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Question posted - January 16 to January 22, 2012:

When and why would I need to stripe coat if I’m using an edge-retention primer?


Selected Answers

From Kiran Pawar of Berger Paint Bahrain on January 18, 2012:
I am in total agreement with Brian.

From M Ehab of North Valley on March 21, 2012:
When? Whenever there were edges to get enough film thickness. Why? Because edges, rivets and so on are main corrosion spots and cost much more to repair.

From Tom Schwerdt of Texas Department of Transportation on January 18, 2012:
     I have seen numerous "edge-retentive" coatings which had an edge thickness half that of nearby flat areas. Some are better, some are worse. Non-edge-retentive coatings may be down at 25% of the thickness of nearby flat areas. In addition, there is not a good way of verifying edge thickness in the field. (Lab testing requires cutting through the substrate, mounting and polishing a section.) Magnetic gauges, ultrasonic gauges and even the PIG (Tooke gauge to some of you) are not good choices. Even if you do have an edge-retentive primer which works at 100% of flat thickness when properly applied, your field inspector cannot verify the thickness of the coating at the edge. Your inspector can visually verify the presence of a stripe coat.

From richard d souza of stoncor middle east llc on January 17, 2012:

     Regardless of the type of primer, a proper specification should include stripe coating of each of the subsequent coats to make sure the edges or weld seams receive enough coating film thickness to ensure longetivity of the coating system. Primer alone will not protect the surface from failure, and 80% of coating failures occur at these critical areas. And, usually, every coat should be followed by a stripe coat until you reach the finish coat, in  which case the stripe coat using the finish coat should precede the finish coat application.     

     If possible, the stripe coat should be tinted a color different than the main coating and must be brush- or roller-applied, depending on the job size and accessibility.

From Brian Chapman of Cadillac Fabrication on January 17, 2012:
     Stripe coating serves more than one purpose. Edge retention is just one of the many possible reasons for using this technique. Added protection on stitch-welded areas, tight corners or radiuses and irregular surfaces such as welds and flame-cut edges is provided by stripe-coating to ensure adequate coverage.

From Mark Edmonds of Vigor Shipyards Inc. on January 18, 2012:

     Your use of the word "primer" could infer an additional coat of paint is to be applied, perhaps for cosmetic purposes or an additional coat of protective coating. In the world of US Navy tank coatings, edge-retentive paints do not use the word "primer." The US Navy does in fact allow single coats of edge-retentive paints without a stripe coat. The caveat is that you have to take additional DFT readings to confirm the edges have the specified millage, usually 20-30 mils dft.

      This method of application and checking has many years of research data along with in-service data on board US Navy vessels/tanks to back up not having to apply a stripe coat. For reference see mil spec MIL-PRF-23236 Type VII and NAVSEA Standard Items 009-32 FY 12 (Chg 1) Note 23 and 24.

From George Musterer of Hecate Painting & Sandblasting on January 18, 2012:
     Wet films tend to back away from edges during curing as the film shrinks, leaving thinner cured material at the edges. That is the main purpose behind developing edge-retentive primer. The two main purposes of stripe coating are to get coating to areas that cannot be accessed or have limited access to spray application, behind bolts, rivets, threads etc. Another purpose is to break surface tension. When spraying, paint/coatings are not always in a hurry to flow into cracks, crevices, etc. due to surface tension. Using a brush will break the surface tension and force the paint/coating into those cracks & crevices, sealing up potential points of entry for moisture/water/electrolyte.


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Tagged categories: Primers; Striping


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