Cast Iron Discoloration After Using Boeshield Rust Free


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I just applied Rust Free to my cast iron tops. Following the instructions on the bottle, I applied it directly and let it sit for a few minutes before removing. After letting the product rest, a black "sludge" appeared on the table surface. The tables had been previously waxed, so I assume that I should have removed the wax before applying the product (even though this is not mentioned in the instructions). For those that use Rust Free, do you typically remove previous coatings like wax and t9 before applying?

After scrubbing the sludge off with a scotch brite pad, there was discoloration and rings that remained on the cast iron (pictures below). Has this happened to anyone before, and if so, is there a way to remove it?

I had to go out of town and my garage is miserably humid right now, so I applied T9 to the tables before leaving; the pictures were taken after the t9 application.

 

20220802_051608.jpg

20220802_051520.jpg

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Online it looks like the directions warn about this. As you mentioned, it doesn’t say anything about removing surface coatings, but it appears that it is more designed for rough milled cast iron. The thing that concerns me is that it says not to use it on polished cast iron surfaces (I added the bold and underline below). Some reviews also complain about staining/spotting on tool tables. I like the T-9 but I don’t think I’d use the Rust Free unless it started in really bad shape. They may have some guidance on how to reduce the staining, but it might not all go away.

Copy/paste from the Boeshield website below-

For light rust on steel or cast iron, spray RustFree™ on a rag and wipe surface. Do not spray directly on surface, as it may cause spotting.

CAUTION! RustFree™ is acidic and should be used with care.

    • Test on hidden area before use.
    • Can cause spotting on cast iron and steel.
    • Rinse off painted surfaces thoroughly and neutralize with soap and water.
    • Do not use on guns or black oxide tools.
    • Can dull paint and plastics.
    • Not for spot cleaning of table tops.
    • Do not use on polished cast iron surfaces.
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On 8/3/2022 at 8:54 AM, Mark J said:

That's because the directions shouldn't be different.

+1

I haven’t seen the product in person but it’s unfortunate and irresponsible if it doesn’t give any similar warnings. 
 

The sliver of good news is that it should not affect the performance of the table. 

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The Rust Free  have is years old so maybe the labels were different.  The insert that came with it says to apply to a rag and then wipe the area to be treated.  The version I have of Rust Free is quite corrosive.  Gloves are a must and a respirator is a good idea.  Spraying directly on cast iron does just what you show.  It does work miracles on deep shadows.  A great product but one that must be used with care.  I have gotten overspray on some surfaces and had the discoloration you show.  It either fades over the years or I've just stopped noticing :(

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I copied the response from Boeshield below. They should really clarify the language on the application time to indicate that it should be left on for no more than 60 seconds.

Will sanding with a scotch brite pad damage an ROS? I just upgraded to the festool ets and have no interest in screwing it up.

Kudos to them for the quick response at least. 

 

Regarding geedubs comment, I don't have the can in front of me, but there was definitely language on there saying that you could spray the product directly onto tough stains?

 

 

Sorry to hear about the issues of staining.

 

I can suggest that you clean the surface with simple green or any degreaser. Then spray your cast iron surface with Boeshield T-9 and use a Scotch-Brite pad on a random orbit sander to remove the rings and discoloration. You can also try it by hand before using the orbit sander. Make sure to go across the entire table with the Scotch-Brite pad and try not to focus on just the spots with rings.

 

Please note the instruction on Rust Free Bottle say, allow to Penetrate for 30 to 60 seconds. If you let it sit for a few minutes it will cause rings like you are describing.

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On 8/3/2022 at 12:18 PM, TomInNC said:

Will sanding with a scotch brite pad damage an ROS? I just upgraded to the festool ets and have no interest in screwing it up.

I don't think so. I've sanded my bandsaw cast iron table many times using my Dewalt ROS and DW40, it was messy but without any noticeable damage to the sander.

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4 hours ago, TomInNC said:

Will sanding with a scotch brite pad damage an ROS? I just upgraded to the festool ets and have no interest in screwing it up.

Festool has their own "scotchbrite" pads called Villes i think? They are expensive but are essentially the same thing. If your worried about the dust I wouldn't festool targets the automotive industry. If your worried about the hook and loop just put some sandpaper on the sander and set that on top of the scotch brite. Or use an interface pad.

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On 8/3/2022 at 4:06 PM, Chestnut said:

Festool has their own "scotchbrite" pads called Villes i think? They are expensive but are essentially the same thing. If your worried about the dust I wouldn't festool targets the automotive industry. If your worried about the hook and loop just put some sandpaper on the sander and set that on top of the scotch brite. Or use an interface pad.

Thanks. I forgot about all of their Vlies stuff. I will take a look. I was going to just use an angle grinder, but the guy from Boeshield recommended against it because of the possibility of putting too much pressure on certain parts of the table. 

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Although I slightly envy those with showroom cast iron finishes, I found long ago that in humid areas like ours, rust free surfaces are the best I can ask for, regardless of the hue. 

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On 8/3/2022 at 4:06 PM, Chestnut said:

Festool has their own "scotchbrite" pads called Villes i think? They are expensive but are essentially the same thing. If your worried about the dust I wouldn't festool targets the automotive industry. If your worried about the hook and loop just put some sandpaper on the sander and set that on top of the scotch brite. Or use an interface pad.

So when I reached out to Festool, they said to use the Scotch Brite pad with the 50 dollar sanding pad (which I don't own). Isn't the only point of the buffing pad to prevent liquid coming back into the sander when polishing with some kind of compound? I don't really feel like dropping 50 bucks on a sanding pad I don't need at this point. 

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I was thinking this guy.https://www.festoolusa.com/accessory/492271---ip-stf-d1208-j It's a super soft pad that can be used to sand contours.

If you remove the DC hose from the sander it doesn't have much or any suction of it's own. At least mine doesn't. I've used mt ETS to sand out finishes with a layer of mineral oil and mineral spirits on the surface for lubrication.

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On 8/5/2022 at 9:02 AM, Chestnut said:

I was thinking this guy.https://www.festoolusa.com/accessory/492271---ip-stf-d1208-j It's a super soft pad that can be used to sand contours.

If you remove the DC hose from the sander it doesn't have much or any suction of it's own. At least mine doesn't. I've used mt ETS to sand out finishes with a layer of mineral oil and mineral spirits on the surface for lubrication.

Thanks. Did you attach this to a standard soft or hard pad, or were you using a buffing pad?

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I was using the 1000 grit sand paper can't remember what it's called. For your application it's just an inexpensive way to protect your hook and loop. They are also good to have if you need to sand anything that isn't flat. Mine gets pulled out from time to time.

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