{"id":892,"date":"2026-06-22T02:58:00","date_gmt":"2026-06-22T02:58:00","guid":{"rendered":"https:\/\/rohitbhatt.online\/ramdev\/?page_id=892"},"modified":"2026-07-10T05:42:54","modified_gmt":"2026-07-10T05:42:54","slug":"surface-preparation","status":"publish","type":"page","link":"https:\/\/rohitbhatt.online\/ramdev\/surface-preparation\/","title":{"rendered":"Surface Preparation"},"content":{"rendered":"\t\t
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SURFACE PREPARATION<\/h1>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t
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1. Importance of surface preparation<\/h2>

Surface preparation (or pretreatment) is used to define the mechanical or chemical treatment on a substrate prior to coating. Surface preparation typically provides better adhesion of paint and helps prevent the spread of corrosion thus extending its useful life. With the exception of some precious metals such as gold, silver and platinum, all metals react with water and air to form an oxide layer on their surface, called rust. Application of paint over rusted metal prevents it from forming a tight bond to the substrate and if the contaminant lifts off, so will the coating. Hence, surface preparation is one of the most important steps in ensuring that the paint will perform as intended. The performance of paint is directly related to the condition of the surface that it is applied to.<\/p>

2. Methods of surface preparation<\/h2>

Different substrates demand specific surface treatment. It has been done by considering the length of service required and the nature of environmental exposure. When considering the length of service, one should determine whether the environment is rural, coastal or industrial and also the nature of chemical contaminants present.<\/p>

2.1 Mild steel<\/h3>

Mild steel is one of the most widely used construction materials. The rate of corrosion of mild steel is very high. It forms various oxides of iron within few hours of sand blasting. Hence, it has to be protected immediately after adequate surface preparation. There are various methods for this, which are as follows:<\/p>

A.\u00a0 Blast cleaning<\/h4>

Blast cleaning is the most effective technique which involves blasting of abrasive with high kinetic energy on metal surface. It can be with a hand operated jet or automatic impeller. It is very effective for removal of mill scale, rust and old coatings. However, lubricants (like oil and grease) cannot be removed with this technique. Most common grades of blast cleaning are mentioned below.<\/p>

a.\u00a0 Dry blast cleaning<\/h5>
  • White metal blast cleaning (Swedish Standard – Sa 3)<\/li><\/ul>

    A white metal blast cleaned surface when viewed without magnification, shall be free from all visible rust, mill scale, paint and foreign matter. It is used for conditions where corrosion resistance is very important and the environment is highly corrosive.<\/p>

    • Near white metal blast cleaning (Swedish Standard – Sa 2\u00bd )<\/li><\/ul>

      A near white metal blast cleaned surface when viewed without magnification, shall be free from at least 95% of visible rust, mill scale, paint and foreign matter. Hence, 5% of the cleaned surface may have visible residues. It is used for harsh environment where the product is exposed to heavy usage.<\/p>

      • Commercial blast cleaning (Swedish Standard – Sa 2)<\/li><\/ul>

        A commercial blast cleaned surface when viewed without magnification, shall be free from at least 67% of visible rust, mill scale, paint and foreign matter. Hence, 33% of the cleaned surface may have visible residues. It is used where comparatively less corrosive environment is present.<\/p>

        • Brush-off blast cleaning (Swedish Standard – Sa 1)<\/li><\/ul>

          Blast cleaning of all except tightly adhering residues of mill scale, rust and old coatings, exposing numerous evenly distributed flecks of underlying metal. It is acceptable in non-corrosive environment where long-term coating life is not expected.<\/p>

          Blast cleaning – surface preparation standard according to ISO 8501-1<\/h4>
          Grade<\/td>Description<\/td><\/tr>
          Sa 3<\/td>

          Blast cleaning to visually clean steel<\/p>

          When viewed without magnification, the surface shall be free from visible oil, grease, dirt and shall be free from mill scale, rust, paint coatings and other foreign matter*. It shall have a uniform metallic colour.<\/p><\/td><\/tr>

          Sa 2 \u00bd<\/td>

          Very thorough blast cleaning<\/p>

          When viewed without magnification, the surface shall be free from visible oil, grease, dirt and shall be free from mill scale, rust, paint coatings and other foreign matter*. Any remaining traces of contamination shall show only as slight stains in the form of spots or stripes.<\/p><\/td><\/tr>

          Sa 2<\/td>

          Thorough blast cleaning<\/p>

          When viewed without magnification, the surface shall be free from visible oil, grease, dirt and shall be free from mill scale, rust, paint coatings and other foreign matter*. Any residual contamination shall be firmly adhering.<\/p><\/td><\/tr>

          Sa 1<\/td>

          Light blast cleaning<\/p>

          When viewed without magnification, the surface shall be free from visible oil, grease, dirt, poorly adhering mill scale, rust, paint coating and foreign matter*.<\/p><\/td><\/tr><\/tbody><\/table>

          *Foreign matter includes water soluble salts and welding residues. These contaminants cannot be completely removed from the surface by dry blast cleaning. For this, hand and power tools, flame cleaning or wet blasting may be necessary.<\/p>

          b. Wet abrasive blast cleaning<\/h5>

          Wet abrasive blast cleaning is performed with low or high pressure fresh water to which a relatively small amount of abrasive is introduced. The most obvious advantage is dust control. Water can be used to trap the dust created during the blasting process giving environmental benefits as well as ensuring personnel and equipment safety. Another advantage of introducing water is to provide an additional cleaning agent which can reduce the presence of chlorides and salts on the blasted surface. However, as of 2013, the Wet Abrasive Blast Cleaning Standards have not been published by SSPC or National Association of Corrosion Engineers Institute (NACE).<\/p>

          B. Mechanical cleaning (Power tool and hand tool)<\/h5>

          Mechanical cleaning is mostly adopted when blast cleaning is not possible due to location. It does not result in the complete removal of mill scale, rust, paint and foreign matter particularly at corners, angles and pits. Hence, mechanical cleaning is considered to be a less effective method of surface preparation. There are many mechanical and power tools available like needle guns, chipping hammer, grinders, wire brushes, sanders, scrapers, knives, emery papers, etc.<\/p>

          Power and hand tool cleaning – surface preparation standard according to ISO 8501-1<\/h5>
          Grade<\/td>Description<\/td><\/tr>
          St 3<\/td>

          Very thorough hand and power tool cleaning<\/p>

          As for St 3, the surface shall be treated much more thoroughly to give a metallic sheen arising from the metallic substrate.<\/p><\/td><\/tr>

          St 2<\/td>

          Thorough hand and power tool cleaning<\/p>

          When viewed without magnification, the surface shall be free of visible oil, grease and dirt, poorly adhering mill scale, rust, paint coatings and foreign matter.<\/p><\/td><\/tr><\/tbody><\/table>

          Note: St 3 is usually only achieved by mechanical wire brushing and St 2 is usually achieved by hand wire brushing. Care must be taken to avoid over brushing a particular area causing burnishing, a condition with a highly polished surface which has an adverse effect on adhesion.<\/p>

          C. Acid pickling<\/h5>

          Acid pickling involves the use of acid for removal of rust and mill scale by spraying or dipping in acid solution. This method is good for surface cleaning however, the surface profile of the metal cannot be made rough and desired surface profile is less than blast cleaning. There are certain disadvantages of this method such as careful selection of acid solutions and potential health and safety risks due to acid fumes, leakage and spillage. Generally, Hydrochloric acid, Nitric acid and Hydrofluoric acid along with certain inhibitors are commonly used.<\/p>

          D.\u00a0 High pressure water jetting<\/h5>

          High pressure water jetting involves high pressure water (1,000 \u2013 10,000 psi) and ultra high pressure water (25,000 \u2013 35,000 psi) for cleaning most surface contaminants, particularly soluble salts, rust, dirt, grease, oil and mill scale. Unlike blast and power tool cleaning, this method does not produce sparks and dust. Hence, it is used commonly in petroleum refineries, oil and gas industries. This method is relatively economical. Water jetting provides the highest degree of cleanliness but does not produce the desired surface profile on the metal.<\/p>

          High pressure water cleaning – surface preparation standard according to ISO 8501-4<\/span><\/p>
          Grade<\/td>Description<\/td><\/tr>
          Wa 1<\/td>

          Light high-pressure water jetting<\/p>

          When viewed without magnification, the surface shall be free of visible oil and grease, loose or defective paint, loose rust and other foreign matter. Any residual contamination shall be randomly dispersed and firmly adherent.<\/p><\/td><\/tr>

          Wa 2<\/td>

          Thorough high-pressure water jetting<\/p>

          When viewed without magnification, the surface shall be free of visible oil, grease and dirt and most of the rust, previous paint coatings and other foreign matter. Any residual contamination shall be randomly dispersed and can consist of firmly adherent coatings, firmly adherent foreign matter and stains of previously existent rust.<\/p><\/td><\/tr>

          Wa 2 \u00bd<\/td>

          Very thorough high-pressure water jetting<\/p>

          When viewed without magnification, the surface shall be free of visible oil, rust, grease, dirt, previous paint coatings and all other foreign matter, except for slight traces. Discolouration of the surface can be present where the original coating was not intact. The grey or brown | black discolouration observed on pitted and corroded steel cannot be removed by further water jetting.<\/p><\/td><\/tr><\/tbody><\/table>

          E. Flame cleaning<\/h5>

          This method of flame cleaning (Oxyacetylene) is utilised to expand rust and mill scale and to delaminate it from the metal surface. It also removes dirt, oil, grease, old paint and water from the surface. However, tightly adherent mill scale cannot be removed with flame cleaning. Hence a power tool is often required after flame treatment.<\/p>

          F. Solvent cleaning<\/h5>

          This method of surface cleaning is normally done prior to other types of surface cleaning and it does not remove rust or mill scale. It is performed by wiping or washing a surface with solvents. The primary objective of solvent cleaning is removal of old paint, oil and grease. Many solvent based formulations are available. The solvent cleaning must be done with skilled manpower since there is a risk of fire hazard associated with it.<\/p>

          3. Stainless steel<\/h3>

          Since the rate of corrosion of stainless steel is very slow, it will not normally be coated with paints. However, in certain instances when pipeline identification is required, it is coated with paints. Stainless steel is a very hard and inert surface for which careful surface preparation is required. To ensure good adhesion of paints, blast cleaning is the most effective surface preparation. Aluminum oxide is the most preferred abrasive for blast cleaning. Though it is expensive, it can be recycled. It creates a surface profile essential for paint systems.<\/p>

          4. Non-ferrous metals<\/h3>

          Apart from steel there are many non-ferrous metals which are used in construction like copper, zinc, aluminum, galvanised steel and bronze. These metals are painted for decorative and corrosion protection purposes.<\/p>

          A.\u00a0 Aluminium, copper, brass and bronze<\/h5>

          Aluminium is the most common metal used in construction, aviation and shipping industries. The surface should be degreased and lightly abraded using power tools or sweep blasting at reduced pressure, prior to the application of coatings. An etch primer will be suitable.<\/p>

          B. Galvanised metals<\/h5>

          Most paint systems fail when applied to galvanised steel, usually because of the absence of a correct primer or insufficient surface preparation. All galvanised steel should firstly be degreased. The acidic copper solution reacts with galvanised steel and turns it black, where oil | grease is still present on the surface. New galvanised steel should be treated with mordant (T-wash) solution. Where oil and grease is still present on the surface, the mordant solution will not be effective and hence it is required to thoroughly degrease with a wash primer.<\/p>

          5. Surface preparation standards<\/span><\/h3>

          Surface preparation must be in accordance with available standards. There are many standards available, however there is no single universally accepted standard. Generally, United States refers to SSPC or NACE standard while Europe and Asia refer to Swedish or British standards.<\/p>

          The new international standard ISO 8501-1:2007 \u2018Rust grades and preparation grades of uncoated steel substrates and steel substrates after overall removal of previous coatings\u2019 defines photographic guidelines for identification of rust grades and removal of previous coatings. A general description of rust grades is given below.<\/p>
          Rust grade<\/td>Description<\/td>Type of occurence<\/td><\/tr>
          A<\/td>Steel surface largely covered with adhering mill scale but little, if any, rust<\/td>Freshly produced steel after rolling<\/td><\/tr>
          B<\/td>Steel surface which has begun to rust and from which the mill scale has begun to flake<\/td>Steel left outside in a fairly corrosive environment for less than 9 months<\/td><\/tr>
          C<\/td>Steel surface on which the mill scale has rusted away or from which it can be scraped, but with slight pitting visible under normal vision<\/td>Unprotected steel stored outside in a fairly corrosive environment for about 9-12 months<\/td><\/tr>
          D<\/td>Steel surface on which the mill scale has rusted away and on which general pitting is visible under normal vision<\/td>Unprotected steel stored outside in a corrosive environment for 18 months to 2 years<\/td><\/tr><\/tbody><\/table>

          Classification of flash rust<\/strong><\/p>
          Rust grade<\/td>Description<\/td><\/tr>
          L<\/td>

          Light flash rust<\/p>

          A surface when viewed without magnification, exhibits small quantities of yellow | brown rust layer through which the steel substrates can be seen. The rust (seen as a discolouration) may be evenly distributed or is present in patches, but will be tightly adherent and is not easily removable on gentle wiping with a cloth.<\/p><\/td><\/tr>

          M<\/td>

          Medium flash rust<\/p>

          A surface when viewed without magnification, exhibits a layer of yellow | brown rust that obscures the original steel surface. The rust may be evenly distributed or present in patches, but it will be reasonably well adherent and will lightly mark a cloth that is gently wiped over the surface.<\/p><\/td><\/tr>

          H<\/td>

          Heavy flash rust<\/p>

          A surface when viewed without magnification, exhibits a layer of red-yellow | brown rust that obscures the original steel surface and is loosely adherent. The rust layer may be evenly distributed or is present in patches and will readily mark<\/p>

          a cloth that is gently wiped over the surface.<\/p><\/td><\/tr><\/tbody><\/table>

          Description of surface preparation<\/strong><\/td>Nearest equivalent standard<\/strong><\/td><\/tr>
          Swedish Standard SIS 05 59 00 1967<\/strong><\/td>ISO 8501-1:1998<\/strong><\/td>British Standard BS-4232<\/strong><\/td>SSPC*<\/strong><\/td>NACE*<\/strong><\/td><\/tr>
          Blast clean for complete removal of all visible paint, rust, mill scale and other surface contaminants. The surface should have a uniform metallic colour.<\/td>Sa 3<\/td>Sa 3<\/td>First quality<\/td>SSPC SP-5
          White metal<\/td>          		NACE #1<\/td><\/tr>
          Blast clean for complete removal of all visible paint, rust, mill scale and other surface contaminants from 95% of surface area.<\/td>Sa 2 \u00bd<\/td>Sa 2 \u00bd<\/td>Second quality<\/td>SSPC SP-10
          Near white metal<\/td>          		NACE #2<\/td><\/tr>
          Blast clean for removal of almost all rust, mill scale and foreign matter. The remaining surface should have a greyish colour.<\/td>Sa 2<\/td>Sa 2<\/td>Third quality<\/td>SSPC SP-6
          Commercial blast<\/td>          		NACE #3<\/td><\/tr>
          Blast clean for removal of loose rust, mill scale and foreign matter.<\/td>Sa 1<\/td>Sa 1<\/td>No equivalent<\/td>SSPC SP-7
          Brush off blast<\/td>          		NACE #4<\/td><\/tr>
          Wire brushing and scraping \/ grinding to remove all loose mill scale, rust and foreign matter, leaving the surface with an obvious metallic sheen.<\/td>St 3<\/td>St 3<\/td>No equivalent<\/td>SSPC SP-3
          Power tool clean<\/td>          		No equivalent<\/td><\/tr>
          Good wire brushing, scraping and grinding to remove all loose rust, mill scale and foreign matter, leaving the surface with a faint metallic sheen.<\/td>St 2<\/td>St 2<\/td>No equivalent<\/td>SSPC SP-2
          Hand tool clean<\/td>          		No equivalent<\/td><\/tr>
          Acid pickling<\/td>No equivalent<\/td>No equivalent<\/td>No equivalent<\/td>SSPC SP-8<\/td>No equivalent<\/td><\/tr>
          Solvent cleaning \/ washing<\/td>No equivalent<\/td>No equivalent<\/td>No equivalent<\/td>SSPC SP-1<\/td>No equivalent<\/td><\/tr><\/tbody><\/table><\/div>

          SSPC: Steel Structure Paint Council, NACE: National Association of Corrosion Engineers<\/p>

          The method of application and the conditions under which paints are applied have a significant effect on the quality and durability of the coating. Standard methods used to apply paints to structural steelwork include application by brush, roller, conventional air spray and airless spray. Other methods such as dip application can also be used, where applicable.<\/span><\/p>

          A.\u00a0\u00a0\u00a0\u00a0 Brush application<\/h3>

          Brush application is the most basic application by which most decorative and industrial paints have been applied. This is the simplest method but also the slowest and, therefore, most expensive. Nevertheless, it has certain advantages over other methods, for example, better wetting of the surface, and can reach complex areas with low wastage and less contamination of surroundings. The traditional method of brush application provides very high shearing forces between the liquid paint and the substrate. This greatly assists the intimate wetting of the substrate and results in better adhesion. It is labour intensive (that is costly) and may be considered too slow when very large areas are being coated. Despite this, where the highest standard of surface cleaning has not been specified, brush application is preferred.<\/p>

          B.\u00a0\u00a0\u00a0\u00a0 Roller application<\/h3>

          Roller application process is much quicker than brushing and is used for large flat areas, but demands suitable rheological properties of paint. Generally, it is most common for household coating of water based acrylic paints. The surface finish is better than brush coating. Roller coating does not thoroughly wet the surface and also does not often achieve the desired film thickness. However, structural steel surfaces are never ideally flat and roller application will ride over high spots and miss edges. It is not suitable for coating awkward corners and bolt heads, and is therefore a less preferred method for industrial coatings.<\/p>

          C. Conventional spray<\/h3>

          In conventional spray application, the paint is atomised into fine droplets and then projected onto the surface to be protected where the droplets join together to form a continuous film. The atomisation can be accomplished in a number of ways. In conventional air spraying, the paint is atomised by mixing it with a stream of compressed air in a conventional spray gun. Typically, the air pressure will be 40 – 100 psi. There are two methods by which paint can be sprayed – pressure feed and suction cup.<\/p>

          A. Pressure feed method<\/h3>

          The paint is stored inside a pressure pot. The pot is connected to the gun by a fluid hose and air hose. Generally, the air hose has large diameter (3 – 4 inch). The paint is forced through the fluid hose to the gun. The air hose is directly attached to the gun. When the paint reaches to the gun tip, the air pressure atomises the paint and sprays it on the surface. This method is suitable for high solid paint (high viscosity) and is faster than the suction cup method.<\/p>

          B. Suction cup method<\/h3>

          A suction feed gun is fitted with a cup (or container) which contains paint. When the trigger of the gun is pulled, suction gets developed which allows entry of paint into the airway. Thus, paint is atomised and sprayed. It is suitable for low viscosity (low solid) paints. This technique is relatively slow in comparison to pressure feed gun.<\/p>

          D. Airless spray<\/h3>

          For airless spraying, the paint is hydraulically compressed and released through a small orifice of an airless spray gun. By using this method, the paint gets atomised and projected onto the surface. By changing the orifice size and shape and by varying the hydraulic pressure, atomisation can be accomplished for a wide range of paint consistencies from thin to thick, to give a wide range of rates of deposition. The equipment required is much more expensive than for air-assisted spraying, because it must withstand the much higher pressures involved. For air-assisted spraying, the maximum air pressure will normally not exceed 690 kPa (100 psi); for airless spraying, hydraulic pressures of up to 27,500 kPa (4,000 psi) may be required. A variant of the above involves heating to reduce the consistency of the paint rather than adding diluents. In this way, greater film thickness per application is achieved. This method can be used for the application of solvent-free materials such as two-pack products which can be mixed at the spray gun nozzle at the moment of application. The use of expensive equipment and highly skilled labour is necessary for achievement of optimum result<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\n<\/div>\n\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"

          SURFACE PREPARATION 1. Importance of surface preparation Surface preparation (or pretreatment) is used to define the mechanical or chemical treatment on a substrate prior to coating. Surface preparation typically provides better adhesion of paint and helps prevent the spread of corrosion thus extending its useful life. With the exception of some precious metals such as […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"elementor_header_footer","meta":{"footnotes":""},"class_list":["post-892","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/pages\/892","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/comments?post=892"}],"version-history":[{"count":25,"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/pages\/892\/revisions"}],"predecessor-version":[{"id":1293,"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/pages\/892\/revisions\/1293"}],"wp:attachment":[{"href":"https:\/\/rohitbhatt.online\/ramdev\/wp-json\/wp\/v2\/media?parent=892"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}