Best DIY refractory cement recipe

[Colton C]

Not sure if this is the right forum to post this, someone let me know. Ill delete it and post in the correct forum if needed

 

I built a small knife charcoal forge, my first one ever, and I was wondering about what the best homemade refractory recipe. 

I have seen a couple that use portland cement and perlite that people say work well, but others say not to use those because it will cause cracking and crumbling. I was wondering if someone could share a recipe that worked well for them.

I have a ton to learn so any advice people can give me on refractory in general would be awesome. 

[Frosty]

Welcome aboard Colton, glad to have you. Yeah, I suppose this should go in the solid fuel forge section or maybe there's a home brew refractory sub section or thread. No big deal let Admin move it if they feel it's important enough. You won't be in trouble, we all bobble now and then, even Admin. 

No need for a refractory liner in a solid fuel forge, even if some folks use it it's not really necessary. NO PORTLAND CEMENT in a HOT fire!! It can spall explosively throwing burning coals a considerable distance not to mention HOT SHARP shards of concrete hard enough to stick in your hide while it burns you. 

If you need a liner say you're making a JABOD (search the term in your favorite engine and add "Iforgeiron" to the terms. It'll lead back here but the resident search engine stinks) Anyway, a good liner for a solid fuel forge can be packed clayey, sandy soil. Figure about 1 pt. clay to 3-4 pts sand just damp enough to pack hard under a mallet. That's IF you really want a formula for a liner. In most cases you can just dig up a bucket full from the garden, a ditch, road bank, etc. It really just needs to pack hard if you beat on it some.

Check out the JABOD (Just A Box Of Dirt) threads, it's an excellent forge of a type that's been in constant use for thousands of years before coal and bottom blast forges. They're still used today, think Japanese Sword smiths for example. Hmmmm?

Oh as a last word about the gang here on Iforge, we LOVE pictures! Anything you'd show a young child you don't have to explain . . . STUFF to. 

Frosty The Lucky.

[Colton C]

Thanks a ton for such an extensive reply!

I picked up some fire clay and I was going to mix that 50:50 with silica sand, add some water, let it dry, then slow heat it to get rid of all the water. Do you think that would work better for my application? I just need somewhere for the coals to sit above the pipe attached to the blower.

I will post a picture of what I have built so far. The black container is going to hold used oil eventually.

[Irondragon Forge ClayWorks]

What are you planning to use to control the air blast? Charcoal takes very little air, more is not better. I think 50/50 mix is a little too much sand. Have you read the JABOD thread? Lots of good info there.

[Colton C]

I was going to use a ball valve on the pipe to control air flow

[Frosty]

1 hour ago, Colton C said:

Do you think that would work better for my application?

Nope. Silica sand and hot steel tend to bond wonderfully and any scale falling off will turn right to extra sticky clinker. This is a good way to make clinker with a charcoal fire.

If you already have the fire clay use it, if not buy something cheaper or take shovel to a likely place and adopt a bucket. Same for the sand if you already bought the silica use it, if not find a creek or beach, take a couple buckets. The ratio of 1 pt. clay to 3-4 pts sand is good enough. (Cal it 4:1 for the discussion)

Just add a LITTLE water, you do NOT want mud or plaster, it'll shrink as it dries and crack, called shrink checking. Look at a dry mud puddle for a good example. The best way I know to get well tempered casting sand is to mix the material and cover it over night to allow the moisture to distribute through the clay and test the next day. Squeeze a handfull HARD, if it forms a lump look at your hand if your palm is damp it's too wet add a LITTLE more 4:1 mix thoroughly and temper over night again. If your hand is clean break the ball in half if it crumbles it's too dry add a LITTLE water, as in ounce or two by sprinkling it over the rest, mix thoroughly and temper over night. If it makes a hard lump that breaks "cleanly" it's good.

Ram it into your forge. 

You do NOT need to be that finicky about getting the moisture content right, the above technique is for green sand casting but if you get close it will NOT shrink check on you. Just moist enough to ram hard is plenty good for a forge, icky sticky is NOT so good.  

This isn't rocket science you can dig a hole in the ground, place the blast pipe go to work and be in good company with professional blacksmiths working today. Honest, as we type.

Frosty The Lucky.

[Colton C]

I already have the silica sand and fire clay so I can use those in a 4:1 ratio? 

[Frosty]

Yeah, it's a good ratio but if it's crumbly it might want a little more clay. We're not baking a cake here, close is good enough.

Frosty The Lucky.

[Colton C]

Thank you a ton, I really appericiate everyones help. I will definatly be more active on this site, its an amazing community.

[Frosty]

You're welcome. We practice being amazing, it's like a super power you know. 

Know any good jokes, puns?

Frosty The Lucky.

[Colton C]

Got it all rammed in there, used a 3kg sand to 1kg clay ratio. Mixed with water till I had a "cookie dough" consistancy. 

Do I need to slowly heat it to fully dry it?

[Frosty]

Cookie dough is pretty wet but what the hey. Light it up now, letting it dry will take a long time to no significant improvement. If it checks ram it again without adding more water.

Frosty The Lucky. 

[Colton C]

Just fired it up and it all held together perfectly. I even got to start hammering some steel!

Thanks again for all your help

 

[Frosty]

We be happy to help. Enjoy the ride.

Frosty The Lucky.