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I Forge Iron

48 hours later, cast still soft?

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Hey guys,

I cast my forge exactly 48 hours ago, and it's still mushy. It's just soft enough that I would not be able to remove it from the mold.

The mix is Ultra Express 70, and I used a somewhat high slump, but nothing extreme. The cast is a 10" tall cylinder with a 6" inside diameter and walls of 1" (making it 8" from side to side).

According to the data sheet, set up can take up to 48 hours, but I would expect something much harder by now. It has been cool outside, around 42F at night (I live in Florida).

Is this an issue? Should I take a heat gun to it or set up a space heater near it? I wish I could take it out of the mold but I think it's too soft.

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Hang a light bulb in it, Fl is high humidity.

If you used sonotube try pealing through the waxed layer by unrolling it carefully. This will help it dry.

While it's still somewhat plastic and still in the mold is the perfect time to make the holes for the burner ports. I use a sacrificial hole saw.


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I've had a set back, hopefully I can re connect it so I won't have to begin all over.

As you can see, my cast broke into two pieces as I removed the plastic container. I basically pressed the container to try and separate the suction between it and the mold, instead it split it in half.

Here are my ideas.

-Use gypsum cement in small amount to re connect the pieces.
-Use steel bands to re connect them.
-Do nothing, just set one on top of the other.

Any other ideas?


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What are you making??????? If it's a gas forge, why not just use a piece of 8-10" pipe?

This is the inner shell of a gas forge, it will have 2" wool wrapped around it and then placed inside a 12" paint/chemical can.

I want to eventually weld so this layer will need to stand up to the flux, that's why I'm not just using wool.
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Any other ideas on how this can be repaired?

I have found an ITC repair kit, it sounds promising, has anyone used it?

Ross I think you may be over-engineering this gasser.
If the concern is to prevent flux from eating your liner, then the only area of the gasser in question is really the floor where your work would rest on as it soaks.
How about just lining the shell with 2" of Kaowool like you were planning, treat it as you usually would for a gas forge, but then cut the remnants of your casting into sacrificial floor panels. From the looks of your casting, you should be able to carefully cut several floor sections - as the floor panel of the forge wears away, pull out another section you stored away and replace it. Check out the diagram below - I hope this explains what I mean in a better way.
Does this make sense? I've never made a gasser before so this is just an idea. Good luck with your forge.
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Frosty, I noticed you mentioned this before about the best time to put the holes in it. Will it not be able to be drilled once it's totally set?

BTW, I didn't find any sonotube in my area, I had to go the stove pipe route.

Sure but it increases the chance of breaking the liner as it's a lot more brittle AND it really wears on the hole saw.

Next time you use plastic for the form wrap it with a couple layers of newspaper so it'll slip free. The damp newspaper is very weak but there's a chance it'll bunch up so be careful.

Furnace cement should hold it together well enough. Make sure the breaks are horizontal in the finished forge.

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Aeneas, thanks for the diagram, that looks like a good idea. I actually thought about doing this and using a soft brink as the floor. My concern was welding temp, from what I understood it might not be a god idea to go that high with wool lining the interior.

Frosty, I just used a mix 3/1 mix of cast refractory/gy[sum cement. The gypsum should be okay if I fire it properly.

Would steel bands be an option?

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You said you used a high slump? The datasheet for Ultra Express 70 says it only needs 7.1% water for a self flowing mix and 4.5% for vibration casting. My experience with high alumina refractories is that if you go much over the recommended amount of water, the result will be weak, and the aggregate might even separate out. Also, the refractory will continue to cure and gain strength for weeks after casting, but only if it doesn

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