When preparing painting surfaces, touch all the bases

What makes a good paint job? Certainly, a well-specified coating system is one part of the equation. Another part is proper application of the coating. But don't forget what's underneath it all. It is estimated that up to 80% of all coatings failures can be attributed to inadequate surface preparation.

01/01/2006


What makes a good paint job? Certainly, a well-specified coating system is one part of the equation. Another part is proper application of the coating. But don't forget what's underneath it all. It is estimated that up to 80% of all coatings failures can be attributed to inadequate surface preparation. Like a strong foundation, proper surface preparation lays the groundwork for coating performance.

The best results from any coating system are achieved when the substrate is properly prepared. Mildew, oil, grease, dust, dirt, loose rust, peeling paint or other contamination must be removed before painting to ensure proper adhesion. Premature paint failures such as delamination and blistering can result from improper surface preparation.

Methods of surface preparation include solvent or detergent cleaning, detergent washing, high-pressure water blasting, power-tool cleaning, hand-tool cleaning, acid etching, wet abrasive blasting, and dry abrasive blasting. Preparing plant surfaces for painting requires knowledge of these methods, as well as knowledge of the substrate and the environment in which the coating system must perform, so the best method can be chosen for the circumstances.

Getting to the bottom

"When it comes to surface preparation, getting to the bottom of it all — including the bottom line — means asking the right questions. These include:

  • What is the substrate?

  • Is the substrate new?

  • Is it previously coated or uncoated?

  • Is it rusted or deteriorated?

  • Are there harsh chemicals or corrosive agents present in the environment?

  • Can desired surface preparation equipment be used given the machinery present in the environment?

    • Using abrasive blasting methods around mechanized conveyors and computerized tracking systems, for example, can damage moving parts and bearing mechanisms, so other surface preparation methods should be considered.

      Economics is another factor that affects surface preparation choices. Cost per square foot for surface preparation can range from approximately 45

      Making the grade

      The majority of metal surfaces in industrial plants are aluminum, galvanizing and ferrous metal. They all require protection to keep them from corroding in aggressive environments. Standards for surface preparation for various substrates are available in the form of joint standards issued and approved by NACE International (formerly National Association of Corrosion Engineers) and SSPC (The Society for Protective Coatings).

      Aluminum, for example, is often used for railings, equipment supports, structural steel for roofs and ceilings, and elevated walkways in plants. Before painting aluminum, all oil, grease, dirt, oxides and other foreign contaminants should be removed per SSPC SP-1 Solvent Cleaning. This standard specifies the use of water, solvents or alkaline cleaners to remove foreign matter from the surface of the substrate. Rags and the cleaning solution should be changed frequently so that deposits of oil and grease are not spread over additional areas during the cleaning process.

      Galvanized metal typically used for guardrails, handrails, catwalks, platforms and other plant surfaces should be allowed to weather a minimum of six months and prepared per SSPC-SP1 Solvent Cleaning. 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. Allow the coating to dry at least one week before checking adhesion. If adhesion is poor, brush blasting per SSPC-SP-7/NACE No. 4 is required.

      When blasting is the required surface preparation for steel, abrasive size, air pressure and distance from the surface determine the depth of profile and cleaning rate. BlastingSurface profile, it increases the surface area of the substrate and provides an irregular surface, both of which promote adhesion by mechanical bond. A surface profile that is too deep may leave exposed steel at the peaks, resulting in pinpoint-rusting above the coating.

      Two types of abrasive are available. Steel shot is round and provides a peened profile. Grit is irregular in shape with jagged edges. It provides better cutting action than shot and imparts an angular profile. In many cases steel grit and shot are mixed together to achieve a surface profile acceptable for coating.

      Previously painted surfaces should be evaluated before coating using ASTM-D3359 Method A X-Cut Tape Test to ensure the existing coating is acceptable for overcoating.

      Preparing concrete surfaces

      Properly prepared concrete surfaces should have the texture of medium-grit sandpaper and should be tightly adherent, not powdery. Surface preparation of concrete is addressed in International Concrete and Repair Institute (ICRI) Technical Guideline No. 03732 Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, Polymer Overlays. This guideline outlines the proper procedure for surface preparation using various methods, and provides visual standards to determine if the preparation standards are achieved. The preferred method of concrete surface preparation, particularly for concrete floors, is shot blasting with vacuum equipment that recycles the spent shot.

      New concrete should be cured for a minimum of 28 days at temperatures of above 70°F. Concrete must be as free of excessive moisture as possible, keeping in mind that the moisture content of concrete seldom falls below 15%. All grease, dirt, paint, oil, tar, glaze, laitance, efflorescence, loose mortar and cement should be removed prior to coating. Hollow areas, bug holes, honeycombs and voids should be opened and filled. Fins, form marks, protrusions and rough edges should be ground.

      Surface preparation for concrete includes dry abrasive blasting, shot blasting, mechanical scarification, or suitable chemical cleaning. Detailed descriptions of the above preparation methods are described in ICRI Technical Guideline No. 03732. Remember that different methods of preparation impart different depths of surface profile, so it is important to select the method of surface preparation that matches the thickness of the coating system that will be applied.

      Conclusion

      Surface preparation methods, environmental conditions, and supporting documentation (surface profile readings, replica tape, visual documentation, etc.) should be recorded through inspection reports. Documentation of these results should be retained for future reference. Taking the time to properly prepare surfaces for painting is always a good call.

      The Bottom Line...

      • Proper surface preparation can extend the life of an industrial paint job; improper preparation can shorten that life.

      • Asking the right questions about the condition of the surface will help match the right paint to the job.

      • There are different techniques for surface preparation, and different materials must be used depending on whether the surface is metal or concrete.


        • <table ID = 'id3001716-0-table' CELLSPACING = '0' CELLPADDING = '2' WIDTH = '100%' BORDER = '0'><tbody ID = 'id3001870-0-tbody'><tr ID = 'id3001707-0-tr'><td ID = 'id3003024-0-td' CLASS = 'table' STYLE = 'background-color: #EEEEEE'> Author Information </td></tr><tr ID = 'id3003033-3-tr'><td ID = 'id3003035-3-td' CLASS = 'table'> Doni Riddle is vice president, industrial and marine marketing for The Sherwin-Williams Co. </td></tr></tbody></table>

          What caused this paint failure?

          Problem: Blistering

          Characteristics: Round projections, either small or large, like pimples appear on the coated surface.

          Causes: May range from exposure of the coating system to high humidity or water immersion, entrapped solvents, poor adhesion, or direct or stray cathodic protection currents.

          Reasons: Many, ranging from improper surface preparation to application during poor weather conditions.

          Problem: Chalking

          Characteristics: A powdery layer appears on the coated surface.

          Cause: Chalking occurs as the coating degrades. It results from the coating formulation and is not a negative event for epoxies, which are designed to provide chemical and solvent resistance but not necessarily maximum resistance against weathering.

          Reason: Improper coating selection for environmental conditions. (Except for epoxies.)

          Problem: Cracking, checking, alligatoring

          Characteristics: Cracking is paint film rupture in long lines. Checking is when film rupture occurs generally over the coating and in a kind of checkerboard pattern. Alligatoring is brittle film separation in a pattern resembling that of an alligator hide.

          Causes: For cracking and checking, the cause is shrinkage within the film during aging. For alligatoring, the cause is different expansion rates when a hard film is applied over a more flexible film

          Reason: Improper coating system selection.

          Problem: Flaking, peeling and delamination.

          Characteristics: Flaking occurs when a coating comes off in small flakes. Peeling is when a coating comes off in larger sections or sheets. Delamination results when flaking or peeling occurs between coats.

          Cause: Poor adhesion

          Reason: Improper surface preparation; poor choice of primer; or improper application, for example, improper weather conditions or film thickness.

          Problem: Lifting and Wrinkling

          Characteristics: The coated surface is rough and ridged.

          Cause: Different (not smooth, uniform) rates of drying of the coating.

          Reason: Wrinkling results from rapid surface drying of the coating. Lifting occurs when solvents in a coating soften the previous coat, resulting in wrinkling and also in loss of adhesion to the substrate beneath.

          Bush names Crown chairman Dicke to Export Council

          President Bush has named James F. Dicke II, chairman and CEO of Crown Equipment Corporation, as a private-sector member of his Export Council.

          The announcement, made by Secretary of Commerce Carlos M. Gutierrez, said business leaders like Dicke are one of the best resources for identifying trade barriers and opportunities for U.S. exports, as well as for helping promote the President's trade policy.

          Formed in the early 1970s, the President's Export Council advises the President through the Secretary of Commerce on export enhancement and works with industry encouraging U.S. companies to increase exports and enter new markets.

          Crown owns and operates nine manufacturing facilities in four countries, including Australia, Germany, Mexico, the United States and is expanding into China. The company supports its company-owned and independent distributors in North America, Europe, the Middle East, Africa, India and the Pacific Rim.

          Under Dicke's direction, Crown, a privately held company, has grown into one of the largest manufacturers of lift trucks in the world. These heavy-duty electric lift trucks are used in transporting materials and goods in warehouses and distribution centers throughout the world.

          Register for NA 2006

          Both registration and booth space are filling quickly for NA 2006, sponsored by the Material Handling Industry of America. The event is slated for March 27 through March 30 at the I-X Center in Cleveland.

          NA 2006 focuses on the productivity solutions provided by material handling and logistics. The four-day event is designed to offer productivity solutions and information by showcasing the products and services of over 400 material handling and logistics providers.

          Industry professionals from the United States, Canada, Mexico and around the world are expected to attend. More than 400 exhibitors from industry, commerce and government will display their productivity solutions on the 150,000 square foot show floor. The newly designed NA 2006 Education Conferences offer focused, half-hour seminars in specially designed "theaters" constructed right on the trade show floor.

          For registration information, go to

          Invensys maps wireless strategy

          Invensys Process Systems strategy for its wireless communications will use a managed network approach, focusing on shared access-point technology and common data and security models for all wireless devices - regardless of vendor or application. The company announced its strategy in December.

          "Wireless communications will provide a powerful new enabling technology for asset performance management," said Chris Lyden, vice president of marketing at Invensys Process Systems. "Wireless technology makes it possible to incorporate new strategic measurements and other data that simply were either not practical or even possible to implement in a wired communications environment.



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