The joints and mortar to brick walls

At present, the preparation of mortars or weld on site arouses among both contractors and preservationists at least mixed feelings. For many of them this is a kind of muddy sand - the kind that are known, like you know that you can go, but few know how to do it, about taking responsibility not to mention.

For many years, only in a few places works are carried out to allow to assess the strength and usefulness of the old mortar, and how "ready" prepared by the already mentioned often "Great Producers" fulfill the hopes placed in them. One such place is the Nicolaus Copernicus University in Torun, and one of the researchers, Prof. dr hab. Wieslaw Domasłowski.

Below reprint any of the articles, which appeared in the journal Renowacje (Restoration). own translation.

Authentic mortar in the joints of the wall were not and basically still are not protected. This fact should be considered incompatible with the principles of conservation - one of the demands contained in the Charter of Venice is "restaurant (...) is based on respect for the former substance and the elements constituting the authentic documents of the past." Authentic mortars, like bricks, constitute no doubt mentioned in the Charter documents the past and should be protected from destruction. Replacing them with new, modern, it impoverishes the authenticity of the monument, so its most important value.

prof. dr hab. Wiesław Domasłowski

Renowacje (Restoration) nr 4/1999 ss. 19-25

Why we rabbet the walls

Synonymous with durability materials are in accordance with the current statement, wall, iron, concrete, however, only insiders know that they, too, depending on the quality and the conditions in which they are, are slowly or quickly destroyed. As a result of a dissolving action of water, the freezing temperature changes, water-soluble salts, aggressive gases, air pollutants, microbes and other factors it is easily destroyed lime mortar used to build the wall. The same fate befalls bad brick (not suitable composition, badly burned), iron (very quickly corrode), as well as concrete and reinforced concrete (relatively easily disintegrate if used to receive poor cement, aggregates of inadequate granulation and proportions, the wrong attitude aggregate cement, too much or too little water or binding concrete proceeded under unfavorable conditions). Iron and concrete can be protected from destruction. Iron purified (removes the so-called rust) and covers the protective coatings. Concrete normally sealed and also prevents the coating using, in the case of formation of destruction removed weathered guide, purified and protects the reinforcement, and complete loss of new mortar.

It's different in the case of brick walls. Since lime mortar is not protected against destruction, damaged mortar is removed to a certain depth and joints filled with new mortar. The same shall apply with damaged bricks. Only in recent years they began to "respect" authentic brick, complementing them small cavities mortars. Sometimes preservationists complement the large cavities, and even entire face bricks.

The fact that the authentic mortar in the joints of the wall were not and basically still are not protected, must be considered incompatible with the principles of conservation. One of the demands contained in the Charter of Venice (provisions and resolutions of the First International Congress of Architects and Technicians of Historical Monuments in Venice, 1964) reads: "restaurant (...) is based on respect for the former substance and the elements constituting the authentic documents of the past." Authentic mortars, like bricks, constitute no doubt mentioned in the Charter documents the past and should be protected from destruction. Replacing them with new, modern, it impoverishes the authenticity of the monument, so its most important value.

The position is well known and generally all conservationists agree as to its validity. Why allow so to destroy the mortar and bricks, and sometimes whole walls? The reasons are complex. In the recent past, the reason was the lack of appropriate means and methods of their protection and maintenance. Now, with the manufacturing industry preparations with excellent properties and conducting research laboratories growing body of research on the maintenance of mortar and brick, in the way of universal protection and conservation of brick walls facing economic issues - the treatments are expensive. Much cheaper and easier, you can remove the grout and damaged tile, and then the wall wyspoinować and embed new bricks.

Research on the protection of mortar and bricks

The issue of protection brick walls from damage had already been taken in the so-called. interwar period. It was suggested, among others, the use of paraffin waxes (hydrophobization while often sealing), and soaps of polyvalent metals (hydrophobization), not less substances have not found wide use because of the defect, and also causing harmful side effects (easily dirty the surface of the wall, instability of the security accelerating the destruction of bricks and mortar due to pore sealing, et al.). Only the production of organosilicon compounds and, above all, silicones and preparations based on ethyl ester of orthosilicic acid has created a framework for sound protection from damage and maintenance of these monuments. Thanks to them underestimated the problem of maintenance of the walls has become a subject of research in educational science and conservation. Various institutions have also started to organize conferences on these issues (most recently in a and b and Bressanone in France (1992), Warsaw and Legnica (1994).

Issues comprehensive maintenance of the walls were also devoted to the study conducted by a team of staff teaching and research of the Institute of Monuments and Conservation Nicolaus Copernicus University in Torun (KBN grant). They published the results of allowing lasting protection against damage and maintenance of both mortars, like bricks (W. Domasłowski, M. billets-Lewandowska, J. W. Lukaszewicz Research on maintenance brick walls, Torun, ed. Nicolaus Copernicus University in Torun, 1998). It is worth noting that the proposed methods and means do not cause adverse side effects, ie. Accelerated destruction of mortar and brick, which often observed when using untested preparations and mortars.

The reasons for the destruction of mortar joints in the limestone walls

Why limestone mortar found in the walls are destroyed? The answer is simple. Llime have low mechanical strength (according to the Polish Norm strength of code mortar of lime should be 0.8 MPa = 8 kg / cm²), are resistant to freezing and crystallization in the pores of water-soluble salts are completely water-resistant (primarily all containing carbonic acid), and completely stable to atmospheric pollutant strong acids (sulfuric, nitric). These factors cause the gradual destruction of mortars found in the outer parts of the walls, which manifests itself mainly in their granular disintegration (decay grainy) and scatering. Gradually mortar breaks down deeper and deeper, it can cause loss of bricks from the wall. Particularly field extend these phenomena mortars salty, prone to rapid and deep moisture, where the walls are dry lime mortar does not degrade, and their strength over time increases. Well-preserved mortar encounter so in the interiors of buildings, as well as in places protected from water and in deeper layers of the outer face of the walls remain outside the soaking water. Physical and mechanical properties of mortar of lime and their resistance to the destructive depends on several parameters, primarily on the quality of the lime. Quicklime to be obtained from the pure raw materials rich in calcium carbonate and without contamination. Limestone should be burned at the appropriate temperature, and then the lime properly extinguished (transition quicklime in extinguished, ie. CaO to Ca(OH)₂. Good quenching (forests) lime takes place using a precise amount of water and temperature controlled. The correct extinguished quicklime is not determined, however, good quality lime. the reason for this is the inability to complete conversion of calcium oxide hydroxide during the brief mixing slaked lime with water. the resulting during the mixing of the calcium hydroxide formed on the surface of the grains of the calcium oxide-tight coating (gel) makes the access of water to the unchanged calcium oxide particles. this phenomenon also occurs in the preparation of the so-called hydrated lime (dry slaked). the use of this lime of construction and maintenance is unfavorable, because in place of the small particles of calcium oxide in the mortar (plaster, joint wall) are produced as a result of hydration, followed by carbonization larger particles of calcium hydroxide, calcium carbonate, and finally, grains increase the volume and consequently formed in the mortar stresses and microcracks. This leads to a weakening of mortars and, in extreme cases, to chipping pieces of plaster (ie. Shooting plaster). To avoid this, slaked lime stored in earthen pits for several dozen years. Under these conditions both slow the hydration of the calcium oxide, sedimented impurities and soaking into the ground with an excess of water contained in the salt, lime is in these conditions, a fine-grained, homogeneous, and acquires the thixotropic properties (sol stationary enters the gel state and vice versa).

These lime, called pits, characterized by the highest quality. Mixed with aggregate is gradually carbonation without the negative effects described above. Providing a good lime does not guarantee to obtain a good mortar. This is determined by the type and amount of aggregate, its granulation, the amount of water, and the conditions in which there is a binding mortar. With these factors have the most trouble conservators ensuring mortars suitable binding conditions in the joints of the wall. Binding conditions are valid when the mortar dries slowly and it remains wet for an extended period. In such circumstances there was a slow carbonization of surface films of calcium hydroxide, and in the deeper parts, along with the evaporation of water gradually crystallized dihydrate calcium hydroxide. To carbonization occurred in the deeper parts of the mortar must be fulfilled two conditions:

• water filling capillary should evaporate
  
• mortar should not be completely dry
  

In the first case, the water filling the capillary prevents the penetration of seasonings into the air containing carbon dioxide required for the carbonization hydroxide. Whereas when the mix is ??completely dry, air and carbon dioxide can freely penetrate the capillary, but in a dry atmosphere carbonization reaction can not occur. For this purpose it is necessary to a certain amount of water - Mortar should be moist. Sufficient water to effect this reaction can give a moist air - penetrating into the pores, it gives some of its water contained in the walls of the mortar (it is called sorption), the quantity of regenerating water increases with decreasing temperature

To fulfill the first condition (= bonding mortar), there must be free evaporation of water in temperate and not very high humidity.

Alternatively, to meet the second condition, the hardening process (= carbonization) must occur in an atmosphere of high humidity and low temperature (of course more than 0 ° C). It's easier to meet these conditions for building a new house or his plastering. It is difficult, however, when spoinuje the wall, ie. Introduces a layer of mortar between the bricks, mostly on small depth, depending on the depth, which was removed from the damaged mortar joints original. By joining the grouting, it is recommended to remove the weathered mortar joints clean, moisten it with water, enter the mortar and provide the conditions for good setting and hardening. Unfortunately, they rarely last requirement is fulfilled. Frequently after the completion of stage undresses and leaves mortar at the mercy of nature. Contractors appreciate in this case, lack of sunlight and humid air. If it is warm and sunny, it creates a weak grout that can be blurred by the strong side rain, destroyed by hurricane wind, burst asunder by crystallizing salts or through the ice. With examples of poorly connected, weak lime mortar met (meet?) Often residents of the houses in which plastered the apartment without adequate moisture conditions. Scratch the paint and a thin layer of plaster reveals a weak, dropping a mortar. You could say that good conditions for grouting are with us in the spring and fall, unless they happen to frost. Of course, you must then reckon with the need to protect the walls from rain, but from experience we know that the contractor carry out this type of work throughout the season, whatever the weather.

Contemporary, according to standard lime mortar should be after 28 days of aging compressive strength of about 0.8 MPa (1 MPa = 10 kg/cm²). It is the strength of small, so no wonder that the mortars are not weather resistant. The most important for them is the initial period, because over time their strength increased with full carbonation, crystallization processes and reactions occurring between aggregate and binder limestone. In the latter case, the formed calcium silicate is permanently bonding grains of sand. Such a mortar with good, we meet in the interiors of historic buildings. They know the conservators, which fell to forge bricks from the wall. They have to spend a lot of manpower and effort, realizing this task. The excellent properties of the old lime mortar we can see an example of the wall of the castle of the Teutonic Knights in Torun (XIII-XIV c.). It was blown up by the Torun in 1454, and its remains uncovered from the earth in the years 1958-1966. Observing fragments of the ruins, we can conclude that the mortar occurring originally in the interior of the wall has not been destroyed by intensive operating elements.

Poor properties of lime mortars were well known in antiquity. Our ancestors in the distant centuries developed - leading to perfection - the technology of lime mortar and lime. Epochal discovery was the pits of lime and mortar modification using ceramic additives, especially pozzolana. Pozzolan made a breakthrough in the construction industry. They contained in dispersed colloidal silica (so-called active) is reacted with lime, creating a durable and water resistant calcium silicate. The mortar achieves high mechanical strength, water resistance, and - this is crucial - mortar with these additives may involve underwater - a hydraulic mortar. Research pozzolanic mortars Roman establish that they have a compressive strength of about 20 MPa (modern standardized lime mortar about 0.8 MPa, and the hydraulic lime about 2.5 MPa). Pozzolan mortar did not immediately achieve the specified mechanical strength, but very quickly uzyskiwały strength sufficient for the erection of large buildings, and most importantly water-resistant hydraulic machinery (baths, bridges, aqueducts). Compared with pure lime mortars we can be considered as rapid-setting mortar. Mortars are undoubtedly forerunners of Portland cement mortars and concretes pozzolan name (Italian: Pouzzolo) comes from the village of Pouzzoli, located in the vicinity of Mount Vesuvius. It is dust from the volcano was the first active dopant comprising silica in a state of high fineness which are currently known pozzolans.

Romans used not only the volcanic ash of Vesuvius, discovered new pozzolan around Rome, as well as on the islands of Santorini and Aspronis. In the area of ??Naples, the Rhine and Bavaria also discovered an active volcanic tuffs (the so-called route). To contemporary pozzolana include diatomaceous earth, pumeksy, rocks, Geza, clay, furnace slag, ash and others. Most pozzolana activates at an elevated temperature. Currently, only one company offers on the Polish market mortar additives pozzolana (routing) - it is a company Tubag.

Pointing masonry cement mortars?

As already explained, pointing mortar, lime walls does not give good results because of the inability to ensure proper binding of the joints, as well as because of their poor mechanical properties. Besides these, there are other reasons for not allowing to receive in the joints of lime mortar with optimal properties. One of these is the inability of compaction, the compaction of the mortar in the joints. They are usually applied loosely so that they have high porosity and water absorption and thus poor mechanical strength and more susceptible to destruction by standards than mortar.

The fact that the rapid destruction of mortar of lime introduced into the joints was widely known after appearing on the market of Portland cement began to be used widely not only in construction, but also for pointing brick walls and other renovation and restoration. Used for this purpose cement mortar have radically different properties of limestone. Simple bound, had less shrinkage, it can be applied in layers of any thickness and volume, have a high mechanical strength (more than a mortar of lime and bricks), lower water absorption (the mortar of lime and brick - approx. 10%) and poor capillary properties - due to the small diameter of the capillary move in an effort them water. It would seem that the Portland cement will solve the problem of stability of joints. After years of experience, it appeared that the welds were indeed durable, but the destruction began to undergo in contact with them bricks. The blame for this state of affairs was attributed to water-soluble salts contained in cement.

It was claimed that they migrate from the mortar to bricks, crystallize in them and they rozsadzajš. Further observations have shown, however, that the mechanism of destruction of the bricks is different. The reasons for the negative impact of cement on bricks were mainly their weak capillary properties and high mechanical strength. Better capillary properties bricks causing faster evaporation of water from the mortar than brick. This phenomenon takes place mainly in the vicinity of the contact bricks with mortar, which is most intense evaporation of water, resulting in the accumulation areas followed salts in the bricks and mortar, crystallization, reducing the disintegration of bricks. In the case of large amounts of salt are crystallized over the entire surface of the bricks, but they do not accumulate in the mortar (migration of water from the mortar to brick), in the process destroying the bricks also took an active part water, which freezes into ice expands. This process occurs primarily in batches, in which the pores are filled to the greatest extent by the water. These are the areas in contact with the bricks with lime mortar. In the end, as one, also an important cause, replace the different coefficient of thermal expansion of cement and bricks. When temperature changes occur between them the shear stresses that lead to a loosening of the cohesion between them, loss of adhesion and the formation of cracks or breakage or disintegration of bricks weaker. As a result, progressively destroyed face bricks, then the process involves deeper layers thereof. They formed as if the cells divided into a grid of cement mortar. Cement mortar caused the destruction of, among others, bricks and stones of Krakow Barbican. The expert's report commissioned PP PKZ in 1970, found that the cement fills the weld has an average absorption of 6.8% and 21.5% of bricks. Bricks were weak, while the mortar very strong. In the case of limestone mortar with wide pores, and thus good capillary properties and high water absorption (about 20%), the opposite phenomena occur. Mortars are the type of the filter astringent water and salts contained in it. So these are the mortar drying and accumulating salts. Prevent the destruction of bricks, but the same are destroyed, the easier they do not have high mechanical strength. Therefore, the presence of authentic mortars in the outer walls, exposed to atmospheric agents is rare. From the point of view of conservation mortars are good, safe from the point of economical while mortars are bad. Every few years, parts of the walls should be grouted.

Negative results pointing masonry mortars, lime and cement has focused the attention of conservators at the possibility of using mortar cement and lime, and they are many years widely used.

The properties of these mortars depend on many factors. They decide about them: the brand of cement, lime cement ratio, the ratio of aggregate to binder, granulation aggregate (usually sand) and the amount of mixing water. Depending on the ratio of cement lime is obtained with characteristics intermediate between lime and cement mortars. This relationship is commonly known, but the contractor of renovation and restoration seldom realize what mechanical and physical properties have used their mortar. Typically, he mixes the individual ingredients "by eye" and does not carry out laboratory testing mortars. The statements of contractors and documentation work indicate that they use a few percent additions of cement, and in rare cases, retain ratio of 1 to 1. That is not the case, that applies a small amount of lime, a large cement brick testify destructible and hardness and low water absorption mortars. Contractors are trying to make their mortars were stable, that testified to the well-done their work, they do not realize, however, that seem sentence of doom on the bricks.

Technology research grouts walls

Protection against the destruction of authentic mortars occurring even within the walls, as well as technology-based grouts, corresponding to the demands of conservation and economic, has been the subject of research conducted by the staff of the Institute of Monuments and Conservation under that grant KBN. It was found that to strengthen and harden the destruction of the lime mortar, are particularly useful formulations based on czteroetoksysilanie (orthosilicic acid ethyl ester). Good results were obtained (Dr. J. W. Lukaszewicz) preparations Remmers (Remmers Steinfestiger OH and Funcosil Steinfestiger 510). They reinforce the fracture very weak lime mortar (0.6 MPa) of 400% (Funcosil OH) to 600% (Remmers 510), the advantages of these formulations include their hydrophilic properties and the fact that they reduce water absorption lime mortar only 25%. Taking these data into account, we conclude that the enhanced mortar will not undergo rapid destruction (increased strength) and will be accumulated in a destructive processes (good capillary), protected from decomposition of bricks. Before taking technology research mortar for pointing brick walls (W. Domasłowski) formulated demands of conservation, which should correspond to the mortar. It would be best if they had the same physical and mechanical properties as a brick. Unfortunately, this condition is not feasible, because the properties of the bricks are very diverse, and you can not get mortars of the same properties, despite the use of the same ingredients and their amounts, as well as methods for their preparation. Therefore, we assume that the properties of the mortar should be "only" similar to the existing bricks in the wall. The fulfillment of this condition is to avoid the devastating impact of mortar on the bricks. The most important demands are similar or better properties than the capillary mortar bricks. Such mortars do not constitute barriers to the free movement of water in the wall, and will constitute, in what has already been mentioned, filters astringent water and accumulating salts. Other features of the cement brick is less than the mechanical strength similar to or higher water absorption and a similar thermal expansion coefficient. In addition to said properties of mortar should match within a few hours, fresh and hardened mortar should have good adhesion to the bricks do not shrink during the setting and hardening, to be resistant to water, freezing, water-soluble salts and microorganisms.

Taking into account the results of their own and other authors of Torun, it was found that the bricks found in Gothic churches in the northern Polish have a compressive strength from 6 to 9 MPa, water absorption after 24 hours from 9 to 16%, and pull up the water on the road capillary height of 5 cm for 20 to 60 min. These parameters were taken into account, leading of the survey. Examined the usefulness of modified mortar of lime (hydrated lime), cement and cement-lime "clean" and modified. To modify metakaolinit used as the most active source of silica. Also examined the usefulness of mortars factory production Max Krusemark Mineros-Werk (Fugenmirtel 0.7 and 2.5) and Remmers-Fugenmirtel. Unfortunately, the mortar has proven to be unsuitable for pointing bricks. Mortar Mineros podcišgały very hard water (to a height of approximately 2 cm for 24 hr.), And the compression strength was 17-18 MPa. Slightly better properties have mortar Remmers-Fugenmirtel. By 24 hours pulled up water to a height of 2,8-4,7 cm, and its compressive strength was 9,6-15,1 MPa. Research on the listed mortars lime and cement have allowed however to conclude that the selection of the appropriate binder and a certain amount of sand, mortar can be obtained by any of the properties, and therefore the parameters suitable for grouting walls made of various bricks. The basic condition for obtaining zaprawo good properties is the use of cement high brand (used Dyckerhoff 45). Such a cement may be mixed with a large amount of aggregate, which makes it possible zaprawo requested mechanical properties together with good capillary properties. An additional advantage of these mortars is their very low shrinkage. Good grout is also achieved using a mixture of cement (also high brand) of hydrated lime. Depending on the ratio of the binder and the amount of aggregates is obtained zaprawo many different physical and mechanical properties. Another group are the mortar of lime, cement and cement-lime modified metakaolinitem. With the addition of the mortar of lime as discussed obtaining a very high mechanical strength (15 MPa) - the formation of calcium silicate (pozzolan). In the case of cement additives metakaolinite prevent leaching of free calcium hydroxide, followed by their stabilization.

Of the subjects tested mortar, grouting gothic walls they may be used such that a compressive strength of 4 to 8 MPa, time of capillary water to a height of 5 cm should be up to 60 minutes, and the water absorbability of 10-20%. These mixes are also characterized by a very small cramp (particularly cement). These properties have the following mortar (weight ratios):

• cement: sand = 1: 6
  
• cement: metakaolinit: sand = 1: 0.5: 9
  
• cement: aggregate brick = 1: 4
  
• cement: sand: aggregate, brick = 1: 1: 3
  
• cement: lime: sand = 1: 1: 6
  
• cement: lime: metakaolinit: sand = 1 : 1 : 1,25 : 19,5
  

As is apparent from the above formulas, to 1 part cement (grade 45) and 1 part of a mixture thereof with metakaolinitem must be added 6 parts of sand, and the binder, lime-cement "clean" and the metakaolinitem - 3 parts. Aggregates brick, due to its high surface area can add less. Increasing the amount of aggregate, mortar weaken, but to improve their properties and increases capillary absorption. Conversely, if you reduce the amount of aggregate. Worsen the capillary properties of mortars and increases their mechanical strength. The experience also made it possible to establish that the increasing amount of lime in cement-lime mortar is a sharp decline in strength, and with the reduction worsen capillary properties. The ratio of 1: 1 should be considered optimal. Suitable properties have also modified lime mortar metakaolinitem and burned clay:

• lime: metakaolinit: sand = 1 : 1 : 10
  
• lime: clay: sand = 1 : 1,5 : 7,5
  

They have the following characteristics: time of capillary water to a height of 5 cm - 57 and 55 minutes, a compressive strength of about 4 MPa and a water absorption of 14 and 16%.

It should be added that in the Nicolaus Copernicus University in Torun also developed the technology of cement mortars modified acrylic resins and hydrophilic epoxy glues.

Conclusions

Considering the above, we can conclude that the main criterion for suitability grouts brick walls are their similar properties to the bricks. in particular capillary and mechanical properties. First, there should be higher and the other lower. In order to avoid frequent replacement of the mortar in the joints, the compressive strength should not be less than 4 MPa.