May 11th, 2024 by . Posted in In Focus, In Focus Industrial, In Focus Marine

The Perfect Stripe Coating

How to do stipe coating?

Introduction:

The purpose of a stripe coating is to assure that the specified dry film thickness is reached on all areas to be conserved. A second purpose is to avoid air entrapment.

Stripe coating is recommended to be applied by brush to assure maximum penetration and the highest possible film build.

Following recommendation should always be specified to any project:

  • On all areas to be conserved, each coat shall show a uniform continuous closed film without defects (like i.e. cracking, pin-holing, holidays, bubbles, etc) and within the specified dry film thickness.
  • Special attention shall always be given to welds seems, seems, cavities, pittings, crevices, rough or irregular steel, rivets, nuts, bolts, joints, sharp edges, corners and hard to reach areas.
  • Use the right tinner and respect the maximum amount as indicitad in the product technical data sheet or recommended by the coa
  • The stripe coat will always have a 5cm overlap starting from the specified area to be stripe coated.
  • For best results, the colour of the stripe coat should be clearly different from the previous coat or substrate and the next coating manufacturer.
  • The viscosity of different coaitngs may slightly vary per batch and also depending on the age of the product. Also temperature and duration of use might influence the viscosity. Dilute as necessary to assure good flow into cavities.
  • Always brush stripe coat BEFORE applying the full primer coat areas that are sensitive to primer bridging or to air entrapment and/or where the primer will have difficulties to penetrate when applied by spray.

PRIMER STRIPE COAT:

  1. Surface Preparation according to specified standard.
  2. Stripe coat by round or oval brush all welds seems, seems, cavities or pittings (*), crevices, rough or irregular steel, rivets, nuts, bolts and joints. It may be required to dilute the primer by 5 to 10% to improve penetration.
  3. Spray apply the full primer coat at recommended DFT in the shortest possible term. It is recommended but not required for the stripe coat to be fully cured before applying the full coat. A wet in wet application is also possible as long as the total max. DFT is respected. The stripe coat shall not be permitted to dry for a period long enough to allow rusting of the un-primed steel. Where it is felt that a long drying period of stripe is necessary, but the precoated steel will deteriorate in the interval, the full prime coat of coating may be applied, allowed to dry, and the stripe coating then applied. Dilute the primer as much as necessary for the paint to flow into the cavities.
  4. Brush apply primer stripe coat (NOT diluted) to:
    1. Internal and External corners with a radius being less than 2mm. (As described in ISO standard 12944-3)
    1. Sharp edges
    1. Hard to reach areas by spray
    1. Holidays

The areas described in paragraph 4 could also be stripe coated before application  applying the full coat, but here are some reasons why it could be beneficial to stripe coat these areas after application of the full coat:

  • To reduce the time between stripe coating and application of the full coat.
  • Because these areas are not sensitive to air entrapment
  • To make sure the painter has checked all the areas since he has to coat all the edges and corners.
  • To make sure he builds up maximum DFT on edges and corners by NOT using a thinned coating.

(*) With regards to cavities or pittings:

On cavities or pittings that can easily be reached by spray, a cross (+) spray painting technique can be used to fill the cavities or pittings with paint. It is of importance that the paint is sprayed into the open cavities or pittings out of two angels. This spray technique can be supplemented by back rolling, but this is usually not necessary if the correct spray technique is used and the paint is sufficiently diluted. Back rolling is done by rolling with a clean dry short nap roller in a cross angle over the pittings shortly after application of the spray coat. The final goal is to assure full coverage and penetration and to avoid shadow painting at all times. Make sure the paint is diluted sufficiently for it to flow into the pittings.

Often, back rolling is difficult or impossible to use because:

  • The spray painter moves too fast and the paint is to dry to back roll it.
    • The spray painter creates to much mist hindering visibility.
    • The area is no longer accessible after spray painting like i.e. a tank bottom.

Note: Back rolling is only necessary and considered for areas of pittings when stripe coating is not feasible.

This cross (+) spray painting application method can only be used over caveties or pittings if they are:

  • not of the omega type, these should be opened first
  • easy to reach by spray
  • open, profound and wide
  • do not enclose the danger of air entrapment
  • do not enclose danger of shadow painting caused by their size, shape or position

STRIPE COATING PROCEDURE FOR INTERMEDIATE COAT:

The second stripe coat is primarily intended to assure full coverage on all the areas within the specified DFT.

  1. Stripe coat by brush welds seems, seems, cavities or pittings (*), crevices, rough or irregular steel, rivets, nuts, bolts, joints, sharp edges, internal & external corners with a radius less than 2mm and hard to reach areas by spray. Always remember the law of Faraday when spraying into narrow areas.
  2. Spray apply full coat at recommended DFT.
  3. Check for holidays and touch up
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