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Holly Coulter (Unregistered Guest)
Unregistered guest
Posted on Saturday, January 15, 2005 - 03:29 pm:   Edit PostDelete PostPrint Post

I have a painting system for my existing steel door frames that is for use with a surface preparation that allows "tightly bound rust". Does anyone have experience with this type of painting system (Sherwin Williams Recoatable Epoxy Primer + SW Macroepoxy 646 Fast Cure)? Will the "tightly bound rust" allow premature failure of the paint?
Richard L. Hird P.E. CCS
Senior Member
Username: dick_hird

Post Number: 18
Registered: 02-2004
Posted on Sunday, January 16, 2005 - 08:05 pm:   Edit PostDelete PostPrint Post

Tightly boded rust generally refers to mill scale, which can only be completely removed by near white sandblasting - SSPC SP 10. Commercial sand blasting SSPC SP6 removes most "mill scale" and that is what they are probably asking for. The differenc is just a percentage of the surface with mill scale, and you would need a microscope to see the difference.

I doubt that an existing frame could be sandblasted to either level from a practical point of view. On improperly prepared steel and normal environmental conditions, it will not provide any longer term service. You will eventually see a failure, It is just a matter of when.
Unless you have a corrosive environment, or you want a very high gloss finish, there would be no advantage to using an epoxy.
Robert C. Wagner
Member
Username: wagnerest

Post Number: 3
Registered: 01-2005
Posted on Wednesday, January 19, 2005 - 09:04 am:   Edit PostDelete PostPrint Post

If you are writing for remodel projects there could be minor rusting that has occurred on bare metal. SSPC SP2 hand tool cleaning is usually adequate in a non corrosive environment, followed by an alkyd iron oxide pigment primer (standard red metal primer), and standard alkyd or waterborne finish coats. In my experience this system will last as long as any other in a normal exposure environment. Iron oxide does a great job of stopping rust as long as it is tight to the metal and is not exposed to any other corrosion accelerating conditions, and alkyd resins do a good job of getting it into the microscopic pores in lightly rusted metal.

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