i have read a lot on Fireplace Mortar being used to line forges and i have a few qustions 1 is it suitable for a coal forge that will be used for welding and will it shatter or crack if the water i use to help the coal to coke up hit the hot mortar

I used some 2700 degree fireplace mortor to line my gas forge-- thinned it with a little water, then smeared it over the kaowool. It seems to work pretty well, a little brittle because it doesn't have a solid backing. It's also not resistant to liquid borax, that put a hole in it pretty quickly, though with a thicker layer, it might work pretty well. It's a xxxx of a lot cheaper than ITC, though I have been thinking of lining my forge with the ITC for it's reflective quality, to increase the heat in the core.

Backyard smith,
I am assuming with this post that you are talking about the actual mortar and not castable refractory.

When I lined my forge I got the firebricks from a local supplier. They carried hard brick, castable refractory , and firebrick mortar. The mortar was relatively cheaper than the castable refractory, so i mentioned just using the mortar to line the forge. Their recommendation was to not use the mortar because it doesn't have the structural integrity that the castable refractory has. Instead I ended up just getting the hard brick and lining the forge with that (no mortar or castable).

It has actually worked out better with the loose bricks, because I can rearrange them to deepen the fire, and if the crack or break and need replaced, i just pull it out and put a new one in (once it's cool off course )

All the mortar is designed to do is bond two firebricks together.

My Canady Otto rivet forge had the bottom of a 55 gal drum for a fire bowl when I got it. It was just lined with a clay like soil called gumbo that is prevelent in Montana. I relined the bowl using hard fire brick and fireclay. It worked fine except for the fact that it took 2 men and a boy to move it around. I fianlly made a new fire bowl using the bottom of a pressure tank from a water well and I left it unlined. While I don't use my coal forge on a daily basis, the unlined steel has not suffered greatly from the effects of the fire. If it eventually does burn through, i sill simply toss it out and make a new fire bowl. I figure it is easier and cheaper to do that than to mess around with a bunch of brick and clay or mortar.

Woody