Gick in Char

This is not really a cider press post - but it does seem to be the right forum heading.

I am wondering about gick in char to be used as biochar. It just occurred to me that a friend of mine is a firefighter and I may be able to get near unlimited amounts of char from him. But I also wonder about chars ability to pick up nasty paint and insulation and particle board gick. I know they do lots of training fires some of the are just lumber and plywood - which I think I would be comfortable with but I'm wondering where I should dry the line.

Charring does wonders to detoxify things. Nasty organic pesticides, fungicides, herbicides, those mostly get burnt to CO2 and water. Even the arsenates that are used to make "treated" lumber, a lot of their arsenic gets volatilized -- which is why your don't want to be downwind of a treated lumber structure when it is blazing away. Was there lead paint in the building that caught fire? If so, then you might be able to find detectable amounts of lead oxide in the char. But that is a different animal from saying that the lead is bioavailable for plants growing in such char to pick up.

The other thing to realize about char is that it may contain a good deal of creosotes from incomplete combustion. The kind of creosotes that are used to make railroad ties. And we know what a low rep the use of railroad ties has with some Permies. If the char is very friable and crumbles to dust between the fingers, then the combustion was complete and few creosotes remain. If it still has the feel of wood, bends instead of snaps, smells like a dirty fireplace, then it probably has remaining creosote and then you are faced with the problem of having fungi do the rest of the de-toxification for you.

I would say draw the line at treated lumber. That means if you go to salvage from a house that was burnt down, leave the sill plate and the back deck and the front porch char pieces. But structural studs and joists, I'd take them and add them to the garden.