Crushing biochar in bags

Until quite recently, I was crushing biochar between panels of plywood.  I knew not to burn the plywood in the biochar, but some people have been telling me that even crushing the biochar between the panels of plywood is risking too much contamination from the glues.  So I had to make a decision. How am I going to crush the biochar now? I had read about people crushing it in bags, but I imagined many tiny bags being run over and that didn't seem feasible.  I went to check in on my good old buddy Craig and his list.  There was a guy selling large jute bags for organic fair trade coffee for $1.  They were quite large: 3'4" by 2'4". Four of them laid out were about the size of the plywood panel.  Seemed like a good option.  

Setting up the biochar to be crushed was certainly different.  Instead of dropping the biochar on a large flat board, I had to put my arms in the bags to get the char off of some of the partially burned last pieces.  I couldn't just reach over and even out the piles, because they were inside the bags. I had to reach in the bag and even them out.  I wasn't using a large flat board to flatten the char. The tires were directly crushing them.  I had to sit on the ground to reach in the bags, but I think I managed to get the char pretty even inside the bags.  They seem to be crushing pretty well. The truth will come out in a couple of days when I need to take some out to charge it.  

I will keep you posted.

John S
PDX OR

Interesting...looking forward to further reports on how it goes.

I wonder if animal feed bags might work better than the porous burlap bags. I could see those bags you have leaking a lot of dust. I wonder if they'd help with your "reaching into the bag" problem, too?

Interesting idea. What are animal feed bags made of? Where would I get them?

THanks,
John S
PDX OR

John Suavecito wrote:Interesting idea. What are animal feed bags made of? Where would I get them?

THanks,
John S
PDX OR

Hi John. The bags I've always ended up with hold 50 pounds of grain and tend to be made a strong plastic that I think would hold up well to driving over or otherwise crushing char in.

If you know anyone who owns livestock, it's worth asking them if they can save them for you. If you have any quantity of animals, they tend to pile up.

To avoid contamination from the plywood you could use a layer of steel or aluminum flashing between the plywood and the charcoal.

I'm not sure I want plastic in my biochar any more than I want toxic glues.   The average person eats one credit card of plastic every week any way.  

I like the idea of sheet metal. I've been checking my friend Craig and his list for that.  So far, not exact matches, but could happen.

Thanks,
John S
PDX OR

John Suavecito wrote:I'm not sure I want plastic in my biochar any more than I want toxic glues.   The average person eats one credit card of plastic every week any way.  

You probably shouldn't eat the biochar afterwards, regardless.

Anyone else starting to miss the "good old days" when we were just full of lead and asbestos?

So today is the day when I got to dissect the post mortem autopsy of char crushed in large bags for the first time.  And the envelope, please............

It worked really well!  It seems to crush the char better, which isn't surprising, since the tires are directly on the bags of char instead of dispersing the weight throughout the plywood panels.  I picked up the bags and emptied them directly into the bucket.  With the plywood, I would scoop it up with a dustpan, so it was clearer to see and I didn't have to stick both arms inside the bags and flip them out.  It was a little harder to get it out of the bags.  Also, I think I left more char in the bags, just because it's harder to get it out of the bag than out of a flat surface.  I think it is just a blip, though.  Although there is some in there on the first time, it won't keep adding up. There is a limited amount of crushed char that will get stuck in the bag.  

In addition, there was almost no char that leaked out of the bags onto the surface, at least this first time.  The bags seemed to suffer little to no damage.  I would think that in a rainier week, more char would leak out of the bags.  There was actually more char that escaped from between the plywood panels.  Here is what it looked like:                

Episode 2 of crushing biochar in bags:
The direct pressure of the tires really does seem to crush the char better. As such, I need more liquid for the same volume of char, when I inoculate it afterwards.  I think a larger mass of char is crushed into a tighter volume, so it needs more liquid to charge it.   Also, I just removed all of the partially burned pieces by hand (there were only 2).  So then I could just dump the char from the pot I use to remove it from the barrel directly into the bag.  Easy.

It rained today for the first time in weeks, so we're going to see if there is residue leaking out of the bags.  

Seems like this new bag system is going to work fine.

John S
PDX OR

I used to need to use the truck instead of the car because it was parked over the biochar, so I would crush biochar every time I used it. Now, in bags, it is so efficient that I don't really need to go out of my way to crush it.  In fact, I may have crushed it more than optimal last time.  I was trying to follow the protocol I used with the boards.  Now I think I will just try to crush it once or twice.   I may even remove the bags afterwards so they don't become excessively crushed.  

We get over 100 degrees F some days in each typical summer now.  During that time, there are many days of 90's F and absolutely no rain for say, 2 months.   It's very hot and very dry.  In these conditions, you don't want maximally crushed biochar.  It's better to have larger chunks, like at least say 1/2-1  inch or 2-3 cm.  I don't need it all to be that big, and it wasn't even before with the boards.  You just want your plants to find something that they can reach.  Having it buried helps retain the moisture.

In addition to the biochar, I have been increasing my mulch.  I used to add wood chips every year.  Now I'm starting to add them twice a year.  I noticed a garden at a church here that does the "Back to Eden" Paul Gautschi method of deep mulching and they had great looking vegies on Sept 30th after not watering their garden a single drop.  It was inspiring.  The deep mulching and the biochar go well together.

JohN S
PDX OR

I did limit the amount of drive over crunching I did with the biochar in bags this time. No extra driving just to crunch the biochar.  It seems to work better.  I am getting an optimal mix of different sizes of biochar chunks from 1" down to about 1/8".  It doesn't seem to take so long to take up the inoculation liquid mix.   It also doesn't increase in size like it did last time.  No extremely slow flow of liquid through the char.  

This is the first time that I removed the char from wet bags.  It was a little uncomfortable, but posed no problems, really. I just poured it into the buckets for inoculation. I did leave the bags out on the driveway so they would dry quickly and they did.  They didn't noticeably leak biochar stuff during the rain, but I'll watch to see more closely in the future.  I think I may remove the bags of char before I crunch them much more, as they are at a perfect state of crunchedness way earlier than with the boards.  

John S
PDX OR

Burned biochar again today. The nice thing about the bags is that because it crushes better, you leave it in there a couple of times, drive over it, check it, and drive over it one more time if you need to.  I checked and ran it over one more time.  Perfect.  It is very easy to remove the empty or full bags and put them off to the side.  I am very appreciative of those other permies who clued me into the idea that there are toxins in the plywood so I could change to the new system.  

John S
PDX OR

I was having a hard time checking on the size of the char inside the bags, because it is black and dusty.   I know the dust is bad for your lungs.  Coal miners get black lung disease.  I decided to leave a spray bottle there by the bags to cut down the dust and so I can see the size of each piece to determine if I need to crush it more than it is.  Spraying it helps with both: I can see more clearly, and I breathe less dust.  

John S
PDX OR

One advantage of the short period of time required for breaking down the char in bags is that it's more flexible.  I can wait if I need to, because it won't take as many days.    If it's going to rain on my next regular burn day, I can wait and burn the biochar in a few days when it's dry, so there will be less smoke and more char out of the wood.

Another thing that I just realized is that since the burlap bags are portable, I can put them in the rain to decrease dust.  I can also fill my inoculation buckets up to just the right amount out of the bags. If I have some char left over in the bags, no problem.  It can wait in the bag until the next round of inoculation.  I can even choose during the next burn to use a little less wood, to try to fill the bucket up exactly right the next time.

John S
PDX OR

Another factor I've noticed with the bags is that the size of each piece of the char is more variable. This isn't really a problem.  I think a mix of sizes is probably good.  I have to break up a few of the pieces with my hands.  If I kept all of it under the tires until they were all the right size, I would have a lot of char dust. It sounds like star dust, but it's not really optimal.  It would retain much less moisture in the soil that way.   It's just a slight difference to how it used to be.

John S
PDX OR