Eco-observatory...hey Paul
The problem is you not only have to get rid of the fruiting bodies, but also the hyphae, which if they remain, you'll have to use the dear stuff to kill them and seal the floor.
Personally, I would've never used chipboard in the first place....it'd cruddy stuff at the best of times and once moisture gets into it, that spells permanent trouble.
Many fungi hate alkaline environments, so you may be able to get rid of them with slaked lime. But that could ruin the chipboard.
You could try something like "Exit Mold" and see if that works or maybe something with borax in it...mushies and such don't like borax.