Stripe Coating A Key Component for Extending Coating

Stripe Coating: A Key Component for Extending Coating Service Life James D. Machen KTA-Tator, Inc.

Stripe Coating Webinar Learning Outcomes Attendance at this webinar will enable you to: 1. Describe the importance of stripe coating 2. List proven field methods/steps for applying effective quality stripe coats 3. Describe structural design considerations that can improve coating performance and help minimize stripe coating 4. Employ specification language for stripe coating

Protective Coatings Glossary (SSPC 00 -07) “Stripe Coat”: A coat of paint applied only to edges or to welds on steel structures before or after a full coat is applied. The stripe coat is intended to give those areas sufficient film build to resist corrosion. 3

SSPC Paint Guide No. 11 (SSPC PA Guide 11) “Stripe Coat” or “Striping”: A way of providing extra corrosion protection measures on edges, outside corners, crevices, bolt heads, welds, and other irregular surfaces, including optional surface preparation techniques for sharp edges to improve coating performance. 4

Simplified Example of Stripe Coating 5

Typical Surfaces Stripe Coated • • Crevices Back-to-back members Nuts/bolts, rivets Welds Outside corners Pitted Steel Built-up steel members Other irregularities 6

Typical Surfaces Stripe Coated (cont. ) • Typical Back-to-Back Bolted Angle 7

Typical Surfaces Stripe Coated (cont. ) • Typical Nut/Bolt Arrangement 8

Typical Surfaces Stripe Coated (cont. ) • Typical Riveted Connection 9

Typical Surfaces Stripe Coated (cont. ) • Typical Built-up member 10

Typical Surfaces Stripe Coated (cont. ) • Typical Corrosion Pitted Steel 11

Why Stripe Coat These Surfaces? • Surfaces all have in common. . . “EDGES” and/or “CREVICES” • Need to apply uniform coat and sufficient thickness • Specialized treatment for crevices presented later – Address treatment/removal of pack rust areas – Use of penetrating sealers and caulking to seal pack rust and minimize rust bleed from crevices 12

“EDGES” • • Shrinkage and surface tension draws coatings thin Thin coating = Reduced corrosion protection Thin coating = Edges susceptible to damage Higher Solids Coating = Improved edge retention (thicker) – Must still be “worked in” by brushing 13

“CREVICES” • Typically a combination of “Outside Corners (Edges)” with a “CREVICE” in between • Same shrinkage and surface tension stresses apply • “Flow out” of coating reduced in crevices • May combine stripe coat with penetrating sealers/caulking • Removal of rust scale/pack rust 14

Minimizing Shrinkage/Surface Tension Effects • Spread extra film build by brush application (preferred) • “Brushing In” coating helps overcome surface tension • Coating forced into crevices rather than bridge over • Other specialized applicators (rollers, swabs) 15

Stripe Coat Application Methods • Airless Spray or Conventional Spray plus “Back Brushing” – Faster, 1 sprayer/1 brusher – Improved uniformity and thickness – Conventional spray improves applicator control 16

When Is The Cost and Extra Effort of Striping Warranted? • Immersion Service (water or chemicals) • Highly corrosive exposures • Built-up structural members • Complex structural configurations • Structures with existing pitting corrosion, crevice corrosion, pack rust, and rust bleed problems • Milder exposures may not warrant stripe coating

When Is The Cost and Extra Effort of Striping Warranted? (cont. ) • Highly Corrosive Exposures -Roadway Splash zone on bridge 18

When Is The Cost and Extra Effort of Striping Warranted? (cont. ) • Complex structural configurations 19

When Is The Cost and Extra Effort of Striping Warranted? (cont. ) • Immersion 20

When Is The Cost and Extra Effort of Striping Warranted? (cont. ) • Structures with existing corrosion, pack rust, and rust bleed problems 21

Structural Design Considerations • Minimize need/improve effectiveness of stripe coating • Edge grinding • Full seal weld vs. Stitch weld • Alternate structural configurations (i. e. , tubular vs. I-Beam) • Addition of weep holes for drainage UNFORTUNATELY. . . ALL OF THE ABOVE CAN BE COSTLY/LABOR INTENSIVE 22

Structural Design Considerations (cont. ) Full seal weld vs. stitch weld 23

Stripe Coat Before or After Full Coats? Before… • Blast cleaned steel may rust back • Improved appearance • Easier to visualize irregularities needing stripe • Improved localized protection • Easier to inspect 24

Stripe Coat Before or After Full Coats? After… • No rust back problem • Need contrasting colors • Striped areas may be more visible after completion 25

Apply Wet-On-Dry or Wet-On-Wet? Wet-On-Dry • Must dry for a certain period before full coat – Usually manufacturers Dry-to-Recoat interval – Separate and distinct operation • Can be applied with any coat • Requires more time • Allows better visibility for inspection 26

Apply Wet-On-Dry or Wet-On-Wet? (cont. ) Wet-On-Wet • Typically requires manufacturers approval • Coating typically allowed to release most of solvent – Becomes “tacky” before next wet coat • Requires inspector presence during application to verify • Less time consuming Both Methods Achieve Goal. . . extra thickness and insurance of coverage. 27

Simultaneous Stripe Coat with Full Coat • Spray on and brush-in at same time with full coat – Requires two applicators • Not really true stripe coat – No extra thickness – Better than nothing – coating worked in to irregular surfaces • Inspector cannot verify, except by witnessing process 28

Stripe Coat Thickness • Not usually measured – Visually inspected (contrasting colors important) – Surface configuration prevents accurate DFT measurement • Control to apply as thin as possible in uniform film • Overly thick can result in film defects – Solvent entrapment, pinholes, cracking 29

Combining Stripe Coats With Penetrating Sealers/Caulking • Penetrating sealers and caulking with stripe coats improve effectiveness • Helps with. . . – Sealing crevices – Mitigating pack rust (all loose pack rust removed) – Helps prevent rust bleed from crevices 30

Combining Stripe Coats With Penetrating Sealers/Caulking (cont. ) • Penetrating sealers flow into crevices and seal – Low viscosity, high solids, epoxy penetrating sealers – Calcium sulfonate alkyd penetrating sealers – Must be compatible with coating system – Typically applied after prime coat with zinc rich primers – Before prime coat with non-zinc primers (i. e. epoxy, alkyd MCU) – Brushed or “flooded” into crevice, excess wiped off 31

Combining Stripe Coats With Penetrating Sealers/Caulking (cont. ) • Caulking – Moisture cured urethane or polysulfide type – Paintable or match finish coat color – Applied between coats or after complete system – Must be compatible with coating system – Intercoat application can result in crack (i. e. harder coating over softer caulk – Matching color caulk may hold dirt or discolor differently than coating – Caulking prior to finish coat, most common 32

Combining Stripe Coats With Penetrating Sealers/Caulking (cont. ) • In some instances caulk only top/sides of members – Leave bottom un-caulked to allow moisture to escape 33

Stripe Coating Research • Designed to evaluated effectiveness of stripe coats with and without penetrating sealers/caulking • Coating systems tested included: – IOZ/OZ/E/U (with striping of various coats and without striping) – IOZ/OZ/EPS/E/U (with striping of various coats and caulking) – IOZ/OZ/E/U/CSA PS/CSA – (stripe CSA/PS and CSA finish only, no caulking 34

Stripe Coating Research (cont. ) • Bottom Line. . . – Stripe coat improved overall coating performance vs. no stripe coat – Systems with stripe coats/penetrating sealers/caulking appear most effective 35

What Specification Wording Should Include. . . • Manufacturer’s products to be used • What surfaces/areas are to be caulked – All nuts/bolts, welds, edges, rivets, inside/outside angles, corrosive/harsh exposure surfaces – Exposures over structure may vary, stripe coats may not be needed in all areas • Separate/distinct brush stripe coats prior to full coats 36

What Specification Wording Should Include. . . (cont. ) • If penetrating sealers/caulking is to be applied • Before or After full coats • Wet-on-Wet, Wet-on-Dry 37

Typical Hierarchy of Stripe Coat Scenarios in Specifications. . . • “Good” – Brush stripe coat of primer – If zinc rich primer, brush stripe coat of intermediate over zinc rich • “Better” – Brush stripe coat of primer and intermediate coat – If IOZ primer, stripe coat with OZ primer and intermediate coat • “Best” – “Better” approach plus added stripe coat of penetrating sealers and caulking in crevices – Particularly effective if pack rust /rust bleed problems are present – Approach may be limited to critical corrosive harsh exposure areas 38

In Summary. . . • Stripe coating definitely extends coating service life – Most widely used and most effective in corrosive environments – Can be combined with penetrating sealers/caulking to improve performance – The entire structure may consist of multiple (mild to harsh exposures) – Extra cost of stripe coat not warranted in some areas – Use Good/Better/Best approach based on corrosion protection goals/budget 39

Stripe Coating: A Key Component for Extending Coating Service Life Questions? James D. Machen KTA-Tator, Inc.