Masonry, finishing and special mortars

Masonry mortars. Masonry mortars are applied at the brick and stone laying, arranging of leveler layer at installation of reinforced-concrete structures, grouting columns etc. The composite cement-lime and cement-clay mortars are used mostly at the wall construction. Cement mortars without inorganic plasticizing agents are expedient only for structures which are erected below groundwater level. Lime mortars and mortars on different lime-containing binders (lime-slag, lime-ash and other) are applied in mass low-rise building. Thus an air-hardening lime is used in mortars for the laying at the air relative humidity in apartments up to 60%, hydraulic lime-containing binders – in mortars which perform in the moist conditions. Portland cement is widely applied for the different building mortars. The special cements for building mortars, which contain active mineral admixtures or microfillers, are also used.

Along with the coarse, middle and fine sands it is allowed to apply very fine sand with the fineness module 1-1.5 at the building mortars production. Application of fly ash is rational for the producing of effective mortars for ordinary stonework and also for the wall from the large-size elements. But it is undesirable to use the mortars with ash additive in winter time due to slow speed of their hardening at a decreased temperature.

If the fly ash is used in the cement mortars than, usually, the cement content goes down on 30-50 kg/m³ at the simultaneous improvement of workability of mortar mixture. Excess of cement content at a complete replacement of sand by the ash can be removed with adding of lime in little quantity. The admixtures of cement kiln dust and other active microfillers are effective in building mortars in addition to the fly ash.

It is possible to provide the increase of masonry mortars strength in winter by application of chemical admixtures (Table 12.2). Sodium nitrite, potash, urea, calcium nitrite with urea, sodium and calcium chloride, and also some other salts are applied as antifreezing admixtures at making of mortars in winter. Thus it follows to take into account the row of limitations: mortars with the chlorides of calcium or sodium can be applied only for the non-reinforced underground structures and also for wall laying of non-residential buildings. It is forbidden to apply all of the types of admixtures at the building of constructions which are exploited at a temperature higher than 40°C or at humidity over 60%, in the conditions of aggressive factors influence, in the areas of variable water level and under water without the special insulation. For constructions on the surface of which the formation of salt efflorescences are not permissible, mortar with admixtures should be preliminary tested on salt efflorescences.

Finishing mortars.Finishing mortarsare intended for plastering. According to the purpose they are divided on the mortars for ordinary and decorative, external and internal plasters.

Plaster coverage consists of two or more layers. Bond with the base surface is provided by preparatory layer with thick not more than 5 mm on brick and concrete surfaces and 9 mm on wood. Basic layer 5-7 mm thick is used for the plane surface making. The types of the improved plasters include also covering (decorative) layer in thick not more than 2 mm.

Table 12.2

Approximate strength of mortar with admixtures depending

on the temperature of hardening

Plaster machines can be used for production of plastering mortars, their delivery to the workplace and placing on a processing surface.

All the types of plaster mortars should have specified flowability, ability to not disintegrate at the production and also to provide required strength and good adhesion to the base.

The required flowability of the mortar mixture depends on the location of layer in plaster coverage. The most plastic mortar which fills all of surface voids is applied for a preparatory layer. The basic layers are produced from comparative viscid mortar which forms the required thickness of plaster. Mortar for decorated or covering layer has the consistency which allows smoothing it surface. The maximal sand fineness also depends on the type of plaster layer. For preparatory layer it equals to 2.5 mm, for the covering layer - 1.2 mm.

The mortars for ordinary plasters are divided into cement, lime, cement-lime, lime-gypsum and gypsum.

Cement mortars are applied for external plasters which are subjected to the systematic moistening and internal plasters - in apartments with relative humidity of air over 60%.

Waterproofing admixtures (for example organic silicon liquids) can be used to increase the water resistance. The volume ratio between cement and sand is accepted for preparatory layer 1:2.5-4, basic layer 1:2-3, covering (decorative) layer 1:1 -1.5.

Cement-lime mortars are applied at plastering of both facades of buildings and internal apartments. Application of lime sharply increases the plasticity of mortars. The content of lime paste depends on the layer assignment. The volume content of lime can be for preparatory layer, usually, 0.3-0.5; for basic layer 0.7- 1; for covering (decorative) layer 1-1.5. The cement-lime mortars can be manufactured with two methods: making dry sand-cement mixture which is moistened by lime milk to the required workability; or adding of the cement to sand-lime mortar.

The mortars, based on the air-hardening lime are applied for plastering of surfaces in apartments with relative humidity of air up to 60%. They can be used for external plasters which are not subjected to the systematic moistening. It is better to add a lime as lime milk into the mortar. The slow hardening is the main lack of lime mortars. Gypsum plaster can be added to accelerate the hardening of lime mortars. The lime-gypsum mortars are the most appropriate at the plastering of wooden surfaces into apartments. The hydraulic admixtures: tripoli powder, diatomit, slags, fly ash and others are added into mortars to increase their water-resistance.

Gypsum mortars are applied in areas mainly dry by climate for plastering of wooden and gypsum walls. Dry gypsum plaster mixtures are intended for the mechanized placing of plaster coverage. They are made in a factory conditions with the purpose of the centralized supply to the building objects.

Decorative mortars are applied at the facing of external and internal walls. The ordinary and coloured Portland cements are used as binder in the decorative mortars. The coloring ingredients and fillers from natural or ground up materials also can give the color to mortars. The mica or ground up glass can be added to impart the surface brilliance of decorative layer.

The lime-sand, terrazite and stone-like decorative mortars are used for decorative plasters.

Lime - sand decorative mortars are the most economic. Quartz, marble or limestone sand is added to their composition depending on a required color. The different methods of placing and finishing of covering (decorative) layer can be used.

The facades of buildings are plastered with the coloured lime - sand mixtures. Mortars with the enlarged content of cement are used for plastering of surfaces from a dense concrete, and also structures, which are subject to the intensive moistening.

Terrazite plasters, besides binder and quartz sand, include stone chips of different fineness and certain amount of mica and coloring agents if it is required. They are manufactured, usually, from preliminary proportioned dry mixtures. Terrazite plaster can be treated with the help of sand blasters, brushes and other tools for obtaining of the finish surface which imitates the sandstone, tuff or other rocks. The terrazite finish depends on maximal fineness of filler grains. Fine-grained fillers in terrazite mixtures have grains 0.15-2 mm, middle-grained 2-4 mm, coarse-grained 4-6 mm. Coarse-grained terrazite at facade finishing can be used for plastering of socles and ground floors, middle-grained for the wall surfaces, fine-grained for the cornices.

Stone-like mortars imitate different rocks depending on the type of stone chips and method of surface treatment.

Stone-like plasters are applied mainly at finishing of facades and socles. Portland cement is main binder for these mortars. Lime paste is added in an amount of 10-20% to provide required plasticity of mixture and cement brightening. The grain composition of the stone chips has a great importance and can take into account the method of surface treatment of hardened mortar and the required finish.

Polymer-cement mortars have the improved decorative properties, reduced wearability, high tensile strength, enlarge adhesion to the different bases. They are made from mixture which consists of complex binder (Portland cement and the plasticized polyvinyl acetate dispersion or latex), fillers, aggregates, coloring agents and the water.

Polymer-cement mortars can be applied for floors in apartments with intensive movement of people and enlarge requirements for the cleanness (public places and buildings, shops, stores etc).

Polymer-cement mortars also can be applied for gluing of different finishing materials, finishing of facades etc.

Special mortars. Special mortars include the mortars for waterproofing, injection, tamping, acid-proof, heat-resistant, heat-protection, acoustic, X-ray plasters and others.

Waterproofing mortars are applied for creation of waterproofing coverages of reinforced-concrete pipes and other structures, for dampproofing of tubings seams, etc. The activity is very important at the selection of cements for waterproofing mortars. With the increasing of cement strength the water impermeability of mortars improves. The sulphate resistant cements can be applied at production of waterproofing mortars, intended for service in the conditions of aggressive waters. The main influence on water permeability of mortars has a water-cement ratio with the increasing of which the system of voids and capillaries develops in the mortar. As a rule, for waterproofing mortars water-cement ratio is in the range of 0.3-0.5.

Admixtures for increasing of mortars water impermeability are divided into microfillers, plasticizers, for mudding, polymer and combined. Usually, inexpensive materials such as stone powder, fly ash and others can be used as microfillers. Microfillers must compacts and create the fine-grained structure of mortars. Chlorides of iron, aluminium and calcium are widespread used for mudding. Liquid glass, sodium aluminate, calcium nitrate and other admixtures can be also used for waterproofing mortars manufacture.

Plasters, which are placed by spraying method, perform especially reliably. They are applied for coverage of pool walls, pipelines, tunnels, basements which are subjected to the action of ground water.

Injection mortars are used for filling of channels of prestressed reinforced concrete structures, providing of compatible operation of armature with a concrete and protect it against corrosion. The compressive strength of injection mortars should be not less than 30 MPa.

Grouting mortars are used for closing (tamping) of water-bearing cracks and voids in rocks and structures. The method of cement mortar injection in cracks and voids of rocks and structures is called cementation. This method is widely used, for example, in hydraulic construction for the soil compacting.

Also, cementation is successfully applied for recovery the defects and damages in concrete structures. The complex of requirements to grouting mortars is provided by the application of plasticizers, special cements and cement-clay mixtures processed by the special reagents, using of the high-speed turbulent mixers etc. Oil-well Portland cement, Pozzolanic cement, Blast furnace cement are applied in the conditions of pressure and aggressive waters.

The plasticized and hydrophobic cements are the effective types of binders for grouting mortars. Water-cement ratio in such mortars is accepted depending on rock fissuring and changes in the wide range.

Acid-proof mortars are produced from mixture of acid-proof aggregates and dispersible fillers with the fluorsilicate sodium that are mixed with the liquid glass.

Quartz sand and also sands which are produced by crushing granite, andesite and other rocks are used as the aggregates of acid-proof mortars. Fine-grain quartz sand, marshalite and other siliceous powder materials can be used as fillers. Fluorsilicate sodium content which is needed for the accelerated hardening of liquid glass is 5-8% by it weight.

The active mineral admixtures – tripoli powder, diatomite and others can be added to increase the waterproofness of acid-proof mortars. Polymer admixtures in composition of acid-proof mortars increase their density and the impermeability.

Mortars with the light aggregates are applied for thermal-insulation plasters.

The sound absorbing light mortars with an average density 600-1200 kg/m³ are used for acoustic plasters. The sand grains of fineness from 3 to 5 mm from porous materials: pumice, slags, expanded pearlite, claydite and other are used as aggregates in such mortars.

Heavy-weight mortars with the average density 2200 kg/m³ and higher are applied for plastering of x-ray cabinets and apartments in which the work with the radioactive isotopes are carried out. The Portland cement or Blast furnace cement is applied as the binder materials in such mortars, as aggregates are used barite or other heavy-weight rocks.

Dry mixtures

Initial materials and admixtures.The type of the binders defines conditions of hardening and operational properties of dry mixture, including humidity conditions of work, frost resistance, firmness to cyclic moistening and drying. The hydraulic binders are applied in the mixtures assigned for dry and damp conditions; air-hardened binders assigned for dry conditions.

By fineness of aggregates and fillers dry mixtures can be divides as concrete, mortars and mixtures for thin-layer technologies with filler fineness no more than 1.25 mm which called also disperse. Disperse mixtures are also divided into coarse, small and fine-dispersed.

For manufacturing of dry mixtures in most cases ordinary and white Portland cements are used. Application of Portland cement without mineral admixtures that provides demanded stability of chemical-mineralogical composition and properties of the binders is the most preferable. To provide accelerated hardening of mixtures is required to apply high dispersion cements. White cement is used for spackling manufacturing, decorative plasters and special kinds of glue.

For rapid-hardening mixtures, which used for repair works; and also extending compositions alumina cement is used as binder.

The gypsum binders are applied as the admixtures in cement mixtures and as the basic binders in spackling and other finishing compositions.

Hydrated lime can be added in cement mixtures to increase plasticity and for regulation of some other properties. Humidity of hydrated lime should be no more than 2 %, high requirements are presented to completeness of slaking and to grain composition of lime.

Polymer binders in dry mixtures are applied in powdered state.

Quartz sand, chalk, limestone, microsilica, kaolin, dolomite, etc are applied as fillers for dry mixtures.

The widest nomenclature of dry mixtures is made with application of quartz sand. The content in sand clay (more than 0.5-1.5 %) and powder-like impurities, which sharply increase water requirement and shrinkage, reduce strength and adhesion with the base, decrease frost resistance is undesirable. At the same time some increase in sand the fine-grained fractions improves the water-retaining ability of mixtures and their density.

The stone crumb (granite, marble, etc.) with fineness no more than 2.5 mm can be applied in the protectively-finishing compositions along with quartz sand.

The type of filler dependson the assignment of dry mixture. In dry mixtures which assigned for high water resistance coverings the bentonitic clay is applied as filler. In dry mixtures also organic fibrous fillers: polypropylene, acrylonitrile, cellulose are used. They have positive influence on strength of materials, increase their crack resistance and reduce shrinkage.

The humidity of dry mixtures should not exceed 1% by weight.

Mortars are obtained by mixing the dry mixtures and required volume of water in the ratio, specified in the standard documentation on a dry mixture or in the instruction of it application. During manufacturing and application of mortars the harmful substances should not escaped in environment in the amounts exceeding maximum permissible concentration.

Regulation of technological and operational properties of dry mixtures can be realized by application of various chemical admixtures. For the mixtures which placed by a thin layer on porous surfaces, it is important to provide required water-retaining ability. Fast absorption of water by the base leads not only to loss by a plasticity material, but also to insufficient hydration of binders, decrease of strength, adhesion and frost resistance.

Modifying of dry mixtures for improvement of their water-retaining ability, plasticity, suitability is achieved by application of admixtures on the base of cellulose esters - hydroxyethyl cellulose and hydroxypropyl cellulose (0.05-0.5 % by weight).

Methylcellulose has wide application – that is cellulose methyl ether, well soluble in water to density 1.29-1.31 g/cm³, with bulk weight 0.3-0.5 g/cm³ At swelling in water the volume of methylcellulose increases in many times. Macromolecules of methylcellulose even in the diluted water solutions are inclined to aggregation. Water solutions are stable at рН from 2 to 12. Methylcellulose has good surface-active properties in water solutions, at heating to temperature 35- 36°С it is observed gelling. At temperature reduction lower than gelling temperature gel collapses. Methylcellulose is capable to keep the properties after dissolution in water, repeated drying and dispersion.

For increase of water-retaining ability of dry mixtures can be added also bentonitic clays - natural aluminum silicates which are characterized by high dispersion, swelling capacity, ion-exchange ability. These clays consist of montmorillonite minerals with the general formula Аl₂О₃·4SiO₂·nН₂О. Bentonitic clay, modified by the organic compounds is recommended to use for dry mixtures manufacture. They make less considerable affect on water-retaining ability of building mortars, than methylcellulose. Montmorillonite clay, microsilica, etc are used as stiffeners, which connected free water in mortar mixtures, along with bentonitic clay.

Ether of starch (5-20 % by weight of cellulose ethers) can be often added into dry mixtures as stiffener alongside cellulose ethers.

Higher level of modification is provided by application in composition of dry mixtures the redispersible polymer powders, which can represent itself as the admixture or the polymer binder. Redispersible powders are obtained by drying of water dispersions of polymers usually by a spray drying method. Redispersible polymer powders (RPP) are capable at mixing to create the water dispersions similar to initial, i.e. to redisperse.

Widely known representative of group redispersible powders is the thermoplastic polymer known as Vinnapas (commercial name). In a combination with mineral binders redispersible powders Vinnapas are successfully used for dry mixtures manufacture. The basic fields of application are glues for a tile and the thermal protection systems; self levelling compositions; repair compositions for the concrete; all kinds of plasters; dispersive and powder cement-lime paints; waterproofing compositions; filling paste for seams, and also spackling compositions.

Table 12.3

RPP general characteristic

Unlike liquid and paste-like products the mixtures modified by polymers are resistant to the influence of low temperatures and bacterial pollution.

A number of chemical admixtures can be added into dry mixtures to increase thixotropy and diluting effect; regulate setting time; accelerate hardening, etc.

The most effective diluents are super- and hyper plasticizers - products of polycondensation of naphthalene and melamine formaldehyde, polycarboxylate, polyethylene glycol. Some effective types of super- and hyper plasticizers are resulted in Table 12.4. Super plasticizers can be added into composition of dry mixtures in quantity 0.05-1.5% by weight of binder for increase of mortars fluidity; decrease of water content and, as consequence, increase of final strength, density and uniformity of the hardened mortar. Such admixtures are particularly recommended in self levelling mixtures as plasticizers, dispersants and shrinkproof agents.

Table 12.4

Types of super- and hyper plasticizers

Admixtures (citric acid, etc.) which delay the setting time of the gypsum binders are applied. They allow to increase an operating time of gypsum proportionally to their dosage (0.01-0.08 % by weight). Effective hardening-accelerating admixtures are calcium formates and their modifications. Their content is 1-4 % by weight of the binder.

Dispersants, porophores, defoaming and water-repellent agents, etc. can be added into a compositions of special chemical admixtures.

Principal types of dry mixtures.Gluing dry mixtures are widely applied for plaster works, surfacing preparations, floor making and filling of seams.

Gluing mixtures are the polymer-mineral systems containing mineral binder, filler and polymer admixtures, regulating physical-mechanical and rheological properties of mortars.

Gluing mixtures of all groups should:

– provide strength of jointing of facing materials with the various bases – concrete, stone, cement-sand, gypsum plaster, foam concrete and wood-particle plates – not less than 0.5 MPa and to keep this indicator from influence of various operational factors – negative temperatures, the water environment, static and dynamic loadings;

– have long term of serviceability of mortar mixtures – not less than 60 min;

– have high fixing ability (resistance to displacement of the tile put on the mortar mixture) – no more than 0.5 mm;

– have high adhesion to pasted facing material and the basis;

– provide duration of a correcting of tiles position during not less 10-15 min.

Basic compositions of gluing mixtures and the basic indicators of quality of trademark "Ceresit" mixtures are resulted in Tables 12.5 and 12.6.

Table 12.5

Basic compositions of gluing mixtures mark "Ceresit"

Mixtures for plaster works represent the polymer mineral systems containing mineral binders, aggregates, fillers and various admixtures, raising vapor permeability and reducing srinkage of mortars.

By the type of main binder the dry mixtures are divided into cement, cement-lime and gypsum.

Depending on filler fraction they can be: fine-grained (not more 0.315mm), medium-grained (0.315-1.2 mm) and coarse-grained (1.2-2.5 mm and more).

Cement mixtures should have adhesion with the base not less than 0.5 MPa, their vapor permeability – not less than 0.1 mg / (m×h×Pa).

Upon termination of gypsum hardening process on a surface should not be formed cracks.

Cement mixtures of all groups should:

- provide at performance of external works high firmness of coverings to influence of a moisture and various climatic factors, including the negative and raised temperatures, to have factor of water absorption no more than 0.2 kg/(m²×h);

- be easy placed and leveled.

Table 12.6

The basic quality characteristics of gluing mixtures (trademark "Ceresit")

The basic characteristics of cement mixtures of different groups are resulted in Table 12.7.

Gypsum mixtures are intended for finishing of internal surfaces of premises. Into their composition can be added: lime, fillers, polymer modifying components, retarders of set and other admixtures.

Gypsum mixtures should:

– not collapse at periodic short-term humidifying;

– provide possibility of regulation setting process in a wide time range.

The basic characteristics of gypsum mixtures:

Table 12.7

The basic physical and mechanical characteristics

of cement mixtures for plaster works

Wide application in painting and decorating is found the mixtures for polymer-cement and polymer decorative plasters. They are intended for external and internal decorative finishing of surfaces of buildings on the concrete and brick bases, in systems of a thermal protection of facades, on the bases from gypsum, gypsum cardboard, wood-shaving plates.

In Table 12.8 compositions and specified properties of polymer-cement decorative plasters obtained from dry mixtures are resulted for example.

Polymer-cement decorative plasters are classified on:

- A – coarse-disperse, for internal works, without water protective properties, possesses low resistibility to abrasion and adhesion to the bases;

- B – coarse-disperse, for external works, it is recommended for finishing of constructions from a brick and light-weight concrete;

- C - intended for finishing of building structures with the raised density of structure (heavy-weight concrete, asbestos-cement sheets, etc.);

- D - improved, placing on glazed tile is possible;

- Е - fine-dispersed, with water protective properties, for internal and external works.

Table 12.8

The basic technical characteristics polymer-cement decorative plasters Ceresit

Mixes for surface preparation represent the systems containing mineral binder, fillers and various admixtures, including, reducing sticking cement mixtures to the tool.

They should:

– have adhesion to the base not less than 0.5 MPa;

– Vapor permeability should be not less than 0.1 mg / (m×h×Pa);

– be frost-resistant (for external works) and withstand not less than 50 cycles of freezing and thawing;

– have firmness to crack formation and minimum shrinkage (no more than 0.2%);

– be ground and painted, including paints on organic solvents;

– not flow down from vertical surfaces;

– be waterproof (on the cement base).

At surface finish preparation for wall-paper, paints, decorative coverings there are applied spackling and priming mixtures. Unlike plaster they are put thin (0.2-3mm) a layer. Compositions for surface finish preparation should provide adhesion to the bases – not less than 0.5 MPa, vapor permeability – not lower 0.1 mg/(m×h×Pa), crack resistance - at placing by layer to 5 mm.

After hardening of mixtures covering should be ground and painted well, if required to have sufficient water- and frost resistance, to get demanded colors and shades.

The basic physical-mechanical characteristics of mixtures for surface finish preparation and some their compositions are resulted in Tables 12.9 and 12.10.

Table 12.9

Compositions of some spackling mixtures

Dry mixtures are widely applied to obtaining of the mortars intended for the making of floor coverings.

Mixtures for the making of floors are polymermineral compositions, containing mineral binder, aggregates, fillers and various admixtures, including raising crack resistance, abrasive resistance, frost resistance and water resistance of mortars.

Mixtures for the making of floors should:

– harden quickly (maintain small loads through some time);

– have high abrasive resistance;

– be frost-resistant (not less than 75 cycles of freezing and thawing) in not heated premises and out of premises;

– provide required firmness of facings, layers and coverings with high adhesion between layers.

Floor coverings are applied when it is required to level a surface, to hide communication pipelines, to distribute loadings on heat - and to a sound-proof layer, to create required biases.

Table 12.10

The basic technical characteristics of spackling mixtures Ceresit

Coverings applied mainly consist of the mixtures on the basis of cement, gypsum and the anhydrite, forming self-leveling floors. Characteristic compositions of such mixtures are resulted in Table 12.11.

For filling seams at tile facings of walls and floors the special mixtures are applied which are carrying out simultaneously decorative and protective functions.

Mixes for filling seams are represented by polymer-mineral systems containing mineral binder, filler and reinforcing mineral binder admixtures, and also the admixtures raising adhesive and deformative characteristics of mortars (the elasticity module) and reducing shrinkage.

Mixes of all groups for filling seams should:

- give required decorative properties to surfaces together with facing materials;

- protect constructions from moisture penetration;

- possess firmness to atmospheric, shrinkable or mechanical influences;

- harden quickly;

- have frost resistance not less than 50 cycles of freezing and thawing;

- be characterized by abradability no more 0.7 g/cm² and shrinkage no more than 2 mm/m;

- have strength of adhesion to the base not less than 0.5 MPa.

Table 12.11

Mixtures for floors

Some basic mortars compositions for filling seams are resulted in Table 12.12.

Technological lines on production of dry mixtures provide storage of binders and fillers in a silage warehouse which is rational for placing over the equipment for dispensing, mixing and packing of components. Weighing of components is carried out on batch scales giving on which is carried out in modes of "rough" and "thin" streams. Mixing of dry loose materials is carried out in the mixers providing uniform distribution of admixtures and dispersion of components, inclined to agglutination and to formation of lumps.

Table 12.12

Basic mortar compositions for filling seams between facing tiles

The optimum mode of mixing is characterized by high speeds of shift and provides at mixing suspension state of components. Mixes are packed in valve bags by packing machines. Technological lines are equipped with computer control systems.

Date: 2015-12-18; view: 979