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Thread: Does Cast Iron Deeply Absorb Protectant Over Time?

  1. #1
    Join Date
    Jul 2012
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    Punta Gorda, FL
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    Does Cast Iron Deeply Absorb Protectant Over Time?

    I'm trying to figure out why some cast iron tops in my shop are more resistant to rusting than others.

    When rust appeared on my old contractor's table saw I cleaned it up and applied protectant. One time I took a RO sander to it, with some rust preventative on the disc. It seemed that held pretty well. I did the same to the bandsaw. When I moved to Florida, rust was a bigger issue and the cast tops required more attention.

    Since purchasing the new cabinet saw, I've found the cast top on that requires considerably more attention than the other cast iron tops. So now I'm wondering if it's the metal they used to make the top or if the cast top will absorb protectant over time to the point it will only require attention as much as the other cast tops in the shop.

    ???
    ďTravel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  2. #2
    There are many types of cast iron which more likely is the cause of the variant you are seeing vs iron absorbing protectant. Even for a given type there are varying recipes and processes.

  3. #3
    In my experience, "yes".

    Erik
    Felder USA Territory Representative: Central & South Texas

  4. #4
    Join Date
    Sep 2016
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    Modesto, CA, USA
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    Yes but, cast iron is water proof so it can not absorb too deeply. But some engine blocks have to be sealed at the factory if they are too porous. Once the pores are full it will hold no more. I use paste wax. I thin it with paint thinner for the first few times so it can soak into the bottom of the pores.
    Bill D

  5. #5
    As others have said, yes.
    I usually explain it to people like a well seasoned cast iron skillet.
    Newer cast, depending on the recipe of alloys in it of course, may not act the same as old iron.

  6. #6
    Join Date
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    Isnít there a slow oxidation that takes place over a long period of time similar to the patina of our time-honored hand planes? Itís been my experience that newer cast is definitely more susceptible to rust.

  7. #7
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    Thank you for the replies. The analogies make sense.

    Taking a closer look yesterday, I noticed the cast iron router table extension, that was added over a month after the cabinet saw arrived, has not been as susceptible to rust. The surface looks different, too. And the additional detailing on the router table extension indicates there was more care taken in the design and production. So maybe they used a different "recipe" for the cast iron.

    I forgot to include the JP top in the initial post. The JP is a Hammer A3-31. From the get go, the cast iron on that machine has, from a rust standpoint, "performed" far better than the Harvey cabinet saw top, but not as well as the old Delta contractors saw, which was purchased in 1997 and made in the US.
    ďTravel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain

  8. #8
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    I'm also surprised at the different amounts of rust that develop on my SawStop table saw, Felder bandsaw and jointer, MLCS router table top, and especially my Jet oscillating spindle sander (a rust magnet).

    All basically get treated the same with protectants (I tend to spray them all on the same days), yet seem very different in susceptibility to rust.
    - When God closes a door, he opens a window. Our heating bill is outrageous & six raccoons got in last night. Please God, this has to stop!
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  9. #9
    Join Date
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    Some cast iron is apparently more porous than others.

    From the manual for the cast iron Robland sliding table on my PM66:
    "The table surface must be kept clean and free of rust. White
    talcum powder applied with a blackboard eraser rubbed in vigorously
    once a week will fill casting pores and form a moisture barrier."


    I've used this method on several cast iron pieces with good success. Note that the talcum powder must be real talc, not the baby powder stuff which may have cornstarch and other things. I found talc marketed for billiards use: https://www.amazon.com/gp/product/B005U4A9KW There's enough in the 13 oz container to last for 100 years.

    JKJ

  10. #10
    This has been my experience:

    -Very important to get that first coat of paste wax onto the tables as soon as possible after delivery. As in, "within an hour or two of stripping the cosmoline or packing grease". I've watched freshly stripped cast iron tables haze over with light oxidation within an hour, just from humidity in the air. Or your palm print, which sometimes becomes permanent.
    -Very important to to keep re-applying more wax after every use for the first few months. Basically, make sure the pores get and stay filled with wax. At some point, the cast iron tables just become so permeated with wax that they have this almost non-stick feel. Not unlike a seasoned cast iron skillet.
    -For whatever reason, many of the the mass-produced East Asian machines seem to favor a shiny finish to their table tops, which is like its own rust generator. Perhaps they are so shiny that wax or other protectants simply have nothing to adhere to? If I had one of those machines, I would probably get after the table tops with an R/O sander and scotchbrite pad. Give it a little bit of a matte finish for the wax to cling to.
    -Lastly, like they say, rust never sleeps. Some level is inevitable. Just do your best to keep it of the work surfaces and guideways.

    Erik
    Felder USA Territory Representative: Central & South Texas

  11. #11
    Not really. Where would it be absorbing to? A well seasoned skillet is just a dirty pan, there's nothing below the surface. The porosity of cast iron simply creates a way for coatings to create a mechanical bond, like glue on a hairy forearm. The coatings are not seeping in like oil on wood or butter on toast. That's why they don't last forever, because they eventually just get wiped off during regular use.

  12. #12
    Johnny, I think we're saying the same thing. That is my point: The shinier table tops simply don't have enough open pore structure to hold wax. You run wood over it once and all the wax gets scraped right back off. If you look at the tops on most European machinery, they have a fly-milled or Blanchard-grind type finish, with a noticeable "grain" that traps wax. With a table top like that, even if you scrape the wax off the surface, there (hopefully) still enough of it to prevent oxidation.

    Erik
    Felder USA Territory Representative: Central & South Texas

  13. #13
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    I'll be a jerk, I live in AZ and have never had to worry about rust

  14. #14
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    I don't live in AZ and still haven't had an issue with rust on my tools that have cast iron surfaces for some reason and I'm thankful for that! None of my current crop of tools have "shiny" tops. They are either "swirly ground" or are just smooth without polish. All of them have been hit with the ROS a few times over two decades and either waxed or had something else applied.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
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    Quote Originally Posted by Joe Jensen View Post
    I'll be a jerk, I live in AZ and have never had to worry about rust
    Here in North Central Washington rust is pretty much of a non issue. Once or twice a year a cleaning an protective spray is sufficient. The protection is for corrosion not rust. Chemical and sweaty palms are the culprits. When I read about how some of you fight with rust all the time my heart goes out to you,it makes me grateful that that Iím able to reside here.
    In the last year I got a new large bandsaw and notice the the table seems more susceptible to corrosion then other items Iíve purchased.

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