ED, I JUST TRADED FOR THIS FORGE. IN SHIPMENT SOME OF THE FB GOT BROKE AND SOME OF THE MORTAR IS LOOSE. I BELEIVE I SHOULD REBUILD IT. IF THIS WAS YOUR FORGE AND DECIDED TO REBUILD IT, WHAT WOULD YOU DO TO MAKE THE FORGE BETTER. THANKS FOR ANY HELP WITH THIS MATTER.
KEN

Not to sound obnoxious, but the first thing I would do is throw that one away, and build a forge with a round design. :evil:
But, I suspect that is not an option at this point. OK, being that insul-board is such an expensive thing, I would likely replace the insul-board with fiber-blanket, for the top and sides. For the bottom (where most of the contact will be with work pieces, flux, etc.) I would figure out a way to use some kind of castable, that would be durable. You could either do this by casting it directly onto the forge floor, or by casting a "plate" matching the dimensions of the forge floor. If that proves un-doable, the next choice would be fiber blanket, with some half cuts of firebrick covering it. Anyway you go, whether it be insul-board or fiber blanket, it will have to be replaced on a regular basis. Niether of these materials were designed to be very durable.
I'm not at all keen on the coatings that folks put on fiber blanket either.(which some will tell you is the answer) It does not add enough durablility to justify the labor and cost. Having tried it several times, I'm also of the opinion that is degrades the refractory's qualities as an insulator and heat reflector.
If your only going to do general type blacksmithing work, the square design is OK, but I feel it is ill suited to the needs of a bladesmith.
There are times that we must work with whatever tools we have, but given the ease of building a castable forge, along with the modest costs compared to a commerical model, I can't image that people spend the kind of $$ that a commercial forge costs.

I APPRECIATE YOUR OBSERVATIONS ED AND I'M GLAD YOU LIKE MY FORGE. I THOUGHT I WOULD ALSO CUT SOME FIREBRICK ON THE RADIUS AND PUT IT IN THE UPPER AND LOWER CORNERS OF THE FORGE. I THINK THIS WILL HELP ROUND IT OUT ON THE INSIDE AND HELP KEEP THE HEAT MOVING AROUND THE CENTER. I PLAN ON USING THE FORGE FOR ANNEALING AND HT. AGAIN, THANKS FOR YOUR REPLY AND OPINIONS.
KEN