One of the fun things about a blog is that I get to see the search terms that got you here. Over the last week or so, I’ve gotten quite literally dozens of hits from people searching on compost bins. My design may not be the end-all, be-all of home-built composting systems, but it’s working really well for us, our neighbors, and our friends. It handles that much material that well!
So, because I love the idea of more people composting, I’m laying it all out there: materials list, step-by-step instructions, everything. My bin may be a tad overbuilt- Thadd did refer to it as the compost bunker, after all- but that’s because I plan on using this for a long time. So let’s get started. First, a review of what I have:
We built a 3-bin system, which seems to be the standard for a heavy-use setup. All upright posts are set in dry-pack concrete, and the lumber used is a mix of locally sourced white oak (I got a great deal) and some pressure-treated boards. I realize that there are concerns about using pressure-treated lumber in compost that may end up around food crops, and while I’m not completely convinced it’s a danger (before you tell me arsenic kills, note that copper is now the primary treating agent and arsenic is no longer in use), cedar would have been my first choice. But, I’m a landscape guy and this was done over the winter- cedar just wasn’t in the budget.
Because I’m tall, I built my bins to a height of 40 inches. This gives me plenty of room inside the bins, but thanks to my long arms I can still get all the way to the bottom with a pitchfork. I didn’t include height dimensions here, because you should build these compost bins to the size that’ll be the most comfortable for you to use.
For this design, here is the materials list:
- (16) 80lb bags of Quikcrete (whatever the cheapest pre-mix is; no need for high strength or fiber-reinforced)
- (8) 4x4x8ft posts
- (3) 2x6x16ft boards
- (12) 5/4x6x16ft deck boards (you could also use 1x6x16ft boards, but I happened to have a cheap supply of 5/4 board)
- (2) 2x2x8ft
- 10 ft of 1/2- inch hardware cloth/ poultry netting
- Box of 3-inch deck screws (if using pressure treated wood, be certain to get z185 galvanized OR stainless steel screws)
- Staples for attaching the hardware cloth- the ones you pound in one at a time with a hammer hold more securely than a staple gun
You’ll also need stakes, stringline, tape measure, circular saw, drill, and a level. If you can swing the five bucks for a post level- a little L-shaped piece of plastic with two levels and a rubber band attached to it, it is money well spent. For setting the posts, you’ll need a shovel and whatever else helps you get through your local soils, and a digging bar (spudbar) is a big help for packing the concrete mix. Let’s start!
Begin by picking a relatively flat, level part of the yard that drains reasonably well. If you get standing water in a spot, it’s not a great candidate for a compost bin. Next, you’ll want to lay out the footprint of your compost bin using stakes and stringline:
Here, I opted to run a string line parallel to my back fence. Then, I measured from the side fence to get the distance I wanted to offset in, and ran a line perpendicular to to the first line. From that line, I measured over the width of the bins, and set my third string line. The final step was to run one more string line for the front face of the bins, measuring off the first stringline.
This gave me a box, within which I could dig my footers. However, note that there are also four intermediate posts in the design; normally I would set two more string lines, one for each set of posts, but this is a rotbox, not a deck. A shortcut here or there isn’t going to mess you up- however, you want to make sure the post spacing is exactly correct. If you lay the posts out as I have drawn, you’ll have a the same-sized opening for each bin, which means that the removable slats are interchangeable.
So as you can see, I dug a footer under each intersection of stringline. Here in Virginia, our frost depth is between 18-24 inches, depending on who you ask. I dug a 1 foot x 1 foot hole to frost depth for each footer, then poured in a bag of Quikcrete, and tamped the heck out of it with the flat end of the digging bar. I then stood the 4×4 post in the hole, aligned with the intersection of the strings, and made sure it was perfectly plumb (this is where the post level is a huge asset). I then poured in the second bag of Quikcrete, tamped it around the post (continually checking the post for plumb), and then backfilled and tamped the soil. Dry-packing like this is a great way of setting posts for fences and things like bins, because it’s much easier to get the posts level and you don’t have to brace them while wet concrete sets up. I still recommend having a helper, especially if you don’t do this type of thing regularly; but in a pinch, this is a great way of getting this done by yourself.
Portland cement loves water, so it’ll pull water from the surrounding soil and set up hard as- um, concrete- in a day or two. If you’ve done a really good job of tamping the concrete and soil around your post, you *should* be able to screw to it immediately after setting. However, since I’m only an occasional carpenter, I prefer to give the mix time to set up.
Now that your posts are set, it’s time to build structure. Cut your 2x6s according to the plan, and attach them with the screws. Start with the longest boards first, on the back of the structure. Then attach the left and right side boards, so you have now created a 3-sided bin. Now, you can attach the 2x6s that divide the bins. If you look at the plans, you’ll see that the way I laid them out, not every bin is the same size. This isn’t a mistake; my goal, when I designed this composter, was to use the simplest means of attachment that would also be very strong. Minor variations in bin size are a non-issue here; the important thing was to keep the bin openings consistent.
Ok, now that we’ve made a frame sturdy enough to hold a truck, let’s go about keeping our materials in the bins. Cut your 5/4 boards as called out, and attach them to the backs and sides of the bins. I left a gap between each board to facilitate air flow; a little compost falls through when I turn it, but not enough to matter.
Now, take your poultry netting and cut it to fit. Attach it to the 2x6s, and also to the posts. Be generous- the staples are cheap, and you’ll be cooking a lot of material here.
The final step is to create your channels to hold the front slats in place. Cut the 2x2s to length, and screw them to the centers of the posts (check the spacing as you go, of course!). Now, screw a 5/4 board over each 2×2. All that’s left is to rip your slats to length (34 inches, if you put it all together as drawn), and you’re ready to compost!
If you opt to build your bins based on these plans, or a variation thereof, please let me know in the comments. Also, if you take pictures, I’d love you to post a link in the comments, whether they be on your website, flickr account, or whatever it may be.