Zymurgy wrote in message
. ..
I've tried burning with a blowlamp and scraping it off without much
success.

Can't use paint remover as the plaster's porous. Belt sanding it off is too
dusty.

What's next ? hot air stripper ? tedious hand scraping

Please help !
Why do you need to remove it? As long as it's flat you should be able to
paper, paint, or whatever over the top. I'd coarse sand it by hand and
anything that's still on there can be regarded as sound.