I'm not sure what exactly you'd call that thing, but it's the plastic part beneath the dash pad. Mine's got some large glaring cracks in it.

I was thinking that I'd just epoxy it back together, but I figured that someone here might know of a way to do it right. I'm not sure what to use or how to go about using it.

 

personally I would just replace the dash with another one. Not sure how it could even crack like that unless someone tried removing it, maybe doing a heater core replacement.

 

I had the usual cracks in mine. Around here it is pretty much impossible to find a replacement without cracks, so I took it off and used plastic epoxy reenforced with a fine mesh to glue it back together. I haven't driven it much yet to see if it lasts, but I had to twist the dash some putting it back in and the repairs held up to that. I think the best way to fix it would be plastic weld, but I am not good enough at that to try it on my car.
Even repaired the cracks are visible, just not too ugly. The only way to completely cover them would be to refinish the surface using a bumper and cladding coating like Microtex.

 

Thanks for the tips. I bought some epoxy today, but I felt that it was too late in the day to attempt taking the dash apart.

How hard is it to take out? Are we talking about a ton of screws and laying all of the dash's innards on the seats, or does it just come out with relatively few screws?

 

Short of replacing it with a new one, plastic epoxy will probably be your best bet. I'd also recommend that you cut some ABS plastic and glue it to the backside as a reinforcement. I've used that plastic epoxy with very good results... it's super strong, and as long as you wipe the excess glue away as soon as you put it together, the seam should be almost un-noticable.