Overview of definitions

16.1      Thinning

 

The paint is supplied at the manufacturer's viscosity for application via spray painting, including airless spray painting, as well as for application by roller and brush. If requested, the paint can also be supplied at a specific viscosity. If the paint is too viscous (thick), for example in case of cold weather, then a small quantity of thinner may be added to obtain the required viscosity. The recommended amount of thinner to be added is specified by the manufacturer for various application methods. Excessive thinning can negatively affect the results. Addition of a small quantity of thinner will not significantly affect the dry paint film. However, if too much thinner is added, the user should realize that addition of thinner lowers the concentration of solids in the paint. As a result, it will be necessary to apply a thicker wet paint layer to achieve the same desired dry film thickness.

 

16.2      Mixing ratio

Two-component products are supplied in the form of an A component (primary) and a B compo­nent (curing agent), packaged in the correct mixing ratio. It is important to always use this same ratio, even if not all of the product is used. Start by mixing component A until a homogeneous mass is obtained. Then add component B and mix until a homogeneous mixture has been obtained. Make sure you completely remove all of component B from its container, if necessary with the help of a small amount of thinner, to ensure that the correct mixing ratio is obtained. The curing reaction starts as soon as both components are mixed together, and the mixed product remains usable for a limited period of time, the so-called pot life. Do not mix more product together then you can effectively utilize within the pot life of the product.

 

16.3      Induction time

 

The induction time is the recommended waiting time between the mixing of both components and the start of the application process, in order to allow the curing reaction to get underway. It applies only to certain types of two-component epoxy products, as specified on the product data sheets.

 

16.4      Theoretical coverage

 

The theoretical coverage is defined as the number of square metres (m²) which can be covered by one litre of paint. The wet film thickness used for calculating the coverage is the film thickness realized in practice with the help of the most commonly used application method. Based on the volume percentage of solids, it is then possible to calculate the dry film thickness. The theoretical coverage, expressed in m²/l, is then calculated as follows:

 

Theoretical coverage in m²/l         volume percentage of solids

                                                 = _________________________  x 10

                                                    dry film thickness in micrometres 

 Some illustrative figures are presented in the table below:

 

 

Theoretical coverage in m²/l

 

 

 

 

 

 

 

 

If, as is the case for spray painting, extra thinner is added to the paint, then the volume percentage of solids in the ready to use paint mixture will decrease. The volume percentage of solids in the thinned down paint is then equal to:

                                                                                                  

volume of paint before thinning (l) x volume percentage of solids in paint before thinning

volume of paint before thinning (l) + volume of thinner added (l)

 

16.5      Practical coverage

 

In actual practice, the following factors affect the practical coverage:

 

surface profile/roughness

absorption by substrate

application loss

 

The loss depends upon a great many factors including: skill and experience of paint applicator, application method, size and shape of object, nature of substrate, film thickness applied, and conditions during application. It is therefore not possible to specify a generally applicable value for the practical coverage. We do not recommend spreading the paint layer out as much as possible. It is better to ensure that the desired film thickness is actually realized.

 

16.5.1   Calculations

 

The practical coverage is calculated by multiplying the theoretical coverage by a factor which depends upon the surface profile, the application method and the application conditions (see table below). The values specified in this table should be viewed as a rough guideline, as the working procedure also has a great influence on the practical coverage.

 

 

16.6      Recommended film thickness per layer

 

This is the thickness of the dry or wet paint film used as a basis for the information in the product data sheets. Depending upon the desired degree of chemical or mechanical resistance, other film thicknesses may be recommended.

 

16.7      Drying time

 

16.7.1   Dust-free

 

Drying rates are specified in terms of the time required for the paint film to become dust-free and tack-free respectively. These times are temperature dependent and specified for 20°C. Enclosed areas need to have sufficient ventilation to remove the evaporating solvents in order to achieve acceptable drying times. Solvent evaporation is one of the factors affecting drying of the paint film. For two-component paints which require curing and for paints which depend upon oxidative drying, the drying process also depends upon a chemical reaction. This chemical process for paints is called curing. The speed of this process depends upon the temperature: faster at higher temperatures and slower at lower temperatures.

 

16.7.2   Curing time

 

For two-component paints, curing times are specified based on an average ambient temperature of 20°C. As a rule of thumb, an increase in temperature of 10°C reduces the curing time by half.

 

16.7.3   Recoatability time

 

This is the required drying time between the application of successive layers of paint. As is the case for the other drying times mentioned above, this also depends upon temperature. For some products, this time interval is also limited to a maximum value, as adhesion between the successive layers may diminish with time. If the maximum interval is exceeded, it may be necessary to roughen up the surface to ensure effective adhesion of the following layer. Some products are also available for which the drying time between paint layers is not that critical. However, primer coatings should not be left exposed for too long in aggressive environments. The drying time specified between paint layers applies to successive layers of similar products. For different types of products, different times may apply. A freshly painted surface that has been exposed to a contaminated environment must always be thoroughly cleaned before a subsequent layer is applied.

 

16.8      Flashpoint

 

The flashpoint is the lowest temperature of a product at which just enough vapour exists in the air to enable it to be ignited in the air. The flashpoint is determined with the help of the Abel-Pensky closed cup method. The values specified are rough estimates and can serve as a guideline within the framework of local safety regulations with regard to fire/explosion hazard during transport, storage and processing. If significant changes occur in the composition of the product, relevant to the flashpoint, an updated product data sheet will be issued. Addition of thinner can significantly alter the flashpoint of a paint.

16.9      Density

 

The density is the mass (weight) of the paint in kilograms per litre at 20°C. For two-component products, the density is specified for the mixed product, unless specified otherwise. The density may vary somewhat with colour. The values specified are averages.

 

16.10    Solids

 

The percentage of solids per weight or per volume is specified under ‘volume of solids.’ It is calculated on the basis of the paint formulation and gives the relationship between the wet film and dry film thickness:

 

                  Dry film thickness = wet film thickness x volume percentage of solids

                  Wet film thickness = dry film thickness____   x 100     

                                                   volume % of solids

 

The volume percentage of solids can vary somewhat, and the values specified are average values.

 

16.11    Heat resistance

 

Heat resistance is specified in terms of the maximum temperature to which the coating can be continuously exposed without suffering damage. Yellowing and/or discolouration may occur.

Some rough general guidelines are given below.

 

 

Very heat-resistant paints (450°-500° Celsius) often have special binders such as silicones or silicates.

16.12    Application conditions

 

This generally refers to:

 

ambient temperature (i.e. surrounding temperature)

surface to be painted and selected paint

relative humidity

If the surface to be painted is wet or moist, it may also impact the paintwork. A term which is often used, correctly or incorrectly, is the dew point. What exactly is the dew point, and what does it have to do with paintwork or protective coatings?

To understand this, we must first explain what is meant by the term relative humidity (RH). All air contains water vapour (moisture), which is invisible. Warm air can hold more water vapour than cold air. The maximum concentration of water vapour (saturation value) in air at various temperatures is specified in the table below.

 

 

Usually, the air around us contains less water vapour than its maximum saturation value, in which case the relative humidity is less than 100%. Relative humidity is defined as:

 

RH = the quantity of water vapour (moisture) contained by air at a specific temperature divided by the maximum quantity of water vapour which the air can contain at the same temperature. To convert this value to a percentage, it is multiplied by 100.

 

Example:

Ambient air temperature = 20°C. The air contains 12 g of water vapour per m³. What is the RH? At 20°C, air can contain a maximum of 17.3 g per m³ of water vapour. RH is therefore:

 

12

17.3 x 100 = 69%

 

If we introduce a cold object, for example a glass of water with ice cubes, into air that contains water vapour, then the water vapour contained in the air may condense onto the object, as the air coming in contact with the object will cool down and therefore be able to hold less water vapour. We usually notice this in the winter when moisture condenses upon cold windows. The surface temperature at which water vapour will just start to condense on an object is called the dew point. The larger the value is for the RH of the air, the smaller the difference will be between the dew point and the ambient temperature. The relationship between air temperature, RH and the dew point is illustrated in the following table.

 

 

Explanation: Gram = grams of water per m³ dry air at the specified air temperature in °C

Dew point is the temperature to which the air in question would have to be cooled to achieve a relative humidity of 100%.

 

 

 

 

 

Explanation: Gram = grams of water per m³ dry air at the specified air temperature in °C

Dew point is the temperature to which the air in             question would have to be cooled to achieve a relative humidity of 100%.

 

The tables above can be used to read off the dew point value for the most common combinations of temperature and relative humidity. Only the moisture-curing polyurethane paints, such as the Poluran MC products, may be applied on a moist surface. Other solvent-containing paints must be applied to a dry surface, the temperature of which must be at least 3°C above the dew point to allow for the fact that evaporation of the solvent causes the surface to cool down. One should also take into account that moisture may penetrate into the wet paint film after painting has been completed. It is therefore risky to engage in painting activities late in the afternoon if the skies are clear and the relative humidity is high. To be on the safe side, the surface temperature of the object being painted should be at least 3°C above the dew point. At a relative humidity of 85%, the lowest acceptable object surface temperature is equal to the ambient (surrounding air) temperature.

 

For the above reasons, outdoor painting work may be carried out only if the relative humidity does not exceed 85%. At a relative humidity of 90%, the difference between the temperature of the steel object and the dew point is only 2°C, which means that the margin of safety between the dew point and the ambient air temperature is very small. It can be increased by raising the temperature of the steel by 1°C. At a relative humidity of 70%, the relationship between an acceptable surface temperature and the ambient air temperature is presented in the table below:

 

 

In spite of the fact that the temperature of the steel surface in the above table is clearly lower than the ambient air temperature, no condensation will occur under these conditions.

If the lowest acceptable temperature is 5°C and the ambient air temperature is the same, then the air could be warmed up, in which case the relative humidity would decrease as illustrated below:

 

 

 

16.12.2 Attention

 

In enclosed spaces, sufficient ventilation must be applied to remove solvent vapours. Ventilation to provide fresh air during application of the paint and during the drying process is then required from the viewpoint of health and safety and also to ensure adequate evaporation of the solvent from the paint film.

16.13    Application at construction site or workshop?

 

In order to realize maximum lifespan and optimum performance for the paint system concerned, we recommend that most layers of the paint system and, if possible, the entire paint system be applied in the workshop. For aesthetic reasons, a decision may be taken to apply the finish layer at the construction site after assembly.  

The advantages and disadvantages of applying the entire paint system in the workshop are as follows;

 

 

The decision whether to apply the finish coating at the construction site therefore depends largely on the type of object/construction concerned and whether there is much risk of significant mechanical damage during assembly. Another important aspect is whether the object will be exposed to the elements for a long period of time before protection becomes available in the form of a roof. If that is the case, then we recommend applying the finish layer at the construction site.

 

16.14    Film thickness

 

The dry film thickness of a single paint layer applied to a surface.

 

Method: ISO2808:1991(E)

Classification: not applicable

 

Nominal film thickness

 

Description:

The recommended dry film thickness per layer, or for the entire paint system, which is required to achieve the desired durability.

The effective average dry film thickness per layer, calculated on the basis of 10 measurements per component, may not be less than 80% of the nominal film thickness. A maximum of 10% of the measurements may have a value between 80% and 100% of the nominal film thickness if the overall average value is equal to or larger than the nominal film thickness.

 

Extremely high film thicknesses should be avoided. Information on maximum film thickness per product is provided in the product data sheets. We recommend calibrating the film thickness measuring equipment on the same surface as the one that will later be coated.

16.15    Gloss

 

Gloss is the visual impression created by the light-reflecting properties of a surface and depends upon the incidence of light and observation.  

Method: ISO2813-1978(E), measurement angle: 60°  

Classification:  

 

 

16.16  Blasting profile

 

This is the profile of peaks and valleys produced by blast cleaning the surface.

Method: ISO2632, Rugotest, Ra-value

Classification:

The Rz value is also often used. This is defined as the difference between the highest peak and the deepest valley of the blasting profile as determined over 5 measurement areas.

We recommend blast cleaning the surface in such a manner as to ensure that the value of Rz does not exceed 70 µm.

If the priming coats will be exposed to a contaminated atmosphere for a longer period of time, we recommend that Rz not exceed 50 µm.

The roughness of the surface profile influences the variation in the film thickness of the paint system, and this should be taken into account when applying the paint. In case of a high average film thickness, a normal roughness profile (Rz = 50 µm) will not affect the durability. However, for priming coats, the variation in film thickness caused by a high Rz value can lead to early rust formation, in particular on ‘peaks’ which are not well coated.

16.17    Adhesion (determination)

 

The checkerboard incision test: adhesion is determined with the help of a ruler and a Stanley knife with a straight knife edge. A pattern of lines is cut into the surface whereby 6 parallel lines are first cut, followed by a second set of 6 parallel lines perpendicular to the first set. Tape with the required characteristics (adhesive strength 10N, 25 mm wide) is then lightly pressed onto the surface. Finally, the tape is pulled away from the surface in one smooth motion at an angle of 60°.

 

The extent to which the paint squares in between the lines are pulled off the surface is a measure of the adhesion.

Baril Coatings recommends the use of Sellotape type 1112 or 1401 or Scotch tape 828.  

Method: ISO2409:1992(E)

 

 

 

Depending upon the film thickness, the distance between the lines is as follows;

0-60 micron dry film thickness              1 mm interval

60-120 micron dry film thickness           2 mm interval

120-250 micron dry film thickness         3 mm interval

>250 micron                                         St Andrew's cross cut test or Elcometer test (ISO-4624)

If the paint coating may be subjected to mechanical forces, the adhesion of the paint system should be class GT0/GT1 or better. If no mechanical loading factors are present, it should be GT2 or better

16.18    Anti-Graffiti

 

Graffiti goes back a long way and has been a contemporary art form throughout history. In the present day, graffiti is also used to permanently or temporarily ‘decorate’ less attractive surroundings.

However, every form of undesired graffiti is perceived by owners and residents as a form of vandalism. It is a form of damage which can usually be repaired but which nevertheless entails significant costs. As it is practically impossible to prevent its occurrence, objects must, where necessary, be protected against irreparable damage from undesired graffiti. No single product or system has yet been developed which works for every type of surface and/or type of graffiti. As a result, various products and systems have been developed. In choosing a system, a great many factors should be taken into account, including:

 

which protective systems are possible/applicable

what will the consequences be in terms of the requirements demanded of the surface

what surface preparation is required

what will visibility, durability and maintenance be

what will the environmental impact be (including the cleaning process for the system) and last but not least the total price

 

Anti-Graffiti Systems are basically nothing more or less than ‘barrier coatings’ which protect the surface from sustainable penetration and/or adhesion by the graffiti and therefore facilitate cleaning without damaging the surface itself.

 

The many different anti-graffiti systems can be classified on the basis of the behaviour of the system relative to the cleaning agents and/or methods.

 

Permanent systems:

These systems are not damaged or dissolved by the cleaning agents used when the graffiti is removed.

 

Self-sacrificing systems:

These systems are themselves completely removed when the graffiti is removed. Immediately after the graffiti is removed, the system must be applied anew.

 

Semi-permanent systems:

These systems are often a combination of a permanent priming coat and a self-sacrificing top coating. But this group also includes single-layer systems on the basis of a single product which becomes partly dissolved upon removal of the graffiti, and which therefore must also be reapplied after the cleaning process.

 

In cases where large works of graffiti must be removed, one can first use a high-pressure steam cleaner in combination with an industrial cleaning agent such as Enviclean 4951.

For graffiti which is more difficult to remove, white spirit can be used with or without the addition of water. Stubborn areas can be treated with undiluted white spirit by hand or with the help of a rotary cleaning lance. This will cause the finish layer to lose some of its gloss, but this effect will be only temporary.

Finally, one should realize that an anti-graffiti system always consists of a ‘barrier coating’ together with the relevant cleaning agents. Protective systems and/or combinations of cleaning agents other than the ones recommended may cause damage to the surface system and may therefore not be applied.

 

16.19    Low-solvent paint

 

The term low VOS (volatile organic solvents) is often used to indicate that the paint has been formulated with as little solvent as possible.
Low VOS paints should therefore contain a substantially lower concentration of solvent than their traditional competitors in the same area of application.
A low VOS paint is not by definition a high-solids paint.

 

16.20 Solvent concentration

 

The concentration of solvents in the paint product is expressed in gram/litre.

 

16.21    High-solids

 

A paint product is described as a high-solids paint if the concentration of solvent does not exceed 250 gram per litre. In actual practice, for the coatings commonly used, this is equivalent to a volume percentage of solids equal to at least 70%.

A high-solids paint is therefore also a low VOS product.

A medium-solids paint has a solvent concentration of between 250 and 450 gram/litre.

If the solvent concentration exceeds 450 gram per litre, then the paint is described as solvent-rich.

 

16.22 ISO 12944 part 1 to 8 (incl.)

 

Protection of steel constructions against corrosion with the help of paint systems

ISO 12944: deals with the protection of steel constructions with the help of paint systems and includes all factors which are important for realizing adequate protection against corrosion

ISO 12944-1: in addition to a general statement regarding health, safety and environmental protection, this section describes several basic concepts and definitions used in relation to the protection of steel.

ISO 12944-2: this section describes the environmental factors and conditions which encourage corrosion, including a detailed description of the atmospheric categories.

It describes the corrosion factors to be expected in situations where steel constructions are surrounded by water or are located underground.

These corrosion factors are important to take into account when selecting a suitable corrosion protection system.

This section is important for the principal /architect.

ISO 12944-3: this section provides information on design criteria for steel constructions with the aim of improving their resistance to corrosion.

This section is important for the architect/design engineer.

ISO 12944-4: this section describes the various types of surfaces/substrates to be protected. It also describes the various types of preliminary treatment methods..

This section is particularly important for the painting contractor.

ISO 12944-5: this section describes the various types of protective systems, arranged according to atmospheric load, which have proved suitable for controlling corrosion on constructions.

The examples of paint systems given here are representative of the current global knowledge available in this area.

This section is of particular importance to the supplier of paint products, the principal, and consulting firms.

ISO 12944-6: this section describes accelerated test methods which can be used to determine the durability of paint systems. These test methods can be of assistance in particular for paint systems regarding which insufficient practical experience is available and for encouraging their application. With the help of these test methods, new products can be introduced and applied more quickly.

The indoors B.A.S. low VOS paint systems in particular are the subject of these accelerated tests.

This section is important for all parties involved in providing recommendations for protection.

ISO 12944-7: this section describes the working procedure for applying the coating in the workshop or at the construction site. It deals with the methods for applying and storing coatings, inspection, maintenance advice, and the use of reference sections.

This section is of particular importance for the painting contractor, general contractor and the inspection/certification body.

ISO 12944-8: this section describes the management of projects dealing with the protection of steel constructions against corrosion. Various types of specifications are distinguished such as: project specifications, paint system specifications, paint application specifications, inspection specifications, and test specifications.

Project management activities are simplified and standardized with the help of model forms for planning, reference sections and inspection activities.

This section is important for all parties involved.

 

16.23 Shelf life

 

Shelf life is the minimum period of time for which the product can be stored without being opened at temperatures between 15°C and 30°C.

Generally speaking, the product can actually be stored for a considerably longer period of time than the minimum time specified.

 

16.24    Coverage and cost per m²

 

Guidelines for calculating the amount of paint used and the cost of paint per m²

It is all too easy to categorize paint as simply being expensive or inexpensive on the basis of the price per litre or, even more questionably, the price per kg. What really counts is the price per square metre of painted surface.

16.25    Theory and practice

 

The determining factor for the coverage realized with a paint, in other words the surface that can be painted with one litre, is the wet film thickness to be applied. After the solvent has evaporated, the thinner and dry paint film remains behind.

The difference between the wet and dry film thickness is determined by the volume percentage of solids in the paint. In practice, the question asked is often: how many m² can be painted per litre assuming a particular dry film thickness in micrometres? The table below specifies the coverage as a function of the volume percentage of solids and the dry film thickness. The formula used here is:

 

volume percentage of solids

dry film thickness in µ                    x 10 = theoretical coverage in m²/l

 

 

To calculate the practical coverage actually realized, the theoretical coverage has to be corrected for paint lost during the painting process. This can vary quite a lot depending upon various factors such as the application method, type of object, surface, professional skill etc.

As a rule of thumb, one may assume that between 5% and 10% is lost in the case of roller/brush application. The paint loss in the case of spray painting can vary between 20% and 80%.

 

Quantity of paint required and cost of materials per m²

 

The quantity of paint required for a paint job can now be calculated with the help of the following formula:

L = S                         

                 VS       x      1     L

              dft/10          1 x 100

 

Where:

 

-  L            = quantity of paint in litres

-  S            = surface in square metres

-  dft          = dry film thickness in micrometres

-  VS         = volume percentage of solids in the paint

-  L            = estimated loss percentage

 

In addition, the cost of the paint per square metre can now be calculated by dividing the cost of the paint per litre by the coverage. This can be illustrated by an example from the table above in which the film thickness is 50 microns and the volume percentage of solids is 40%. If the price of the paint is € 11.35 per litre and the loss percentage is 10%, then the cost of materials per m² becomes:

A) 25:8 + 10% = € 0.70.

Compare this with a paint that costs only € 9.53 but has a volume percentage of solids equal to 20%:

B) 21:4 + 10% = € 2.62.

Although paint B costs € 1.81 less per litre, the user will end up paying much more per square metre of surface actually painted.

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