Summary for powder coating over hdg Discussion
Powder coating over HDG metal is the focus of this thread, with a landscape architect asking why some finishers refuse warranties on duplex systems and what pretreatment and product choices improve adhesion and service life. The questioner notes that railing projects in coastal and high-altitude New England settings often specify hot dip galvanizing plus powder coating, and asks whether cleaning, profiling, or preheating can help release trapped gases. The excerpt shown does not include the technical answers themselves, but it does show that the issue is a common one for finishers and that some companies will proceed while others will not warranty the work. The practical takeaway from the discussion title and question is that warranty resistance is tied to the risks of coating over galvanized steel, so any successful duplex specification depends on the finisher’s own process controls, pretreatment, and willingness to stand behind the job.
Q. As a Landscape Architecture firm working in 5 New England states, we have frequently designed custom steel railing systems for high altitudes, ocean-side and waterfront settings. We typically specify Hot Dip Galvanizing and powder coating (often to match light posts and signage elsewhere on the project) In some cases we have had resistance from the powder coating companies hired to do the painting to offer warranties when finishing over HDG metal. Most project have budgets that support an extra cost in trade for long term durability, so it is difficult to understand the challenges they are expressing with powder coating on galvanized material.
Some finishing companies have proceeded with the work with out question, while others have opted out. We often conduct cleaning and profiling, of the HDG materials, and it has been suggested we pre-heat the parts prior to applying the powder coating to release trapped gasses.
Please advise on 1.Why some powdercoat finishers resist a duplex approach. 2. The best pre-treatment steps (process, materials and products )to insure good adhesion and a long product life that we can get powdercoaters to uniformly warranty.3.The best powdercoat product to apply on HDG surfaces.
Arek Galle
Landscape Architect – East Providence, Rhode Island, USA
May 25, 2010
 | A lot of people have trouble with Powdercoat over HDG. I hope the foregoing assists bill doherty Like many coating operations, the pretreatment is the most important stage. If a coater doesn’t have the required pretreatment for HDG then applying powder to it will surely disappoint. A competent pretreatment from HDG to finish will typically include: The question of preheating the material is far from clear. Some people claim that the so-called degassing stage will prevent gassing (or blowholes) in the powder, claiming that this gas comes from within the HDG coating somehow. There is little definitive science based research on this to prove or disprove it. If the material is preheated too hot then some pretreatments (zinc phosphate for example) can be detrimentally affected. The best coater to powdercoat on HDG is one specialising in that, not one doing a little HDG occasionally. Specialists can and do offer warranties on the coating up to Most reputable branded powders can be used on HDG. An additive (which slows the jelling action in the powder setting) can be used with powders to be used on HDG to good effect.
|
Great responses, gentlemen. Thanks!
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
June 1, 2010