Konserwacja kamiennego portalu z Ołbina w kościele Marii Magdaleny we Wrocławiu PRESERVATION OF THE STONE DOORWAY FROM OŁBIN IN THE ST. MAGDALENE CHURCH AT WROCLAW
The Romanesque doorway from Ołbin whose origins
may be dated as early back as to the late 12-th century
was built from blocks of arkose sandstone. During
the long course of history its state of preservation
gradually deteriorated and thus it had many
times to be subjected to conservating treatments. Its
surface was, among the others, reinforced by means
of liquid glass and chemicals of the fluosilicate group.
It seems, however, that the treatments applied
did not bring intended effects and this probably was
the reason why one part of the doorway has been
coated with cement milk whereas the others co-ered
with a protective layer of a hardly distinguishable
polymer-type organic matter. Nevertheless, these superficial
coatings have proved to be unable to prevent
advancing decay and the stones were getting more
and more disintegrated, maybe at even higher rate
as it was the case at earlier date. Finally, the layers
next to the stone surface begun to split and exfoliate
and from underneath poured the powdered sandstone.
This increasing decay has led to substantial decrements
in the total mass and also to deformations in
the plastic appearance of the doorway.
In effect of investigations carried out it became possible
to find that these destructions were, in the first
line, caused by the action of water-soluble salts and
water penetrating into the doorway from the church
interior which the both occurrences were due to the
fact that the outer surfaces of walls have been faced
with clinker bricks hardly permeable for water. Although
several expert bodies were meeting with this
object in mind no clearly outlined programme of preservation
works for the said doorway has been worked
out in conclusion. The works carried out within
the first stage comprised the following measures:
encasing of the doorway to protect it against the immediate
weather influences (mainly the waters'), securing
the fragments by glueing the paper on their
surfaces, removing the clinker bricks from the immediate
neighbourhood of the doorway, and, finally,
building of a cellar under it to stop the flow of ground
waters. The undertaking of a full-scale treatment
has become possible only on completion of examination
of possibilities to apply epoxy resin solutions
for structural impregnation and also on working
out of the s.c. pocket-type method for stone saturation.
Investigations in this respect were conducted at the
Copernicus University, Toruń to order of the Historical
Monuments Documentation Centre, Warsaw.
The conservating works themselves were carried on
in the years 1967 and 1968 and their plan covered the
actions named below:
a) superficial strengthening of pouring, delaminating
and exfoliating portions of stones from which the
doorway is built, .
b) reinforcement of the breaking away fragments of
doorway with the application of putties and fillings,
c) removing of the superficial built-up layers with
the aim to restore the stone porosity and ipso facto
enable the impregnation,
d) removing the cement and gypsum putties and fillings
by means of which the former decrements in
stones were filled up,
e) extraction of water-soluble salts,
f) structural impregnation of the entire doorway with
the aim to reinforce the deepest stone layers,
g) filling with putties the holes and pin cracks.
The superficial reinforcing of stones was carried out
by means of the 20 per cent methylbenzene solution
of epoxy resin. The resin was hardened by treating
it with triethylenetetraamine. For reinforcing of stone
fragments that have broken and exfoliated thus threatening
to flake the putty has been applied obtained
by mixing the epoxy resin with powdered sandstone
in 1 : 15 proportion. The putty was filled into pin
cracks and then pressed. With the putties hardened
a durable junction was obtained between the loose
fragments and their bed. Thanks to the properties
possessed by existing built-up layers they could be
removed with the use of either chemical or mechanical
means. Chemically were removed the layers
formed in result of an usual action exerted by atmospheric
components, and the 3 to 6 per cent hydrofluoric
acid was applied for this purpose. Portions
on which the afore-mentioned built-up layers have
been found comprised well under 10 per cent of the
total doorway area.
The layers consisting of cements and organic matter
not soluble in solvents available were removed mechanically
by means of scrapers. With the dark-coloured
built-up layers removed the stones of which
the doorway is composed have regained their original
colour, texture and plasticity. (However, it has
proved impossible to restore to the superficial stone
layers their original porosity. The reinforcing substances
with which the stone pores were filled are
unremovable and their porosity could be restored only
by means of grinding-off the superficial layers
being, of course, an inadmissible practice. The cement
putties and some gypsum putties, too, applied during
the former restorations of the doorway were removed,
for they contributed to the accelerated destruction
of stones, in addition forming black spots on the
brighter coloured background.
On completion of the above-mentioned works the
next stage has been started, consisting in removing
of water-soluble salts. A method of their forced migration
to paper layer was applied using the fivefold
coating of the entire doorway with water saturated
paper sheets. Already the fourth consecutive paper
coating did not reveal the presence of salt. The above
method allowed to remove the salts from pores next
to the stone surface which the fact is due to limited
permeability of water into the deeper stone layers
in effect of earlier applied treatments (N. B. migration
of salts occurs only in parts saturated with water).
As the superficial impregnation of doorway carried
out by means of epoxy resin solution is able to
prevent decay for a limited period of time only it
has been decided to reinforce the structure of the
doorway stones in their deepest possible layers (structural
impregnation). This treatment was carried out
using 10 per cent toluene-and-methyl alcohol solution
of epoxy resin in the respective proportion of
1 : 2 and 1 : 3. The amount of methyl alcohol present
in 'Solution was deciding for the rate of resin precipitation
from it. At the 1 : 2 proportion the precipitation
was beginning after about 20 hours whereas at
1 : 3 after about l'O hours. The first of the above solutions
was applied in cases in which the need occurred
to saturate the stones for more than 12 hours,
the other one — for saturation periods not reaching
the time given above. Solutions were prepared in portions
of 1 to 4 litres to which 15 per cent of triethylenetetraamine
was added in proportion to resin amount.
They were introduced into the doorway stones by
means of s.c. pooket-type method. The pockets were
prepared in such a way that on the stone surface were
put 5 to 6 layers of the water-saturated paper onto
which, starting from their edges, the gypsum mortar
was imposed forming the 1 to 2 cms wide framing
at all sides. In the upper parts of so formed lining
a filler was made from a piece of paper and the whole
covered with gypsum .
The separate stages of the pocket-forming may easily
be seen from illustrations. All the elements of doorway
were covered with pockets. With the gypsum
mortar dried the tightness of pockets was examined
by means of solvents and leakages removed. The impregnation
has been carried out by pouring the solution
into pockets and its steady supplementing so
that the pockets could be kept full throughout the
entire period of saturation. During one-day operation
were saturated the doorway elements with sizes
allowing to complete saturation and removing the
pockets themselves within 30 hours. It has been found
that within this period the epoxy resin gel forming in
gypsum pores was still thin enough to enable the easy
removal of pockets. They could be removed without
damaging the stones as the object after impregnation
was secured with cellophane having inhibitory effect
on evaporation of solvents.
Since the rests of gypsum remained on the stone surfaces
they had to be removed at once thus not permitting
their hardening by the active resin. After cleaning
operation the saturated elements were insulated
by means of cellophane from the ambient atmosphere
for a period of 10 to 14 days to allow the maximum
rate of precipitation of resin from the solvent.
Three hundred ninety litres of resin solution
were used for this purpose of which the amount some
295 litres have been introduced into stone, the
balance being absorbed by gypsum and lost during
the operation.
Within the last operation the supplementing of slight
stone decrements in form of holes and pin cracks
with the epoxy putties has been carried out. For
this purpose, much the same as in the course of the
above-described operation, a mixture composed of
1 part of epoxy resin and 15 parts powdered sandstone
has been applied. To this mixture containing hardener
(15 per cent) petroleum spirits were added to
obtain better conditions for hardening. The putties
prepared for this operation are characteristic of their
higher degree of porosity at the same time showing
good water-repellent properties and impact strength
similar to that of actual stone.
For preparing the putties the white sandstone powder
was used so that after their hardening it proved
necessary to patinate them together with traces left
by pockets („crabs”) using mineral dyes with 1 per
cent addition of epoxy resin solution acting as hardener.
The illustrations show the doorway in state
after preservation operations.
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