Plasters as a finishing coatings in Thermal Insulation Systems

 

The shaping of the surface of an insulating system can be accomplished in many different ways. Along with natural stone, tiles and other ceramic coatings, plasters are most commonly used as a finishing coating and lining material. In some regions their share is nearly 95%.

The choice of finishing plaster depends on one side of the perceptions and desires of the developer on how would it the building look like and on the other side on the technical and technological qualities of the plaster, the way of its application and its operating properties. Considering the diversity of existing plasters it can be argued that there is no universal coating – suitable for all cases and applications.

The choice of plaster depends on many partially conflicting criteria:     
   - rain protection (watertightness and water vapor diffusion)     
   - crack resistance (elasticity)     
   - resistance to microbiological attacks and dirt     
   - choice of colour and degree of reflection ob light (HBW)     
   - fire protection     
   - compatibility with the base

 

Criteria such as workability, resistance to efflorescence, speed and resistance to fading also play an important role.

The separation of the plasters can be performed according to different criteria. However, the most used classification is according to the binding substance in them on which is based the difference between the mineral (lime- and/or cement-based), polymer (synthetic resins based), silicon (silicon resins based) and silicate plasters (potassium water glass based). There are many other definitions and terms according to which, for example, mineral plasters are called also: non-organic bonded and the polymer – organic bonded plasters. The latter can be seen too like dispersion plasters.

The qualities of a plaster depend mainly on the bonding substance in it. It determines its hardness and strength, as well as its diffusion properties and resistance to weather conditions, elasticity and crack resistance, its pH-value and the stability of the colour in addition to its adhesion to the base.

Plasters can also be classified according to their optics and structure – dragged, scratched, etc.

Mineral (noble) plasters

They are produced and delivered as a ready for use mixture and consists of lime and/or cement, mineral added ingredients (additives). They are offered on the market in dry powder and when water is added they become ready for use consistency. Mineral plasters, which are suitable for insulation systems consist of thin layer noble plasters or thick noble scratched plasters.

The thin layer noble plasters are supplied in sizes from 0,5 to maximum 6 mm and acquire their typical surface through friction, structuring or stepping with the help of appropriate tools. With this type of plasters the formation of micro cracks cannot be excluded.

Due to different water absorption and/or temperature of the base at the coloured mineral plasters is possible to occur difference in the tone or smoothness of the colour. Also, the change in the working conditions during the application of the plaster and its drying time can cause changes in the tone of its colour. Here must be made distinguish between the formation of spots, efflorescence of calcium carbonate and a change in the colour tone. The last one does not represent a functional disturbance and could be neutralized by countervailing painting.

Special place among the noble plasters occupy the noble scratched plasters. There is no other plaster which can form such an open and natural surface that is obtained by scratching the surface of the plaster (where comes its name from). Particularly beautiful effects and “living” surfaces (depending on the sunshine and geometry of the building) can be achieved by adding colourful particles in the plaster.

The layer thickness of the coating at the noble scratched plasters is about 10 mm but also are possible such with thickness up to 20 mm. Therefore the reinforcement layer of thermal insulation system on which the plaster is applied should be scratched (disheveled) in order to achieve sufficient mechanical connection. Decisive in the handling of this type of coating is the time of its structuring. Once a surface is structured (scratched), it remains and it cannot be undone. If certain areas are damaged or later must be„ additionally scratched“, this places remain visible. Alternatively the entire surface must be once more structured. The risk of forming micro cracks in the scratched noble plaster is considerably less, since by “scratching” surface tensions in the plaster are reduced.  

Silicate plasters

The group of these plasters is united under the brand TERMOFLEX® PRO SOLID. They are very suitable for old bases, when retrofitting buildings with architectural monuments. The resulting finishing coating is extremely resistant to aging and weather conditions and the proper application ensures the extended life of the facade, its water repellent properties and mechanical protection. TERMOFLEX® PRO SOLID are plasters that are extremely resistant to cracking and are perticularly suitable for use in areas with large temperature variations, long winters and high air humidity. When applied very evenly are distributed and the process of drying is less sensitive to the ambient temperature – which greatly facilitates the process of working with them and making them easy for application and structuring.

The silicate plasters are often being lined next to the mineral plasters due to the fact that they have relatively good diffusion properties, high affinity for mineral bases and on the basis of their composition possess certain “mineral” character. The silicate plasters represent coatings connected on the basis of potassium water glass and organically enhanced by the addition of synthetic resins. Through this addition the colour stability and adhesion of the plaster to the base are significantly improved. In the practice is necessitated that silicate plasters should contain maximum 5% organic additives. The properties of the silicate plasters: such as water absorption, diffusion properties, colour stability and adhesion to the base can be significantly affected depending on the choice of polymer dispersion. The silicate plasters are distinguished by their weather conditions resistance, colour stability and especially high vapor permeability.

As a main bonding substance in the plaster the water soluble glass binds not only due to water evaporation (physical) but also by the chemical processes that take place: in which airborne carbon dioxide bonds and forms a water-insoluble polymeric silicate rid and potassium carbonate. This process is described by the term silicification. What it is important is that the formed potassium carbonate is water-soluble and at silicate plasters it can lead to white efflorescence which in time is washed away by the rain. The process of silicification is mainly influenced by the temperature, air humidity and the type of the base. At temperatures +5°С, this process is delayed and the water glass remains partially water soluble, while at temperatures around 0°С it stops. The silicification process is also prevented by the long-term high air humidity. When there is rain, fog or dew on the surface the plaster collects water which transport on the surface layer the not yet silicified water glass. All of these problems in the process of sicilification lead to the appearance of white spots and efflorescence in the coloured silicate plasters.

The unbounded water glass in the silicate plasters is highly caustic and the drops from the plaster which stumbled upon glass, wood, metal and others when applying it cause corrosion and damage that later cannot be removed. Therefore, before applying silicate plasters, all parts that can be damaged in this process should be properly packed and covered.

Silicone plasters

The group of these plasters includes the brand TERMOFLEX® PRO ELASTIC. They are distinguished by an exceptional elasticity, very high vapor permeability allowing the so called “breathing” of the facade. The plasters TERMOFLEX® PRO ELASTIC provide greater colour stability and allow easy maintenance of the purity of the facades. The high humidity resistance of the coating made with this plaster makes it suitable for areas with high humidity as well as for regions with air saturated with sea salts. It is also suitable as a finishing coating in urban environments – on facades of buildings on busy city streets, intersections, and others because it is extremely resistant to acid rain and air pollution depositions on the surface of the plaster as they do not enter into chemical reaction with the plaster. The very good resistance to mechanical influences makes it suitable for outdoor locations where are possible hails and places with a lot of people passing by.  TERMOFLEX® PRO ELASTIC has very good water repellent properties. It is extremely resistant to biological contamination, mold, fungi, and others. and very suitable for application on the north or shady facades.

The silicone plasters like the silicate ones are not normatively regulated, which leads to huge differences in the quality of plasters offered on the market. They are also, like the silicate, sold as a ready to use paste-like mixture; however, the binding substance is composed of silicone resin emulsions and dispersions of polymer resins. Since the silicone resin emulsion is relatively expensive, often it is only added silicone oils and water repellent additives. Such “silicone” plasters can be recognized by the fact that they get dirtier over a shorter period of time. As a rule, these plasters can be recognized by their low cost too.

Chemically speaking, the silicone plasters stand somewhere between pure inorganic and organic coating materials. The silicone resins used in the production of this type of plasters are highly molecular, three-dimensional braded ties which grid, like the one of the quartz, is formed from silicon and oxygen. The difference is that in the silicone resin every 4th oxygen atom is replaced by an organic alkyl (methyl or propenyl) group. Due to this we talk about the so-called “molecular brush”. The silicone resin plaster produces very good repellent effect and the dispersions – good bonding with the base (adhesion) and high connectivity (cohesion) of substances.

In conclusion it can be said that the silicone plasters combine the advantages of inorganic and organic connected plasters: as on their vapor permeability they can be compared with the mineral and silicate plasters, and on their water repellent properties – that of the polymer coatings. Unlike mineral and silicate plasters, the silicone ones dry physically.

Polymer plasters

The group under the name TERMOFLEX® PRO TECH contains plasters which have high elasticity, low water absorption, good adhesion to the surface and resistance to mechanical damage. The acrylic polymers which are the binding substance in them are extremely soft and make them very suitable for installation on thermal insulation systems. During installation the plaster are sensitive to weather conditions.

The polymer plasters (on the basis of artificial resins) represent organically connected coatings with similar to the appearance of plasters look. The binding substance there is added under the form of a polymer dispersion or solution – finely divided polymers or synthetic resins in liquid (in most cases water). It is formed a stable, colloidal system which looks like a dense substance and in which the water forms a so called outer phase, in which under the form of dispersion (fine opened), the particles of the resins or the polymer form the inner phase. For this reason these plasters (on the basis of water dispersion) can be diluted with water.

The polymer plasters are connected by means of physical drying and therefore when they are freshly applied they should be protected from hail. Upon drying, the water evaporates and the polymer particles initially thicken, then with the drying process in progress they stick together and merge – forming in the end an overall film. This process of aggregation and fusion  (coalescence) leads to the formation of water-insoluble and water repellent surface after the complete drying of the plaster, which, however, is vapor permeable.

The main advantages of the polymer plasters are in their high water repellent abilities (resistance to heavy rain loadings), their unlimited variety of colours in which they can be coloured and in their very high crack resistance. Thanks to their high elasticity, the polymer coatings are very suitable as finishing layer on thermal insulation systems, because they can absorb the temperature conditioned changes in the insulation boards very well. The reason for this lies in the flexibility of the polymer plasters, due to which they take and discharge the emerging tensions. These plasters possess an elongation at break of 2 cm/m, which is about 100 times greater that the one of the mineral plasters.

In conclusion it can be said that some of the disadvantages of the binding substance in the plasters can be corrected by adding a variety of different additives. For example, all organically bounded plasters can be improved with various biocides, fungicides and algaecides supplements, which increase their resistance to biological contamination and damage. The mineral plasters can be further water repelled and thus their waterproofing abilities increased. The gluconate and alcohol additives in the polymer plasters increase their resistance to freeze. 

Property

Silicate plasters

Silicone plasters

Polymer plasters

  Bonding substance

potassium water glass, dispersion

emulsion of silicone resins, dispersion

polymer
dispersion

  Elasticity, Plasticity

-

+

+++

  Water repellency

++

+++

+++

  Vapor permeability

++

++

+

  Diversity and colour stability

+

+

++

  Suitable bases

+

++

++

  Resistance to biological    contaminations

++ 1)
   - 2)

++ 3)

++ 3)

  Resistance to efflorescence

+

++

+++

  Suitable for painting/retrofitting

++

+

+

  1) freshly applied   
  2) after lowering the alkalinity   
  3) with the help of additives

 

   -      none/bad    +     low   
  ++ 
high  
  +++
very high/very good

 

 

Special place among the polymer plasters have these with natural or coloured pebbles. There organically bounded coatings as a rule are not applied on large areas on thermal insulation boards, but mainly in the area of the wall-base or have a decorative character in the system. Under certain conditions, these plasters may look slightly milky. This does not constitute a change of their colour (fading) in the classic sense or see-through the base. In this case we talk about an optical illusion, which is caused by the way of processing the plaster. In these plasters the bonding substance is transparent and if the plaster is stirred too much before the application or too strong, it is possible that tiny air sacs are going to get in the plaster. They cause another refraction of light that looks like a milky film. This optical defect remains and cannot be removed. Its appearance is possible when there is extremely high air humidity during its application and drying. However, in this case it is reduced with time. In order to improve the water repellent properties of these plasters in the area of the wall-base is possible that they be sealed with a transparent primer after their drying.

 

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