GB2094845A - A method for protecting or restoring outdoor objects of absorbent mineral building materials, and a set of impregnation agents for use in the method - Google Patents

Abstract

A method and a set of impregnation agents for protecting or restoring outdoor objects of absorbent mineral building materials. Impregnation is made with a first agent containing barium salt and calcium salt of a carboxylic acid, e.g. acetic acid, and a water soluble protein, e.g. casein, and optionally silicon tetraalkylester, and immediately thereafter with a second agent containing one or more mono- or dialdehydes, e.g. glyoxal and formaldehyde, and optionally, after drying, with a third agent containing a hydrophobing agent, e.g. a siliane, dissolved in a slowly evaporating hydrocarbon oil. The treated material shows decreased water absorption and increased compression strength.

Description

SPECIFICATION Protecting or restoring absorbent mineral building materials Technical Field of the Invention The present invention relates to a method for protecting or restoring outdoor objects, e.g.

buildings, building frontages, reliefs, and sculptures of absorbent mineral building materials, such as sandstone, concrete, tile; tuff or travertine, by treatment with impregnation agents, one of which contains alkaline earth metal salts of carboxylic acids, and a set of impregnation agents for use when carrying out the method.

The method according to the invention can be used for protecting outdoor objects of absorbent mineral building materials, e.g. buildings and sculptures, against the destructive effects of rainwater, temperature variations, against acid compounds, floating dust and soot contained in the air, and against condensed water and absorbed water containing chemical compounds.

The method has primarily been developed for the impregnation of sandstone, but also other absorbent mineral materials, such as concrete, tile, tuff or travertine, may be treated according to the inventive method. In fact, any mineral material being sufficiently able to absorb the impregnation agents comprised in the set of impregnation agents as described in the present specification and claims may be treated in accordance with the inventive method. Thus the term "absorbent mineral material" as used in the present specification and claims is intended to mean any mineral material sufficiently able to absorb the inventive impregnation agents.

By the treatment in accordance with the inventive method the absorbent material being treated would only absorb the impregnation agents within a certain depth from the surface. For example, a penetration of the impregnation agents to a depth between 9 and 1 3 mm was found by cutting a stone in halves (Example 4). Accordingly, the term "impregnation" as used in the present specification and claims means absorption into a certain depth of the impregnation medium in question, and does not mean that the absorbent mineral material has to be impregnated throughout with the medium.

As mentioned above the present method was primarily developed for the treatment of sandstone.

This is a material formed by cementation of sand, which may be present either as smoothed grains ground to round grains during transport or by the action of flowing water, or as sharp-edged grains being formed by the weathering of granite or gneiss. The grain material mainly consists of quartz, SiO2, and furthermore felspar, e.g. K(AISi3Os), Na(AISi3O8) and Ca(AI2Si208) and mica, K(AISi3O8). H20 (+Mg, Fe, Cr) and smaller amounts of many other minerals. The cementation material or binder can be amorphous silicic acid, calcite CaCO3, clay substance and/or various iron compounds, notably calcite being a frequently occurring cementation agent in sandstone.

Among the types of sandstone used as building stone in Denmark can be mentioned Gotland sandstone wherein the cementation agent is calcite, and Hälsingborg sandstone, where the cementation agent comprises calcite and furthermore iron compounds. These types of sandstone have a high porosity giving a tendency to easy absorption of rainwater, condensed water and other water into the capillary system of the stone.

During the last half century, the increasing pollution i.a. involving an increasing acidity of the rainwater, has caused an increased erosion of sandstone buildings.

Recently, the attention has been drawn to the fact that many buildings, bridges and other constructions of concrete, especially those built in the sixties, are in a bad condition due to erosion.

Although a great effort has been made in attempts at limiting or preventing such erosion of sandstone, concrete and other building materials, only very limited results have been obtained by the efforts till now.

Technical Background of the Invention Several methods have been proposed for solving these and similar problems. Thus, in DE published patent specification No, 1,003,116 a method to render form members of stone mass waterrepellant has been proposed. By this method free lime is converted into combined forms by treatment with fluorides orfluorosilicates, preferably by repeated applications of up to 500C hot, preferably highly concentrated solutions. After drying impregnation is carried out with 12% solution of sodium methylsiliconate. This method is very laborious and will not be suitable for the treatment of mineral building materials in existing building constructions.Furthermore, it does not give a sufficient protection against absorption of water and attacks from the chemicals of the air, and the diffusion from the stone of water present therein is too poor, whereby there will be a risk of erosion unless a regular, careful and expensive treatment is carried out, e.g. each year.

A method for the protection of buildings and sculptures of sandstone against destruction caused by acid-containing air contamination is known from DE patent publication No. 2,108,796. By this method the acidic contaminations, notably sulphuric acid, are neutralized and precipitated with, for example, bariuim hydroxide, or with organic bases such as benzidine or p,p'-diphenyldibisguanide.

Hereby insoluble compounds blocking the pores in the sandstone are formed. The treatment is terminated by a treatment with a dispersion binder. This method gives a too heavy blocking of the capillary system whereby water cannot diffuse therefrom. The dispersion binder used also contributes to prevent the diffusion, and furthermore it may change the colour of the material treated. Moreover, the treatment method is laborious, demanding several treatments with the basic preparation with intermediate drying, after which further 4 weeks must pass prior to the treatment with the dispersion binder.

From DE patent publication No. 2,246,412 there is known a method for the preservation of sandstone, especially natural sandstone, in which the surface of the stone is treated with an acidic aqueous solution containing alkaline earth metal and aluminium formates and/or acetates and heavy metal ions, after which the surface is preferably treated with an aqueous solution of hydrogen peroxide and isopropyl alcohol, or first treated with hydrogen peroxide and then with isopropyl alcohol. The method is based upon the fact that a solid network, i.e. containing dolomite, CaMg(CO3)2, is formed by the influence of aqueous vapour and carbon dioxide from the air.In this way, a very substantial, unelastic mineral mass is formed in the capillary system of the material treated, especially in mineral materials in which the binder is calcium carbonate, whereby the capillary system is blocked, which entails hindrance of water diffusion as well as risk for burstings.

A method for the preservation of stone containing at least 5% by weight of calcium carbonate is known from DE published patent specification No. 2,046,482, in which method the stone is treated with a solution of a barium or strontium salt of a monoester of sulphuric acid such as barium and strontium diethylsulphate. After penetration of the solution into the stone, treatment is carried out with a slight excess of a barium hydroxide solution, whereby the monoester is hydrolysed. The latter process requires immersion of the stone in the solution at 1 000C for an hour, at 75"C for several hours, at 500C for several days or at room temperature for several weeks, and it leads to the formation of insoluble barium sulphate in the capillary system of the stone.By this method, however, the capillaries are filled up too heavily, whereby the diffusing away of water present is hampered. Since either heat supply of a long reaction time is required for ultimate hydrolysis, a great risk of failures occurs when carrying out the method in practice, which renders the method less suitable for the treatment of stone in old buildings. Furthermore, a method requiring immersing of the treated objects obviously cannot be used for buildings, frontages or biggish statues.

From SE published patent specification No. 367,616 a method is known for impregnating brickwork and inorganic oxides on the basis of organic siliceous compounds, in which alkyltrialkoxysilanes dissolved in an alcohol or low boiling hydrocarbon are applied to the brickwork.

However, this method does not give a sufficiently effective protection of the material treated when used alone.

US Patent No. 11,811 describes a composition for preparation of primary paper, leather, and cloth, but also walls, which preparation is based on casein in alkaline aqueous solution with formaldehyde added and, optionally, also containing a mineral such as clay or talc. This known composition gives, however, a completely insoluble coating not admitting diffusion of water. Therefore, this composition cannot be used for impregnation of absorbent mineral building materials.

GB Patent No. 16.157 discloses a method for protecting concrete by applying a hot glycerol containing glutine solution and adding a formaldehyde solution after drying, by which method the concrete becomes impervious both to oil and to other liquids, which means that diffusion of water is impossible.

DE Patent No. 192,589 discioses a method, by which sandstone or other quartziferous or siliceous varieties of stones or limestone is impregnated with an earth alkali salt or aluminium salt of a volatile acid and treated with heat at elevated pressure. By the pressure treatment the acid is liberated and may be re-used, and the salt is transferred to a hydroxide, which is combined with the silicic acid of the stone material to form silicates. However, this method cannot be used for the impregnation of sandstone, concrete or the other materials in question in case of building materials in existing buildings, because the pressure treatment involves that the materials are to be placed in a pressure tank.

Object of the Invention From the above it appears that the known methods are connected with various problems. Thus, by some of the methods a too tight closure of the pores of the absorbent material takes place, whereby water possibly present, which may result from condensation, from absorption through cracks or from other absorption, cannot diffuse away from the material. By some methods an outer layer is produced or directly applied, which layer may result in an undesired change of the colour of the material surface, and further this layer may hamper diffusion of water from the material.

Other methods give insufficient possibility of stopping the migration of chemical compounds, or give insufficient sealing of the pores of the material against acid attack. It is also a problem to obtain a sufficient increase of the strength of the material when, on the other hand, it must at the same time be ensured that the material does not become too hard.

Finally, the operation in practice of many of the known methods is troublesome, which means that they require too much labour and thereby become too expensive.

It is the object of the present invention to provide a method of the above kind by which the above drawbacks are diminished or altogether avoided.

Furthermore, it is the object of the invention to provide a set of impregnation agents to be used in the method in question.

Brief Explanation of the Invention Accordingly the present invention relates to a method as stated in the preamble for protecting or restoring outdoor objects, e.g. buildings, building frontages, reliefs, and sculptures of absorbent mineral building materials, and is characterized in a) first impregnating the object with a first impregnation agent at least containing a barium salt and a calcium salt of at least one C1~20 aliphatic carboxylic acid, and a water-soluble protein, b) immediately thereafter impregnating the object with a second impregnation agent containing one or more aldehydes selected among C18 mono- and dialdehydes, and c) optionally at a later time, when the object treated has dried, after-treating with a third impregnation agent containing a hydrophobing agent preferably dissolved in a relatively slowly evaporating hydrocarbon oil.

The invention also relates to a set of impregnation agents for use in carrying out the abovementioned method, said set being characterized in that it comprises a) a first agent at least containing a barium salt and a calcium salt of at least one C,~20 aliphatic carboxylic acid, and a water-soluble protein, and opionally a silicon tetraalkylester, b) a second agent containing one or more aldehydes selected among C18 mono- and dialdehydes, and c) optionally a third agent containing a hydrophobing agent preferably dissolved in a relatively slowly evaporating hydrocarbon oil.

Best Embodiments of the Invention Known The said barium and calcium salts, which may be salts with the same acid or with different acids, are salts of aliphatic acids having a PHA value of at least 4, i.e. a dissociation constant not exceeding 0,0001. As an example of such acids could be mentioned those having 2-6 carbon atoms such as acetic, propionic, butyric, isobutyric, valeric, pivalic, capronic, crotonic, acrylic, hydracrylic, succinic, glutaric or adipic acids.

The barium salt and the calcium salt form insoluble or sparingly soluble compounds with the oxidized and hydrated products of SO2 and CO2 in the atmosphere under catalytic co-action by heavy metals originating from floating dust. The presence of both barium ions and calcium ions ensures the precipitation of both sulphate ions, carbonate ions and sulphite ions, viz. as BaSO4,CaCO3andCaSO3, respectively. The major part of the hydrogen ions originating from the content in the atmosphere of SO2, CO2, NO, NO2 and HCI after a possible oxygenation and hydratisation, are bound to the aliphatic acid residue, e.g. acetate, to form the undissociated acid, e.g. acetic acid.

In this manner 200 ml rainwater of pH 5.0--4.7, which is the average in Denmark and corresponds to 0.1-0.2 mg of H2SO4 per 200 ml, yield 0.12-0.24 mg acetic acid. Although the concentration of the aliphatic acid is low, no dissociation takes place as there is an excess of the corresponding acid residue. A dissociation of the aliphatic acid will only occur when the deposit of barium salt and calcium salt after many years is about to be used up, at which time a renewed treatment according to the invention should be carried out.However, for example Gotland sandstone has a large content of CaCO3. The amount of CaCO3 to be dissolved by the aliphatic acid, if the latter is dissociated, makes up a thousandth of the CaCO3 content of the sandstone and thus has no practical significance.

As mentioned the first impregnation agent also contains a water-soluble protein, preferably casein which is well known for its good adhesive properties and which is also readily available, e.g. in the form of a skim-milk plasma, i.e. a dispersed product consisting of 10% skim-milk powder in water. Other usable water-soluble or dissolved proteins which could be mentioned are size, potato steep water., i.e. a waste product from the preparation of potato starch, or possibly fish protein, e.g. from waste water from fishmeal production. The criterion whether such protein can be used is mainly that it should be available at an advantageous price and that it should have an appropriate adhesive effect.The protein partly in itself and partly by virtue of an aldoxime condensation with the aldehyde compounds in the second impregnation agent imparts to the material treated an ultimate strength several times increased.

Because of the properties of the protein as a colloidal solution/emulsifier/real solution a less hard and more flexible sealing is obtained than that obtained by means of solely inorganic compounds. Hereby there is obtained possibility for the water present to diffuse away, which is necessary to counteract disintegration of the mineral material. Together with the hydrophobing agent, e.g. silane, which is added as a third impregnation agent, the protein contributes to stop a possible efflorescence.

Preferably, the first impregnation agent also contains a silicon alkyl ester, preferably a silicon tetraalkyl ester such as silicic acid tetraethylester. The latter conduces considerably by virtue of its low surface tension to increase the absorption depth. It is essentially instrumental in repelling water without stopping the necessary diffusion away of water possibly present. The silicic acid tetraethylester is gradually hydrolysed to amorphous SiO2 and ethanol, which disappears by evaporation.

Accordingly, the first impregnation agent has the effect that the barium acetate and the calcium acetate neutralize the acids of the atmosphere forming BaSO4, BaCO3, CaCO3andCaSO4, and the effect that the protein by the aldoxime condensation increases the ultimate strength and further acts as a "resilient medium" both giving a cementation and still permitting an appropriate diffusion of minor amounts of water. Furthermore, if present, the silicon alkylester such as silicic acid tetraethylether by hydrolysis yields amorphous SiO2 which contributes to the strength of the mineral material.

The second impregnation agent comprises aldehydes for the aldoxime cdndensation with the amino groups of the protein included in the first impregnation agent. Thus, the second preparation comprises one or more mono- and/or dialdehydes, preferably a dialdehyde such as glutaraldehyde or preferably glyoxal, and a monoaldehyde compound as for example acetaidehyde and especially formaldehyde. Thus, the second agent advantageously contains 2% by weight of glyoxal and 2.5% by weight of 37% formaldehyde, and 1 to 2% by weight of 2M NH3 which acts as an antioxidant in the solution before use. As an example of other antioxidants sodium ascorbate may be mentioned. The aldehyde compounds together with the amino groups in the protein of the first agent form a solid condensate by an aldoxime condensation.Together with the other ingredients in the impregnation agents used in the method, said condensate contributes considerably to increase the ultimate strength of the mineral material to the 4- to b-fold in a resilient manner, at the same time permitting diffusion of water to some degree.

The second impregnation agent should be applied immediately after the application of the first impregnation agent, i.e. before this has started drying. In case the first impregnation agent has become too dry, the absorption of the second impregnation agent will be reduced.

Both the first and the second agent should comprise a growth inhibiting agent for bacteria and fungi, e.g. 1.5% by weight and 1% by weight, respectively, of 2-phenylethanol and/or a bactericide and fungicide such as phenylcarbinol, e.g. in an amount of 1.5% by weight A possible excess of glyoxal, after oxidation to oxalic acid will result in the formation of barium oxalate and calcium oxalate, which are both sparingly soluble and contribute to increasing the strength of the mineral material.

When the mineral material has dried after the treatment with the first and the second agent, which generally lasts 5 to 8 days, and when the weather is adequately dry, it is preferred to treat the mineral material with a third impregnation agent which contains a hydrophobing agent, preferably an organosiloxane, polysiloxane or silane, advantageously dissolved in a solvent with slow evaporation, e.g.

a hydrocarbon oil such as "crystal oil K30" from Shell. As usable but less suitable hydrophobing agents silicontates or silicones may be mentioned. The third agent must have a suitably low viscosity so that it penetrates deeply into the stone. It must be non-adhesive and must be applicable even in case of a minor amount of moisture remaining in the mineral material. Due to the properties of the ingredients in the first and the second agent the hydrophobing agent will not close the pores of the mineral material, but gives a suitable water repellant effect without affecting unfavourably the above advantageous properties of the first and the second impregnation agents.

The first impregnation agent should also contain an oxygen donor. This may be in the form of a heavy metal salt in its highest state of oxidation, e.g. a cobaltic salt orferric salt. Thus, the first impregnation agent normaliy comprises about 0.004% by weight ferric chloride (FeCI3. 6H20).

The salts used in the first impregnation agent may advantageously be barium acetate and calcium acetate, firstly because such salts are readily available and secondly because acetic acid has a suitable low dissociation constant, viz. 0.000018 corresponding to a PKA value of 4.76.

In practice, e.g. for the treatment of Gotland sandstone, the treatment may advantageously be carried out by using a first impregnation agent containing 10 to 40% by weight of a barium salt, preferably 20 to 30% by weight of a barium salt such as barium acetate, 2 to 10% by weight of a calcium salt, preferably 3 to 6% by weight of a calcium salt such as calcium acetate, 0.5 to 5% by weight of skim-milk powder, such as 0.5 to 3% by weight, preferably 1 to 2% by weight of skim-milk powder, and 5 to 1 5% by weight of a silicon tetraalkylester, preferably 8 to 12% by weight of a silicon tetraalkylester, wherein alkyl for example may be ethyl, said ingredients being dissolved and suspended, respectively, in water.As the second impregnation agent one advantageously uses a preparation containing 1 to 10% by weight of a dialdehyde and/or 1 to 10% by weight of a monoaldehyde, especially 1 to 3% by weight, preferably 2% by weight of a dialdehyde, such as glyoxal, and 1 to 5% by weight of a monoaldehyde, e.g. 2.5% by weight of 40% formaldehyde dissolved in water.

Normally one proceeds so as to impregnate with the first impregnation agent until saturation is established, after which the second agent is applied in an amount by weight of 1/2 to 1/10, especially 1/3 to 1/5, preferably 1/4 of the amount by weight of the first agent employed.

As the possible third agent a hydrophobing agent is used, e.g. a silane. Thus this agent may be an 80% alkyltrimethoxysilane as that sold under the trade name "Wacker"8290, dissolved in the proportions 1:5 to 1:12, preferably 1:8 in a slowly evaporating hydrocarbonoil such as crystal oil "Shell"tH)K 30.

The consumption of the above agents per m2 of the object to be treated may be 300 to 600 g, preferably 400 to 500 of agent 1; 25 to 200 g, preferably 90 to 175 g, notably 120 to 1 50 g of agent 11, and 0 to 500 g, notably 200 to 400 g and preferably 250 to 300 g of agent Ill.

The treatment with the second impregnation agent should take place immediately after the treatment with the first impregnation agent, i.e. before the latter has dried so as to promote the absorption of the second impregnation agent. A shown in Examples 3 and 4 below the treatment with the second agent should be carried out a few minutes after the treatment with the first agent. However, it should be emphasized that even by the unsuitable treatment according to Example 2 below, wherein three days passed between the treatments, a substantial improvement of the ultimate pressure strength was obtained, viz. from 335 kg/cm2 to 1 135 kg/cm2.

As will be seen from the examples below, especially good results are obtained by the use of a set of impregnation agents which apart from the optional third impregnation agent consists of a first impregnation agent containing 1040% preferably 2030% of barium acetate, 210%, preferably 36% of calcium acetate, 0.53% preferably 12% of skim-milk powder, and 515% preferably 8-1 2% of silicium tetraethylester dissolved and suspended, respectively, in water; and a second impregnation agent containing 1-1 0%, especially 13%, preferably 2% of glyoxal and 110%, especially 15%, preferably 2.5% of 37% formaldehyde dissolved in water, all percentages being % by weight.

An untreated stone of Gotland sandstone or H lsingborg sandstone of about 3 x 6 x 11 cm, which corresponds to a total surface area of between 225 and 250 cm2, by immersion in distilled water becomes substantially saturated in 10 minutes or a little longer while absorbing about 25 to 35 g of water. A similar test stone having the same dimensions and treated by the method of the invention, whereby normally between 3.5 and 4.0 g of barium and calcium acetate taken together would have been absorbed, absorbs between 0.6 and 0.9 g of water when immersed in distilled water for an hour, which corresponds to a penetration of 0.2 to 0.3 mm from the surface. After immersion for 24 hours in water the stone absorbs about 6 to 6.5 g corresponding to 250 to 285 mg per hour or 1.1 to 1.2 mg per cm2 per hour.

The method according to the invention has the advantage of being easily and rapidly carried out in practice, since the two first impregnation agents may be applied immediately after each other, and the last impregnation agent 5 to 8 days later, and since no heating of the agents applied or other laborious or long-lasting measures are required.

By the method according to the invention a deep absorption of the impregnation agents is obtained, there is obtained a repelling of water, both on the outer surface of the absorbent mineral material and its interior, at the same time a possibility for condensed water, crack water or absorbed ground water possibly present of diffusing away being sufficiently in existence, whereby disintegration or bursting is avoided, there is obtained a neutralization of the acids originating from rainwater or the atmosphere, there is obtained a considerable increase of the ultimate strength of the mineral material, which is seen from the test results below and which leads to a substantial increase of the lifetime of the treated buildings or constructions, one avoids a surface coating, which might change the colour of the mineral material, there is obtained a decrease of the roughness of the surface so that floating dust and soot do not adhere to the surface, a stability against cold and heat is obtained, efflorescence of chemicals is prevented, and overgrowth with algae, lichens and mosses is prevented.

The method according to the invention is further illustrated below by some Examples and some test results.

EXAMPLE 1 The impregnation agents used in this example are prepared as follows.

Impregnation Agent I This agent is prepared from three stock mixtures called A, B and C.

Mixture A is prepared by dissolving 3840 g of barium acetate, 600 g of calcium acetate and 0.62 g of ferric chloride (FeCí3- 6H20) in 7560 g demineralized water at room temperature. This carried out by slowly adding the components in the order mentioned to the water under continuous vigorous stirring until all matter has been dissolved.

Mixture B is prepared by slowly adding 200 g of skim-milk powder to a mixture of 1 800 g of demineralized water and 30 g of 2-phenylethanol under vigorous stirring at room temperature.

Mixture B thus prepared should stand at least 24 hours before it is admixed with mixtures A and C in the manner described below.

Mixture C consists of 1 500 g of silicium tetraethylester.

Impregnation agent I is prepared from the stock mixtures by pumping mixture A as a vigorous jet through a small nozzle into mixture B. Then mixture A + B is pumped as a vigorous jet through a small nozzle into mixture C. The formed mixture A + B + C = impregnation agent I stands while being stirred or shaken some times a day for 4 to 5 days before use. During use the impregnation agent should be frequently stirred.

Impregnation Agent II Glyoxal polymer 80 g Formaldehyde, about 37% by weight 100 g 2 M NH3 80 g 2-Phenylethanol 40 g Demineralized water 3700 g 4000 9 The ingredients are mixed at room temperature. A solution results after standing for about 24 hours without stirring.

Impregnation Agent Ill Alkyltrimethoxysilane 80% ("Wacker290") 1000 g Crystal oil ("SheIIK 30") 8000 g 9000 g The ingredients are mixed, whereby a solution is formed.

When treating old sandstone, e.g. for the restoration of Kronborg Castle, which is exclusively built of sandstone, one proceeds as follows: The absorption ability of the stone is examined by spraying with demineralized water. In case of large differences the absorption ability is examined within smaller areas, and the need for cleaning is estimated on basis of the results obtained. An absorption test with impregnation agent I is also carried out in order to estimate the particle size of the latter relative to the capillary dimensions of the sandstone.

After drying the first treatment is carried out in suitably dry weather by applying impregnation agent I until incipient saturation. Immediately thereafter impregnation agent II is applied in an amount corresponding to about 1/4 of the amount used of impregnation agent I.

After appropriate drying and considering the weather conditions, impregnation agent Ill is applied until full saturation after about 5 to 8 days. If desired, the treatment with impregnation agent Ill may be repeated after 10--15 days.

A series of stone samples of Gotland sandstone of about 3 x 6 x 11 cm, i.e. with a surface area of about 234 cm3, which means between 225 and 250 cm2 in practice, were treated as described above with the abovementioned impregnation agents I, II, and III as shown in the following table below. After drying the absorption ability by total immersion in water for 60 minutes was tested.

Impregnation agent Water Stone absorption, No. Date I il Ill g 1 78.03.10 8.0 2.0 78.03.15 2.4 78.03.21 0.4 78.03.29 0.7 2 78.03.31 10.0 3.8 78.04.05 6.8 78.04.10 0.8 3 78.10.06 8.0 2.0 78.10.13 6.6 78.10.23 2.0 78.11.27 0.7 4 78.11.29 9.0 3.0 78.12.07 3.0 79.03.20 2.0 79.04.02 0.4 5 79.02.29 13.4 4.5 79.03.05 6.3 79.03.14 0.9

Normal consumption per mZ by the treatment of Gotland sandstone, Hälsingborg sandstone or Lemuda sandstone (from the Vissingsö area) is: Impregnation agent 1 400-500 9 Impregnation agent 11 120-1 50 g Impregnation agent III 250-300 g Treatment of new sandstone is made in a similar way including the preceding investigation mentioned.

EXAMPLE 2 A test sample marked G 136 of Gotland sandstone, of 3 x 6 x 11 cm2 corresponding to a surface area of 234 cm2, and having a weight of 431.1 g, was treated as follows.

On June 6, 1 975, the sample was coated with 9.0 g of impregnation agent I having the following composition: Barium acetate, 40% 5.24 g Calcium acetate, 25% 1.30 g Skim-milk,10% 1.64 g Silicic acid tetraethylester 0.82 g 9.00 g On June 9, 1975, the sample was coated with 0.8 g 4% glyoxal (impregnation agent II).

On June 13, 1975, and February 13, 1976, the sample was coated with 4.3 and 3.7 g, respectively, of a 8% silicone resin "W 190" (impregnation agent III).

The three days between the application of impregnation agents I and II gave a poor adsorption of preparation II of only 0.8 g. This was a result of a drastical drying after the application of agent I.

However, the test sample had a suostantially improved ultimate strength of 1135 kg/cm2, which appears from the tests hereinafter. After the above mentioned treatment and drying, test stone G 1 36 weighed 435.6 g on June 19, 1976.

EXAMPLE 3 A test sample marked G 161 of Gotland sandstone, of 3 x 6 x 11 cm corresponding to a surface area of 234 cm2, and having a weight of 434.3 g was treated as follows.

On July 1 975, the sample was coated with 9.9 g of impregnation agent I having following composition: Barium acetate, 40% 6.13 g Calcium acetate, 25% 1.53 g Skim-milk, 10% 1.28 g Silicic acid tetraethylester 0.96 g 9.90 g Immediately thereafter, i.e. after few minutes, the stone sample was coated with 2.3 g of 3% glyoxal (impregnation agent II).

On July 1975,4.7 g of a 8% silicone resin "W 190" (impregnation agent Ill) were applied.

After drying the test stone it weighed 436.4 g. It is seen that impregnation agent II was absorbed substantially better by application immediately after agent I, cf. Example 2. The test stone had an ultimate strength of 1 51 5 kg/cm2. On July 31, 1 975, the test stone absorbed 850 mg of distilled water by immersing for 60 minutes.

EXAMPLE 4 A test sample marked G 193 of Gotland sandstone, having the dimensions 3 x 6 x 11 corresponding to a surface area of 234 cm2, and having a weight of 41 6.5 g, was treated as follows.

On February 14, 1 977, the sample was coated with 9.5 g of impregnation agent I having following composition: Barium acetate, 40% 5.88 g Calcium acetate, 25% 1.47 g Skim-milk, 10% 1.23 g Silicic acid tetraethylester 0.91 g 9.49 g Immediately thereafter 2.2 g of impregnation agent II in the form of 2% glyoxal were applied.

On February 21, 1977, impregnation agent Ill was applied in the form of 7.0 g of an 8% silicone resin "W 190." After drying the test sample weighed 420.1 g. The sample was undamaged after a climate test carried out according to the test description hereinafter. After the climate test the dry sample was immersed in distilled water at 200C and an absorption of 500 mg of water in 40 minutes was measured. Before the ultimate pressure test mentioned in the test description the stone was cut in halves, whereby a penetration of impregnation agents to a depth between 9 and 1 3 mm was found.

EXAMPLE 5 The following absorbent mineral building materials were treated with impregnation agents I and II having the composition given in Example 1. Impregnation agent I was applied with a brush until saturation, i.e. until further amounts of the agent could not be absorbed. Immediately thereafter a suitable amount of agent II was applied, determined on basis of the amount of agent I used.

The amounts of impregnation agents I and II appear from following table.

Surface Area Agent I Agent II Material (cm2) (G) (G) Common Concrete 240 3.4 1.4 Gas Concrete 240 14.5 6.6 Sand-Lime Brick 240 15.2 9.5 (Artificial calcereous sandstone) Travertine 240 10.6 3.5 Tile Brick, Yellow Type 240 5.0 2.0 Tile Brick, Red type* 1 240 2.1 0.9 *The method less suited, the capillary dimension is usually too poor.

Tests A comparison of the compressive strength of samples of Gotland sandstone treated according to the invention relative to untreated samples has been carried out.

The tests were carried out after halving the test samples prepared according to the above Examples, which means that both the treated and the untreated stones had a length of 6 cm, a width of 5.5 cm and a height of 3 cm. The thrust load was applied vertically on the height dimension in the form of a circular steel punch having a diameter of 29 mm corresponding to 6.6 cm2.

The results appear from following table.

punch pressure Compressive strength Sample at break, kg kg/cm2 Untreated sample A 2200 835 Untreated sample B 2200 335 G 136 (Example 2) 7500 1135 G G 161 (Example 3) 10000 1515 It is seen that the treated samples have a substantially improved compressive strength as compared with the untreated samples.

Furthermore, sample G 1 93, of the above dimensions, of Gotland sandstone, treated according to Example 4, was pressure tested after a climate test consisting of 8 cycles of each one hour in water at room temperature and one hour at frost of about 200 C.

After the fourth cycle there was a pause of 6 days during which the pieces were maintained at about 230C.

By a pressure test as described above, break occurred at a punch pressure of 10000 kg corresponding to a compressive strength of 1 515 kg/cm2.

Thus it appears that this sample has maintained its compressive strength during the climate test.

Industrial Use of the Invention The invention may be used for the protection and restoration of objects, such as buildings, frontages, reliefs and sculptures of absorbent mineral building materials, such as sandstone, concrete, tile, tuff or travertine.

Claims (10)

1. A method for protecting or restoring outdoor objects, e.g. buildings, building frontages, reliefs and sculptures, of absorbent mineral building materials, such as sandstone, concrete, tile, tuff or travertine, by treatment with impregnants, one of which contains alkaline earth metal salts of carboxylic acids, wherein the object is initially impregnated with a first impregnant at least containing a barium salt and a calcium salt of at least one C1~20 aliphatic carboxylic acid, and a water-soluble protein, thereafter impregnating the object with a second impregnant containing one or more aldehydes selected among C18 mono- and dialdehydes, and optionally at a later time, when the treated object has dried, treating the object with a third impregnant containing a hydrophobing agent preferably dissolved in a relatively slowly evaporating hydrocarbon oil.

2. A method according to claim 1, wherein the first impregnant contains barium acetate and calcium acetate.

3. A method according to claim 1 or claim 2, wherein the protein in the first agent is casein, preferably in the form of skim-milk powder.

4. A method according to any one of the preceding claims wherein the first agent further contains a silicon alkylester, preferably a silicon tetraalkylester.

5. A method according to any one of the preceding claims, wherein the second agent contains both a dialdehyde and a monoaldehyde.

6. A method according to any one of the preceding claims, wherein the first impregnant contains 2030% by weight of a barium salt, 3-6% by weight of a calcium salt, 1-2% by weight of skim-milk powder, and 812% by weight of silicon tetraalkylester in water, and impregnation continues until incipient saturation is noted, wherein the second impregnant contains 13% by weight of a dialdehyde and 15% by weight of a monoaldehyde in water, using the second agent in an amount by weight corresponding to 1/3 to 1/5 of the amount of weight used of the first impregnant, and wherein the third optional impregnant contains a hydrophobing agent, preferably a silane dissolved in the proportion 1:5 to 1::1 2 in relatively slowing evaporating hydrocarbon oil.

7. A method according to claim 6, wherein 400-500 g of the first impregnant, 120-150 g of the second impregnant, and 250-300 g of the third impregnant, are applied per m2 of the object to be treated.

8. A method according to claim 6 or claim 7 wherein the second impregnant contains about 2% by weight of glyoxal and about 2.5% by weight of 40% formaldehyde in water.

9. A set of impregnants for use in carrying out the method according to claim 1, comprising a first impregnant at least containing a barium salt and a calcium salt of at least one C,~20 aliphatic carboxylic acid, and a water-soluble protein, and optionally a silicon tetraalkylester, a second impregnant containing one or more aldehydes selected among C18 mono- and dialdehydes, and optionally a third impregnant containing a hydrophobing agent, preferably dissolved in a relatively slowing evaporating hydrocarbon oil.

10. A set of impregnation agents according to claim 9, comprising a first impregnant containing 2030% by weight of barium acetate, 3-6% by weight of calcium acetate, 1-2% by weight of skim-milk powder and 812% by weight of silicic acid tetraethylester in water, a second impregnant containing 1-3% by weight of glyoxal and 1-5% by weight of 40% formaldehyde in water, and optionally a third impregnant containing as hydrophobing agent a silane.