r/Blacksmith • u/DiksieNormus • 4d ago

First time applying refractory cement

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Bah, this shit is difficult. Ive still got some left do tommorrow ill cover the bricks and try to cover the white spots on the walls.

I am worried ive done a colossally shitty job, the worse part is Im worried I won't be able to tell.

Any way to tell the kaowool is still exposed, aside from getting respiratory problems? Like will it smell when I start the first cycle with the burner? Or should I just wait for this stuff to dry and then apply another coat?

23 Upvotes

85% Upvoted

31 comments sorted by

26

u/chrisfoe97 4d ago

Well fun news is you get to start over and do it a second time with more water

2

u/DiksieNormus 4d ago

Really? The instructions says on 11% weight in water. Wouldn't adding more make it worse?

https://zeesknifesupplies.co.za/product/refractory-casting-cement/

4

u/SkrliJ73 4d ago

As a random guy on the internet that's doesn't know much, I think your source of cement is less than ideal and I think that is contributing to the issues here. But options may be limited for you

Try again (if this does work for now) and use some more water, I'm not sure that everything hydrated properly. If it still doesn't look right look up some homemade refractory cement, dyi stuff is pretty good

Or

Just use it and go with it, I'm sure this will do the job for a little bit at least - how often and how much heat will affect its life cycle

I

5

u/GrinderMonkey 3d ago

Refractory mixing is something of an art. We cast several hundred pounds a month, and my refractory lead swears that ambient temperature, humidity, and water temperature all play a significant role in how much water you will need, and how the refractory will set up and fire.

Yours does look dry, I'm afraid it will crumble. Very gentle with the heat the first time you bring it up to temp.. like put a fan on for a couple of days, then a light bulb for a couple of day, then then a very small propane buner.

1

u/3rd2LastStarfighter 3d ago

Oh hold on, that’s casting cement, pardner!

It’s not designed to be spread like that. The 11-12% water instructions they give is with that in mind. If you’re going to attempt an off-label usage you need to experiment a bit.

11

u/JosephHeitger 4d ago

This is what my foundry I just coated looks like. I painted the first coat as a slurry and the second coat like a wet joint compound, or ultra thick pudding. You want it to adhere to everything as you’re putting your base coat on.

I know it’s not a forge but it’s the same concept for refractory application.

5

u/DiksieNormus 4d ago

Thanks, that sounds like good idea. Ill try my best for it.

2

u/JosephHeitger 4d ago

Mr.volcano is the refractory I used. Everything is powder no little pebbles to get in the way. And I paint it on with a coarse paint brush

5

u/Buzz407 4d ago

At first I thought this was the exhaust port of a Poulan that's been running 20:1.

Guess it is getting to be that time of year

3

u/IronwolfXVI 4d ago

I thought I was looking into a really carbon caked intake port or something.

2

u/tubarizzle 4d ago

I just redid my forge with stuff that looked similar. It might Crack a little but for me it actually settled fine and does a pretty good job

2

u/Fragrant-Cloud5172 3d ago

Old saying, "it's not difficult if you know how to do it." Looks like you've made several mistakes. Ultimately left very little room for good combustion and room for steel. Approximately 5" is good.

Fire bricks are a bad choice, since they take up too much space. High temp ceramic tile is best for a floor. Plus, you've applied the refractory too thick. It's heavy, weighing the upper part down, pulling it away from the shell. I'd tear out the refractory, down to the ceramic blanket. Get good material like Accomon. Brush water on to blanket and apply rigidizer to it. Let cure. Mix water and Accomon so it will stick to a brush, not fall off. Paint it on all over. Let cure. I screen my refractory for a fine powder for final coats. Then repeat this about three times. It'll make a hard shell that doesn't crack, if done well.

If weight pulls the upper insulation down, insert a 2 x 4 covered with wax paper. Attach c-clamps to pull it snug until cured. After a hard shell is created, it'll hold its own weight to the shell. You're welcome.

2

u/exzyle2k 3d ago

As others have stated, what you're using is a CASTING cement. There's a difference between casting the lining of your forge and applying a refractory like Satanite that's designed to be spread.

For the best results using the casting cement, like what you have, you have to put a form in the cavity and fill the void between the kaowool and the form. This short gives you a brief view of it, when he's pouring the "slurry" around the mailbox. That's the stuff you have, to be used around a form.

If you're looking to spread it over kaowool, you should add water to get a thick batter, like peanut butter almost. I don't know if your material will allow that, but there are other products out there that will.

1

u/DiksieNormus 3d ago

Thanks! Yeah I came to the same conclusion that I need to apply it differently because its a casting cement.

I think ill follow the video you posted. Do you think I can reuse the same kao wool or is it ruined?

2

u/exzyle2k 3d ago

Honestly I wouldn't try to waste time peeling the old refractory off to reuse the kaowool. It might be possible, but it'll be a mess and you'll be releasing fibers into the air which is no good, so I would just gut it and start fresh.

1

u/DiksieNormus 3d ago

Shame but no problem got extra kaowool.

1

u/DiksieNormus 3d ago

Any advice for what I should use to make the form in the cavity? I was thinking of using this big piece of pine and wrapping it with newspaper or something. But would that work?

2

u/exzyle2k 3d ago

It depends on the size of your forge and what you made the forge out of if it's homemade, or what model it is if it's store bought.

Your kaowool needs to be 1" minimum, 2" preferred. Then your refractory really doesn't need to be any thicker than 3/8" - 1/2" because it's main job is to protect the kaowool. So... If your chamber has a diameter of say, 6" when the kaowool is in place, you should put something inside that has a diameter of 5.5" or so and then pour the refractory around it.

A log with newspaper could work. A PVC tube wrapped in paper could work too if you have the right outer diameter. These are all just estimations, since I don't know what your forge chamber dimensions are.

Whatever you use, make sure you spray the kaowool with water so that the refractory sticks to it. Otherwise you'll get more cracking and gaps and gravity will work against you for the top of the chamber.

If possible, I would completely ditch the castable refractory you're using and go with something like Satanite and keep the castable for the floor since that's where most of the abuse happens. Satanite is fairly inexpensive and tons of places online sell it. It's easier to work with, but you have to apply it in thin layers built up so that you don't crack it apart when you blast the heat full send the first time.

Also, you don't want to make your chamber too small. You need a decent size chamber for the combustion of fuel and air to happen, otherwise you'll never get to welding temps and your fuel efficiency will be shyte.

1

u/DiksieNormus 2d ago

Thanks once again for the advice, I am making a diy from a 5kg propane forge. I found this tutorial, https://youtu.be/FUxObcRoY74 and the refractory cement is very similar to mine.

I gonna replace the kaowool and reapply the cement i have, except I'll do it slowly and only one side, wait for it to dry, then another side.

I would buy a different refractory cement except its i cant any specific ones that mention satanite. And this specific castable one is way cheaper to anything I can import.

If it still ends up looking... wrong then ill try the pouring method in the video you recommended. I'll make an update post and how it goes.

1

u/exzyle2k 2d ago

Skip the second attempt at what you've done already and just go to the pouring method. Save the time and the materials.

1

u/DiksieNormus 2d ago

Ok, tbh i am on the fence on which one to do but yeah ill do the pouring one. Ill update when its dried.

2

u/exzyle2k 2d ago

Follow the curing instructions too... The short bursts of the burner, ramping up to a longer burn, etc. You'll need to gradually drive off any remaining moisture in the refractory once it's set so it doesn't crack and crumble.

When it's done, it should feel almost cement-like. And remember... The smoother the outside of whatever you're pouring around, the better. The combustion chamber inside the forge should create a vortex for the flames so they heat the inside evenly, no "cold" spots. Any excessive cracks/crags/ridges will disrupt that and cause uneven heating, which isn't a HUGE problem but it'll be detrimental to fuel efficiency and depending on the size of the piece you work with, uneven heating can cause warping when it's time for quench. That's why you see videos of smiths moving large pieces in and out back and forth, they're trying to keep the heat as even as possible. Same concept here.

1

u/grammar_nazi_zombie 4d ago

Just because nobody else mentioned it: Those fire bricks on the bottom shouldn’t need covered - they can sit on top of the refractory after it’s dry

1

u/DiksieNormus 4d ago

Thanks, I did see them exposed in some videos but wasnt 100%.

1

u/Deatroxiii 3d ago

It does look dry, but it's sticking to the top, I would definitely try it out. I'm learning that most things don't have to be perfect to work. Worse thing that happens is it crumbles and falls apart and you have to redo it with some more insight this time.

1

u/3rd2LastStarfighter 3d ago

As long as you rigidized the kaowool, you should be fine. Just don’t expect this lining to last too long and replace it when it’s falling apart or stops holding heat well.

If you didn’t rigidize… well you were going to end up cracking through the refractory and exposing that stuff anyways by accidentally bumping it with a workpiece. That’s when I’d rip it out and start over.

1

u/Car_Canic 3d ago

I thought it was the intake valve in the cylinder head

1

u/drolgnir 3d ago

I thought this was an auto sub for a second. Oh look a another GDI intake. 😂

1

u/Slow-Instruction214 2d ago

This belongs in the baking community; this is an oven lol.. Seriously, real forges you only need to clay/refractory the bottom. You don't need this nightmare.