Does Cast Iron Deeply Absorb Protectant Over Time?

[Julie Moriarty]

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.

???

[Charles Coolidge]

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.

[Erik Loza]

In my experience, "yes".

Erik

[Bill Dufour]

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

[Edward Weber]

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.

[Jeff Bartley]

Isn’t there a slow oxidation that takes place over a long period of time similar to the patina of our time-honored hand planes? It’s been my experience that newer cast is definitely more susceptible to rust.

[Julie Moriarty]

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.

[Alan Lightstone]

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.

[John K Jordan]

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

[Erik Loza]

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

[johnny means]

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.

[Erik Loza]

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

[Joe Jensen]

I'll be a jerk, I live in AZ and have never had to worry about rust :)

[Jim Becker]

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.

[Bernie Kopfer]

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 I’m 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 I’ve purchased.

[Joe Wood]

When you use a ROS, what grit should you use and should the paper be for metal or will one for wood work?

[Rick Potter]

I don't have much trouble with rust, but sweat drops mark the cast iron quickly. When I notice a haze of discoloration on my tools I use a fine sanding sponge, then wax. Sponges are sturdy enough to stay flat, and easily clean up with soap and water.

Each time I enter the shop I see a round ring on my DJ20 Jointer from a soda can someone set there when it was new 30 years ago. No idea who did it, but I constantly use it as a 'what not to do' example to 'guests'.

I used to have a Delta 14" bandsaw (used) from the 70's which had a darkly colored table that looked like a seasoned frying pan. I don't know what was used on it, or if it was the way the cast iron was made, but it NEVER showed a sign of rust. Had it for 10 or more years, and don't remember ever waxing it. Paid $200 for it at a garage sale, sold it ten years later for double. Sold it because it only had 1/2 HP.

[Erik Loza]

When you use a ROS, what grit should you use and should the paper be for metal or will one for wood work?

I use a grey or red scotchbrite pad under the orbital head. Sandpaper would be for heavily rusted surfaces. I think if it was bad enough to need sandpaper, I would probably have a machine shop regrind the surface. Jut my opinion.

Erik

[Joe Wood]

yeah I don't have any rust. Do they make those scothbrite pads for ROSs?

[Erik Loza]

yeah I don't have any rust. Do they make those scothbrite pads for ROSs?

Maybe?... I have always just cut pieces to fit. Doesn't need to be attached to the backing plate for this type of work.

Erik

[Doug Dawson]

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.
I think this may be one reason why the CRC 3 36 product works so well for me. Immediately after removing the Cosmoline, I saturate the surface with the CRC product, which is very runny, and work it hard into the pores, and just let it sit there til the next day, when I wipe off the excess and apply several coats of paste wax. Never a problem with rust (unless I have to reapply due to some “mechanical” scrape etc.)

[Erik Loza]

I think this may be one reason why the CRC 3 36 product works so well for me. Immediately after removing the Cosmoline, I saturate the surface with the CRC product, which is very runny, and work it hard into the pores, and just let it sit there til the next day, when I wipe off the excess and apply several coats of paste wax. Never a problem with rust (unless I have to reapply due to some “mechanical” scrape etc.)

That makes sense. We had a tech who swore by Boeshield in the same way. I have never personally used it for this type of application but can't see any reason why not.

Erik

[Gabriel Marusic]

yeah I don't have any rust. Do they make those scothbrite pads for ROSs?

Definitely, I use this attached to my Rotex at low speed. Don't use the vacuum attachment though. In the past I've used Barkeepers friend as well to help clean it up.

[Frank Pratt]

I'll be a jerk, I live in AZ and have never had to worry about rust :)

Well Joe, we can be jerks together. I live in Alberta & keep wondering what this "rust" is that people keep complaining about. :)

[Richard Coers]

Back in the day, cast iron was left outside to "season". It was a method of stress relieving the casting with temperature cycles over a long period. The casting would be a huge pile of rust that just a light pass on a milling machine would remove. If the casting was porous, the rust would be 1/8" thick. There is usually a fair amount of graphite in the iron mixture for machine castings. This grey iron machines easily and adds some rust resistance.

[Jacob Mac]

When I got my J/P combo machine, I stripped off the cosmoline with mineral spirits, and I literally watched it rust in real time. It started creating black spots instantly. To be fair, I think I had a little citrus cleaner on my rag, so maybe that did it? To this day, despite all kinds of effort, that machine will rust if you look at it wrong.

I have a bandsaw from the same company, and that tabletop won't rust at all. I have it very close to the garage door, and it looks as good as the day I got it. Same shop, same rust prevention efforts, same everything. But the results are miles different.

[John K Jordan]

When I got my J/P combo machine, I stripped off the cosmoline with mineral spirits, and I literally watched it rust in real time. It started creating black spots instantly. To be fair, I think I had a little citrus cleaner on my rag, so maybe that did it? To this day, despite all kinds of effort, that machine will rust if you look at it wrong.

I have a bandsaw from the same company, and that tabletop won't rust at all. I have it very close to the garage door, and it looks as good as the day I got it. Same shop, same rust prevention efforts, same everything. But the results are miles different.

If you want your bandsaw to rust so it won't feel left out, just cut a chunk of green oak and let it sit flat on the cast iron table for a bit. Won't take long.

[Julie Moriarty]

and especially my Jet oscillating spindle sander (a rust magnet).

Another tool I forgot to mention. But rust hasn't been much of a problem with my Jet OSS, but it's kept in the house, in my inside workshop. Yet there are a lot of hand tools inside that have shown some rust since moving to FL.

[Alan Lightstone]

Another tool I forgot to mention. But rust hasn't been much of a problem with my Jet OSS, but it's kept in the house, in my inside workshop. Yet there are a lot of hand tools inside that have shown some rust since moving to FL.

Yup, that 110% humidity is torture on tools and machinery. Even in climate controlled shops. And garage shops are much tougher. And you're 150 miles south of me.

If you ever move that Jet OSS into your shop, just save time and paint it rust colored.:eek:

[Julie Moriarty]

That makes sense. We had a tech who swore by Boeshield in the same way. I have never personally used it for this type of application but can't see any reason why not.

Erik

When I purchased the A3-31 I also bought Felder's Supergleit and Metallglanz. The JP has only seen those two treatments and rust hasn't been much of an issue. Could Felder have formulated them specifically for their cast tops?

[Erik Loza]

...Could Felder have formulated them specifically for their cast tops?

I wouldn't say Felder formulated them specifically for their cast iron tops as much as "found a chemical that works really well for that". I'm certain we're just reselling some other manufacturer's chemicals. The Supergleit is really good stuff. Also, our edgebanders come with a bunch of these little things stuck inside the cabinets: https://www.zerust.com/products/vci-emitters-diffusers/zerust-activcapsule/

Erik

[Tom Bender]

Long ago I worked in a foundry. There was a lot of chemistry going on, with an on site lab checking and ordering adjustments in each melt due to the varied scrap that went into it. And there were different types of cast iron, (grey iron, nodular, and another I can't remember)

Clearly the flavor of cast iron makes a huge difference in the tendency to rust. Do the manufacturers of our equipment consider rust when selecting a type of iron? Maybe some do.

[Brian Holcombe]

I like a planed surface, or the surface SCM applies. High polished surface is terrible on anything except machines that do not require wood to slide over them.