×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Chalking of steelwork

thread332-419646

Chalking of steelwork

Chalking of steelwork

(OP)
Hi All,

I have been contacted for technical advice on a coastal/beach development in Dubai (UAE, Middle East). The existing top coating of the external steelwork has been affected by the "chalking" phenomenon (see attached pictures).
The paint system has been specified by the Client as follows:
- Preparation, Grit bast clean to BS 7079,
- Primer. Zinc-rich Epoxy primer (60 microns DFT min)
- Build and finish coats. High build epoxy micaceous iron oxide (MIO) (min 200mirons DFT)
- Finish coat: Acrylic Polyurethane (60 microns DFT)

Do you have any experience with "chalking"? Causes and mitigation measures? Do you believe the specified paint specs mentioned above are suitable to an aggressive beach environment exposed to direct sunlight? if not, why?

Thanks

Regards

Simone

RE: Chalking of steelwork

Photos not attached.

RE: Chalking of steelwork

Chalking is almost always caused by degradation of the resin component of paint due to UV exposure. It could also be caused by poor application which resulted in the paint film not coalescing properly. An example would be applying a water based paint at a time of high humidity. Epoxy paint is typically poor in UV resistance, but urethane top coats with UV absorbers should be good.

RE: Chalking of steelwork

The specified system is a typical selection for a medium to high durability in a corrosive marine environment, Category C5-M. Refer to ISO 12944-5. The polyurethane should be aliphatic polyisocyanate cured for good resistance to chalking. When the paint manufacturers make a proposal get them to support their offers with test data including chalking resistance.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Chalking of steelwork

Hi Simone,

Steve is correct. I would recommend an acrylic aliphatic polyisocyante. Acrylics have excellent UV & Gloss retention. 2 urethanes our facility uses is Rustoleum 9800 & Gulf Coast Paint CT-398. Both products have over 3500 hours in the QUV which shows the weathering effect on coatings.

Thanks,

Andy

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login

Resources

White Paper - PLM and ERP: Their Respective Roles in Modern Manufacturing
Leading manufacturers are aligning their people, processes, and tools from initial product ideation through to field service. They do so by providing access to product and enterprise data in the context of each person’s domain expertise. However, it can be complicated and costly to unite engineering with the factory and supply chain. Download Now
Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close