Is painting over flash rust ok?
Is painting over flash rust ok?
(OP)
On our ship we use a company that uses hydroblast (UHP) Ultra Hight Pressure guns.
The result if fantastic, very fast and effective. However after just a few hours or less, the metal clean surface goes light brown, I believe it is called "flash rust" and the company says it is perfectly fine to paint over it. This goes against everything I ever learned about corrosion protection and painting.
Is he correct, or will I see the paint peel off in six months time?
The result if fantastic, very fast and effective. However after just a few hours or less, the metal clean surface goes light brown, I believe it is called "flash rust" and the company says it is perfectly fine to paint over it. This goes against everything I ever learned about corrosion protection and painting.
Is he correct, or will I see the paint peel off in six months time?





RE: Is painting over flash rust ok?
There are products that can be sprayed on the clean surface that will prevent the rust and can be painted over.
RE: Is painting over flash rust ok?
However, in many cases, the flash rust is not acceptable and that must be clearly stated in your specification, so the cleaning contractor will co-ordinate his work with the painter, who will apply the primer coat within the time specified by the cleaning contractor.
If you don't have that detailed specification, you must make sure the primer is a rust inhibitive type and that it will be applied rather sooner than later after the blast cleaning.
Cheers,
gr2vessels
RE: Is painting over flash rust ok?
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04
RE: Is painting over flash rust ok?
RE: Is painting over flash rust ok?
I will check our paint specs. We use Hemple marine paints:
I will attach the maunals for you to see.
About the rust inhibitor, please tell me more, we use Reverse Osmosis water onboard and that is very aggresive which doesnt help.
RE: Is painting over flash rust ok?
RE: Is painting over flash rust ok?
RE: Is painting over flash rust ok?
http://www.deforest.net/corrosion.html
We use one of their products (DePhos 8028) in an immersion tank for leak testing, but we are looking for corrosion inhibition of multiple metal types (copper-based, zinc, steel).
You might try using a rinse that has been treated with enough trisodium phosphate (TSP) to raise pH above 9 or so. We did this when washing some steel parts that needed to be degreased prior to painting, adding a TSP rinse helped to prevent (or at least drastically reduce) flash rust as the parts dried. The solution could be considered hazardous, but if you are spraying high pressure water, you should already be collecting the waste stream, and wearing protective gear. TSP may leave a residue, but we find it wipes off easily with a dry rag prior to painting.
There are also more involved phosphating treatments for steel which provide better, longer-term corrosion protection, better paint adhesion, etc. etc. yadayada. You can google for those also.
RE: Is painting over flash rust ok?
http://www.holdtight.com/index.html
RE: Is painting over flash rust ok?
RE: Is painting over flash rust ok?
RE: Is painting over flash rust ok?
Hg
Eng-Tips policies: FAQ731-376: Eng-Tips.com Forum Policies
RE: Is painting over flash rust ok?
I'm certainly not advocating applying these primers over rusted surfaces, but the epoxy part of the zinc filled epoxy primer does provide a degree of barrier protection, while the IOZ does not. In situations where poor surface preparation is inevitable, a barrier type primer (e.g. Carbomastic 15) should be used.