The Voice of the Finishing Industry since 1936

  • PF Youtube
  • PF Facebook
  • PF Twitter
  • PF LinkedIn
12/1/2000 | 1 MINUTE READ

Prepaint Treatments

Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon

Question: We are currently plating zinc and yellow chromate for a customer.


Facebook Share Icon LinkedIn Share Icon Twitter Share Icon Share by EMail icon Print Icon


We are currently plating zinc and yellow chromate for a customer. Our customer, because of shop soils and fingerprints, precleans all the zinc/yellow chromated parts we have plated prior to painting. Their cleaning process includes:

  1. Spray cleaner station (152F, pH 10.6)
  2. Spray rinse station
  3. Spray iron phosphate station (132F, pH 4.9)
  4. Spray rinse station
  5. Spray sealant station

The customer is seeing slough-off of the yellow chromate after the spray cleaner stage but only in sporadic spots. We have tested the surface and no chromate remains. If the parts are baked at 250F prior to cleaning, they are fine. This tells me that the chromate film is not fully cured. We have addressed that by setting a 48 hr cure before shipping and made new chromates, but the spotting keeps returning. I would like to get your opinion on the customer’s pretreatment process on our plating. From all my inquiries, this is not a normal process to be done, and I’ve never heard of it being done. All our customers that paint parts that have been zinc plated and yellow chromated, paint without cleaning. Seems to me that our customer set up this line to pretreat steel prior to painting and that it was convenient to run zinc plated parts through there also. I would appreciate any help you can give us. Thank you. K.H.


I agree with your assessment of the situation—he finds it convenient to run the parts through his phosphate pretreatment in an attempt to remove shop and finger oils. Although it may be well intentioned, it is causing more harm than good. I would never process pretreated parts through another pretreatment because of the effect of the process chemicals on the pretreatment. It’s no wonder that you and your other customers have never heard of it being done.

I have no problem with cleaning parts that have been handled before painting. Your customer is also aware that he must remove oily soils before he paints. However, this could be done by degreasing using solvents, detergent solutions and even the alkaline cleaning and first rinse stage of his pretreatment system.


  • 2020 Vision: The Future of Coatings

    The year 2020 will be here before you know it, signaling the beginning of a new decade and bringing changes to the world as we know it.

  • Masking for Surface Finishing

    Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.

  • Zinc Phosphate: Questions and Answers

    Specific questions about zinc phosphate and pretreatment are answered in one article...


Thanks for considering a subscription to Products Finishing. We’re sorry to see you go, but if you change your mind, we’d still love to have you as a reader. Just click here.