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Thread: Cast Iron Repair - Best Epoxy?

  1. #1

    Cast Iron Repair - Best Epoxy?

    I have to repair a piece of cast iron that has a very clean break. This is the base of my jointer fence, so it doesn't get much stress in-use. So, since I want to make the repair as "invisible" as possible, I don't want to weld / braze.

    Any ideas on which epoxy would be best? There are several factors involved:

    1: Obviously, the ability to bond cast iron well. - not just tensile strength. In fact, tensile strength is probably the least important factor in this case.

    2: The ability to bond when the pieces are clamped tightly. Most epoxies work best with LESS clamping pressure than typically used with wood glues, but I want this break to disappear as much as possible, so....

    3: A cured color that comes as close to cast iron as possible. Something "too light" can always be darkened, but not vice-versa.

    ---------------

    JB Weld is always a consideration, but I fear it might be too thick.

    Standard 30-minute epoxies are incredibly strong, and thin, but I can't find any data on them, re cast iron.

    System Three recommends their "Met Weld." The cured color looks pretty close, and the stuff is STRONG, (!) but again I fear it might be too thick.

    Permatex 84109 also looks promising.
    -------------------------------------------

    Your thoughts / recommendations?

    thx.
    Last edited by Allan Speers; 01-02-2020 at 3:13 PM.

  2. #2
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    I would use JB Weld (not Quick) and if it's too thin add a drop of two of acetone.

  3. #3
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    JB weld was my first thought as well.

  4. #4
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    If you've got it, I'd use West Gflex. It's real tough stuff. If not, I'd use whatever's on hand. The key is getting it wet out well at the epoxy-to-metal interface. Haven't used JB Weld, but if it's too thick, you might want to put a tack coat of some other kind of epoxy on the metal before using JB Weld (or adding a filler to whatever you're using), and be sure to add the second layer (i.e. with filler or JB Weld) before the tack coat fully hardens (should still be able to dig your fingernail into it). That way, the two epoxies will chemically bond and you won't need to deblush. If you have it, West 404 would be my choice of filler, but lacking that, just about any real fine powder should work, and you don't need much...just enough to thicken it enough to keep it from dripping out before it hardens. I wouldn't worry too much about color, since I suspect the "glue line" will be so thin that it will disappear. If you're left with a glue line that you can see, you probably used too much filler, resulting in a glue line that's too thick. It shouldn't be more than a few mils, if I'm visualizing what you're doing right...
    Last edited by Jacob Reverb; 01-02-2020 at 2:36 PM.

  5. #5
    +1 for JB Weld. I've used it to repair engine parts numerous times. Be aware: Like any coating, the long-term success depends on surface prep. The rougher, the better, and zero traces of grease or oil. Good luck with it.

    Erik
    Felder USA Territory Representative: Central & South Texas

  6. #6
    Quote Originally Posted by Jacob Reverb View Post
    If you've got it, I'd use West Gflex. It's real tough stuff. If not, I'd use whatever's on hand. The key is getting it wet out well at the epoxy-to-metal interface. Haven't used JB Weld, but if it's too thick, you might want to put a tack coat of some other kind of epoxy on the metal before using JB Weld (or adding a filler to whatever you're using), and be sure to add the second layer (i.e. with filler or JB Weld) before the tack coat fully hardens ...
    Thanks, Jacob, but I'm not sure what "wet out" means.

    Also, wouldn't this procedure make the epoxy layer itself too thick? Again, I want the crack to come back together as tightly as possible. My assumption (based on nothing, really) was that a thin layer / thin viscosity would be better, and that this could work because the cast iron is so porous, that it would hold enough epoxy in its pores to have a good bond.

    But that's just an assumption, which is why I'm asking you guys.

    And again, I worry the same way about JB Weld, which was designed specifically for filling in cracks and gaps, not specifically for strength or cleanliness of the repair. My thought is, why use an epoxy that contains fillers, when the break is clean?

    Have you guys done this sort of thing, specifically on cast iron, and achieve a very tight repair?
    Is Dave's idea to add a little acetone the answer? (Sure that will thin the epoxy, I fear that might also weaken the bond. Why not just use regular epoxy?)
    Last edited by Allan Speers; 01-02-2020 at 5:16 PM.

  7. #7
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    Depending on where the break is, perhaps you could strengthen the joint with machine screws, perhaps countersunk. I've drilled and tapped cast iron several times. Perhaps epoxy plus screws?

    And is the area of the break painted? If so, repainting could make a joint invisible.

    JKJ

  8. #8
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    Regular epoxy would probably work just fine, possibly with just a tiny amount of very fine filler. With the tiny clearance between the broken pieces of cast iron, it's really a balancing act between "just enough" epoxy remaining in the joint, and not enough. With unthickened epoxy, my concern would be a "glue-starved joint." In other words, I would add a tiny bit of filler (to get it somewhere between the consistency of molasses and ketchup) to prevent too much of the epoxy from squeezing out of the joint. But you can add too much filler, too. With something like JB Weld (which, again, I have not used – but isn't it about the consistency of peanut butter?) my concern would be that it would have too much filler, and thus create too thick of a glue line, as well as possibly not "wet out" the bonding surfaces enough. By "wet out," I mean you want to really work the unthickened epoxy into all the pores and voids with a brush, the same way you would jam the bristles of a paint brush to get paint "wetted out" into rough wood, or voids in the wood – or the same way you "wet out" fiberglass cloth with polyester resin or epoxy, by pushing the resin down into all the voids in the fabric with a squeegee or paintbrush. When you do this with fiberglass cloth, the cloth changes from opaque to transparent, indicating that the fabric is fully "wetted out." You can also suck out the air by vacuum bagging.

    Probably if you got some regular vanilla unthickened epoxy (like the Loctite epoxy sold in Walmart for example), mixed it up, maybe added 10% acetone by volume, then really worked it into both pieces of cast iron with an acid brush or something like that, then waited a few minutes for it to tack up a bit, then put some unthinned epoxy on top, and clamped it, you'd be in good shape.

    Good luck, and let us know how it works out. If you're still apprehensive, shoot some pics of the pieces you want to glue -- it might help us advise you.

    ETA: I would also echo Erik's comment about surface prep. You really want to degrease the living daylights out of it. I would use brake cleaner.
    Last edited by Jacob Reverb; 01-02-2020 at 6:03 PM.

  9. #9
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    Is silver solder an option?

    Regards from Berlin

    Derek

  10. #10
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    I've never had one of these 3M DP epoxies fail under any use I've put them to. They aren't exactly cheap, and you need mixing nozzles, and a special gun to operate them at their best. I've also used a number of the different JB Weld epoxies for a variety of things, and never had one of those repairs fail either. My first choice would be one of the 3M's.

    https://www.3m.com/3M/en_US/company-...94857497&rt=r3

    It's thin enough that the parts should go closely back together. I can loan you a gun, and send a nozzle, if you want to go this way.

    I also recently threaded some holes in cast iron, up to 1", so can offer some advice from experience, if you go that route.

    edited to add: I use the black version of this acrylic adhesive to glue golf club heads on with. It may even be stronger than the epoxies, but I don't remember comparing the specs. This price is Way off though, for some odd reason. I think the single unit price must be for a case.

    https://www.ellsworth.com/products/b...pak-cartridge/

    You can get any of them through Amazon, but of course, you have to pay a higher price to cover the "free" shipping. https://www.amazon.com/s?k=3m+dp810&...l_4yvlwbyfne_e
    Last edited by Tom M King; 01-02-2020 at 6:10 PM.

  11. #11
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    I would use and epoxy without any filler in it. When cast iron breaks, there is usually little or no deformation of the metal adjacent to the break. So you want an adhesive the will allow the metal to fit as closely as possible at the break. Use a slow cure and warm up the metal before applying the epoxy.

  12. #12
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    Belzona Molecular Metal.
    JB Weld is a great product, but there is no comparison between the two.

  13. #13
    Man, this got more complicated than I expected! lol... Too many choices!

    I greatly appreciate all the thoughtful responses, guys.


    Still no idea how I'll proceed, though I'm better armed to decide now.

    Silver soldering is an interesting idea, but I think it might be hard to make sure enough material gets in, without it flowing to the surface of the crack. That could be dealt with, aesthetically, but since I don't need a lot of strength here, I figure it's not worth the trouble. (Maybe with a hand plane, or an adjustment wheel, etc, it would be worth trying.)

    The whole "wetting" thing seems to be the most important factor, now that I understand it, esp since cast iron is so porous. there's not a lot of "immediate surface area" to make a good bond. But too much epoxy and those some pores would inhibit squeeze-out. So I really like Jacobs idea for applyin the stuff- Wetting / filling both sides first, then maybe wiping down the surfaces, then brushing on a final thin coat once the first application is semi-cured.

    So the application is set, I just still have to decide on the product.

    I'm ruling out that acryllic stuff, despite Tom's generous offer (thanks!) & even though it looks like a great product for some applications. Its forte seems to be impact resistance (golf clubs) and fast cure time, but its tensile strength is actually fairly low. It might actually be perfect, but until someone literally uses it for cast iron repair, I think I'll go with a more "known" compound.

    Thinned JB Weld still worries me, strength-wise, unless someone knows of a test that shows the resulting strength. So that's out.

    Regular JB Weld is still in the running, esp if I will be filling the pores first with the same stuff, but I remain hopeful of using a thinner product.
    ----------------------------------------------------------------------------

    I wonder: Could I use a "filler" epoxy like JB Weld, Belzona, Met Weld, etc to fill the pores, but then use a different, thinner epoxy to actually mate the two pieces together?

    Or alternatively, maybe use a thin compound, like G/Flex or regular old 30 minute epoxy, but add fillers for the "wetting" layers, but use it thin for the "mating layer?
    Last edited by Allan Speers; 01-03-2020 at 4:16 PM.

  14. #14
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    Only the 810 I linked to is one of their acrylics. The others, in the first link, are all epoxies. I expect any regular epoxy will work fine, and don't think the fillers will be beneficial here. 24 hour cure is stronger than the quick cure stuff. I think you can even get some two part epoxy in a syringe in the box stores under the Locktite brand, which is fine.

    I wouldn't worry about the porosity of cast iron. By putting a generous amount on both parts, and then clamping it together, it will be about as good as you can do anyway.

    I'd brush it on both parts, then squeeze, and clamp together. I've even used a tourniquet on some odd shaped parts when any other type of clamps wouldn't work. Just clean off the squeeze-out with paper towels, and acetone, while it's still wet.

  15. #15
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    My opinion

    Quote Originally Posted by Allan Speers View Post
    I wonder: Could I use a "filler" epoxy like JB Weld, Belzona, Met Weld, etc to fill the pores, but then use a different, thinner epoxy to actually mate the two pieces together?
    I have permanently repaired many things around the farm.

    I personally would not worry a bit about the porosity in the cast iron. Porosity in cast iron is nothing like the porosity of wood. With a clean break with no missing pieces you will have two rough surfaces creating a large surface area. If you can fit the pieces together now with a tight line I think normal epoxy is fine mixed according to instructions with no thinning or additives. I prefer 1-hour epoxy where I want strength. West System G/Flex and Systemthree T-88 are good for general purpose. Note that you can call the epoxy makers and tell them your application and they can recommend a specific adhesive.

    Blow off any dust or tiny cast iron chips/grains, wash with acetone and dry with compressed air filtered to remove oils, and apply epoxy - I use a spatula or small glue brush. If using a brush make sure no bristles come loose and remain on the surface. With a tight fit I see no need to put epoxy on both surfaces. Clamp tightly together with some method. Wipe off squeeze-out with paper towel slightly dampened with acetone or wait until cured and scrape/cut it off if surface scratches won't bother you. Do not heat but let it set in a warmish place at least overnight before using.

    If it were mine I'd use JB-weld which has proven to me over and over it will bond incredibly well to metals. It does contain fine iron particles and may show a grey line. If I absolutely wanted the part to look like new I'd buy a new part and forget the repair.


    I still don't see where you posted a photo of the two pieces which might have minimized assumptions and helped experienced people make useful suggestions.

    Sliver solder is a type of brazing and can leave the binding metal on the surface.

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