GeolCarp_Vol50_No5_405

GEOLOGICA CARPATHICA, 50, 5, BRATISLAVA, OCTOBER 1999

405–408

QUANTIFICATION OF SALTS IN EXTRACTS FROM BRICKS

(„WALL OF BRICKS” AT THE WAWEL CASTLE IN CRACOW)

MARIOLA MARSZAŁEK

Department of Mineralogy, Petrography and Geochemistry, University of Mining and Metallurgy,

al. Mickiewicza 30, 30-059 Kraków, Poland

(Manuscript received February 18, 1998; accepted in revised form December 9, 1998)

Abstract:

The concentration of soluble salts in the retaining wall of the Wawel Castle was estimated. This wall bears

the pressure of a steep, earthen slope of medieval fortifications. The analyses have shown that the samples contain
mainly sulphate, nitrate, chloride, calcium, sodium and potassium. The concentration of the ions increases distinctly
from the inner side of the wall toward the outer, exposed part. Due to the specific position of the wall and in contrast
to most other buildings, water penetrates the retaining wall from the side abutting the scarp, while capillary suction
from the foundations is of minor importance.

Key words:

soluble salts, bricks, Wawel Castle, Cracow.

Introduction

Bricks as a construction material began to be widely used in
Poland in the 14th century (Gothic). Like any other stones they
also undergo similar processes of deterioration. Durability of
brick walls depends, among others, on the composition of clay
raw materials, firing conditions, and also on the composition
of mortar. Bricks were used in construction of the retaining
wall between the foothill and the Herbowa Gate of the Wawel
Castle in Cracow (Fig. 1). Different parts of the wall were
erected in various periods. Its outer part comes from the 1920s,
the core from the mid-19th century, and the foundations from
the Renaissance, resulting in different states of preservation of
the bricks (Kozłowski & Stępień 1997). The wall is situated
on the northern side of the castle hill and bears the pressure of
a steep, earthen slope of medieval fortifications. Besides its ar-
chitectural value, its other asset is in a number of stone tablets
commemorating sponsors who rendered financial assistance

toward restoration of the castle after World War I (Fig. 2). The
wall was strongly damaged, and salt efflorescences can be
seen at its surface. As the wall was poorly preserved, display-
ing numerous cracks and loosenings, it had to be renovated.
During renovation and conservation of the wall, the author
took brick samples to estimate the concentration of soluble
salts.

Fig. 1.

View of the Wawel Castle in Cracow.

Fig. 2.

„Wall of bricks” at the Wawel Castle with stone tablets

commemorating contributors who rendered financial assistance to-
ward restoration. (Photo P. Stępień).

Sampling and methods

Considering the specific localization of the wall, which

tightly abuts an earthen scarp from one side, the samples
were taken through the wall in three horizontal profiles, at
different heights above the ground level. The profiles A, B, C
were situated 5 m, 2.5 m and 0.5 m above the level of the

406 MARSZAŁEK

Profile

Sample
locality

Cond.

µ S/cm

A1
A2
A3

142
242

9.51
9.65
8.82

0.5
0.2
1.9

2.8
4.3
5.6

9.5
9.0

14.0

3.3

13.8

107.0

0.2
0.4
0.2

3.5
8.7
6.8

7.0

10.1
11.1

4.8
4.5

38.7

0.11
0.09
0.82

B1
B2
B3

66
81

1262

9.30
9.20
8.34

0.2
0.2
1.5

1.7
2.3

16.5

2.2
5.9

130.0

6.0
8.2

485.5

0.3
0.4

b.d.

3.9
2.8

77.4

5.4
6.0

100.5

4.9
6.3

90.5

0.06
0.09
0.51

C1
C2
C3

384
307

9.62
9.08
8.90

0.3
0.2
0.3

1.1
3.8

21.4

1.7
9.0

91.2

2.5

27.1
75.5

0.4
0.3
0.1

5.9
4.1

46.5

7.1
7.0

40.7

7.1

14.5
16.5

0.02
0.52
0.72

b.d. value below the detection limit

Table 1:

Chemical analyses of water extracts from the “wall of bricks” at the Wawel Castle (mg/kg leached surface — the nine last columns).

pavement, respectively. In every profile three samples were
taken from the inner side of the wall (abutting the earthen
scarp), central part and outer side of the wall.

In the laboratory, salts were extracted from the crushed

samples of bricks (ca. 2 g) in redistilled water (pH = 7.2,
cond. = 2

S/cm). The solutions were then filtered, using Po-

rafil membrane filters (CA type, 0.45

m), and the conduc-

tivity and pH of the filtrates measured. The contents of chlo-
ride, sulphate, nitrate, phosphate and fluoride anions were
analysed using liquid ion chromatography (LIC), and those
of sodium, potassium, calcium and magnesium cations using
atomic absorption spectroscopy (AAS).

Results

According to the chemical analyses, the degree of contam-

ination varies in the analysed profiles (Table 1). Sulphate, ni-
trate, chloride, calcium, sodium and potassium have been
found to be the main ions. Concentrations of fluoride and
phosphate ions were much lower and sometimes even below
the detection limit. Magnesium was very low as at the pH
observed this element forms the insoluble hydroxide.

PROFILE A

The samples situated at the highest part of the wall show

intermediate conductivities and contain sulphate, nitrate,
chloride, sodium, potassium and calcium. The pH values
vary from 9.51 (inner wall) to 8.82 (outer wall) (Table 1).
The concentrations of ions grow from the inner side of the
wall towards the outer side (Fig. 3).

PROFILE B

The samples situated 2.5 m above the pavement level show

low conductivities in the inner and central parts of the wall
but high conductivities in the outer part of the wall. The pH
value is the lowest in the sample from the outer part. The
dominant ions are sulphate, potassium, calcium and sodium.
The concentrations of nitrate and chloride are lower. The
concentrations of ions increase distinctly from the inner side
of the wall (i.e. that abutting the scarp) toward the outer, ex-
posed part (Table 1, Fig. 4).

Fig. 3.

Concentration of ions in the „wall of bricks” at the Wawel

Castle in Cracow. A — horizontal profile situated 5 m above the
level of the pavement, 1 — inner side of the wall (abutting the earth-
en scarp), 2 — central part of the wall, 3 — outer side of the wall.

PROFILE C

Extracts from the samples close to the pavement exhibit

low (in the inner part) to intermediate (in the central and out-
er part) conductivity. The pH value decreases from the inner
(9.62) to the outer (8.90) parts of the wall (Table 1). The
analyses have shown that all the samples contain mainly ni-
trate, sulphate, chloride, also potassium, sodium and calcium
ions. There is a distinct horizontal variation in concentrations

QUANTIFICATION OF SALTS IN EXTRACTS FROM BRICKS 407

Fig. 4.

Concentration of ions in the „wall of bricks” at the Wawel

Castle in Cracow. B — horizontal profile situated 2.5 m above the
level of the pavement, 1 — inner side of the wall (abutting the earth-
en scarp), 2 — central part of the wall, 3 — outer side of the wall.

Fig. 5.

Concentration of ions in the „wall of bricks” at the Wawel

Castle in Cracow. C — horizontal profile situated 0.5 m above the
level of the pavement, 1 — inner side of the wall (abutting the earth-
en scarp), 2 — central part of the wall, 3 — outer side of the wall.

of ions (Fig. 5). The highest level has been found in the outer
part of the wall.

Conclusions

The analyses have shown that conductivities of the sam-

ples examined vary from low — below 100

S/cm — to high

— above 1200

S/cm. The pH value varies from ca. 9.65 to

8.34. The highest conductivities and lowest pH have been
found in the samples from the outer part of the wall, espe-
cially those situated 2.5 m above the level of the pavement.

The samples contain sulphate, nitrate, chloride, calcium,

sodium and potassium ions with the dominance of SO

and

, especially in the profile situated 2.5 m above the pave-

ment. The relationship between concentration of different
ions in profiles situated 5 m and 0.5 m above the pavement is
not so clear.

The concentration of ions and conductivities increase dis-

tinctly from the inner side of the wall (i.e. that abutting the
scarp) toward the outer, exposed part. In several cases the
salt concentration is so high that efflorescences were found
on the wall surface.

In many cases the crystallization of salts represents the

major damaging factor especially in the outer part of the wall
(i.e. in the evaporation zone). In contrast to most other build-
ings, water penetrates the retaining wall from its long „back”
abutting the scarp, while capillary suction from the founda-
tions has a minor role. This penetration has caused frost dam-
age, most serious at a distance of ca. 20 cm from the face of
the wall, where at full water saturation temperatures were
low (Kozłowski & Stępień 1997), and saturated it also with
water-soluble salts.

Sulphur was introduced by atmospheric pollution. The ori-

gin of chloride and nitrate is related to regional air pollution
as well (Turzański 1991, 1997; Manecki et al. 1997). A high
content of chlorides found close to the outer face of the wall
may result from de-icing of the pavement with NaCl or
CaCl

in winter. Sodium, calcium and potassium originate

mainly in the process of leaching of the bricks and mortar.
Air pollution could be the second source of these cations.

Acknowledgements:

The author thanks P. Stępień, M.Sc.,

and M. Skolicki, Eng., for their co-operation during sam-
pling. Thanks are also due to Dr. W. Sikora (Ms.) for LIC