I've been thickening my surfboard epoxy with milled glass fibers, and wood flour, and the last time as I did not have enough wood flour on hand, sawdust.
For absolute maximum adhesion to steel, usually I have had rusty steel which I treat several times with Ospho. The rust turns black and hard and the paint primer over the rust bubbles and then comes off, but the good paint does not. I usually scrape off all the paint the Ospho lifted, then the bigger rust patches, now black, can be chiseled off revealing more rust below. One can keep applying ospho, wait for it to turn black, then chisel it off, all the way down to bare pitted steel if they really want to. Awesome product. Ace hardware has it for half price of any online purveyor.
The Ospho etches the metal. Scrubbing bare steel or rusted steel with a scrubbie pad and ospho, and good gloves, is almost cathartic.
If left on overnight there is usually a bunch of white flakey leftovers, which come off with acetone and a rag. Touch that acetone wiped Ospho etched steel, and one can feel just how well paint/ epoxy/primer, whatever, will stick to that surface.
Depending on the steel, it is not always easy to gouge some mechanical tooth into it.
The diamond coated cut off wheels on a dremel, can really rough up the surface nicely if one chooses the right rpm and moves the tool over the surface at a good steady rate.
Sometimes i will use a new sharp razor blade, and more than one new one as the edges dull, and gouge an X pattern into the steel, holding the razor at 60 degrees one way and then the other way to, then do the other portion of the X as well.
Sandpaper might work well too, otr it might not. It should be 60 grit or rougher, and once the small section of sandpaper dulls, say the portion under a fingertip, or equally sized tool, then move the tool face to a new section of sandpaper press as hard as one can, and pull sandpaper and tool across the area needing roughing. Moce tool to a new section of sandpaper, and repeat.
If one imagines the stress on the joint, then one can tailor the gouges in order to have the maximum possible grip in the orientation needed.
Here is a good chapter of System3's 'The Epoxy Book" which is very applicable to this topic:
https://www.systemthree.com/blogs/epoxy-...with-epoxy
Somewhere in one of the other chapters of the epoxy book,
https://www.systemthree.com/blogs/epoxy-...gLZgfD_BwE
....they say a lot of acetone is reclaimed with impurities which can affect adhesion. I've not had this issue, with acetone, but have with denatured alcohol and Isopropyl alcohol. If one wipes a section of the wiped portion, with distilled water, and has a good lighting, one can see if the water is repelled in places, as if there is oil still on the surface. Not so easy to see when one has gouged the steel deeply for maximum mechanical tooth, but it behooves one to actually completely degrease the surface previous to gouging that mechanical tooth, as if there are contaminants they can simply get pushed deep into the grooves where wiping will do nothing in their removal.
JB weld is awesome stuff. I think it should be in every emergency kit with baling wire and Gaffer's tape.
The bottom tank of my aluminum radiator was weeping where the tubes meet the tank. I could not really clean it as well as hoped for, but did what i could with what i had, thinned the JB weld with 91% isopropyl alcohol ( should really use Xylene for this) and sucked it up in a syringe and injected it at the bases of the weeping tubes.
5200 miles later, 2 cross country journeys, I've not lost a drop of coolant.
Yeeee diddly ding dang haw!
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