Filler

[Alex'n'Ane]

I have some filler on the roof of the project which is beginning to crack and break off, and was wondering what is the best way of removing the rest, are there any acids etc which will break it down, or heat etc?

[Sidney'61]

Wire brush drill bit?

[polo2k]

start tapping the panel from the rear and it will probably come off in chinks, the remnants can be cleared with a wire brush in a grinder.

[Roni]

I'm just finishing stripping a body shell using a system suggested by the car painting business. All I can tell you is the name it is known of here in NZ, Tergostrip BO.
http://www.tergo.co.nz
("Tergostrip Brush-On is an aggressive, heavy duty paint remover and will effectively remove most paints and powder coatings including baked coatings, acrylic enamel, melamines, two pot epoxies and urethanes, road markings and anti-fouling marine paints.")
It is a very efficient stripper of paint and filler. I'm sure there will be something similar available where you are. You do have to be very careful using it though.

[chickenjohn]

Quickest and least messy way to get rid of old filler is to heat the area with a heat gun to soften the filler and remove it with a scraper.

[MarkyB]

Don't breathe the fumes though, at best they stink!

[chickenjohn]

Don't breathe the fumes though, at best they stink!

That advice would apply even more to the clouds of harmful filler dust kicked up by the wire brush on drill or grinder or even more so the fumes given off by strong paint strippers.

Of course, work in a well ventilated workshop and wear a dust mask!