Working with stones and cement, DIY info and mixtures
Cement
Our ordinary lime mortar is at least 5000 years old. The art of burning lime has therefore been known for so long, it was originally carried out in very simple ovens. They piled up a wall of limestone and burned a mixture of fuel and limestone inside. In very remote regions, this is still the case today. This simple field kiln was replaced by the shaft kiln, this by the ring kiln and finally by the rotary kiln.The greater or lesser purity of the limestone has a major influence on the properties of the slaked lime and therefore also on the masonry mortar prepared from it. For example, limestone with more than 5% clay is unusable for ordinary masonry lime. However, hydraulic lime is made from this. Lime with a low content of silicates hardens better, the Romans already knew this type of lime.
To make ordinary masonry mortar, about 1 dl of fatty lime is mixed with 3 parts by volume of sand. The hardening of this mortar takes place by absorbing carbon dioxide, whereby the carbonate is formed again from the slaked lime, the calcium hydroxide. For this it is necessary that the air has access to the interior of the masonry and it can therefore be explained that in very thick walls one found completely soft mortar in the interior after 150 years. In a wall of the Bastei in Vienna, only 10% carbon dioxide was found in the interior after 300 years, while it should actually contain 23%.
While no reaction occurs between the lime and the ordinary sand, certain types of sand are known that produce a very hardening mortar. These types of sand then contain weathered silicates, which can react with the lime and thus harden like cement.
Cement is obtained by burning mixtures of lime marl and clay, which contain about 25% clay. In the so-called pozzolan cements one finds more silicic acid than lime. Such a natural cement was already known in ancient Rome. The pozzolan earth (Pulvis Puteolanus) was mixed with lime and could then be used for waterworks. Until the middle of the 18th century, Italy was the source of these cements.
Smeaton in England made the first artificial cement and used it to build the famous Eddystone lighthouse in the English Channel. In 1796 Parker obtained a patent for making hydraulic lime from argillaceous limestone, in 1824 the mason Aspdin made cement from a mixture of limestone and clay and called the cement Portland cement because the color resembled Portland stone. Until about 50 years ago, England almost exclusively supplied cement, after which cement factories were built in all countries and our country also supplies the best types of cement.
Portland cement contains, per 1.7 parts of lime, 1 part of soluble silicic acid, part of the silicic acid being replaced by aluminum oxide and iron oxide. When the mixture of lime and aluminum silicates is burned, a mixture of strongly basic silicates is formed, which are easily decomposed by hydrochloric acid. These basic silicates now have to be ground extremely fine and then have the property of absorbing and binding water. In the beginning, a colloidal solution of hydrates in water probably forms, which crystallizes slowly. With normal cements, the first reaction takes place in about 2 hours, crystallization takes several months, after which the cement thus acquires its actual firmness.
Eddystone lighthouse
made by Smeaton using artificial cement
(painting Anton Melbye 1818-1875)
Sand-lime brick
The production of sand-lime brick is also based on the reaction between lime and silicic acid. Since the normal sand does not react at normal temperature, the mixture of sand and 5 to 8% lime pressed into stones is heated under pressure in closed boilers, whereby sufficient water vapor must be present.The largest amounts of cement are used for making concrete, the strength of which depends largely on the types of sand and gravel used. The great strength of the reinforced concrete is due to the fact that the cement adheres firmly to the iron.
Certain types of pumice stone also have weak hydraulic properties. This is used in the manufacture of the known drifting stones, which consist of ground pumice and lime. The lime reacts with the silicic acid from the pumice stone and the stones become very hard.
In addition to lime and cement, magnesia cement, burnt magnesia and magnesium chloride solution, gypsum and water glass are also used as binding agents.
Stone-like materials
Porcelain, earthenware, chamotte and brick also consist of silicates, but mainly aluminum silicate.Aluminum silicate is found in more or less pure form, our ordinary clay also consists mainly of this compound, but still contains large amounts of iron and other impurities, making the color very dark. The purest clay is kaolin, which was originally only found in China, and which type of clay led to the manufacture of Chinese porcelain. When burning clay to make pottery, the clay is not melted, but only sintered. Only small amounts of the contaminants melt and they bake the infusible particles together.
kaoline
Porcelain was invented in China in the 6th century and in 1695 Tschirnhausen succeeded in copying the porcelain. The alchemist Böttger succeeded in producing large-scale porcelain. Although they tried to keep the method secret, it leaked out and now porcelain factories sprang up everywhere.
Clay is created in nature by the weathering of original rocks, kaolin is created from feldspar. Feldspar is a mixture of potassium and aluminum silicate. The potassium is washed away by the water as soluble potassium silicate, leaving pure aluminum silicate.
In general, the kaolin is now washed away with the other components of the rock and redeposited elsewhere. This mixture is then the ordinary clay and is distinguished from the pure kaolin by the color and especially by the plasticity. Our ordinary clay, which forms the main component of our fertile soils and is baked into the well-known bricks, is also produced in the area of the great rivers by the weathering of the mountains. The material is carried along by the water and finely ground and finally deposited again wherever the water flows slowly enough. , which in turn actually consists of a type of glass, i.e. a fusible mixture of silicates.
Finally, the refractory bricks consist of compounds with the highest possible melting point, which had previously been heated at a temperature higher than the temperature at which they are used. A pure clay containing few low-melting components is taken for this purpose. Part is first baked, coarsely ground and then pressed into bricks with the same clay and baked again. The properties can be varied by adding ground quartz.
Better refractory bricks consist of bauxite, the newest ones consist of almost pure aluminum oxide, almost pure quartz, dolomite, magnesia, circonium oxide, soapstone and silicon carbide.
Concrete
Already in ancient times people knew concrete, a building material consisting of stone pieces and a binder or mortar. The Romans and Phoenicians used broken brick or crushed natural stone as an aggregate and probably volcanic cement and lime as a binder. Nowadays people usually take sand and gravel with cement.The ratio in which the different components are mixed in concrete, if one wants to make a concrete that is as strong and dense as possible, can be roughly determined by applying the following reasoning. The large pieces must carry the whole. The gaps between the large pieces now have to be filled with finer material, so generally sand, and the gaps that remain now have to be filled with the cement, so that all the particles are stuck together.
In general, 1 part of cement is taken with 2 to 3 parts of sharp sand and 3 to 4 parts of coarse gravel. (1:2:3 is a common mixing ratio in countries with a temperate climate)
Depending on the purpose for which the concrete is used, the proportions can be changed. In many cases it is not necessary to achieve the maximum strength and therefore one simply takes less cement. It is very important that the sand and gravel used do not contain loamy components. As a result, the firmness immediately becomes considerably less.
Mixing is done entirely by hand for small quantities, large quantities are mixed with concrete mixers of different construction.
Colored concrete
The coatings on floors made of concrete and cement plaster can be colored with suitable pigments. The pigments must be absolutely resistant to lime, must have the highest possible hiding power and must not contain any components that are harmful to the concrete. As little dye as possible should be added, as all dyes in too large quantities significantly reduce the strength of the concrete or cement mortar. You should never add more than 10%.Brown iron oxides and burnt ochres can be used for brown, while khaki, yellow and similar shades can be made with the aid of ochre, yellow iron oxide hydrate, chrome green and ultramarine green. For green one takes the last two pigments.
Dust-free concrete floors
To this end, the surface of the concrete is hardened using a special water glass solution. This water glass has a specific gravity of 42.25° to 42.75° Baumé, while the ratio of sodium oxide to silicon dioxide is 1:3.25.The solution is diluted in a ratio of 1 : 4 with soft water before use and only applied 2 to 4 weeks after the floor has been poured. The floor must be completely clean, as grease stains, for example, completely prevent the penetration of the silicate solution. The floor is scrubbed well and then left to dry for a few days. Only when it is completely dry is the silicate solution applied, which can now penetrate into the pores. The silicate reacts with the free components of the concrete and the lime silicates formed considerably harden the concrete.
The solution is allowed to soak in and harden for 24 hours, after which the floor is washed with clean water. After this, it is allowed to dry and the operation is repeated. In all, the silicate solution is applied 3 to 4 times.
Acid-resistant concrete
By treating concrete with the same solution of sodium silicate as above, which converts the free lime into the silicate, the concrete becomes relatively resistant to diluted acids, while untreated concrete disintegrates very quickly, since the lime, for example with diluted hydrochloric acid, immediately dissolves. reacts. By repeating the treatment from time to time, for example every year, concrete can remain good for a very long time, even in contact with organic acids.Remove wall rash
Simply dilute strong hydrochloric acid with 10 dl of water and brush off the stains. After about 4 minutes, the acid is rinsed off with clean water. The acid must not act any longer, as concrete and mortar in particular will then be affected and permanent stains will occur. If necessary, the operation is repeated after some time.With very dry concrete, stains can often be removed by rubbing them well with a strong solution of paraffin in petrol. This treatment is also often used to make the concrete water-repellent and to make the color more uniform in colored concrete.
Fast hardening concrete
The simplest method to achieve a high compressive strength more quickly is to mix the mass more intensively. By increasing the mixing time from 1-2 min to 5 min, the compressive strength can be doubled after three days. Moreover, concrete needs a certain temperature and humidity to harden quickly. The temperature should be at least 70° F or 21° C while taking care not to allow the added water to evaporate. The soldiers knew during the great war that their concrete bombproof shelters lasted much longer if they carefully covered the concrete with wet cloths while it hardened.Furthermore, the concrete can be made to harden more quickly by adding a few percent calcium chloride or calcium oxychloride to the mixing water. One takes 2 to 4% calcium chloride and 7 to 10% calcium oxychloride. Usually a concentrated solution is made and the corresponding amount is added to the mixing water for each bag of cement. The effect is not the same for all types of cement, so you must first make a small test.
Hardening of cement floors
Even with old floors, when the bonding strength is already reduced, the strength can be increased considerably by treatment with fluosilicates. These are salts of the mixed fluoro-silicic acid. Usually one takes magnesium salt or zinc salt.These fluates also react chemically with the free lime from the cement and convert it into acid-resistant and hard insoluble compounds. The solidity of the mass is thereby considerably increased.
When treating a floor, it must first be carefully cleaned. After this, it is allowed to dry through and through. The fluorosilicate is now dissolved in water in a ratio of 1:16 for the first treatment. After about three hours you can apply a second amount, the concentration of which is now made 1 : 8. Before the floor is completely dry after the last treatment, it must be washed, otherwise white spots easily remain.
Making concrete and cement waterproof
| Naphtha | 100 | dl | |
| Aluminum stearate | 10 | dl | |
| Glacial acetic acid | 0,3-1,5 | dl |
| The naphtha is heated to 80℃ and then the aluminum stearate is dissolved in it. After everything is well dissolved, the glacial acetic acid is added while stirring well. A clear viscous solution is obtained. Before use, the solution can be diluted with naphtha if necessary. The solution can be applied by brush or spray gun. The solution penetrates deep into the concrete and has a strong water-repellent effect. Aluminum-calcium stearate can also be added directly to the concrete mix. One then takes 100 to 200 g per bag of cement. Ammonium stearate can also be used for the same purpose. |
| Paraffin | 5 | dl | |
| Chin.wood oil | 10 | dl | |
| Standoil | 20 | dl | |
| Petroleum distillate | 10 | dl | |
| Benzole | 40 | dl | |
| or: | |||
| Talc (beef tallow) | 10 | dl | |
| Stand oil | 5 | dl | |
| Paraffin | 1 | dl | |
| Naphtha | 32 | dl | |
| Siccative | 0,1 | dl | |
Foam concrete
Bonding of new to old cement layers
With floors it often happens that holes have to be repaired or the floor has to be completely covered with a new coating. The adhesion of the new layers to the old can be improved considerably by first cutting the old layer clean in the usual way and then smearing it with undiluted water glass. Water glass should be used with a specific gravity of 41.25° to 42.75° Baumé and with a composition of sodium oxide silicic acid as 1 : 3.25. Sprinkle some dry cement powder into the wet water glass and smear it with a brush. This is called burning.The new layer is then immediately applied to this.
Cement resistant to calcium chloride
| Aluminum oxide | 40 | dl | |
| Lime | 40 | dl | |
| Silicic acid | 15 | dl | |
| Calcium chloride | 1 | dl |
Waterproofing bricks by painting
A sure method of waterproofing bricks is oil painting. The appearance is of course completely different. A fairly greasy paint is used as a primer, as part of the oil is absorbed by the stone, diluted with turpentine oil. In order to prevent the sinking of this paint, certain substances are now added as pore fillers. Aluminum palmitate or stearate is used for this. The large molecules of these substances clog the pores. Furthermore, the sulfurized oils are suitable here. A second coat of paint is applied to the base coat, which is not diluted as much. The third coat is a normal paint, preferably a stand oil lead white paint.| Recipe nr. 1. | |||
| Sand | 75-86 | dl | |
| Bitumen | 11-15 | dl | |
| Fireclay | 3-10 | dl | |
| Recipe nr. 2. | |||
| Asphalt emulsion | 1,75 | dl | |
| Cement | 1 | dl | |
| Crushed stone | 5 | dl | |
| Recipe nr. 3. | |||
| Plaster | 10-77 | dl | |
| Asphalt | 4-36 | dl | |
| Sand | 0-86 | dl | |
Terrazzo floors
First, a thin layer of fine sand is applied to the concrete surface, followed by waterproof asphalt paper. The actual substrate is now placed on top of this, namely a layer of mortar, about 3 to 4 cm thick. The mortar consists of 1 dl cement and 3 dl pure, coarse and sharp sand, mixed with as little water as possible.The actual terrazzo mass consists of a mixture of 1 dl cement and 3 dl colored stone pieces. The color and size of the pieces of stone depend on the taste. Sometimes a finer and sometimes a coarser structure is required, sometimes a mixture of coarse and fine is used. This is a matter of personal taste.
When the bottom layer is sufficiently hard, the separation between the different colors is first laid in thin slats, which must be slightly higher than the layer becomes thick. The terrazzo mass, which must be as dry as possible, is now applied and leveled with a straight lath with sawing movements.
After leveling, a roller is passed over the mass in both directions to fill everything well and to bring the stones to the surface. Now, preferably larger stones are sprinkled into the mass until the surface is occupied by the stones for about 85%. The surface is now smoothed with a trowel. The trowel strokes can still be seen.
Once the terrazzo is sufficiently hard, it is ground smooth with carborundum stones, preferably by machine. The floor must be kept sufficiently wet during sanding. The floor is now thoroughly rinsed and the holes that may be visible are filled with cement mortar.
Now the floor is allowed to harden for a week, kept moist during that time and then sanded completely smooth. Before hardening, the temperature must be controlled. This must not come too close to the freezing point, freezing must be absolutely avoided.
Vintage terrazzo floor
Dairy factory floors
By impregnating the floors with paraffin, they become insensitive to the weak acids and alkalis that occur in dairies. One can make a solution of paraffin in turpentine oil and benzene, iron this solution warm and after the solvent has evaporated one goes over the floor with hot irons to evaporate the rest of the solvent.It is better to avoid the solvents completely and to melt the paraffin into the floor using hot irons or possibly with a soldering flame. This makes the floor completely sealed and acid-resistant. The operation must be repeated from time to time.
Protect stone against weathering
| Unboiled linseed oil | 100 | dl | |
| Siccative | 1-5 | dl | |
| Paraffin alcohol | 8-10 | dl |
In countries with a dry climate, good natural stone and brick are almost imperishable, in humid climates all types of stone will eventually be affected. This natural weathering process, to which we also owe all our soil types, is mainly accelerated by the water that is absorbed by the stone. Due to its carbon dioxide and nitric acid content, to which large quantities of sulfuric acid are still added today in the cities, this water dissolves components of the natural stone and makes it porous. Finally, in the winter, the water inside the stone freezes and the expansion of water during freezing causes the stone to shatter.
It has now become apparent that it is almost impossible to make a porous stone absolutely tight. It is better to make the surface water-repellent and still leave it porous. This allows the absorbed water to evaporate again in dry times.
Treatment with ordinary linseed oil is already quite good for this. However, since linseed oil itself also absorbs a lot of water, the preparation can be improved by adding the paraffin alcohols, which are extremely water-repellent.
White cement
| Feldspar | 40-100 | dl | |
| Kaolin | 100 | dl | |
| Limestone | 700 | dl | |
| Magnesite | 20-40 | dl | |
| Table salt | 5 | dl | |
All components must be iron-free as far as possible, the mixture is burned at 1430° to 1500° C and finally finely ground. The addition of table salt converts the iron that is always present into the chloride and this iron chloride evaporates at the heat of the oven. |
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