This presentation is tell about paints and painting process on steel surfaces. It also covers paint failures, surface preparation, type of painting process, etc.

1. By:
Rahul Buswala
Chemical Engineer
Email: rahulbuswala1988@gmail.com
Linkedin:
www.linkedin.com/in/rahul-buswala-93123b40
Contact: +91 9425019979

2. What is Paint?
• Paint is basically a solution or suspension of pigment, binder, mineral
solvent (or water) and some additives that after application on a
substrate forms an adhering film on it.
• Paints are required for:
 Protection of substrate against corrosion, weathering and
mechanical damage.
Decorative function like automotive coatings, household appliances,
etc.
Information signals like traffic signs, information signs, advertising.
Specific applications like electrical conducting paints.

3. Composition of Paint
• Paint is a solution/suspension of following:
1. Binder
Binders are usually resins or oils but can be inorganic compounds such as soluble
silicates. The binder is the film forming component in the paint.
2. Pigment
Pigments are finely ground inorganic or organic powders which provide colour,
opacity, film cohesion and sometimes corrosion inhibition.
3. Solvent
Solvents are used to dissolve the binder and to facilitate application at the paint.
Solvents are usually organic liquids or water.
4. Additives
They are added to paints to improve particular technical properties like leveling
agents (butyl ether of ethylene glycol) to promote smooth, uniform surface on
drying, wetting agents to prevent flocculation of pigments, antifoaming agents,
thickening agents, etc.

4. Paint Film Formation
• Paint film formation can occur physically or chemically.
• Physical film formation from liquid coatings is known as drying whereas from
powder coating is known as melting. Ex: High molecular mass polymer binders
such as cellulose nitrate, chlorinated rubber, polyacrylates, stryrene copolymers,
etc.
• Chemical film formation takes place by chemical reaction between components
that react together on drying to form cross linked macromolecules.
In single pack system: Reactive components are constituents of the coating and
the reaction can be initiated by heat or radiation.
In multi pack system: A reaction partner (hardener/catalyst) is added.
Chemical film formation can also be done by oxidation of coating component(s)
by atmospheric oxygen.
• Physical & Chemical film formation are often combined, ex: in solvent containing
stoving paints, first stage is solvent evaporation and then film is cured by stoving.

5. Classification of Paints
•Paints can be classified on the basis of:
1. Binder
2. Diluent (Solvent)
3. Sheen
4. Task
5. And so on…..

6. Classification of Paints
• Paints/Coatings classification on the basis of binder:
Oil Paints Alkyd Silicone
Cellulose Saturated Polyester Urea, Benzoguanamine and Melamine
Chlorinated Rubber Unsaturated Polyester Phenolic Resins
Vinyl Polyurethane Asphalt, Bitumen, and Pitch
Acrylic Epoxy Silicate
• Paints/Coatings classification on the basis of diluent:
Solventborne Paints Waterborne Dispersion Paints (Emulsion)
Solvent Free and Low Solvent Paints Non-aqueous Dispersion Paints
Waterborne Paints Radiation Curing Systems
Coating Powders Electrodeposition Paints

7. Classification of Paints
• Paints/Coatings classification on the basis of sheen:
1. Flat/Matte
2. Eggshell
3. Satin
4. Semi Glossy
5. Glossy
• Paints/Coatings classification on the basis of Task:
1. Primer
2. Sealer and Surfacer
3. Undercoat
4. Topcoat
Gloss

8. Painting Process for
steel substrate
Surface
Preparation
Etch Primer
(optional)
Primer Coat
Sealing Coat
(optional)
Finish Coat

9. Why Surface Preparation
Metal surfaces having contamination with oil , greases and having oxide film provide
little or no adhesion to paints. Freshly prepared and roughened surfaces are active
(have more surface energy) and provide better adhesion to paint film.
Surface preparation affects the performance of the coating more than other variables.
Surface preparation is to a coating system is just like a foundation to a building.
The investment made in the purchase and application of best coating will be entirely
lost if surface preparation is inadequate.
Basic objective of surface preparation to attain the required cleanliness and surface
roughness for adhesion of primary paint.
Increasing surface energy and surface area to facilitate bonding
Increase in life of paint film.

10. Methods of Surface Preparation
Surface Preparation includes
1. Removal of oil, grease, dirt and swarf followed by
2. Removal of rust by means of mechanical or chemical treatment.
Surface
Preparation
Removal of oil,
grease, dirt and
swarf
Solvent Cleaning
Petroleum Solvent
Cleaning
(Immersion/ Brushing or
Wiping)
Trichloroethylene
Cleaning
(Vapour/ Liquid/
jetting)
Alkali Cleaning
(Immersion/
Electro-cleaning/
Jetting)
Emulsion
Cleaning
(Spray/Dip)
Steam
Cleaning
Rust Removal
Mechanical
Treatment
Chemical
Treatment

11. Methods of Surface Preparation
Removal of Rust by Mechanical Cleaning
Mechanical
Cleaning
Heavy
Localised Rust
Hand Scraping
Power tool
scraping
Flame
Cleaning
General
Rusting
Blast Cleaning
White Metal
Blast
Commercial
Blast
Brush-Off
Blast
Near White
Blast

12. Methods of Surface Preparation
Blasting
White metal blast cleaning : A white metal blast cleaned surface when viewed without magnification shall be
free of all visible oil, grease, dirt, dust, mill scale rust, paint oxides, corrosion products and other foreign
materials.
Near white blast cleaning : A near white blast cleaned surface, when viewed without magnification, shall be
free of all visible oil, grease, dirt, dust, mill scale, rust, paint, oxide corrosion products and other foreign
matter, except for shall be limited to no more than 5% of each square inch of surface area and may consist of
light shadows, slight streaks or minor discolouration caused by stains of rust, stains of mill scale or stains of
previously applied paint
Commercial blast cleaning: A commercial blast cleaned surface when viewed without magnification shall be
free of all visible oil, grease, dirt, dust, mill scale rust, paint oxides, corrosion products and other foreign
materials.
Staining shall be limited to no more than the 33% of each square inch of surface area and may consist of light
shadows, slight streaks or minor discolouration caused by stains of rust. Stains of mill scale or stains of
previously applied paint, slight residues of rust and paint may also be left in the bottom of the pits if the
original surface is pitted.
Brush - off blast cleaning : A brush -off blast cleaned surface when viewed without magnification, shall be
free of all visible oil, grease, dirt, dust, loose mill scales, loose rust and loose paint. The entire surface shall be
subjected to the abrasive blast. The remaining mill scale, rust or paint shall be tight. When painting is
specified, the surface shall be roughened to a degree suitable for the specified paint system. Immediately
prior to paint application, the surface shall comply with the degree of cleaning as specified.

13. Methods of Surface Preparation
Blasting
It shall also be ensured that the shot blasted surface should be subjected to
phosphating or application of priming paint within 4 hours except the jobs which need
pressure testing due to code requirements.

14. Methods of Surface Preparation
Surface Finish Rust Grade

15. Methods of Surface Preparation
Surface Finish Rust Grade

16. Methods of Surface Preparation
Surface Finish Rust Grade

17. Methods of Surface Preparation
Surface Finish Rust Grade

18. Methods of Surface Preparation
Rust Removal by Chemical Cleaning
Acid Treatment should be used only for parts that can be easily and thoroughly washed
free from acid. It may thus be unsuitable for parts of complicated shape. Particularly those
containing narrow channels or blind holes that cannot be properly washed out, or parts
with porous surface layers. The following types of components, therefore, should not
normally be treated with these acids:
1. Parts built up by riveting, spot welding, or similar methods;
2. Cast-iron parts, owing to the possibility of occlusion of pickling acid in porous surface
layers, or with machined cast iron in graphite pockets;
3. Ferrous articles with associated non-ferrous or non-metallic parts because of the risk of
attack of these parts due to electrolytic effects, and acid may be trapped at the joint; and
4. In case of high strength steel having strength more than 1 000 MPa, which are
susceptible to hydrogen embrittlement and pickling may be avoided.

19. Methods of Surface Preparation
Rust Removal by Chemical Cleaning
1. Derusting solution shall be applied for light rust removal in a thin film, using brush or
swab and left for 10 to 15 minutes followed to dry and be brushed down with a clean
dry brush before painting.
2. Pickling with Hydrochloric Acid (room temp), Sulphuric Acid (60-80 deg C) or
Phosphoric Acid (60-85 deg C) can be used to remove heavy rust.
3. Phosphating process includes degreasing by caustic, pickling by acid, phosphating and
passivation with rinsing in between every stage (7 tank process).
4. Electrochemical Cleaning can be done by any of the following way:
4a. Cathodic Treatment in Acidic Solution
4b. Cathodic Treatment in Alkaline Solution
4b. Anodic Treatment in Acidic Solution
4b. Anodic Treatment in Alkaline Solution
Note: Within 8 hours of surface preparation, the job should be subjected to phosphating
or application of priming paint.

20. Methods of Surface Preparation
Inspection
Quality control inspector shall inspect the prepared surface for
1. Freedom from rust, stain, oil or grease before application of priming paint.
2. Surface cleanliness.
3. Profile measurement using profile gauges and appearance of surface to pictorial
standards in case of blasting.
4. Test for assessment of dust on steel surfaces prepared for painting can be carried out
as per the Pressure-sensitive Tape method as per ISO 8502-3-1992(E).
Further, in case of chemical treatment the solutions concentration shall be examined
periodically by shops to maintain them as per desired concentration.

21. Paint Application
Methods of Painting
1. Brushing/Rolling
2. Conventional Spraying
3. Airless Spraying
Mode of Application Viscosity (FC 4 Cup)
Brushing 40-60 seconds
Spraying 28-32 seconds

22. Paint Application
Preparation of Paint for Painting
1. When the containers of air drying paints are opened, the material is observed for
skin formation. The skin formed should be carefully removed and settled pigment
has to be broken up and loosened by vigorous stirring preferably mechanically to
ensure homogenous dispersion. Care should be taken to avoid air entrapment
while stirring. The paint, if required may be strained through muslin cloth or
60mesh sieve.
2. Maturation is an important criterion for two pack products where curing takes
place through chemical reaction when the components are mixed before
application. The mixed paint is normally matured for about 30 minutes to initiate
the reaction process which ensures thickness build up and proper drying of the
paint film unless otherwise specified.
3. Maturation time is, however, to be adjusted depending on pot life and ambient
temperature. Products having a short pot life should be allowed less maturation
time as recommended by supplier to provide the adequate effect during film
formation

23. Paint Application
Points to remember before applying paint
1. Painting shall not be performed when the temperature is less than 3°C above the
dew point of the surrounding air.
2. When the relative humidity of the air is greater than 85%.
3. When the surface temperature is greater than 40°C (unless a higher temperature is
recommended by the paint manufacturer).
4. When the air temperature is less than 10°C (depending on local conditions).
5. When there is the likelihood of an unfavourable change in the weather conditions
within two hours after painting.
6. When there is deposition of moisture in the form of rain, condensation, frost etc.
on the surface.

24. Paint Application
Points to remember before applying paint (cont…)
7. When the available light, ventilation is not adequate for painting.
8. Paints shall not be applied within 50mm of edges which will later have to be
welded. Such weld areas should be taped for a distance of 50mm on either side of
the weld line.
9. When zinc rich primers are used, care shall be taken to avoid any possibility of over
spraying onto duplex or austenitic stainless steels, nickel alloys or 9% nickel steel
components.
Note : Zinc rich primers shall not be applied on equipment made from the above
mentioned materials unless such equipment is located in a shielded position which will
minimise the risk of molten zinc falling onto the equipment in the event of a fire.
10. Extra coats of paint shall be applied on the areas where the shape and/or plane of
application result in thinly applied coatings etc., at edges, welds, corners etc. To
compensate for these effects, stripes coats of paints shall be applied (normally applied
first so that they will be covered by the full coat).

25. Paint Application
Points to remember before applying paint (cont…)
11. Surfaces not to be painted shall be properly masked.
12. Surfaces shall be cleaned by solvent cleaning method to remove oil, grease,dirt,
cutting fluids and other contaminants.
13. Surfaces to be coated shall be blast cleaned with suitable abrasive to the required
surface finish for operating temperatures above 120° C i.e at least near white metal
blast cleaning and a minimum of a commercial blast cleaning for operating
temperatures below 120° C.
14. The average maximum blast profile shall be between 3.5 to 6.0 mils or as per
requirement.
15. All traces of abrasive and other debris shall be removed by brushing, sweeping,
blowing with clean compressed air, and vacuuming before the application of any
coating

26. Paint Application
Painting Process
Surface
Preparation
Check for
Surface
Cleanliness
& Profile
Etch Primer
(Optional)
Drying at
RT for 16
hrs min. or
as specified
in spec
Priming
Coat
Drying at
RT for 16
hrs min. or
as specified
in spec
Check for
DFT (if
required)
Clean the
surface
before
applying
next coat
Sealing
Coat
(Optional)
Drying at
RT for 16
hrs min.
or as
specified
in spec
Check for
DFT (if
required)
Clean the
surface
before
applying
next coat
Finish
Coat
Drying at
RT for 16
hrs min.
or as
specified
in spec
Inspection
Ensure that after thorough mixing of the product of two component systems, the
maturation time as indicated in the manufacturer’s product data sheet is to be
allowed before applying the paint.

27. Paint Application
Quality Check
Following points shall be ensured to achieve overall quality of the job:
(a) Compressed air used for spray application shall be free from oil, moisture and other contaminants.
(b) Steel surfaces to be painted shall be free from burrs, sharp edges, lamination, surface
imperfections and any other contamination detrimental to paint adhesion finish or appearance.
(c) Surfaces to be coated have been cleaned.
(d) All surfaces to be coated shall be completely dry before paint application.
(e) Paint components shall be mixed as prescribed / recommended and mixed paint shall be
consumed with in specified pot life.
(f) Drying / curing requirements shall be fully satisfied.
(g) Damaged paint coating shall be properly touched up before another coating application.

28. Paint Application
Quality Inspection
1. Dry film thickness DFT.
2. Adhesion by cross cut test.
3. Gloss level.
4. Finish.
5. Shade: as per IS: 5 unless otherwise specified.
6. Coated surfaces are smooth and uniform in coverage.
7. There is no visible porosity or pot holes.
8. Unacceptable defects such as peeling, blistering cracking and damage caused by external sources
are clearly marked with a mark-free chalk and with in the specification requirements.
9. Runs and sags, dry spray and over spray are not present in excess of 5% in any given square foot
and cumulatively not in excess of 2% of any surface, unless otherwise specified
10. Drying time/curing time requirements have been satisfied.

29. Paint Failure
Skinning: Formation of a layer of skin on paint surface in the container.

30. Paint Failure
Settlement: The sedimentation of the solid constituents comprising
pigments and extenders from the binder and solvent while standing in
a container. Settlement that occurs after mixing and during application
can result in different shades and performance in different areas.

31. Paint Failure
Sagging: Sags are caused by the downward movement of a coat of paitn
that appear soon after application before setting, resulting in an uneven
area with thick lower edge. They are usually apparent on local areas of
vertical surface and in severe situation may be described as curtains.

32. Paint Failure
Adhesion Failure: Paints fails to adhere to substrate or underlying coats of
paint.

33. Paint Failure
Blistering: Dome Shaped projections or blisters in the dry paint film
through local loss of adhesion and lifting of the film form the underlying
surface. Blisters may contain liquid, vapour, gas or crystals.

34. Paint Failure
Bubbles: Bubbles within a paint film appear as small blisters. They may be
intact or broken (leaving a crater). Can be found in excessively thick paint
films, especially if spray applied and also with roller application.

35. Paint Failure
Chalking: A friable, powdery layer on the surface of a pint film. A change of
color or fading is also seen. Chalking rates vary with pigment concentration
and choice of binder. Chalking is known characteristics of certain paints ex:
epoxy paints.

36. Paint Failure
Cissing: Surface breaks in wet paint film, where the paint has receded to
expose the underlying substrate. The paint is unable to wet out the
substrate. It can be very large.

37. Paint Failure
Orange Peeling: A uniform pock marked appearance in particular of a spray
applied coating in which the surface of the paint film resembles the skin of
an orange.

38. Paint Failure
Crocodiling: Very large crazing/cracking that resembles the skin of a
crocodile. Cracks may penetrate through to the undercoat or down to the
substrate.

39. Paint Failure
Bleeding: Staining of a paint film by diffusion of a soluble colored substance
from the underlying paint to give undesirable discoloration or staining.
Often seen where bituminous or tar based products are over coated with
topcoats in which the tar or bitumen is soluble. Also occurs with emulsion
paints.

40. Paint Failure
Bloom (Blush): A hazy deposit on the surface of the paint resembling the
bloom on a grape, resulting in a loss of gloss a dulling colour.

41. Paint Failure
Bridging: The covering over of unfilled gaps such as cracks or corners with a
film of coating material. This introduces a weakness in eh paint film which
may crack or flake off.

42. Paint Failure
Cobwebbing: The production of the fine filament instead of normal
atomized particles when some solutions of high molecular weight polymer
are sprayed. Traditionally when applying chlorinated rubber coating by
conventional spray.

43. Paint Failure
Cracking: The splitting of a dry paint film through at least one coat to form
visible cracks, which may penetrate down to the substrate. Cracking comes
in several forms from minute cracking to severe cracking.

44. Paint Failure
Cratering: The formation of small bowl shaped depressions in the paint
film. Not to be confused with cissing.

45. Paint Failure
Crazing: Cracks are generally wider and penetrate deeper into the film.

46. Paint Failure
Crowsfooting: Development of small wrinkles in the paint film in a pattern
resembling a crow’s foot.

47. Paint Failure
Delamination: Loss of adhesion between coats of paint.

48. Paint Failure
Fading: Discoloration or gradual decrease in color of paint when exposed to
sunlight/weather. May be accompanied by loss of gloss. In some situations
it may resemble chalking but without the powdery surface. Fading tends to
accelerate in the presence of moisture.

49. Paint Failure
Flaking: A form of adhesion failure.

50. Paint Failure
Grinning: The underlying surface is visible through the paint film due to
inadequate hiding power of the coating material. This is sometimes called
grinning through. Often seen when dark colours are overacted with light
colours.

51. Paint Failure
Heat Damage: Discolouration, detachment and/or blistering and general
degradation of paint film.

52. Paint Failure
Impact Damage: cracks that radiate form the point of impact.

53. Paint Failure
Intercoat Contamination

54. Paint Failure
Mud Cracking: The dried paint film has appearance of a dried out mud flat.
The cracks appear as a network that can vary in size and amount.