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Question posted - January 30 to February 5, 2012:

When the relative humidity in a paint shop exceeds 80%, how can you apply waterborne inorganic zinc so that it cures sufficiently for topcoating in a reasonable time?


Selected Answers

From jesse chasteen of schriener construction on February 3, 2012:
If this is a continous obstacle, they make an incredible piece of equipment: dehumidifier. Cranking the heat up does not always displace air moisture. Two light coats can bite you back, as is stated by M/M. It doesn't like going over itself.

From Vyacheslav Volosiuk of Polymerprotection Ltd. on April 3, 2012:
     Dehumidification, heating and application wet on wet  all go well. The dried film is porous, and if thick enough will readily absorb the binder from the second coat, so let it dry to the point when it only begins to change color to light gray. If dried completely, some addition of binder will help not to obtain a powdery film over the second coat. There are different WB IOZ formulations. Some really do not adhere to themselves and delaminate like scale, either immediately or later in service. Some don't cure at low temp and high RH, leaving irreversibly powdery film down to substrate and must be re-blasted and re-applied. If not thixotropic enough, one full wet coat will sag from vertical surfaces and may leave a crust on horizontal surface which will cure and remain water-sensitive for a very long time, so at least two passes is a must. So be careful and first make sure what material you are dealing with.

From David Zuskin of EXCET/US NAVAL RESERACH LAB on February 10, 2012:
Don't mess with WBIOZ when you can't control the relative humidity and the dew point. If you are close and spray, you add additional moisture to the atmosphere as you apply.....ask me how I know.

From Earl Ramlow of Polyset on February 7, 2012:
    If you were using a high-ratio, waterborne inorganic zinc, RH at 85% would not be an issue. It will cure within minutes, and adheres great to itself, if two or more coats are required for millage.

From Matt McDonald of Carboline on February 10, 2012:
To follow up on my post and the other comments, the high-ratio silicate formula is the most user-friendly and best performing WBIOZ. All of the things discussed (heat the steel, DH, air movement) will help drying in humid conditions. The high-ratio zinc silicate can recoat itself in the initial drying stage. It has to be applied as the first coat is "setting up," almost wet on wet. This would typically be done if the WBIOZ is to be used as a single coat (5 mils dft) . WBIOZ does not recoat itself well after it is completely dry or cured.

From Khalid Shaikh of Munters Pty Limited Australia on February 7, 2012:
     Use a dehumidification unit to control humidity and dew point.

From Matt McDonald of Carboline on February 3, 2012:
Be careful with 2 coats. WBIOZ is meant to be applied to steel and does not adhere well to itself. Heat the steel, and that will drive the water out of the film.

From Josh Inklovich of Total Coating Solutions on February 8, 2012:
     Having worked in a large, industrial painting facility, I can tell you that when the humidity was too high, we broke out the fans and the heat, even in the summer. It seemed to do the trick.

From bryan buckley of corcon inc. on February 2, 2012:
     Apply 2 coats at half the required film thickness. Or maybe just turn the heat up in the shop!


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Tagged categories: Curing; Ease of topcoating; Humidity and moisture; Waterborne coatings; Zinc-rich (inorganic)


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