While looking at the blueprints section, I noticed one of the contributors using fire bricks in the forge. Is this common? Is is used to form the fire to a certain shape, and or hold the heat in? Are there disadvantages to this? Thanks

Yes bricks are used to hold the fire in. The same idea as a wood stove, we are just using gas as our fuel. If you use bricks a soft insulating brick is used as in pottery kilns. If used as i used them they don't stand up very well. i am a full time smith who uses his forge every day. I use an insulating refractory called "Plicast 2800" i find it is very tough and insulates quite well. Refractory is the substance used to make the bricks and their are a myriad of different types. I don't make bricks out of it, i cast my forge in 1 piece instead of separate bricks.
i hope this makes sense to you

Thanks that does make sense, I thought it was a coal fire. here is the link.

I Forge Iron - Blacksmithing and Metalworking * BP0308 Hot to make a Leaf*

I don't have a forge yet.. but I think the idea of using bricks in that coal forge is to contain the fire in a smaller area so the heat is concentrated in a smaller area and will heat the small piece faster.

From what I gather, the hard fire bricks are resistent to heat but to not insulate as well as an insulating brick. They will hold the fire and coal where you need it but will not hold the heat in as well as an insulating brick (usually white and very soft). An insulating brick will not hold up as well to material contact as a hard brick. Coal forge will get more contact use from the coals and tools so a soft brick would be turned to dust quickly.

Gas forges need to use insulating brick to hold the heat in because the flame is usually smaller and you want to contain it to get the most heat out of it.(coal forge.. the coal is the fuel so you can have a large flame area and get a lot of heat out of it since your work piece is put directly in the flame center) They also use a hard fire brick at times on the bottom to have something to set the work piece on so you don't damage the forge.

At least that is how I see it. Hope this helps.

I put bricks on the side of my firepot to keep the coal from spreading out. I like a tall fire because my firepot is fairly shallow (4-5" deep)

The hard firebricks are often used to help tweak a coal forge for burning charcoal. You need a deep fire but any charcoal to the sides will burn too, not helping to heat the piece but heating you and the tools and wasting fuel.

I use fire bricks in two places on my coal forge.
1.) around the firepot to allow a taller fire and easy placement in the neutral zone
2.) on either side of the flue opening helps keep the old beat up side draft hood in shape

In that blueprint you cited, the bricks are, as Thomas said, used to contain the fire. Quite common for using charcoal, as with charcoal, a deeper fire is commonly used. A few bricks would make a coal forge into a charcoal forge fairly easy.

I have seen some designs of gas forges that used bricks stacked as the shell, as well as contained in a metal frame. Some folks like them loose, as it allows changes to the configuration of the interior of the forge without a lot of re-designing and building. Use of bricks in a forge, whether coal, charcoal or gassers, is only limited by imagination, purpose, and pocketbook (as some types of firebrick are much more expensive than other types.)

Thanks that all makes sense.

I know that when we think about bricks in a forge we think about fire bricks.I had a small engine shop that I heated with wood for several years that I heated with a double barrel stove.I didn't have any fire bricks , so I lined the fire box with regular glazed building bricks.I burned several cords of wood a winter, and after approximately three years I tore the stove apart.The bricks were almost perfect.I had one or two cracked bricks, and the others displayed no signs of overheating.I am of the opinion that you don't need fire bricks.My Grandfather was a hundred years old at his death, and he always said that the brick was the best building material that man ever created.He often stated that bricks made that when he was a boy, were just as good as the day that they were made, only the mortor wore out.

thanks for the info. I will experiment with them.

I use fire brick to create a hood on my coal forge, with a piece flat metal on top. I have my forge outside in a fenced in area, and the fence is old wood and the fire brick is just to keep the heat off it. I should build a metal hood, but the bricks were free, and for now they work. So far all I have made is allot of noise and smoke. I did learn how to control the smoke.

this is a photo of bricks in a coke forge the top was cast out of fire cement on a plywood former bent in and then burnt out ,it can easily be dismantled ,it makes good use of the coke, this fire has half of a anvil in it and it brought it up to heat easily

I used fire brick in my coal forge and after one use, the bottom of the bricks were "melting". I wasn't using flux, so I'm curious, did it get too hot or does fire brick not stand up to direct contact with coal?

What kind of fire brick and to what temp was it rated?

Frosty The Lucky.

I've made and used adobe bricks and they hold up just fine.

Only rated for 2000... that's probably the problem. What fire brick do you use?

The bottom of the bricks,  that are not in contact with the fire, was melting? Or is that the firebricks on the bottom of the firepot were melting?  Asking questions is very much a GIGO process!

Bricks are consumables. I've never melted one in less than about four hours though. 

Pnut

 

In a smithy *everything* is a consumable----including the smith!

Bottom of the bricks that were in contact with the fire. 

I worked with brick issue is them that they melt, and now my forge is dislocated.
Need to rebuild forge again, seen that at my blacksmith too they use mud to repair forge.
Today i had small efficiency with forge, i ignored and wanted to continue work but it was frustrating.

I will just  swich side of brick and that hollow one wil be outside now, and maybe use some mud clay to isolate brick.

 

Bricks are good for adapting solid fuel forges to differ shapes and purposes. This makes your forge more efferent or versatile as the case may be. Need a large fire for a large forging? Rearrange the bricks and fill. Need a small fire for small forgings? Rearrange the bricks. Need a furnace? Well you know what to do... you can even do small melts for castings in your forge with a few bricks and a sutable crucible. 
Other uses for bricks is to make a fire resistant work surface or to prop up stuff.

bricks will melt in direct contact with welding heat, but a good use for them is to take up space in your hearth, wile using a fill such as cat litter, mineral soil or fly ash to form the fire pot it’s self. 
Regular bricks and fire brick is still useful with gassforges, just not as a linner

Don't use "Mud" you only want enough moisture in the soil you can compact it hard. When mud dries it cracks and can be a problem. Mud can also trap moisture so steam can't escape when it gets hot causing spalling, small steam explosions that throw hot pieces of clay around the shop. It not only hurts when a handful of hot dirt goes down your shirt, getting it in an eye REALLY SMARTS. 

Frosty The Lucky.