Penetrol Finish

I would like to start with a lesson I learned this week on what I believe to be the most basic and easy-to-apply steel finish, which is Penetrol.  Penetrol was originally made as an additive, or “conditioner” for oil based paints, I am sure of the industrial kind, but I think of it like a lindseed oil or fine arts painters medium that makes the paint more fluid and easier to work with.  Somewhere along the way it was discovered that the Penetrol by itself made an excellent finish or sealant for steel, and a miracle rust stopper.  The Penetrol is applied only as one coat and actually is absorbed into the pores of the steel, which makes it a permanent sealant that should not need reapplication.

The times that we use Penetrol in our shop is when we want to have a clear finish, usually over Hot Rolled Steel.  Penetrol is especially cool over industrial steel parts like flat bar, heavy gauge plate, tube or channel steel, where the millscale is raised and rust is starting to show.  The result is a subtle satin sheen over raw, honest steel.

Where Penetrol is not ideal is if you have shiny spots or grinding, scratches, seams, or any other parts in the steel you want to hide.  These could be pretreated with a patina to blacken, but really, if you are trying to cover up things, this finish is not for you.  I am also not sure how this works in exterior applications.  I am going to google that or ask one of my experts….


3 thoughts on “Penetrol Finish

  1. One aspect of the Penetrol finish that some folks react adversely to is that it is somewhat shiny in appearance– but depending on your application this look might be just this ticket! It’s always a good rule of thumb to ask your fabricator for a final finish sample on steel matching your pieces specifications (hot rolled, cold rolled, HRPO, sandblasted, DA’d, what have you).

    Posted by steelforgirls | 06/23/2011, 11:32 am
  2. Thank you for the great website and sharing your knowledge.

    I’m currently designing a bar and have specified a mild steel counter with a black oxide finish – I have currenlty recommended this is to be achieved with a cold patination fluid, fixed with jade oil before and then sealed with a clear gloss lacquer (to allow the counter to be wiped down and take a bit of wear and tear).

    It sounds as though a Penetrol Finish, instead of a clear gloss lacquer could be a much better final coat. What do you think?

    I’m also entrigued by blackening stainless steel, would this work with the Penetrol Finish as well, as this would allay any fears I have of the coatings being worn off over time and the mild steel beginning to rust.

    Posted by Paul Twynam | 10/17/2012, 7:07 am
    • Hi Paul,

      We checked in with one of our local steel experts — Steve from Twelfth Avenue Iron here in Seattle, WA — and this is what he had to say about finishing blackened stainless steel:

      “For exterior applications like railings, we usually don’t coat blackened stainless steel with anything. For exterior furniture, we might use a thin application of carnauba wax, as a final cleaning process, and to give the piece that nice luster upon delivery. But the wax will break down & disappear pretty quickly outside, and the piece will be just fine.

      We haven’t done a lot of interior blackened stainless work, but we would probably wax it so the client doesn’t get any stinky residual chemical on their fingers. But again, the metal shouldn’t need touching up of the wax over time. In fact, it usually looks better without a coating, showing fewer fingerprints, etc.”

      So there you have it! No topcoat required on blackened stainless steel, or just wax for good measure.

      Thanks for checking out the blog!

      Posted by steelforgirls | 10/22/2012, 2:12 pm

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