Old building mortars

Hanna Jabłczyńska-Jędrzejewska

Old building mortars (Own translation)ⁱ

Kwartalnik Architektoniczno-Budowlany (Quarterly Architecture and Construction) 1958 cz. 1. pp. 85-94

I. The state of research and the current methods for the study of mortars

1. Introduction

Old mortars differ significantly in appearance and properties of mortars currently used. They are, in many cases, excellent mechanical properties, differ in color and texture. Methods of preparation have probably differ significantly from currently used. Unfortunately, not preserved to any more detailed guidance technology, and attempt to recreate the old recipe makes a lot of difficulties.

In 1950 began research on the ancient mortar building in cooperation M.Sc. architect Z. Tomaszewski, who, in the context of analysis of architectural and construction of various facilities receive adequate sample of mortar and together with detailed documentation transmit them to the test. In the first period the work mainly consisted of collecting the materials and the development of research methods. Still they were conducted attempts to use the results for further historical research and technology.

Conducted the study included the following general issues:

a. Separation of major types of technology in ancient mortars based on dated samples of mortars with different objects and Polish neighborhoods from the period X to XIX century.

b. Development of simplified test methods for the differentiation of different types of technology mortars. Current methods are not only a nuisance but not very effective.

c. Study the possibility of applying the results obtained in the analysis of architecture and construction, the development of methods of research and determine their effectiveness and scope.

d. Attempts to restore the old mortar and use the results for the purposes of modern building technology and conservation, and to issues of a wall painting of old and contemporary

Certain portions of these studies have been opublikowane¹, other materials can be found in collective archaeological work (Tum near Leczyca, Wislica, Szczecin, Warsaw, Mirmeki, Opatow et al.)

2. The publications in the field of study of ancient mortars

Publication of research results in the field of technology and composition of ancient mortars are few and scattered. In most concern are plaster and are related to issues techniques in individual objects wall painting. A more detailed study of mortars began recently conducted in the USSR, but also without any further attempts to extend these issues

Muller-Skjold² describes a system of individual plaster the wall paintings in Rome and Pompeii, and gives their chemical composition and technology. Rathgen gives the results of mortar from the pyramid Chefrena3³, Biehl i Grun⁴ describe the study of mortars and Roman waterworks and Eiffel. Eibner⁵ is the study of the plaster wall paintings egejskimi and quoted the results of previous Heaton studies⁶, who also investigated the same plaster.

Berger⁷ also cites a number of studies of ancient mortars, from the point of view of the fundamental goal - the techniques of mural painting. Winner⁸ in his textbook on painting the wall gives a lot of data on the plaster in successive historical periods, together with color photographs of these mortars.

Most data mortars built in Russia, dating from the tenth century to the eighteenth century can be found in the Jung book⁹, who deals with issues of treatment (particularly cement) and the historical introduction discusses in detail the types, chemical composition and technology, and conducts classification on technology groups.

3.Modern building mortars

In the study of ancient mortars were taken as the basis for modern mortars. Binding materials in which calcium and cement10, sand and filler material. Lime and cement are fundamentally different both chemical composition and binding mechanism. A brief summary of their basic properties is necessary for further consideration.

The main component of the lime is calcium hydroxide. In the carbon dioxide from the air on the combined calcium carbonate (often called carbonization process) which was isolated as a fine and permanently binds the weight of the mortar. Required for this reaction is carbon dioxide, which is a constant source of air. Hence the lime mortar is called air. Carbonation weight mortar is slow, especially in the deeper layers, where air access is difficult. For good bonding a lime required is also small amounts of moisture to facilitate both the chemical reaction and the subsequent crystallization is formed of calcium carbonate. Excess moisture affects very negatively on lime mortar, causing it to crushing and dissolution, due to partial leaching of calcium carbonate.

The basic components of cements are¹¹ oxide compounds gypsum, silica, and calcium, which are powdered cement. In the presence of adequate amounts of water they begin between chemical reactions, form hydrated calcium silicates and aluminates, which permanently bind the entire mass. After the initial attachment period, which quickly and throughout the mass, followed by further curing period during which the presence of large amounts of water to form a further quantity of binding compounds. Due to the vital role of water in hardening cement - it was called a hydraulic mortar, or water. Carbon dioxide in the primary reaction of the hardening of cement is not involved. Cement mortars have much greater mechanical strength than lime mortar. Excessive moisture environment, not only does not harm them, but even a positive effect.

In addition to these two kinds of bonding materials and we have a third type - that is intermediate between them, namely air, hydraulic mortar containing in addition to lime in excess, and also components suitable for cement, and so the oxides of aluminum and silicon. This type of mortar is sometimes called the most hydraulic limes. For proper curing such cement is needed, both carbon dioxide and water. Hardening their slow, like the mortar of lime. The first period of hardening, such mortars must take place in conditions suitable for mortars air. In subsequent periods, however, the presence of moisture, not only does not work adversely as lime mortars, but on the contrary results in a further hardening of the mortar and maturation. Air hydraulic mortar are more durable than pure lime, but less durable than cement. Old mortar belong almost exclusively to the type of hydraulic lime, which to some extent explains their excellent mechanical properties and excellent state of preservation in conditions from which mortar pure limestone would long ago have been destroyed.

In addition to binding members - a fundamental influence on cement properties are filling materials (fillers). The most common of these is sand. The addition of an appropriate amount of sand increases the strength and prevents cracking of mortar. Besides sand used as fillers they are now different grits and flour stone, clay, ground blast furnace slag, etc. Some of them have effect only mechanical, others have poor generally hydraulic properties. In the old mortars used as fillers were also bludgeoned with brick, limestone, marble, etc.

4. Existing test mortars methods

Existing test methods mortars based on typical methods used in the examination of modern mortars. These include measurements of physical properties (porosity, water absorption, hardness, strength, etc.), And to determine the chemical composition. The latter is sometimes expressed as the percentage of each oxide in the mass of mortar (calcium oxide, silicon oxide, aluminum oxide, referred to as the oxides of iron, magnesium, sodium and potassium). These designations require a number of complex laboratory procedures.

For determining the composition of the technological mortar is applied isolate and define the percentage of sand compactness, what they are simple chemical treatments and to determine the type and amounts of the other ingredients of the mortar used microscopic examination, based on the methods of petrography. They require the preparation of appropriately thin polished plates of samples tested.

In Soviet studies described by Jung¹²nd performed by Szwecowa and Surowcewa introduced yet additional tests of a general nature to determine the possible presence of nieskarbonizowanego lime and connections hydrolysable (with additives hydraulic). These tests made with alcoholic solutions and aqueous phenolphthalein, a dye which, in the presence of bases becomes amaranth - red. Otherwise Shviecov and Surovcev by calcining samples of mortars in succession at temperatures of 500-550C and 900C, determined indirectly the amount of chemically bound water and the amount of carbonates.

II. The method of classification study of ancient mortars

1. New research methods

The above-described test methods are generally cumbersome, require large amounts of time and a suitable apparatus. Not always well they fulfill their tasks, if it comes to specify the type of mortar. Particularly chemical research, leading to the expression of the mortar composition of the percentages of the various oxides, not only do not give sufficiently clear characteristics of mortar, but in several cases it still obscure. These studies also do not take sufficient account of hydraulic additives. Determine the composition of the mortar only by determining the percentage of sand is not right, because it ignores this important feature of mortar and only in very limited cases, it may give some results.

In search of new ways to study of ancient mortars it was primarily to find methods to quickly and easily research the largest possible number of samples. To facilitate the work of the study were divided into two stages. The first one included the overall classification, and only the second - a closer look at the composition of selected mortars.

General classification was based on certain external features of cement, especially in color and grain, and by chemically determining the amount of lime and fillers. Chemical tests was based on the following grounds:

To characterize mortar construction should take into account the three basic ingredients: lime, sand and additives hydraulic. Of the total amount of lime mortar used for a part it is chemically bound oxides of aluminum and silicon additives, hydraulic lime and the remainder is slowly carbonization.

Among these components - the amounts of sand and the amount of calcium carbonate (lime carbonized) in the mortar is very easy and simple (see. below). If the content of sand and calcium carbonate expressed as a percentage of the total weight of the mortar, then add both figures, in the case of pure lime mortar their sum should be close to 100, in the case of hydraulic lime mortar their sum is less than 100. The more components contained hydraulic dam - the difference will be greater.

In this test method are obtained three numerical values. The first one defines the percentage of sand in a mortar, the quantity of calcium carbonate, and a third addition is hydraulic. This third number for simplicity called hydraulic indicator. It is very useful, provided that the mortar no longer nieskarbonizowanego lime (calcium hydroxide), which should be before the test properly checked. In general, in the old mortar is not found free calcium hydroxide.

In this part of the study determined the kind used for hydraulic mortar additive on the basis of the external characteristics of the mortar and the sludge remaining after dissolution in hydrochloric acid mortar. In some cases, the precise nature of the additive hydraulic was possible only after a more detailed study.

Closer analysis of the composition of the various mortars included depending on the needs of a range of chemical tests and microscopic and try to play several types of mortars to confirm the results obtained in the study.

On the basis of the results of research carried out were attempts to classify the old mortar on individual technology groups. The developed test methods was also used to analyze the architectural and construction mortars for comparing samples from different periods.

2. Sampling mortars

Proper conservation of mortar and its authenticity is essential for research results and interpret them.

Samples were taken from the inside of the walls for the possible elimination of destructive influences, pollution, and possible subsequent additions. Places sampling were accurately quoted (location, height, depth, etc.) and marked on the plan of the building. Samples were taken in the form of pieces (one large or several smaller). Samples of powdered while downloading does not fit research classification.

Based on preliminary research and developed methods of measurement specified sample size for one test at approx. 0.5-1.0 cm³ (0,4-0,6 g). To carry out the test cycle was necessary to sample a total volume of not less than 5cm³. This amount was for two indications chemical and an appropriate provision, if necessary, repeat determinations, further microscopic examination and the archive

3. Initial classification

The collected samples were classified into groups according to appearance. They were taken into account first of all color, grain, and roughness, and further all the other features that distinguish each sample. In general, the results of this initial classification were consistent with the results of closer; Only in the case of mortars belonging to one group technology classification based on external characteristics was seriously hampered. The compatibility of these results was entirely justified, since the appearance of mortar depend on the type and amount of ingredients contained.

4. Determination of basic ingredients

For determination of the percentage of calcium carbonate pulverized a piece of mortar of about 0.4-0.6 g, was poured into a small porcelain crucibles and accurately weighed. Then the crucible was placed inside the device for measuring the volume of gas. Mortar was treated with 3 ml of hydrochloric acid 1: 1 (around 17%) which was dissolved carbonates contained in the sample with separation of carbon dioxide gas. After the reaction was read volume of gas evolved. This volume was reduced to standard conditions (0C, 760 mm Hg), then calculating the corresponding quantity of calcium carbonate (in grams) and the percentage of (the weight) of calcium carbonate in the test sample.

The basis for these calculations was the reaction:

CaCO₃ + 2HCl = CO₂ + H₂O + CaCl₂

which on the basis of an apparent chemical that at 0C and 760 mm Hg one milliliter of carbon corresponds to 0.0044 g of calcium carbonate.

Determination of the percentage of sand. After the indication of carbon dioxide is separated by decanting pan located in the solution, and with it all light deposits (jellies, suspensions, etc.) from the sand and sink into it, into separate tubes without dilution with water, for possible further investigation. Other sand was washed several times with water and then it was dried and weighed. The percentage of the sand was calculated from the weight of the entire sample.

The size ratio of hydraulic obtained by summing the calculated percentages of calcium carbonate and sand and subtracting the resulting number from 100.

Comments:

A. Before testing the samples were dried at room temperature in open pots at several days. In the same way tygielkach dried sand. Drying mortar and sand in an oven at elevated temperatures (105-110C) to constant weight significantly prolong the cycle of research and it was not necessary because the resulting differences between the marks lie below the limit of measurement error.

B. A small portion of the study, after crushing the mortar has been studied an alcoholic solution of phenolphthalein the presence of non-carbonated lime. This study was performed under a microscope for any signs of failure on the red color of individual fine grains of mortar.

C. Used by some authors separation of coarser sand grains prior to the further quantification was passing with the principles of research, so that there have been no such separation. Only in the presence of small pebbles (0.1 g or more) were removed from the sample before weighing.

D. n the above-described basic research also conducted additional research side. These included the examination type sand mortar, and the observation of color undiluted by water solutions of hydrochloric acid, and the sludge washed out during the washing of the sand. Especially these settlements, their color, type and quantity gave a number of additional tips on species mortar.

E. In calculating the content of calcium carbonate, a number of simplifying assumption that the sample does not have to carbonates of magnesium. This resulted undoubtedly a mistake when mortars containing beside calcium carbonate and some amounts of magnesium carbonate. The calculated carbonate content of the sample in this case were a little high. This error was not so large to affect the evaluation of the type of mortar.

F. Described series of measurements were performed for twenty crucibles in a single burst. In this scenario, the time indication of the ingredients of a sample, including a description of its external characteristics, was 30 minutes, so the total time for determining the mortar was one hour (large sample).

5. The accuracy of the determination of basic components:

Before starting the actual determinations were made control measurements to determine the accuracy of the measurement methods used.

Measurement accuracy indication sand was performed as follows:

A. A larger piece of crushed mortar, and then divided into four parts according to the general methods set out in the technology for homogeneous samples. In each of parts indicated by a percentage of the sand. See. tab. 1 item. A.

B. In the same mortar was separated four pieces of suitable size, and in each was determined percentage of sand. See. tab. 1 item. B.

They show that the signs in the first sample range from 2.5% and in the second sample in the range 15.5%. Average marks the first attempt is very close to the average marks of the second attempt. These results indicate that the measurement accuracy is very good compared to fluctuations in the sand content in each sample.

Fluctuations sand content in each sample could be reduced to some extent by increasing the sample size, it would be inconvenient, however, due to the much volume of evolved carbon dioxide and an appropriate extension of testing time, as well as the need to download proportionately more samples of mortars. Also grinding of samples according to the method described above was used as obliterated characteristic for certain high heterogeneity of mortar composition.

Table 1. Determining the accuracy of marking sand

To measure the accuracy of indication of carbon dioxide were weighed four samples cleaning calcium carbonate at about 0.25 g and analyzed for their content of carbon dioxide described above by volume. The results obtained were compared with the calculated theoretical results. Accuracy ranged from + - 0.5 ml of carbon atoms, which based on the weight of calcium carbonate CaCO₃ was 0,0022 g.

Fluctuations in the composition of the mortar. Depending on the type and accuracy of the mortar preparation, the content of the basic components in each sample may undergo some changes. In general, these differences for sand and calcium carbonate varies from 1 to 4%. There are even variations of less than 1%. For large differences between the results (on average more than 6-8%) made two additional measurements.

6. Classification mortars on the basis of external characteristics

Initial classification of the mortars on the basis of external characteristics shows that their color and gorges (grain roughness) show quite significant differences in each sample

Frequently repeated the following types of colorations:

a. white and yellowish-white

b. yellowish and yellowish-gray

c. pinkish, pink, pink-gray

d. gray shades of cold (color similar to cement)

Coloration was dependent on the amount and type of used sand, the color of lime and on the additives used, and in a few cases was probably the result of external influences.

Sand content and thickness underwent considerable fluctuations, which resulted in differences in grain mortar. The roughness of the fracture depend not only sand, but the type of weight of lime and fillers. Frequently repeated the following types of breakthroughs:

a. completely crystallized, completely free of sand, slightly transparent, very rough, very harde

b. chalk, smooth, not too hard

c. grainy and very grainy, quite and very hard

d. average grainy, quite fragile too rough

e. granular medium, hard and very hard

Mortars of similar breakthroughs could the differences between each color, but usually breakthroughs "and" was found in mortars colored gray breakthroughs "b" in mortars white and white-yellowish, breakthroughs "c" - in mortars white, rosé and some yellowish, breakthroughs "d" and "e" in mortars gray - yellowish and yellowish, and mortars gray colored cement.

In addition to these essential characteristics observed, and other properties of fractures, among other characteristic of many mortar presence of smaller or larger lumps of lime, the presence of charcoal, the presence of fragments of ceramic (brick), etc. These ingredients were not taken into account, the main classification, since the presence of they could also be random and not typical.

III. Results and conclusions

1. The results of the classification on the basis of cement essential components

With a detailed statement of the results of dozens of mortar from different periods (see: Tab. II) shows that all the tested mortar can be divided into several distinctly different groups. These groups are specific to certain periods.

Closer interpretation of the results is in the later part of the work, but can be generally stated that among the earliest mortar (construction pre-Romanesque and early Romanesque), we find two types. In one there is in general sand, and the carbonate content is very high, in the second sand content is relatively low and the high content of carbonates with a fair indication of hydraulic fluid. In the following period (construction Romanesque and early Gothic) sand content in mortars significantly increases the content of carbonates decreases, but the rate of hydraulic only slightly decreases. In the. XIV (Gothic building), sand content increases typically above 80%, lime content still decreases and the rate of the hydraulic very clearly declining. In modern times (construction Renaissance, Baroque) sand content decreases slightly, and lime increases, but the rate is still low hydraulic.

It follows that the recent classification capabilities are large mortar, and the mortar later - limited. However - as shown by further research - Mortar and subsequent periods vary from individual type of ingredients used (sand, additives, hydraulic) and the exterior which creates opportunities for further clearer classification. Use it also becomes the use of the band technological brick - mortar and additional classification mortars in an indirect manner by the classification of bricks..

2. The conclusions of the research classification

The study revealed that the classification of mortar can be performed easily and quickly without a thorough analysis of the chemical and technological individual samples.

The resulting numerical results should be regarded as approximate and indicative, however, to a degree quite sufficient for classification. You can even likely to assume that at this stage of research a more detailed analysis of the composition of the samples not only facilitate the classification, but even through the fog the introduction of too many minor details.

It should also be noted that the exact interpretation of an "indicator" hydraulic would be difficult, because the size of this number depends not only on the components actually reinforcing mortar (hydrated silicates and calcium aluminates), but also the presence of various fine suspensions, the solubility of the filler in hydrochloric acid the possible presence of residual calcium hydroxide, etc. this number, however, is characterized by good degree hydraulicznoœć mortar. This is confirmed by, inter alia, the compatibility between the size of the total, and the amount of sludge precipitated from solutions of hydrochloric acid.

The results of classification mortars also indicate that the concerns that the mortar (especially covered the ground for a long time) substantially altered under the influence of the environment, are not justified. However, a necessary condition to use for testing samples of healthy, taken from deeper parts of the walls and non friable during downloading.

The study also showed that there is a clear link between the type of mortar and the period of its use. It should be noted, however, that given the classification can not be the measure of absolute dating for mortar. Interpretation of the results should be cautious and must be agreed with the data obtained on other roads. Further research and a statistical overview of a large number of signs in the largest possible quantities of various mortars will only further assessment of the scope and effectiveness of these methods of classification.

Tabela 2. Classification of mortars based on essential components

^{i This paper was the first part of the study. The second part of the work has not been published in the next issues of the quarterly.}

¹ Report on the research carried out in the period from 7 May to 30 May 1953. Over settlements early medieval and Romanesque architecture in Opatow, Historical Review, 1953, Vol. XLV, no. 4, pp. 691-721; Z. Tomaszewski, Research brick as an auxiliary method in the examination of architectural objects, "Scientific Papers Wroclaw University of Technology - Construction", no. 4. Warsaw, 1955, pp. 31-52.

² F. Muller-Skjold, Uber antike Wandputze, "Angewandte Chemie", LIII, 1940, pp. 139-141.

³ F. Rathgen in the journal "Tonindustrie Zeitung", XXXV, 1911, p. 124.

⁴ R. Grun, w in the journal "Angewandte Chemie" XLVIII, 1935, p. 124.

⁵ A. Eibner, Entwicklung und Werkstoffe der Wandmalerei, Munchen 1926.

⁶ R.J. Gettens i P. Duel, A review of the problem of Aegean wall painting, "Technical Studies", X. 1924, nr. 4; and cited the article by N. Heatron, in "Journal of the Royal Society of Arts", LVIII, 1910, pp. 206-212.

⁷ E. Berger, Beitrage zur Entwicklungsgeschichte der Maltechnik, I-II F., Die Maltechnik des Altertums, Munchen 1904.

⁸ A.W. Winner, Materiały technika monumetalno-dekoratiwnoj żiwopisi, Moskwa 1953.

⁹ W.N. Jung, Osnowy technologii wiażuczych wieszczestw, Moskwa 1953.

¹⁰ Gypsum was not taken into account here, because as a mortar for masonry does not apply.

¹¹ Description refers to commonly used Portland cement.

¹² W.N. Jung, o.c.