Surface preparation is critical for coating performance and longevity. It involves cleaning the surface of contaminants like mill scale, rust, grease and dirt. The level of cleaning depends on factors like the substrate material and coating system. Common preparation methods include solvent cleaning, abrasive blasting and chemical treatments. Proper surface preparation can increase coating adhesion and the protective life of a paint system by over 80%.

2. INTRODUCTION :
To obtain the best results from a paint system the best possible surface
preparation consistent with the degree of sophistication of the system is required.
The quality of the paint and surface preparation (i.e. the removal of rust, scale,
salt, grease, dirt and loose paint) are the most important factors in determining
the lifetime of the paintwork, and therefore the length of time the surface will be
protected. First class preparation has the potential to extend the protective life of
any paint system.

3. What is surface preparation?
 Coating performance is directly affected by surface preparation.
 Coating integrity and service life will be reduced because of
improperly prepared surfaces.
 As high as 80% of all coating failures can be directly attributed to
inadequate surface preparation that affects coating adhesion.
 The majority of paintable surfaces are concrete, ferrous metal,
galvanizing and aluminum.
 They all require protection to keep them from corroding in
aggressive environments.
 Selection of the proper method for surface preparation depends
on the substrate, the environment, the coating selected and the
expected service life of the coating system.

4. The greater the
DFT the greater
the Surface
Profile

5. SURFACE CONTAMINANTS
Mill Scale :The complete removal of mill scale and rust is critical in order to limit its corrosive
properties. Mill scale is generally found on new steel as a hard brittle coating – it consists of
distinct layers of various iron oxides and is formed during the hot rolling process in the
manufacture of steel. Painting over mill scale is not satisfactory, as mill scale is not firmly or
permanently bonded to the steel. Eventually the scale will lift off, causing paint coatings to
flake and corrosion to occur.
Rust: Rust is a form of hydrated ferric oxide formed by the action of water and oxygen on
iron and steel surfaces and occupies a much greater volume than the original steel. It is for
this reason that rust forming beneath a paint layer is able to rupture a coating. All areas of
rust should be completely removed – any rust remaining will act as a nucleus for further
rusting.
Oil, Grease Fat and Perspiration : Oil, grease, fat and perspiration deposits cannot be
removed by mechanical methods of cleaning. The simplest method of removal is to use a
solvent emulsifiable degreaser or biodegradable detergent. Apply the degreaser liberally
to the contaminated surface, allow to stand for a short time, then hose off with fresh
water.

6.  Prepare surface for subsequent processing, such as a coating application or adhesive
bonding
 Improve hygiene conditions for workers and customers
 Remove contaminants that might chemically react with the surface
 Enhance appearance and performance of the product

7. Factors in Selecting a Cleaning
Method
 Contaminant to be removed
 Degree of cleanliness required
 Substrate material to be cleaned
 Purpose of cleaning
 Environmental and safety factors
 Size and geometry of the part
 Production and cost requirements

8.  Various contaminants build up on part surfaces, either due
to previous processing or factory environment
 Principal surface contaminants found in factory
Oil and grease, e.g., lubricants in metalworking
Solid particles such as metal chips, abrasive grits, shop dirt,
dust, etc.
Buffing and polishing compounds
Oxide films, rust, and scale
Contaminant to be Removed

9. What are Non-Ferrous Metals?
Non-ferrous metals refer to metals that are not derived from iron ore, such as
aluminium and its alloys, copper, brass and bronze. Whilst iron (mild steel) will readily
oxidize to red rust (iron oxide), non-ferrous metals usually exhibit only tarnishing
(surface corrosion). Aluminum finds ready use in window- and door-frames, handrails,
balustrades and architectural work generally. Copper is used in water pipes and
guttering.

10. .
Primary Substrates
• Steel
– Carbon Steel – Easily attacked by the
environment in which it is placed and will
begin to revert back to iron ore.
– Stainless Steel - Stainless steel does not stain,
corrode, or rust as easily as ordinary steel.

11. Non-Ferrous Metal Surfaces
Aluminum
Remove all oil, grease, dirt, oxide and other foreign material
by cleaning per SSPC-SP1, Solvent Cleaning.
Galvanized Metal
Allow to weather a minimum of six months prior to coating.
Clean per SSPC-SP1 using detergent and water or a
degreasing cleaner, then prime as required. When weathering
is not possible or the surface has been treated with chromates
or silicates, first Solvent Clean per SSPC-SP1 and apply a test
area, priming as required. Allow the coating to cure at least
one week before testing per ASTM D3359. If adhesion is poor,
Brush Blast per SSPC-SP7/NACE 4 is necessary to remove these
treatments.

12. Ductile Iron
National Association of Pipe Fabricators, Inc. www.napf.com NAPF 500-03 Surface
Preparation Standard for Ductile Iron Pipe and Fittings in Exposed Locations Receiving
Special External Coatings and/or Special Internal Linings This standard summarizes the
surface preparation requirements for ductile iron. Included within this standard are the
following:
NAPF 500-03-01 Solvent Cleaning
NAPF 500-03-02 Hand Tool Cleaning
NAPF 500-03-03 Power Tool Cleaning NAPF 500-03-04
Abrasive Blast Cleaning for Ductile Iron Pipe
NAPF 500-03-05 Abrasive Blast Cleaning for Cast Ductile Iron
NOTE:
Recommended Coating Systems for Non-Ferrous Metals :
A surface tolerant epoxy primer is the preferred primer for most non-ferrous
metals.

13. Concrete
Concrete - used more than any other man-made material in the
world and is easily attacked when placed in chemical
environments.
PROPER SURFACE PREPARATION
Proper surface preparation includes the following:
1. Inspection of the concrete substrate
2. Removal and replacement of non-durable concrete
3. Decontamination of the concrete surface
4. Creation of surface profile 5. Repair of surface irregularities
.

14. METHODS OF SURFACE PREPARATION
Depending upon conditions of the concrete one or more methods of surface
preparation may be required. It is common for decontamination to precede
mechanical preparation, and if necessary a second decontamination to follow

15. Protection Mechanisms
• Barrier Protection
– The coating/lining isolates the electrolyte from
the anode, cathode, and metallic pathway.
• Rust Inhibitive
– The slightly water-soluble pigments permeate
to steel/coating interface and passivate the
substrate.
• Sacrificial
– The coating/lining contains pigments that are
more active than the metal and sacrifice
themselves to protect the substrate.

16. Chemical Cleaning Processes
 Alkaline cleaning
 Emulsion cleaning
 Solvent cleaning
 Acid cleaning
 Ultrasonic cleaning

17. Alkaline Cleaning
Uses an alkali to remove oils, grease, wax, and
various types of particles (metal chips, silica,
light scale) from a metallic surface
 Most widely used industrial cleaning method
 Alkaline solutions include sodium and
potassium hydroxide (NaOH, KOH), sodium
carbonate (Na2CO3), borax (Na2B4O7)
 Cleaning methods: immersion or spraying
followed by water rinse to remove residue

18. Emulsion Cleaning
Uses organic solvents (oils) dispersed in an aqueous
solution
 Suitable emulsifiers (soaps) results in a two-phase
cleaning fluid (oil-in-water), which functions by
dissolving or emulsifying the soils on the part
surface
 Used on either metal or nonmetallic parts
 Must be followed by alkaline cleaning to
eliminate all residues of the organic solvent prior
to plating

19. Solvent Cleaning
Organic soils such as oil and grease are removed
from a metallic surface by chemicals that
dissolve the soils
 Common application techniques: hand-wiping,
immersion, spraying, and vapor degreasing
 Vapor degreasing (a solvent cleaning
method) uses hot vapors of chlorinated or
fluorinated solvents

20. Acid Cleaning
Removes oils and light oxides from metal surfaces
using acid solutions combined with
water-miscible solvents, wetting and emulsifying
agents
 Common application techniques: soaking,
spraying, or manual brushing or wiping carried
out at ambient or elevated temperatures
 Cleaning acids include hydrochloric (HCl), nitric
(HNO3), phosphoric (H3PO4), and sulfuric (H2SO4)

21. Acid Pickling
More severe acid treatment to remove thicker
oxides, rusts, and scales
 Distinction between acid cleaning and acid
pickling is a matter of degree
 Generally results in some etching of the metallic
surface which serves to improve organic paint
adhesion

22. ©2010 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 4/e
Ultrasonic Cleaning
Mechanical agitation of cleaning fluid by
high-frequency vibrations (between 20 and 45 kHz) to
cause cavitation (formation of low pressure vapor
bubbles that scrub the surface)
 Combines chemical cleaning and mechanical
agitation of the cleaning fluid
 Cleaning fluid is generally an aqueous solution
containing alkaline detergents
 Highly effective for removing surface contaminants

23. Phosphating:
Phosphating improves the adhesion of a the coating to
the metal surface and can also improve the corrosion
resistance of the painted surface. Iron, steel, zinc and
hot galvanized surfaces are suitable for phosphating,
and in some cases, Aluminium surfaces.
During phosphating a thin, crystalline phosphate
layer forms on the metal surface, which improves the
adhesion. The most usual phosphating methods are
iron and zinc phosphating.

24. Chromating
Chromating is used as a pretreatment method for light
alloys and galvanized surfaces. The treatment causes
a thin colorless or yellowish coat. There are also
chromating methods which form a substrate which is not suitable for painting.
Chemistry:-
Chromate coating on aluminium may contain the compound
AL2O3.Cr(OH)3.CrOH.CrO4.
On zinc as basis metal, ZnCrO4 has been claimed to appear

25. Mechanical Cleaning
Physical removal of soils, scales, or films from the
work surface by abrasives or similar mechanical
action
 Often serves other functions also, such as
deburring, improving surface finish, and surface
hardening
 Processes:
 Blast finishing
 Shot peening
 Mass finishing processes

26. Blast Finishing
High velocity impact of particulate media to clean
and finish a surface
 Media is propelled at the target surface by
pressurized air or centrifugal force
 Most well-known method is sand blasting, which
uses grits of sand as blasting media
 Other blasting media:
 Hard abrasives such as Al2O3 and SiC
 Soft media such as nylon beads

27. Shot Peening
High velocity stream of small cast steel pellets
(called shot) is directed at a metallic surface to
cold work and induce compressive stresses into
surface layers
 Used primarily to improve fatigue strength of
metal parts
 Purpose is therefore different from blast
finishing, although surface cleaning is
accomplished as a byproduct of the
operation

29. Surface Preparation
Affects on System Selection
• SSPC-SP 1 “Solvent Cleaning”
• SSPC-SP 2 “Hand Tool Cleaning”
• SSPC-SP 3 “Power Tool Cleaning”
• SSPC-SP 11 “ Power Tool Cleaning to Bare
Metal”
• SSPC-SP 7/NACE No. 4 “Brush-Off Blast
Cleaning”
• SSPC-SP 6/NACE No. 3 “Commercial Blast
Cleaning”

31. Uses of pretreatment:-
 To increase the long-life of a substrate.
 To increase the coating performance.
 To increase the surface area for good adhesion
 To remove all contamination from the metal surface
and prevent their re-deposition.

32. Conclusion:
Pretreatment is a part of surface coating technology therefore before
application of protective coating pretreatment is must in order to
have improved properties of the coating and the substrate. It is
expected that technocrats in the finishing industry try to make use of
it and upgrade it as per the requirement.