RECOVERY OF RISING-DAMP DAMAGED MASONRY; EXPERIMENTAL COMPARISON BETWEEN 'SLOW DIFFUSION' AND 'UNDER PRESSURE' PROCEDURES FOR WATERPROOFING AGE!\TTS

Vincenzo Eusebi ', Romualdo Montagna" Marco Pauri', Alessandro Stazi'

1. ABSTRACT

Within the framework of a wider research-project on the remedying of damp masonry a study was carried out on three different waterproofing agents. Each agem was applied with two different techniques on lab masonry models built either with new bricks or with old bricks obtained from a demolition. The agents under investigastion are: alkyl-alkoxy­silane, methyl-siliconate and siloxane-oligomer while the two techniques used are: pressure and gravity injections. Different results are obtained with the two experimental impregnation techniques at O to 75 days from treatment. The pressure technique causes dampness to increase at 45 days and then dampness rate decreases to values similar as those obtained with the other technique. When gravity technique is used the water content decreases progressively. Vaporization curves tend to flatten as the inner part of the brickwork are analysed. Finally the study of the two relative maximum values, which are a common evaporation characteristic for the two impregnation techniques, shows a "reascending wave". Such a wave in the first stage may be corraleted to the injection of waterproofing agents and in the second stage to the hydrophobic process which pushes water beyond the intervention area. An "auxiliary" result of this research is the confirmation of the effectiveness of humidity measuraments by resistivity. Comparing this method with lhe calcium carbide and weight methods only slight differences, in view of their prompt application in building yards, have been detected.

2. INTRODUCTION

Rising damp is a common problem to old buildings and iL~ elimination is an essential part of each and every restoration project. The most common methods to contrasl damp

Keywords: Masonry: Remedy; Rising damp ; Slow diffusion; Under pressure.

'Civil Engineer. Professional. San Benedetto dei Tronto (AP ), ltaly 'Associate Professor, Inst. of Building Tecniques, University of Ancona, Ancona, ltaly 3 Associate Professor, Dept of Science of Materiais, University of Ancona . Ancona. ltaly 'Professor, Institute of Building Tecniques, University of Ancona , Ancona, Italy

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envisage the interposition of impenneable barriers through mechanical, electro-physical and chemical techniques. The mechanical techniques are undoubtedly very effective but also very expensi ve (complex to set up) and can cause movements of the whole masonry system. The electro-physical techniques entail many risks (mainly when dealing with non-standard or very thick brickworks). The use of a chemical method was encouraged by these different considerations. Chemical techniques are based on the observation that rising damp is due to water absorbed from the ground by building materials, as a result of capillarity. The polar contribution of the surface tension of the different bricks is relatively high and the materials which make up the masonry system have more o less hydrophilic properties. Such properties are considerably enhanced by water soluble inorganic salts. They can be either already present in masonry or derive from air contarnination (carbon monoxide or sulfur) or they can be transported by soil through water. The physical problem that chemicals must solve is hence that of creating a low surface tension within the capillary. The agents which are in use now are water or solvent compounds which aim atcreating a barrier in the wall to prevent water from rising. Such a barrier can be created by injecting a solution which cloggs the material's pores or creates a hydrophobic "sheath" in the pores of the brickwork. The effectiveness of these compounds however depends not only on their concentrations and chemical compositions but also on the application techniques and on the diagnostic aspect. Many different factors are involved: degree of air pollution, evaporation, position of wall surfaces, mortar thickness and composition, processing, degree of stress.

3. RESEARCH AND EXPERIMENTAL ASPECTS

In view of these different problems the research project was started. Its main objective was that of testing the effectiveness of different chemical formulations injected on masonry either with the "slow diffusion" (fig.l) or with the "pressure" (fig.2) techniques. Secondary objectives were the confirmation of the reliability of available instruments for the measuraments of water content and "standardization" of procedures and tests for a reliable assessment of lhe durability and quality of remedial actions in case of rising damp. The tests were carried out on two types of bricks differing both in age and production process: a brickwork made of "drawn" bricks, whü;h are easily available from the market, and soft batch, unpressed, hand made bricks dating back to the beginning of this century. In order to bettercompare results ali new bricks were made in the same brick-kiln while the hand-made ones were obtained from the restoration of one single building dating back to the beginning of this century. The oblained values can therefore be "anchored" to two precise realities. The microstructure characteristics linked to rising damp have been analysed during the first stage of the research. The brick samples underwent the following tests: - total porosity test with NORMAL 4/80 (fig.3); - distribution test of the pore mean radius with NORMAL 4/80 (fig.3); - specific absorption test in compliance with UNIlEDL 0114 standard, No. 38 (fig.4); - water absorption test in compliance with UNIlEDL 0114 standard, No. 38 (fig.4). Before starting the second stage of the research the 1ab masonry model was designed. The lab models were to be used to go through ali the different stages of rising damp (from initial propagation to final reclamation) via a measurament campaign (carried out simultaneously both with electric resistivity and with calcium carbide and weight methods) and monitoring of microenvironmental parameters. The models (tank and wall) were built taking into account the following parameters: I) Type of masonry. 2) Lab model of the tanks in which the brickwork is to be soaked. 3) Data collecting system (measurament campaign). A brickwork made of 40 cm thick, solid bricks was selected because statistically this type of brick is the traditional building unit in Italy, in Marches and Abruzzi in particular. In order to build the 12 brick walls needed, about 900 bricks were used, ha1f of which were ancient bricks (dating back to the beginning of this century). A cement mortar was used to bind the bricks . The mortar had known characteristics ("bastard" mortar = cement

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325:2; hydraulie lime: 1; sand : 10). The 12 walls (n06 "new" and n06 "old" walls) had the following mean sizes (old wall: h=76 em, 1=56 em, w=42 em; new wall: h=74 cm, 1=54 em,w=40 em). Each wall weighed about 200 kg (inclusive of mortar). The tanks in whieh the walls were immersed to simulate the phreatie water levei (dimensions h=30 em; 1=80 em; d=65 em) had been filled with aggregate up to 3 em. The seeond stage of the researeh aimed at assessing , through 12 masonry models, following their immersion in a tank to obtain a head of liquid (H20+NaCI), the propogation veloeity of rising damp. The third stage aimed at analysing the penetration and effectiveness of "barrage ehemieals". To this end three impregnation produets differing both in their ehemieal eompositions and in the solutions used for their applications were tested. The produets are: Alkil-Alkoxy-Silane (ASS) water soluble; Methil-Silieonate (MSA) water soluble; Siloxane-Oligomer (OSS) in organie solvent. These formulations were then injeeted in the above mentioned lab models aeeording to the two different teehniques, "slow diffusion " and "pressure" teehniques. Since only rarely the brickworks subject to a remedial action are dry the lab models were eompletely saturated with water. This is a well known procedure because it has already been tested on large samples of material. The materiais' saturation reached the theoretical and praetieal highest values (starting values of water content ranged from 15.9% to 26.06%).

3.1 Slow diffusion injeetion treatment (fig.!)

The three ehemical formulations have been injected via appropriate transfusers inserted in horizontallyaligned holes positioned at the bases of the models. Impregnation follows the same chemicallaws as absorption and rising of damp. Hence a proportion of the formulations aseends in the walls because of capillarity and a proportion descends beeause of gravity. At the end of the treatment the walls appeared to be impregnated in depth to an overall width of 20 em around eaeh hole. The formulations have been injeeted at different stages and they have been observed to impregnate in few hours the very porous masonry of "hand made" brieks. It took themjust over one day to impregnate the more compact models made up of "drawn" bricks.

FIG. 1 - The site of slow diffusion injection treatment; gravity feeded.

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3.2 Pressure injection treatment (fig.2)

The way in which pressure helps the ejection of water from (already saturated) pores is easy to understand if the complexity of the different movements of a liquid in a body is taken into account. Humidity insulating formulations are let in when water is ejected from the pores. To this end pressures up to 5 atm have been applied. Pressure values were monitored by appropriate pressure gauges placed on the injectors. The nozzles were inserted in 10 em diameter holes placed at distances of 10-12 em. The treatment was carried out by altemating perforations and injections increasing the hole depth as soon as the treated wall section was saturated. In this way impregnation was obtaíned at deeper and deeper wall sections. The procedure was altered according to the thicknesses and characteristics of the materials to be treated.

FIG. 2 - The site ofpressure injection; pumping equipment is shown.

The fourth stage of the reserch was the measurament campaign and the control of the "building yard" measuring tools. Through a data collection system for environmental parameters (air humidity and speed, temperature, etc.) with continuous recording two different measuraments were taken, surface and depth humidity values. In this way the models were kept under periodical control. Three different measurament methods were used to detect variation in the models' humidity:

weight method (determination of the water contem by weighing the model before and after drying at 60° C). calcium carbide method (determination of humidity by causing a chemical reaction between calcium carbide and the water contained in the sample. The deriving gas, acetylene, exerts pressure on the container and such pressure is detected by apressure gauge built in the measuring instrument). electric measuraments (determination of the water content via two electrodes placed on the sample surface and measuring the dielectric constant).

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4. RESUL TS Al'ID DISCUSSI00!

The adopted tesring tecniques are more severe than the normal condirions which a masonry wall affecred by rising damp must stand. Only rarely is a brickwall subjecred [O the condirions simulared in the lab. Survey on the staning conditions confirm the data obtained by porosimetric analyses (fig.3): the lowest value of water conrent was obtained in the "old" masonry mode l, 15.09% while lhe highesl value was detected in lhe "drawn" bricks model , 26.06%.

l !~ '3 (~I. '101 ('.,l/j) I I

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The large quantity of data derived from the 432 surveys is useful for sw.tistical analysis. The reported values however must be interpreted as values of lendencies to certain beha viours and not as absolule values because of the experimental approximation entailed in this type of testS and of the hererogeneity of masonry systems (made up of blicks and mortar). The model walls were monitored after 15, 30, 45, 60 and 75 days from treatment with the above mentioned measurament techniques. The test resultS are shown on the graphs indicating the kinetics of the different processes. The graphs show lime on the x· coordinate and on the y-coordinate both the water absorption rate as against the initial weight and the weight increase. The results show that the amount of formulation that can be injected during a certain period of time varies according tO the type of masonry. In the water saturated walls Lhe injected formulations had to replace part of the water. As Lhe formulation was pressure injected the brickwork water was visibly seeping out of the wall. The motions oI' twO non-mixable liquids in a porous sysrem such as a brickwork is a complex evento The graphs of the kinetic processes however show that different behaviours can be obsel\led in Lhe two impregnation techniques used. The water content data obtained Írom ., drawn" brick models show Lhat pressure injection causes an increase of humidity after about 45 days (fig.5). The "hand made" brick models, instead, about 45 days, decrease in water contento Notably 70% of models , during the drying stage, show an increase·decrease stage and then again increase-decrease stage in evaporation. AnoLher feature of evaporation curves is that Lhey tend to f1atren out as measuraments are taken from the inner part of the walls. It can be assumed lhat in lhe "core" of Lhe brickwork. where water is arranged as a dome. evaporation and capillary rising are more active Lhan in Lhe surface areas. By analysing lhe twO relative maximum values. lypical oI' bOlh lechniques. lhe firSI one might be due tO the to rmularion injection stage while lhe second one. defined as "ascending wave". tO the waterproofing agenls lhat push the water beyond lhe

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interventíon banier. By compaling the resullS obtained from the tests on the masomy models and on single bricks it is c1ear that the organic solvent siloxane-oligomer (OSS) is the chemical which diffuses in higher quantity. The other two chemicals, potassium methyl-siliconate (MSA) and alkyl-alkoxy-silane (AAS) which are water soluble, penetrate betler in single bricks rather than in masonry (fig.6). When alkyl-alkoxy-silane or potassium methyl-siliconate are used it can be assumed thar during the waterproofing treatment by immersion of samples pressure exerted by the head of water-repellent agent has a mechanical effect pushing a way lhe solution, being it water or saline solution (fig.7), present in lhe pores. When samples are treated with siloxane-oligomer in organic solvent the watery solutions are probably more resistant to being pushed away (mutual insolubility, organic solvem density lower than water density).

IM1v1ERSION 1--.1ETHOD "Drawn" brick (test nO lI )

IMi\1ERSION IvlETl-IOD "Hand made" brick (lest n03)

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FIG. 4 - Va!ues of w(l(er absorpliOI1 resc (uppc:r) and specific absorpúOI1 lesl (lowc: r) for new (Iefl) mu! o/d (righl) hricks

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Substantial differences in the effectiveness of waterproofing agents and in the behaviours of the two different types of bricks despite the differences in microstruclUre (mean pore radius 3900A for "drawn" bricks and 5000A for "hand made" bricks) (fi2.3) have not been detected. ~ Alkyl-alkoxy-siJane (fig.S) has given better results than the other formulations, at least as far as penetration around the application hole is concerned. The most relevant conclusion derived from this srudy is that no significant redistribution of liquids takes place when the injection is stopped. As a consequence there is no formation oI' an unitenupted chemical banier above the head of humidity.

PRESSURE LNJECTION TREATMEt"-'T "Hand made" mansory modei

PRESSURE l!'iJECTION TREATMEt'IT "Drawn" mansory model

SLOW DIFFUSION LNJECfION TREA TMENT "Hand made" mansory model

SLOW DIFFUSION INJECfION TREA TME.!"-'T "Drawn" mansory model

FIG . S - ResuLts of recovering using Alkil-Alkoxv-SiLane (A SS ); valuesfor neIV and ola bricks resced wich "pressure" and "slow difjilsion" mechods.

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The creation of such a barrier is the aim of every remedial procedure in the case of rising damp. The three formulations have shown littleespecially the use of very closely, not randomly, arranged injection holes are recommended.

FlG. 6 - Diffusion ofwaterproofing agents.

FlG. 7 - Extrusium of sodium sulphate efflorescences through the pores when Akil­Alkoxy-Silane (ASS) is used.

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A funher "auxi liary" result of this study was the confirmation of the measurament instruments' reliability. There are different methods to measure water content in masonries. The reliability of then aI! is not the same; for each test we tOok three different measuraments using calcium-carbide method, weight method and electric resistence method. Comparison has shown that there is no substantial difference using calcium­carbide method or wei ght method. It also shows that use of electrical indicator has no qualitative etTOr, ' bu t it can only indica te if moisture is over or under a stated ratio (in the case 10%) (fig.8). Detailing, we found that, according with a tolerance of 4%, calcium­carbide method and weight method show an identity of values in 8790 of total measuraments. The data obtained wi th the calcium-carbide method are certainl y valid but the fact that such method is a destructive one must be taken into account. This is certainly a drawback for its utilition in this researchwork. The data obtained with electric hygrometers are sufficiently accurate in view of the range of figures they provide ("red light": humidity content higher than 10%, "green light": humidity Content lower than 1090). An easy and rapid monitoring of the surface humidity of damaged masonry is possible than.ks to these instruments. The ranges of the measurament instruments and methods , i.e. their error tolerance, was determined thanks to the measuraments made. Both tested measurament methods ("calcium carbide" and "electric" techniques) compared with the weight method needed accurate calibration. With the "calcium carbide" instrument realiable measuraments can be taken but approximation depends on the way samples are taken. The results obtained with the electric technique are generally reliable though some measuraments, because of the difference in the masonries' salt concentrations, have given non accurate resuJts. However it must be underlined that this method allows a rapid and easy monitoring of the whole walJ surface.

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5. CONCLUSIONS

The tests are unquestionably useful to assess the effectiveness of chemical treatments (both slow diffusion and pressure treatments) and to measure the hygrometric differences between "ancient, hand made" bricks and modem "drawn" bricks. Ancient bricks allow a higher water and saline solution peneteration. Then, as the injection goes on, the formulation penetrates more easily. Unlike "ancient, hand made" bricks, "drawn" bricks becouse of their "closed" structure, react to treatments in a less favourable manner. However, according to the study results, chemical treatments are satisfying provided sufficient quatities of chemicals are injected. Masonry can be made impermeable only through the capillary absorption method, which is possible where the "cuci-scuci" (do­undo) restoration method is used. The effectiveness of the treatment in fact depends exclusively on the masonry capillary ability to be saturated with the chemical formulations. The pressure injection technique, irrespective of the chemical injected, has given better results as for the humidity barriereffectiveness. However an increase in humidity above the injector application barrier, defined as "ascending wave" , was detected. It is assumed that the waterproofing process carried out by the chemicals "pushes" water and the soluble salts, if present, outside the application area. The effect, which can also be visibly observed, must be taken into accountespecially in case of masonries, subject to heads of water because of rising damp, that have in their higher parts artistic paintings. Because of high dispersion a conclusion on the waterproofing formulation ability to create a barrier against rising damp from the chemical point of view cannot be drawn. From the physical point of view the research has shown, as reported above, tendencies of the various solutions to have certain behaviours.

6. REFERENCES

1. Sharpe, "Iniection system for damp proofing", Building and Environment, 1977. 2. Cigni G. et aI., Verifica sperimentale di un sistema di sbarramento verticale

all'umidità, Atti 10 Congresso ASSIRCO, 1981. 3. Gummerson R.l. et aI., Water movement in porous building materials-lII. A

sorptivity test procedure for chemical injection damp proofing, Building and environment, 1981.

4 . Baronio G., Binda G. Durabilitàdi strutture murarie in mattoni pieni, Recuperare, 1983.

5. Pouchol J.M., Ability of methilpolysiloxanc derivate to oppose rising damp in walls, Congress Venice, 1986.

6. Biscontin G., Driussi G., Indagini sulla umidità di risalita a Venezia, Recuperare, 1987.

7 . Solaini G., Capillarità e condensazione nei materiali porosi, Recuperare, 1987. 8. Chan K. et aI., "Water movementand durability of concretestructures", Fourth

Intern Conference on Durability of Building Materiais and Components, Singapore, 1987.

9 . Biscontin et al., "Indagini sull'umidità di risalita a Venezia" , Recuperare, 1987. 1 O. Binda et aI., "Interpretazioni statistiche di alcuni proprietà fisiche e meccaniche dei

laterizi" , L'Industria Italiana dei Laterizi, 1989. 11. L' Ason S.J., The interaction of damp-proofing fluids with porous building

materiais, Building and environment, 1988. 12. L' Ason S.1. et al., Chemical injection remedial treatment for rising damp-11, 1990. 13. Collepardi M., Degradation and restoration of mansonry walls of historical

building, Materials and structures, Rilem, 1990. 14. Pau ri M.G., U degrado degli intonaci per risalita capillare di soluzioni di solfato o

di nitrato, Atti "Le superfici dell ' architettura", Bressanone, 1990. 15. Eusebi, Della Penna, Montagna, Pauri, Stazi, "U comportamento dei laterizi

sottoposti a trattarnenti idrofobizzanti", Convegno Intemazionale: il recupero degli edifici antichi, Napoli, 1993.

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