Soft fire brick

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I'm prepping my first knife for a backyard heat treat and getting ready to build a basic two-brick forge for that purpose. I called the two semi-local fireplace type supply stores, and neither had ever heard that fire bricks came in soft and hard. Both places only have one type, I'm assuming it's the hard stuff.

I've got an angle grinder and a masonry cutoff wheel... would that make working with hard bricks doable? I'm thinking I would make a bunch of relief cuts in the face of each brick, and carve them out with a chisel.

Or should I just drop 30 bucks on these? They don't specify "soft" but they do say "cuts easily with a saw." Anyone who has experience working with the hard bricks and the soft, how much different are they?
 
And I guess while I'm here, a couple questions about my prep work:

I'm afraid I've gone a little bit overboard on my bevel grind and have made the edge too thin. My understanding is that this can cause warping or "baconing" during heat treat? I'm not afraid the take a file and move that edge back a bit, but what thickness should I be aiming for to be safe?

Secondly, what grit do you guys sand to before heat treating? I realize a lot more sanding will be needed afterwards, so there's no sense in going for a high polish. I'm just not sure when to stop and would like to avoid sanding more than is beneficial.
 
Insulating firebrick, rated 2300°F or better is a must. Ideally, you stumble across some older Babcock Wilcox bricks, they were a much better brick for our needs. Hard fire bricks have almost no insulation value and a much higher thermal mass. I'd give Sheffield Pottery a call, or maybe hightemptools.com.
 
you need IFB, insulating fire brick. see if there are any local companies that might stock some. pottery supply, boiler repair such as that. you will get killed on shipping although there may be no other choice. I had good luck cutting mine with a hand hacksaw.
 
Drop the 30 bucks and make sure Delphi is the shipper. There are some other companies that will send them cheaper, but they won't pack them properly and you will probably get a box of dust.
Delphi packs them right.
 
E.Carlson said:
Drop the 30 bucks and make sure Delphi is the shipper. There are some other companies that will send them cheaper, but they won't pack them properly and you will probably get a box of dust.
Delphi packs them right.
Click to expand...
is delphi a pottery supply house or brick seller? can you post a link?
 
Thank, everyone. I'm surprised to hear that the hard bricks lack the insulating properties, I thought it was just a workability issue. Now it seems even more odd that the two fireplace supply stores had never heard of hard vs. soft. I think I'll call them back and ask about the temp rating, just to be sure. If it's low, I'll probably just go through that Amazon link. Looks like hightemptools will ship two in a flat rate box for a few dollars less, but I don't feel very confident that they would survive the trip.

One more thing: How important is it to line the inside of the forge with refractory cement? Is that going to save money on fuel in the long run? Will it help reduce the amount of cracking and crumbling in the bricks? Or is it more of a "might as well" thing?
 
Soft fire brick is not used in fireplaces. It's used in refractory situations.
 
I used to line the insides with ITC-100 and mortar. I found it to be pretty much a waste of time on IFB forges. It makes a very slight difference, but not worth the money. I think I figured around 500 hours of use to justify the cost of the ITC, and by then you would need to re-coat it. It makes a bigger difference on wool based forges.
 
Where are you located? Years ago, when I built my heat treat oven (kiln), I called around to a few local refractory companies / industrial kiln builders, and finally found a guy willing to sell me a case of bricks for about $4ish per brick. Said he had some left over from a build and would let a few go at what he paid for them.

Check your local yellow pages under "refractory" and similar. Also, if you have any steel mills, glass companies, etc... near you, they oven have large kilns onsite with a stock of extra brick laying around.
 
I could not find them locally either. Just went the Amazon route. It’s been a while but I remember both bricks were a bit beat up. Not a big deal if you are going to enclose.
 
Hard fire bricks are actually opposite to what you want. They provide thermal mass and absorb the heat.
Soft brick insulates and reflects it back.
They are only similar in that they can both withstand high temperatures.
 
I could never find new unused ones locally either. I finally found a old ceramic kiln that no longer worked and dismantled it and reused them. For what you pay in shipping of new ones it's probably cheaper to find a used ceramic kiln in local classifieds.
 
If you use: http://www.hightemptools.com/firebricks.html

Then I say click on the flat rate button for three 3" soft firebricks instead of only two. It's only about $6 more for one more firebrick that you can use in the future or use to partially block off the opening (or if you mess up one brick then you got a spare).

I used my third brick to partially block the rear chamber opening when I enlarged the diameter of my two brick to be able to get larger kitchen knives heat treated. I found out the hard way that the enlarged chamber didn't retain heat as well anymore. Note: I'm only using a Bernzomatic TS4000 torch as the burner, so that may not be a problem with a better burner.
 
If you have an art glass/glassblowing or pottery supply place near you, they will sell them or at least be able to bring them in
 
Just as an update, since this thread got some new attention, I went ahead and ordered the ones from the Amazon link in the original post. They arrived intact and as expected. The cost was higher than ideal, but it was a lot easier than making a thousand phone calls and driving all over the state looking for the right thing.

I haven't had a chance to build the forge yet, but I spent a couple minutes "carving" the bricks, and I'm happy with how easy they are to work with. I actually had an idea to quickly grind a rough edge on an empty tomato soup can, and use that to rough out the chamber. The diameter is almost perfect, we'll see if it works. I'm hoping to put some work in during the evenings this week and I'll let everyone know how it turns out.

And while my first knife was waiting for the bricks to be delivered, my second knife got impatient and a profile sprung into existence. I'm thinking that if I completely ruin the first one, I'll be less likely to give up on knife making altogether if I have a second one in the pipeline.
 
Could you fill out your profile so we know where you live? Glad to hear that the bricks arrived intact. I just ordered two cases from a manufacturer and they were all shattered. It seems loaded on a pallet is the only safe way to ship them.
 
I am in Michigan, in the Lansing area. There is a company called Industrial Firebrick Inc. on the west side of the state, and they certainly carry everything to suit my needs and then some, but I decided to risk shipping damage rather than spend several hours driving for them. If I ever have a need for more than two bricks, I know where to find them though.
 
Depending on how many you need Hightemptools will ship three 3" firebricks in a flat rate box for about $32 out the door. That works out to a steal for me since the price per brick on slow boat shipping a case of ten to my location (Alaska) comes to a hair over $14 a brick.
 
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