treated with HEY'DÍ M.S. Siloxane (d) shows that a thin layer
of the polymer has formed, leaving the quartz grain-boundaries visible. This consolidant has
failed to fill fine cracks. In the sample treated with 5% Paraloid dissolved in HEY'DI M.S.
Siloxane (e), the polymer layer has formed nodules on the grain surfaces and precipitated
particles of the consolidant in the pores between grains. The sample treated with Wacker OH
(TEOS) (f) shows the spread of the network structure of the polymer on the grain surfaces and
in depth between the pores.
3 Discussion
This study of the sandstone used in building the Temple of Karnak shows some of the reasons
for the deterioration of the stone. The alteration of potassium feldspar minerals (orthoclase to
seri-cite and kaolinite) was obvious from thin-section analysis. This confirmed the role of
chemical weathering in the deterioration of the structure of the stone, the result of
transformation of the constituent minerals to other minerals more susceptible to mechanical
strain and dissolution.
Even quartz, which is one of the most durable minerals, showed susceptibility to mechanical
deformation as a result of strain from static or dynamic loads.
Iron nodules (containing goethite and haematite) in the sandstone also play a role in the
deterioration process. These minerals can be dissolved, transported to and then leached from
the surface of the temple walls. These nodules would be more susceptible to deterioration than
grains of quartz, the main constituent mineral.
Halite and sylvite salts were found at the surface of the temple walls, an indication of the
influence of the surrounding environment on the deterioration process. Halite (NaCl) is a
natural impurity characteristic of the Egyptian soil. The presence of sylvite (KC1) suggests
the migration of salt solutions containing potassium ions from
Figure 11 SEM micrographs of sandstone samples treated with the following consolidants:
(a) 5% Paraloid in toluene (x500); (b) MTMOS ( x 200); (c) 2.5% Paraloid in MTMOS ( x
200); (d) HEY'DI M.S.Siloxane ( x 200); (e) 5% Paraloid in HEYDI M.S. Siloxane ( x 500);
(f) Wacker OH ( x 200).
the cultivated land beside the Temple of Karnak. Potassium may come from the Nile mud
which was precipitated in a concentrated form during flood periods in Upper Egypt. It is also
found in the artificial manure used on the cultivated land. The potassium feldspars which exist
in the sandstone could form another minor source of potassium ions which, when reacted with
chloride ions, give rise to sylvite.
All these factors—either endogenous from the physical and chemical properties of the stone
or exogenous from the surrounding environment and exchange of ions—are able to transform
the stone from a hard, strong, coherent state to a completely disintegrated, weak state. This
could lead to complete destruction of the stone in the future, as shown by the measurement of
mechanical properties which showed a 30% decrease in compressive strength when compared
with the normal average value for new building sandstone (140kgcm-2) [16].
Thus it was necessary to study some consolidants as a substitute for the natural binding
materials. It is to be expected that friable stone monuments treated with these consolidating
materials will gain new properties, becoming more resistant to deterioration in the future.
The present study concentrated on the silicon resin group of silane compounds having the
dual properties of consolidants and water-repellents. Also included were ethyl silicate and two
familiar resins: an epoxy, representing thermosetting resins, and a copolymer resin of ethyl
metha-crylate and methyl acrylate, representing thermoplastic resins.
The test results showed the success of silane compounds and ethyl silicates in penetrating the
stone in depth, due to their low viscosity (between 1 and 1.1 7 centipoises), and binding the
friable portions to the main hard stone structure. They penetrate the stone in depth even in the
presence of high water-content. Humidity is an essential factor in the hydration and condensation reactions of the polymerization process [17]. In the case of silane compounds, the polymerization product was a network polymer based on the siloxane bond Si—O—Si. In the case
of ethyl silicates, hydrated silica was the
product in the form of a network polymer of glassy appearance binding the stone granules.
The curing time of the silane compounds is long; this prevents the formation of a surface layer
which may inhibit penetration of the consolidating material. Silane compounds also succeeded in reducing the water absorption of the sandstone to a low value. This is due to their
hydrophobic character, a result of the presence of alkyl groups (R) connected to silicon atoms
in the polymer product being positioned on the external surface of the polymer where they
repel water molecules.
The sandstone sample treated with 2.5% w/v Paraloid B-72 in MTMOS showed the highest
values for compressive and indirect tensile strength. This is due to the similarity in the properties of Paraloid B-72 and MTMOS as consolidants for binding the grains of the stone
together. This mixture also gives the most suitable thermal expansion factor, very near to the
normal value of the untreated sample. It is a suitable partial consolidant for stone monuments,
especially in dry regions.
Paraloid B-72 took more time to penetrate the stone in depth, due to its high viscosity (9.9
centipoises when dissolved in toluene 10% w/v). Humidity is considered to be one of the
obstacles to application of acrylic compounds, which are not miscible with water.
SEM examination was used in the study of the physical and mechanical properties of the
sandstone samples treated with different consolidants. It showed the good penetration of most
of the low-viscosity consolidants, represented by Dow Corning silane (MTMOS), Wacker OH
ethyl silicate (TEOS) and methyl polysiloxane oligomer materials. It also confirmed the
failure of Paraloid B-72 to penetrate the internal structure of the stone, either by itself or when
mixed with methyl polysiloxane. This is due to its high viscosity and its partial dissolution in
organic solvent which in the mixed consolidant led to its precipitation, partially filling the
pores between grains. This is the reason for the decrease in water absorption value for the
sandstone treated with Paraloid, which is not water-repellent.
SEM examination interpreted the results of mechanical property tests. It showed the polymer
network structure between grains in a condensed form for the stone treated with a mixture of
Paraloid B-72 dissolved in silane, the invisible grain boundaries indicating the strong bonds
between grains. This examination also showed the relationship between Paraloid B-72 and
silane which gave this treatment a specific character represented by a homogeneous smooth
layer formed on the surface of the grains, the pores not closed but permitting air movement
inside the stone. This also leaves a possibility for salt extraction by solution in situations
where salts exist inside the structure of the stone.
SEM examination explained the low strength given by treatment with methyl polysiloxane. It
showed the fine polymer layer formed on the surface of stone grains where the grain boundaries could be clearly seen. It also explained the high strength of the sandstone treated with
ethyl silicate (TEOS) by showing an extended polymer network completely covering the
sandstone grains and making connections between them.
4 Conclusions
The experimental work shows that:
(1) Silane compounds in the monomer form could be applied as a consolidant at times of
year when the relative humidity and temperature at the archaeological site are suitable. Silane
compounds in the oligomer form failed to pass the tests.
(2) The most suitable months in the year for the application of silane compounds and ethyl
silicates to the stone monuments in Upper Egypt are January, February, November and
December, when the average relative humidity is between 47% and 55% and the temperature
between 22oC and 30oC, which are the ideal conditions for completing the polymerization
process.
(3) It is advisable not to apply consolidating materials consisting of hydrocarbon chains,
such as acrylic compounds and polyvinyl acetate polymers, etc., on stone monuments in
humid regions, because they are not miscible with the water contained in the pores of the
stone. It is also unwise to use these materials on stone monuments in very arid regions
where they are exposed
102
permanently to direct sunlight. Such conditions will lead to a breakdown in the internal
structure of these consolidants, leading to deterioration of the stone.
(4) Epoxy resins should not be used for consolidating stone monuments because they give
rise to a colour change in the treated stone.
(5) In the case of very deteriorated stone where a strong binding agent is needed to hold the
grains together, it is possible to apply a mixture of acrylic compounds of low molecular
weight with silane compounds in very low percentages (not exceeding 2.5% w/v).
(6) Ethyl silicates can be used for consolidation only. They do not have the water-repellency
of the silanes.
(7) Treatment with silane compounds and ethyl silicates can only be considered as a temporary conservation measure for stone monuments. Artificial weathering seems to indicate
a lifetime of more than 10 years. The treatment does not block the pores of the stone, so it is
possible to re-treat it successfully. The monument should be examined periodically and retreatment applied where necessary, generally 10 years after the first treatment.
Suppliers of materials
Paraloid B-72: Rohm & Haas (UK) Ltd, Lennig House, 2 Mason's Avenue, Croydon CR9
3NB, UK.
Araldite AY 103/HY 956: Ciba-Geigy Plastics & Additives Co., Plastics Division, Duxford,
Cambridge CB2 4QA, UK.
Wacker OH: Wacker Chemicals (UK) Ltd, Warwick House, 27-31 St Mary's Road. London
W5 5PR, UK.
Dow Corning Silane Z-6070: Dow Corning Ltd, Bridge House, Reading RG1 9PW, UK.
HEY'DI M.S.Siloxane: HEY'DI Organization Internationa!, Mohandesen, Cairo, Egypt.
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SALEH A. SALEH, BSC Ainshams University, Cairo; PhD in X-ray physics, Warsaw
University, Poland (1964). Chemist in the Egyptian Antiquities Department until November
1966, when he became chief of research and chemical analyses. Director of the Centre of
Research and Conservation of Antiquities, Organization of Egyptian Antiquities, 1969-71. In
July 1980, he moved to the Faculty of Archaeology, Conservation Department, Cairo
University as professor in charge of research into archaeological materials and their
conservation. Head of Conservation Department, 1980; Vice-Dean, Faculty of Archaeology,
1987. Member of the National Council of Crystallography and the Egyptian National Council
of Antiquities. Author's address: Faculty of Archaeology, Conservation Department, Cairo
University, Giza, Egypt.
FATMA M. HELMI, BSC Ainshams University, Cairo; MSc (1974); PhD in physical sciences,
Eötvös Lorand University, Budapest, Hungary (1978). She worked first as a chemist at the
Egyptian Antiquities Department in Cairo, then as chief of the X-ray laboratory and later subdirector of the Research and Conservation Centre, Organization of Egyptian Antiquities. In
1983 she moved to the Faculty of Archaeology, Conservation Department, Cairo University,
where she is associate professor for study of archaeological materials and their conservation.
Member of the National Council of Crystallography and the Egyptian National Council of
Antiquities. Author's address: as for Saleh.
MONTR M. KAMAL, BSC Ainshams University, Cairo; MSc in structural engineering, Cairo
University (1978); PhD in civil engineering, Leeds University, UK (1983). Associate
professor, Building Research Centre, Cairo; consultant engineer for quality control, repair and
strengthening of structures. Member of the Egyptian Engineering Society, the Polymer
Science Society and the Board of the Egyptian History and Monuments Society. Author's
address: Building Research Centre, Dokki, Cairo, Egypt.
ABDEL-FATTAH E. EL-BANNA, BA Cairo University; MA in conservation and restoration of
stone (1990). Assistant Lecturer, Conservation Department, Faculty of Archaeology, Cairo
University. He is preparing his PhD thesis on study of the instability phenomena of some
monuments in the Deir El-Bahari area, Thebes. Author's address: as for Saleh.
Résumé—On a étudié des échantillons de grès provenant du temple de Karnak, Louqsor,
Egypte, par diffraction d'X, analyses sur coupes minces et micro-scopie électronique à
balayage. On a étudié aussi, avant et après traitement, les propriétés physiques, mécaniques et
thermiques des échantillons avec six consolidants différents. Les résultats ont été confirmés
par examen au MEB. Les meilleurs effets en ce qui concerne la consolidation du grès de
Karnak ont été obtenus par le triméthoxyméthylsilane.
Zusammenfassung—Sandsteinproben vom Tempel in Karnak in der Nähe von Luxor
(Ägypten) wurden mit Hilfe der Röntgendiffraktometrie, der Raster-elektronenmikroskopie
sowie an Hand von Dünnschliffen untersucht. Die Proben wurden vor und nach Behandlung
mit sechs verschiedenen Festigungsmitteln bezüglich ihrer physikalischen, mechanischen und
thermischen Eigenschaften charakterisiert. Die Beobachtungen wurden in der
Rasterelektronenmikroskopie bestätigt. Methyltrimethoxysilane ergaben die besten Resultate
bei der Festigung dieser Sandsteine aus Karnak.