Paint Removal from CMU and Brick - Webinar Learning Objectives
Identify SSPC/NACE, ASTM, and ICRI standards and guidelines applicable to the removal of paint from CMU and brick substrates
Describe various methods of paint removal, including advantages and disadvantages of each
Questions to Ask During Project Design
The following questions help to identify candidate coating removal methods for the project:
• Does all coating have to be removed, or just loose coating?
• If all coating must be removed, can small amounts still be permitted to remain in the porosity of the block?
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Questions to Ask During Project Design
(con’t)• Can roughening of the block or brick be
tolerated. If so, can it be heavy or only slight?
• Can large volumes of water be tolerated (environmentally and in terms of potential water intrusion into the substrate)?
• Can airborne dust be tolerated?
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Industry Standards and Guides (con’t)
• SSPC-SP13/NACE No. 6, Surface Preparation of Concrete
• SSPC-SP12/NACE No. 5, Surface Preparation and Cleaning of Metals by Water Jetting Prior to Recoating
• ICRI Guideline No. 310.2 (formerly 03732), Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlays
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Industry Standards and Guides (con’t)
• ASTM Standard Practices– ASTM D4258, Surface Cleaning Concrete
for Coating– ASTM D4259, Abrading Concrete– ASTM D4260, Liquid and Gelled Acid
Etching of Concrete– ASTM D4261, Surface Cleaning Concrete
Masonry Units for Coating
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Surface Preparation/Cleaning Methods in Standards/Guides
• Dry Abrasive Blast Cleaning– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4259
• Water Cleaning/Water Jetting– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4259
• Wet Abrasive Blast Cleaning– SSPC-SP13/NACE No. 6– ASTM D4259
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Surface Preparation/Cleaning Methods in Standards/Guides
(con’t)• Impact Power Tool Cleaning
– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4259
• Power Grinding/Sanding– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4259
• Scarifying/Grinding/Scabbling/Milling– ICRI Guideline No. 310.2– ASTM D4259
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Surface Preparation/Cleaning Methods in Standards/Guides
(con’t)• Acid Etching
– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4260
• Flame Cleaning– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2
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Surface Preparation/Cleaning Methods in Standards/Guides
(con’t)• Detergent Cleaning
– SSPC-SP13/NACE No. 6– ICRI Guideline No. 310.2– ASTM D4258, ASTM D4261
• Air Blast Cleaning, Water Cleaning, Steam Cleaning, Vacuum Cleaning– SSPC-SP13/NACE 6– ASTM D4258, ASTM D4261
• Chemical Stripping– Effective method of paint removal, but not addressed in the
standards/guides12
Candidate Paint Removal Methods for CMU/Brick
• Dry Abrasive Blast Cleaning• Wet Abrasive Blast Cleaning• Sodium Bicarbonate Blast Cleaning• Water Cleaning (Low Pressure <5,000 psi; High
Pressure 5000 -10,000 psi)• High Temperature Pressure Water Cleaning
(<5,000 psi)• Water Jetting (High Pressure 10,000 – 30,000 psi;
Ultra-High Pressure (>30,000 psi)• Power Tool Cleaning• Chemical Stripping
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Dry Abrasive Blast Cleaning
Abrasives propelledby compressed air
Boiler slag, copperslag, nickel slag,garnet, crushed glass,sponge, walnut shells, others
Very dusty – mayrequire containment system
Dry Abrasive Blast Cleaning (con’t)
Difficult to selectivelyremove loose coating
Elastomeric coatings canbe difficult to removedue to bounce back ofthe abrasive
Potential for very heavyroughening of thesubstrate and damageto mortar joints
Wet Abrasive Blast Cleaning
Variation of dryabrasive blastcleaning
Water is mixed with the abrasiveto control dusting
Same potential toroughen the substrate as dryabrasive blast cleaning
Wet Abrasive Blast Cleaning (con’t)
Expendable abrasive,same as dry blastcleaning
Water is mixed withabrasive using:– Water collar– Special nozzle– Special equipment
that creates a slurry
Sodium Bicarbonate Blast Cleaning
Variation of wet abrasive blast cleaning
Sodium bicarbonate (baking soda) is the abrasive
Larger particle size thanhousehold baking soda
Good for removing surface contamination,graffiti, and efflorescence
Water Cleaning Low Pressure <5,000 psi
High Pressure 5,000 to 10,000 psi
Pressure categoriesdefined in SSPC-SP12/NACE No. 5, Surface Preparation and Cleaning of Metals by Water Jetting Prior to Recoating
Despite the title, the methods suitable for CMU/brick
Water Cleaning (con’t) Low Pressure <5,000 psi
High Pressure 5,000 to 10,000 psi
Will effectively removeloose coating
Zero degree rotatingtip improves efficiency
Can remove all coatinggiven ample dwell time
Generally 5.0 to 10.0gal/min
Water Cleaning (con’t) Low Pressure <5,000 psi
High Pressure 5,000 to 10,000 psi
Potential for using largeamount of water, especially for total coatingremoval
Increased dwell time for total removal can lead to water intrusion and wetting of interior surfaces
High Temperature Low Pressure Water Cleaning
(<5,000 psi) Water temperature
250ºF and pressures <5,000 psi
High temperature improves cleaning efficiency when removing all coating.
High Temperature Low Pressure Water Cleaning
(<5,000 psi) - con’t High temperature
softens paint during removal
Water Jetting High Pressure 10,000 to 30,000 psi Ultra -High Pressure >30,000 psi
SSPC-SP12/NACE No. 5
Typically less water volume than low pressure cleaning methods
Efficiently removes existing coating
Water Jetting (con’t)High Pressure 10,000 to
30,000 psi Ultra -High Pressure >30,000
psi Integral vacuum recovery system improves housekeeping and cleanup
Power Tool Cleaning
Power sanding, power grinding, needle gunning, rotopeening
Sanding and grinding remove paint with less damage to substrate than impact methods
Vacuum shrouding available
Power Tool Cleaning (con’t)
Power tool cleaning best used for localized removal
Sanding methods good for feathering
Chemical Stripping
Chemical stripping effectively removes existing paint
Biodegradable strippers are available that do not contain methylene chloride or caustic materials
Chemical Stripping – con’t
Stripper is first applied to the surface by brush, roller, or spray
Dwell time depends on coating type, temperature and thickness, but typically overnight
Chemical Stripping – con’t
Stripper and coating are removed by scraping, bucket and sponge, or pressure washing
Original Project Design Questions
• Does all coating have to be removed, or just loose coating?
• If all coating must be removed, can small amounts still be permitted to remain in the porosity of the block?
• Can roughening of the block or brick be tolerated. If so, can it be heavy or only slight?
• Can large volumes of water be tolerated (environmentally and in terms of potential water intrusion into the substrate)?
• Can airborne dust be tolerated?
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Practical Use of Candidate Surface Preparation Methods
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1 – This table represents the practical application of the various methods when used under normal operations, but it is not absolute. For example, abrasive blast cleaning can partially remove existing coating from CMU or brick, but it is not commonly used for this purpose.2 – Roughening created by power tool cleaning is dependent on the tool being used, ranging from slight roughening with power sanding to heavy roughening with power impact tools. 3 - Slight to heavy roughening may occur. Vacuum shrouding will significantly reduce the volume of water. Without vacuum shrouding, the volume is greater, but typically not as high as pressure washing at < 10,000 psi. 4 – A large volume of water is generated if the stripper is removed by pressure washing. Much less water is involved if removed by scraping and sponge/water, but this is only practical for small localized areas.
Paint Removal Methods Extent of Coating Removal Feasible
Substrate Roughening
Extent of Paint Residue in Porosity
Volume of Water Used
Quantity of Airborne Dust
Generated
Partial Total Slight to none
Heavy Slight Mod Mod Large Little Much
Dry abrasive blast x x x none x
Wet abrasive blast x x x x x
Sodium bicarb blast x x x x none
Pressure water (<10k) x x x x none
High temp water (<5k) x x x x x none
Water jetting (>10k) x x x3 x3 x x3 x3 none
Power tool cleaning x x 2 x 2 x none x
Chemical stripping x x x x4 x4 none
Practical Use of Candidate Surface Preparation Methods
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.
Paint Removal Methods Extent of Coating Removal Feasible
Partial TotalDry abrasive blast xWet abrasive blast xSodium bicarbonate blast xPressure water (<10k) xHigh temp water (<5k) x x
Water jetting (>10k) x xPower tool cleaning xChemical stripping x
Practical Use of Candidate Surface Preparation Methods
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2 – Roughening created by power tool cleaning is dependent on the tool being used, ranging from slight roughening with power sanding to heavy roughening with power impact tools.
3 – Slight to heavy roughening may occur
Paint Removal Methods Substrate Roughening
Slight to none
Heavy
Dry abrasive blast x
Wet abrasive blast x
Sodium bicarbonate blast x
Pressure water (<10k) x
High temp water (<5k) x
Water jetting (>10k) x3 x3
Power tool cleaning x 2 x 2
Chemical stripping x
Practical Use of Candidate Surface Preparation Methods
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Paint Removal Methods Extent of Paint Residue in Porosity
Slight Mod
Dry abrasive blast x
Wet abrasive blast x
Sodium bicarbonate blast x
Pressure water (<10k) x
High temp water (<5k) x
Water jetting (>10k) x
Power tool cleaning x
Chemical stripping x
Practical Use of Candidate Surface Preparation Methods
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3 – Vacuum shrouding will significantly reduce the volume of water. Without vacuum shrouding, the volume is greater, but typically not as high as pressure washing at < 10,000 psi.
4 – A large volume of water is generated if the stripper is removed by pressure washing. Much less water is involved if removed by scraping and sponge/water, but this is only practical for small localized areas.
Paint Removal Methods Volume of Water Used
Mod Large
Dry abrasive blast none
Wet abrasive blast x
Sodium bicarbonate blast x
Pressure water (<10k) x
High temp water (<5k) x
Water jetting (>10k) x3 x3
Power tool cleaning none
Chemical stripping x4 x4
Practical Use of Candidate Surface Preparation Methods
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Paint Removal Methods Quantity of Airborne Dust
Generated
Little Much
Dry abrasive blast x
Wet abrasive blast x
Sodium bicarbonate blast none
Pressure water (<10k) none
High temp water (<5k) none
Water jetting (>10k) none
Power tool cleaning x
Chemical stripping none
Productivity
Production rates for some of the methods can be found in:– Painting and Decorating Contractors of America (PDCA)
Estimating Guide, Volume 2, Rates and Tableswww.PDCA .org (314-514-7322)
– ICRI Guideline No. 310.2 (formerly 03732), Selecting and Specifying Concrete Surface Preparation for Sealers, Coatings, and Polymer Overlayswww.icri.org (847-827-0830)
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Additional Information
• Paper associated with the webinar to be published in Durability + Design daily e-news - week of November 1, 2010
• SSPC 2011 – One day seminar on commercial painting – problems with painting CMU, surface preparation, application, and paint systems Feb 1, 2001
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