Fig. 1: A number of organizations provide written standards and guidelines for surface preparation
Coatings are applied to commercial buildings to protect a variety of materials from corrosion and deterioration, and to maintain the brand and aesthetics of the structure. Three key factors must be addressed during design and construction in order achieve long-term coating performance: selection of the right coating material, thorough surface preparation, and careful application to assure complete coverage of all surfaces at the proper film thickness. This article addresses one of the three factors, surface preparation and, more specifically, relevant industry standards (Fig. 1) produced by SSPC (Society for Protective Coatings), NACE International (formerly National Association of Corrosion Engineers), ICRI (International Concrete Repair Institute), and ASTM International (formerly American Society for Testing and Materials).
Steel Surface Preparation Standards
SSPC and NACE lead the way in the development of written and visual reference photographs for the preparation of steel surfaces using solvents, hand and power tools, pressurized water, and abrasive blast cleaning. The standards are summarized below. When there are multiple standards in a given category, they are presented from the least to greatest degree of cleaning. As can be seen, the numerical designations of the standards cannot always be relied upon to establish a hierarchy. A good summary of the various methods is presented in the SSPC Surface Preparation Commentary, which is published in SSPC Painting Manual, Volume 2, Systems and Specifications.
Solvent Cleaning Standard
Solvent cleaning involves the use of solvents ranging from water and detergent to “thinners” and steam cleaning to remove soluble contaminants such as grease and oil. One industry standard defines the degree of cleaning:
- SSPC-SP 1, Solvent Cleaning* (removes oil, grease, soil, and soluble contaminants from a surface, typically as a precursor to mechanical methods of surface preparation). Reference photographs are not available for solvent cleaning.
*SSPC is in the process of revising SSPC-SP 1.
Hand- and Power-Tool Cleaning Standards and Reference Photographs
Hand and power tool cleaning involves the use of hand-held tools or floor machines to remove paint, rust, and mill scale from the surface. Different levels of cleaning and profiling (surface roughening) are defined for hand and power tool cleaning:
- SSPC-SP 2, Hand Tool Cleaning (removes loose rust, loose paint, and loose mill scale; tight material may remain)
- SSPC-SP 3, Power Tool Cleaning (removes loose rust, loose paint, and loose mill scale; tight material may remain)
- SSPC-SP 15, Commercial Grade Power Tool Cleaning (removes all rust, paint, and mill scale except in bottom of pits; stains can remain on up to 33% of each unit area; 1 mil minimum surface profile)
- SSPC-SP 11, Power Tool Cleaning to Bare Metal (removes all rust, paint, and mill scale except in the bottom of pits; 1 mil minimum surface profile)
Photographs depicting the appearance of hand- and power-tool cleaning over various initial steel conditions are found in SSPC-VIS 3, Guide and Reference Photographs for Steel Surfaces Prepared by Power- and Hand-Tool Cleaning (Fig. 2). The photographs depict the appearance of surfaces prior to and after hand-and power-tool cleaning. The initial coating/steel conditions included in the photographs are
|Fig. 2 SSPC VIS 3, Reference Photographs for Hand and Power Tool Cleaning|
- Condition A – Intact mill scale
- Condition B – Rust and mill scale
- Condition C – Totally rusted
- Condition D – Totally rusted and pitted
- Condition E – Intact light colored paint with minimal rusting (Fig. 3)
- Condition F – Zinc rich paint with rusting along a weld (Fig. 3)
- Condition G – Heavy old coating with rust and mill scale (Fig. 3)
|Fig. 3: Example of three painted reference surfaces prior to preparation|
The degrees of cleaning from SP 2, Hand-Tool Cleaning through SP 11, Power-Tool Cleaning to Bare Metal are depicted for each initial surface condition. Fig. 4 shows the appearance of 4 grades of hand- and power-tool cleaning over rusted, unpainted steel (Condition C steel).
|Fig. 4: Appearance of Hand, and Power-Tool Cleaning over unpainted, rusted steel (WB depicts a wire brush; SD represents a sanding disc, both prepared to SSPC-SP 3)|
Waterjetting Standards and Reference Photographs
Waterjetting standards describe the use of water at pressures from <5,000 psi to >30,000 psi. The degree of cleaning ranges from removal of loose material and contaminants to the complete removal of all paint, rust, and mill scale. Note that prior to March, 2012, the four standards summarized below had been presented in a single document, SSPC-SP 12/NACE 5, Waterjetting. In 2012, SSPC-SP 12/NACE 5 was replaced with the following four standards:
- SSPC-SP WJ-4/NACE WJ-4, Waterjet Cleaning of Metals – Light Cleaning (removes all loose material; tightly adherent material can remain)
- SSPC-SP WJ-3/NACE WJ-3, Waterjet Cleaning of Metals – Thorough Cleaning (removes paint, rust, and mill scale, except that stains and tight residues covering less than 33% of each unit area can remain
- SSPC-SP WJ-2/NACE WJ-2, Waterjet Cleaning of Metals – Very Thorough Cleaning (removes all paint, rust and mill scale, except that stains and tight residues covering less than 5% of each unit area can remain)
- SSPC-SP WJ-1/NACE WJ-1, Waterjet Cleaning of Metals – Clean to Bare Substrate (removes all paint, rust, and mill scale)
Photographs depicting the appearance of various grades of waterjetting over painted and unpainted initial steel conditions are found in SSPC-VIS 4/NACE VIS 7, Guide and Reference Photographs for Steel Surfaces Prepared by Waterjetting (Fig. 5). Six initial conditions are depicted:
- Condition A – Not included in VIS 4
- Condition B – Not included in VIS 4
- Condition C – Totally rusted
- Condition D – Totally rusted and pitted
- Condition E – Light colored paint with minimal rusting over blast-cleaned steel
- Condition F – Zinc-rich paint over blast cleaned steel
- Condition G – Heavy old coating with rust and mill scale
- Condition H – Multi-coat white paint over mill scale
|Fig. 5: SSPC VIS 4/NACE VIS 7, Reference Photographs for Waterjetting|
Each of the degrees of cleaning from WJ4, Light Cleaning to WJ1, Clean to Bare Substrate, is depicted for each initial surface condition. Fig. 6 shows the four grades of cleaning over Condition G steel.
|Fig. 6: Appearance of 4 grades of waterjet cleaning over previously painted Condition G steel|
Abrasive Blast Cleaning (Steel) Standards and Reference Photographs
Abrasive blast cleaning involves the use of high-pressure compressed air to propel abrasives against the surface through specialized blast nozzles. The abrasives remove paint, rust, and mill scale. Different degrees of cleaning can be achieved depending on dwell time. The degrees of cleaning defined in the standards are
- SSPC-SP 7/NACE 4, Brush-Off Blast Cleaning (removes all loose rust, loose paint, and loose mill scale; tight material can remain)
- SSPC-SP 14/NACE 8, Industrial Blast Cleaning (removes all loose rust, loose paint, and loose mill scale; traces of intact material can remain on up to 10% of each unit area; additional material may remain in limited access areas provided it is subjected to the abrasive blast and is intact)
- SSPC-SP 6/NACE 3, Commercial Blast Cleaning (removes all rust, paint, mill scale; only stains can remain on up to 33% of each unit area)
- SSPC-SP 10/NACE 2, Near-White Metal Blast Cleaning (removes all rust, paint, mill scale; only stains can remain on up to 5% of each unit area)
- SSPC-SP 5/NACE 1, White Metal Blast Cleaning (removes all rust, paint, mill scale; no stains remain)
Photographs depicting the appearance of abrasive blast cleaning over various initial steel conditions are found in SSPC-VIS 1, Guide and Reference Photographs for Steel Surfaces Prepared by Abrasive Blast Cleaning (Fig. 7).
The photographs represent the appearance of surfaces both prior to and after abrasive blast cleaning to different degrees of cleaning.
The pre-cleaning conditions that are depicted are
|Fig. 7: SSPC VIS 1, Reference Photographs for Abrasive Blast Cleaning|
- Condition A – Intact mill scale (Fig. 8)
- Condition B – Rust and mill scale (Fig. 8)
- Condition C – Totally rusted
- Condition D – Totally rusted and pitted
- Condition E – Not included in VIS 1
- Condition F – Not included in VIS 1
- Condition G1 – Aged coating with extensive pinpoint rusting
- Condition G2 – Aged coating with moderating pitting
- Condition G3 – Aged coating with severe pitting
|Fig. 8: Examples of unpainted Condition A and B steel prior to preparation|
Each of the degrees of cleaning from SSPC-SP 7, Brush-off to SSPC-SP 5, White Metal, is depicted for the initial surface conditions. Fig. 9 shows the appearance of each grade of abrasive blast cleaning over deteriorated existing paint (Condition G3 steel).
|Fig. 9: Appearance of 5 grades of blast cleanliness over previously painted Condition G3 steel|
Abrasive Blast Cleaning (Non Ferrous Metal) Standard
Blast cleaning of non-ferrous metals involves the use of abrasives to uniformly roughen (profile) the surface. One industry standard defines the degree of cleaning:
- SSPC-SP 16, Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals (uniform roughening of the surface; intact paint may remain)
Reference photographs are not available, but Fig. 10 shows the typical appearance of this degree of cleaning when used on stainless steel.
|Fig. 10: Stainless steel coupon blast cleaned to SSPC-SP 16 for comparison with stainless in a paint failure investigation|
Concrete Surface Preparation Standards
A number of industry standards identify methods of surface preparation that can be used on CMU and other concrete surfaces (e.g., floors, poured walls, pre-cast). Unfortunately, most of the standards do not provide definitive acceptance criteria for judging the degree of cleaning as is the case with the standards described above for steel. Instead, they essentially state that sufficient material must be removed to achieve a sound concrete surface free of laitance, glaze, efflorescence, and incompatible curing compound. They also do not provide acceptance criteria on whether remnants of paint can remain when the goal is to strip a surface (Fig. 11). In addition, standards are lacking for some methods of preparation such as chemical stripping (Fig. 12). The SSPC Commercial Coatings Committee in conjunction with the SSPC Surface Preparation Committee is planning to address these voids and will be developing standards that define various degrees of cleaning of painted and unpainted concrete surfaces.
|Fig. 11: Paint on left was removed as seen in the center of the photo, but residues remain. Standards are needed to define various degrees of cleaning, similar to the standards for steel.|
|Fig. 12: Industry surface preparation standards for some methods of preparation, such as chemical stripping, still need attention|
Methods of Concrete Surface Preparation
The standards and guides available from SSPC, NACE, ICRI and ASTM can be organized as follows by the method of cleaning that is involved. (A brief description of the standards follows the list.)
- Detergent Cleaning- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4258, ASTM D4261
- Air Blast Cleaning, Water Cleaning, Steam Cleaning, Vacuum Cleaning- SSPC-SP 13/NACE 6- ASTM D4258, ASTM D4261
- Chemical Stripping- Effective method of paint removal, but not addressed in the standards/guides
- Acid Etching- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4260
- Flame Cleaning- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2
- Power Grinding/Sanding- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4259
- Impact Power Tool Cleaning- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4259
- Scarifying/Grinding/Scabbling/Milling- ICRI Guideline No. 310.2- ASTM D4259
- Water Cleaning/Waterjetting- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4259
- Wet Abrasive Blast Cleaning- SSPC-SP 13/NACE No. 6- ASTM D4259
- Dry Abrasive Blast Cleaning- SSPC-SP 13/NACE No. 6- ICRI Guideline No. 310.2- ASTM D4259
SSPC-SP 13/NACE No. 6, Surface Preparation of Concrete
This document is closer to a guidance document than a standard because it describes methods that are available for cleaning a variety of concrete surfaces, but does not dictate that a given method should be used, nor does it provide explicit acceptance criteria. It also frequently references other ASTM and NACE standards. The following methods of surface preparation are included:
- Dry abrasive blast cleaning, wet abrasive blast cleaning, vacuum-assisted abrasive blast cleaning, and centrifugal shot blast cleaning with references to ASTM D4259 (described below).
- High-pressure water cleaning or waterjetting according to SSPCSP 12/NACE No. 5 or ASTM D4259 (described below). These methods can remove poorly adherent coating, allowing intact coating to remain, or completely remove existing coating given that adequate pressures and dwell times are used. Note that SSPC-SP 12/NACE No. 5 is entitled, Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating. While the methods described in the standard are suitable for use on concrete, the acceptance criteria for the degrees of cleaning are based on metallic substrates. Note also that as described above, this standard was replaced with four individual cleaning standards in 2012.
- Impact power tools according to ASTM D4259 (described below). These methods include needle gunning and rotary peening, which will remove existing coating, but may fracture and remove concrete at the same time.
- Power grinding, sanding and wire brushing according to ASTM D4259 (described below). While coatings can be completely removed by grinding or sanding, these methods are more commonly used for the removal of loose coating and for feathering edges.
- Acid etching according to ASTM D4260. Acid etching is used on horizontal surfaces to etch bare concrete. It will not remove existing coating.
- Flame (thermal) cleaning. This method is used to extract organic contaminants from concrete, but is not suggested for coating removal.
- Methods used for cleaning contaminants from the surface prior to painting are also addressed. The methods are vacuum cleaning, air blast cleaning, water cleaning, detergent water cleaning, and steam cleaning, all according to ASTM D4258.
ICRI Guideline No. 310.2-1997 (formerly No. 03732), Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays
This guideline addresses methods of surface preparation used on concrete. While the focus of the Guideline is on concrete floors, some of the methods are also suitable for use on vertical and overhead surfaces. The Guideline also includes nine (9) concrete surface profile (CSP) coupons that are replicas of the type of profile (surface roughness) created by the various methods of surface preparation (Fig. 13). The coupons range in texture from very smooth, typical of acid etching (CSP 1) to very rough, typical of heavy scarification (CSP 9).
|Fig. 13: ICRI Concrete Surface Profile Coupons – CSP 1 (right) to CSP 9 (left)|
Methods addressed in the ICRI Guideline are briefly summarized below. In addition to the written text, the guideline includes the typical range of surface profiles achieved with each method. Within each category below, the methods are ordered from least aggressive to most aggressive.
Methods involving water in ICRI 310.2
- Detergent scrubbing – involves the use of detergents and scrubbing to remove surface dirt, oil, grease and loose debris, without altering the texture of the surface. Surface profile CSP 1.
- Low-pressure water cleaning – involves the use of low pressure water (< 5,000 psi) to remove dirt, dust, loose scale or debris without removing concrete or texturing the surface. Surface profile CSP 1.
- Acid etching – involves the use of acids to remove weak cement paste and to slightly profile the surface by exposing fine aggregate. It will not remove coatings. Surface profile CSP 1 – CSP 3.
- High/ultra-high pressure waterjetting – involves the use of high pressure water (from 5,000 psi to 45,000 psi) to remove coatings, the surface of concrete, and water-soluble contaminants. Surface profile CSP 6 – CSP 9.
Methods involving power tools in ICRI 310.2
- Grinding – involves the use of hand held or floor grinders to remove slight surface irregularities and thin coatings. Surface profile CSP 1 – CSP 3.
- Needle scaling – involves the use of hand-held equipment containing hardened small diameter steel rods that are pneumatically impacted against the surface to remove coatings and roughen the surface of the concrete. Surface profile CSP 5 – CSP 8.
- Scarifying – involves the use of hand-held and floor machines containing cutters (toothed washers) that impact the surface at a right angle to remove coating and fracture or pulverize the surface of the concrete. Surface profile CSP 4 – CSP 9.
- Scabbling – involves the use of hand-held or floor machines containing piston-driven cutting heads that impact the surface to remove coatings and the surface of the concrete. Surface profile CSP 7 – CSP 9.
- Milling/Rotomilling – involves a machine that is driven across the surface to remove the coating and top layer of the concrete through the use of cutting teeth that claw and groove the substrate. Surface profile CSP9.
Methods involving abrasive blast cleaning in ICRI 310.2
- Abrasive (Sand) Blasting – involves the use of compressed air to propel particles of abrasive through specialized hand-held nozzles to remove coatings and roughen the surface of the concrete. Surface profile CSP 2 – CSP 4.
- Steel Shotblasting – involves the use of specialized hand-held or floor machines containing wheels that propel a steel abrasive against the surface using centrifugal force. The abrasive is collected by the machine as the cleaning is being performed and reused. This method removes coatings and roughens the surface of the concrete. Surface profile CSP 2 – CSP 8.
Flame Blasting in ICRI 310.2
- Flame blasting – involves the use of an acetylene-oxygen flame to remove paints, contaminants, and contaminated concrete. This is a very dangerous operation and has limited, if any, application to the commercial industry. Surface profile CSP 8 and higher.
ASTM D4258, Standard Practice for Surface Cleaning Concrete for Coating
This practice briefly describes methods of cleaning that will remove surface contaminants such as grease, dirt, and loose material, but will not remove coatings. These methods are used in conjunction with other coating removal methods to assure that the surface is free of contamination prior to painting. The methods addressed are broom cleaning, vacuum cleaning, air blast cleaning, water cleaning, detergent water cleaning, and steam cleaning.
ASTM D4259, Standard Practice for Abrading Concrete
This practice addresses methods for removing material, including coatings, and roughening the surface. The methods addressed are
- Mechanical Abrading – methods involve power tools, both impact and grinding. The power tools are capable of removing coating, but are better suited for localized use. The impact tools can also cause damage to the substrate.
- Water Blast Cleaning – method involves high-pressure water blasting, but the pressures are not defined. Given adequate pressure and dwell time, coatings can be removed.
- Abrasive Blast Cleaning – methods include dry blasting, wet blasting, and a self-contained apparatus that reuses the abrasive. These methods will remove coating, but can significantly roughen the substrate in the process.
ASTM D4260, Standard Practice for Liquid and Gelled Acid Etching of Concrete
This practice addresses the preparation of bare concrete by acid etching, but will not remove existing coatings.
ASTM D4261, Standard Practice for Surface Cleaning Concrete Masonry Units for Coating
This practice addresses the same surface cleaning methods covered in ASTM D4258, with the addition of mechanical tool cleaning for the removal of mortar spatter and efflorescence. The standard is not for the removal of existing coatings.
There are a variety of standards, guides, reference photographs, and roughness coupons available for specifying the type of cleaning required for both steel and concrete, and for determining if the specified degree of cleaning is met in the field. Of the two substrates, the cleanliness of steel is better defined, both in words and in reference photographs. However, the SSPC Commercial Coatings Committee will be addressing the void in concrete by developing cleanliness standards modeled after the steel standards, to define degrees of cleaning in the same manner that SSPC-SP 6, Commerical Blast Cleaning is different than SSPC-SP 5, White Metal Blast Cleaning. The committee will also be developing a guidance document to assist in selecting the method of surface preparation according to project-specific needs. If anyone is interested in participating in this committee work, contact Aimee Beggs (email@example.com) or Ken Trimber (firstname.lastname@example.org).
Kenneth A. Trimber is the President of KTA-Tator, Inc. and is directly responsible for the overall operation, performance, and success of the company. Mr. Trimber has been employed by KTA since 1968, where he worked on a part-time basis until his graduation from college in December of 1974. After graduation, he joined the firm full time. Mr. Trimber serves as a senior consultant and client liaison on many multi-disciplinary projects as well as a principal specification writer/reviewer. Mr. Trimber is a NACE Certified Coatings Inspector Level 3 (Peer Review) (#362), is an SSPC Certified Protective Coatings Specialist (#339-244-0635). He has more than 35 years of experience in the industrial painting field, is a Past President of the SSPC, Chairman of the Committee on Surface Preparation, Chairman of the Visual Standards Committee, and Chairman of the Task Group on Containment. He is also Past Chairman of ASTM D1 on Paints and Related Coatings, Materials, and Applications. Mr. Trimber authored The Industrial Lead Paint Removal Handbook and co-authored Volume 2 of the Handbook: Project Design. He has been formally recognized by industry associations/publications on numerous occasions including being named Coatings’ Specialist of the Decade at the SSPC National Conference in 1990 and being selected by the JPCL in 2009 as one of 25 Top Leaders and Thinkers in the Coatings & Linings Industry for the past 25 years.
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