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I have this 4" jointer that is over 30 years old and has seen little to no usage for the last 15 years. The bed of the jointer had developed a small amount of surface rust. I was able to clean up the rust using steel wool and a lot of elbow exercise.

I want to know what is the recommended surface treatment for the raw cast iron surfaces so as to prevent the return of the rust in the future. I do understand that repeated treatments may be necessary.

Obviously some type of oil is not a good idea because it can get onto wood being fed through the jointer and cause staining of the wood work piece.

Michael Karas
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    I use spray on furniture wax – Ashlar Feb 03 '18 at 02:39
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    Tool waxes exist -- I think the trick is to make the wax layer very thin; Bostick makes an aerosol named Top-cote, which I've used in the past. – Aloysius Defenestrate Feb 03 '18 at 04:46
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    All cast-iron beds can be considered equivalent so there are relevant previous Q&As here, most of them related to table saws. Here's one, https://woodworking.stackexchange.com/questions/1476/table-saw-top-treatment and another, https://woodworking.stackexchange.com/questions/4647/recovering-from-a-rusted-table-saw-top-and-protecting-it-in-future – Graphus Feb 03 '18 at 11:48

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Johnson's Paste Wax works just fine, no need to go further than your cleaning closet or supermarket to look for something fancier.

You'll get a lot faster and better penetration (and therefore retention) if you heat the cast iron gently first. Not hot enough to burn yourself, just hot enough you don't want to keep your hand on there indefinitely (although any heat is better than none). You might leave it in direct sunlight on a warm day, set it on top of or close to a wood stove, remove the tables and stick them in your oven on warm, direct a heat blower on them for awhile, or whatever you can come up with.

Once warm, the paste wax will melt immediately on contact. Keep the surface moist with melted wax, but not so much it drips down the sides (just makes more clean-up work). Once it's sucked up all it will, let it cool completely and wipe off the excess.

You might be surprised to see how much wax it will take. What seems like a solid surface behaves more like a certain type of sponge in this case. Part of this is that paste wax is a mix of wax and mineral spirits (paint thinner to soften wax for application). The mineral spirits is what gives paste wax its characteristic smell. The evaporation of that component is what constitutes the "drying". One consequence of this is that not everything you put on stays on.

If the surface still seems dry and scratchy to the touch after you're finished, you may be able to improve it with a second application. Reports vary on that count.

scanny
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  • I had to go to the hardware store to get paste wax (none such at the supermarket). It worked very well on all exposed metal parts of my small jointer!! Next project now is to reclaim a 6" jointer that I found on Craigs List for cheap. It has more rust. – Michael Karas Feb 04 '18 at 22:23
  • How do you get "penetration" into cast iron? It's not usually porous. – Martin Bonner supports Monica Feb 05 '18 at 10:44
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    @MartinBonner It's an interesting question Martin. It's definitely not casting porosity, that's a much larger feature which as you say, is not usually present on a good quality casting. My best understanding is that cast iron (and other metals) are polycrystalline, meaning they are a bunch of individual crystals smushed together, rather than a single crystal lattice. There is space between the crystals and oil wicks in there. This is why used cast iron needs to be "baked" before welding. So metals aren't quite as "solid" as we might think, cast iron closer to the extreme of the spectrum :) – scanny Feb 05 '18 at 18:17