Cast Iron Repair - Best Epoxy?

[Erik Loza]

[Tom M King]

That was a fun test, but I feel unfair to some of the brands. If he had tested only the fast cure epoxies that each brand sells, and then the slow cure, it would be a more clear test. The slow cure of any brand should always beat a fast cure in that test. JB Weld had the best chance of coming out on top, simply because of the numbers of each brand used.

I don't know about the High Heat version, but I think the JB Original may have been the only slow cure in the lot.

[andrew whicker]

I work with heavy pressurized gas equipment... Belzona is boss. That's all I'm going to say : )

[Tom M King]

I believe you. I've never seen any, but am ordering some to have on hand, as soon as I find it.

edited to add: no longer available from Amazon. The only online retailer I found that has it is on ebay. It's too expensive to justify buying some just to keep on hand. If I ever have a tractor block to repair, I can order it. I have friends in boat repair business, here on the lake, and I've heard them say multiple times that it amazes them how many aluminum outboard blocks, and jet ski blocks are still operating with nothing but MarineTex fixing a cracked block.

Of all the things I've fixed with epoxy, when I was in the boat business, and keeping the Ponderosa operating for 40 years, I can't remember ever having anything fail.

As an extra, useless aside, the reason I use that acrylic 3M DP810 on golf club heads is the same reason a lot of Tour Vans use it. It's plenty strong enough, but the best thing about it is it turns into a crackly, expanded mass, when heated below a temperature that would melt the resin in a composite golf shaft, and is very easy to clean off, back down to bare material. It makes it really easy to try different shafts on the same head. Epoxy, which is also used a lot, is many time harder to clean off the shaft, and out of the hosel.

[andrew whicker]

If you knew anyone in heavy industry, they might hook you up. I'm not sure how much it costs. I think most companies in that old tech, big equipment field would have some handy.

[Tom M King]

I think it was something like $126.00 for 1kg, for both parts. No heavy industry anywhere near us. So far, I've never cracked a block on anything.

[Allan Speers]

I believe you. I've never seen any, but am ordering some to have on hand, as soon as I find it.

edited to add: no longer available from Amazon. The only online retailer I found that has it is on ebay. It's too expensive to justify buying some just to keep on hand. If I ever have a tractor block to repair, I can order it......

Yeah, the problem with some of these more exotic compounds isn't just the price, but the fact that they all have a pretty short shelf life. Typically as little as a year, to a luxurious 3 years for a few. I'd love to have expensive adhesives around just for emergencies, but it's not too economically feasible.

[John K Jordan]

I work with heavy pressurized gas equipment... Belzona is boss. That's all I'm going to say : )

Never heard of Belzona so I looked it up. I want some.

[Jacob Reverb]

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?

Normally, you use thinned/unthickened epoxy to "wet out" the surface of whatever you're gluing. Think of it like pizza dough: The more flour you add, the less likely the dough is to stick to your work board, and the less likely it is to "get into the pores" of that board. If you WANT it to stick to your work board, you should keep it "sticky" by not adding too much flour...or, if too much flour has already been added, by "thinning" it with additional water. Imagine trying to squash pizza dough down into a knot hole, or the rough section of a board. The more flour (filler) it has added to it, the less likely it is to a) squash down into those tiny pores and voids, and b) stick to them once it's in there.

To diagram, the components of your joint "sandwich" should look something like this:

CI | UPTER | OPTIONAL: TE | UPTER | CI

where

CI = cast iron
UPTER = unthickened, possibly thinned epoxy resin
TE = thickened epoxy (optional)

Hope this helps. It's not as complicated as it might sound.

ETA: See the fifth paragraph here for a helpful explanation of what you're trying to do to the resin by adding a tiny amount of filler here (you're trying to make it thixotropic – i.e., "resistant to dripping" – rather than simply "thicker"):

http://www.eagerplastics.com/cab.htm

[Jacob Reverb]

The slow cure of any brand should always beat a fast cure in that test.

I've been messing with epoxies for boat repair for decades, and I've always lived by that same rule of thumb that slow hardeners yield a stronger composite, but...

I don't know whether something recently changed in West's formulations or what, but I recently discovered that West claims their fast hardener yields more tensile strength (about 7.8 ksi vs 7.3 ksi) than their slow hardener. (Although the elongation figures suggest the slow hardener gives more "toughness"/ductility, and "Gflex" gives about 10X as much, though only half the tensile strength.) And I didn't watch the video, so I don't know whether he was testing for tensile strength or toughness. If he was testing for ductility, you're right – slow hardener should fare better – in which case, disregard my comments above.

Anyway, for a comparison of the mechanical properties of various West System resins and hardeners, see:

https://www.westsystem.com/products/...al-properties/

[Pete Staehling]

I'd have just silver soldered or brazed it, but I have never heard of Belzona.

[Mike Cutler]

I'd have just silver soldered or brazed it, but I have never heard of Belzona.

Belzona is "magic" in a tub. We use it at work for large machinery repairs, at times.
There are many different formulations of Belzona, but they definitely have one for CI.

[andrew whicker]

I'm thinking heavier than your engine block. I'm thinking refineries, big CAT engines, turbine mfg'ers, things like that.

Like Greenville, SC (GE builds turbines down there) definitely would have some. But that's an entire state away from you.

[Tom M King]

Fortunately, the last cast iron repair didn't require epoxy, but did require some specialized equipment to rethread some holes up to 1". This Milwaukee magnetic drill press is a Real Beast. I thought I would resell it, when I got through with it, but like it so much, I'm going to keep it. The rethreading part wasn't so bad, once I was able to redrill the holes. Redrilling the holes was easy, once I bought this thing. That's a 3/4" steel plate it clamped itself onto. It also drilled the holes in the plate to mount it to the block. The drill press weighs 85 pounds. That's a 7/8" bit in the chuck.

Little bit of a long story, but these were the loader mounting holes in the block.

[andrew whicker]

What?! You've got a magnetic drill? You're awesome in my book.