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I have built a two story 30' x 40' stick framed shop. The main floor
is separated into two sections, one which I plan to insulate, houses my
machine tools, the other I use for welding, car repair etc. Niether
area is panelled yet and I tying to decide how I should go about it.
My current idea for the welding area is to cover the lower 48" with
cement board ($30 for a 4 X 8 sheet) and the remainder with Aspenite
covered in flame retardent paint ($11 for a 4 x 8 sheet). I do not
want to use drywall because I do not want to tape it and it will get
all bashed up. Does anyone have an opinion on the flame retardent
paint?

So called "intumescent paints" protect fairly well, but not for protracted
exposure. They have a 'bubbling' agent (usually sodium
silicate/metasilicate) that forms a bubbly foam layer on the surface when
heat is applied. Because the silicate bubbles are in large percentage
glass, they protect by forming a layer of heat-resistant insulation when
fire hits the painted object.

They aren't a silver bullet, but can greatly lengthen the exposure time
before a wooden member becomes fully involved in the fire.

If the manufacturer doesn't list the coating as being of the intumescent
variety, I wouldn't trust its ability to resist flame for very long.

LLoyd