Disposable dust masks are generally unsuitable. You'll need a respirator with the appropriate cartridge, such as this...
http://www.bunnings.com.au/protector...ator-_p5820154
...with these cartridges...
http://www.bunnings.com.au/protector...-pack_p5820080
Of course, different brands are available and the comfort will vary, but you just need to ensure the cartridges are Class A-Aus, which is for gas and vapour protection.