Hi
I wouldn't necessarily put it in the compost heap I would put it straight on to the soil as I remember someone telling me a while ago that ash is good but only for a short burst of goodness! If you catch my drift! In theory as it is burnt it doesn't need composting as it is in a useable form already.
I use it just round plants etc and they all seem to thrive. In fact I have put my bean trench over an old bonfire site and I have, after digging and manuring, put loads of ash on the top and planted beans through this. No problem with slugs at all! So presumably if you put it round stuff that could have slug damage the slugs and snails don't like walking on it! Good luck!
Old Bird
::)