If you have the time and materials to build a set of three compost bins then the simplest and cheapest way is to build them using corrugated iron. This post is based on the corrugated iron compost bins that I built some years ago.
The first thing to do is to decide how big you want your bins to be. This will largely depend on how much compostable material your garden generates. For this example we will set the size of the bins at one by one metre, which is the recommended minimum size for the production of good compost.
The next thing to work out is how many bins you will need to build. Three one M2 bins is the number of bins recommended for a large garden. If you have a small garden then consider building just two one M2 bins rather than three smaller sized bins.
For more information on compost bin size and numbers see Compost Bins Size And Placement.
EQUIPMENT
- Posthole digger. (Though a spade will do).
- String line.
- Spirit level.
- Cordless drill. (To drive in the hex screws).
- Measuring tape.
- Tech screw driver tech bit.
- Crowbar. (To pack the soil down around the posts. Though this can be done with a lump of wood).
MATERIALS
- Eight fence posts 125 x 75mm x 1.5m.
- Corrugated iron sheets. One 3 m x 862 mm, four 1 m x 862 mm.
- Nine 200 x 50 mm x 1 metre landscape timber planks. (These will be shortened slightly to fit in slots at the front of the compost bins so do not cut them until you have worked out the exact length required).
- Twelve timber strips 800 x 20 x 20 mm. They will be used as guides to hold the hardwood planks in place at the front of the bins. Approximate sizes only, I used garden stakes for this purpose.
- Tech screws (to bolt the iron to the posts).
- Wood screws or nails. (To secure the timber strips to the posts).
a: Digging the holes
Dig eight post holes in two rows. The holes should be 45 to 50 cm deep and one metre apart, measuring from the centre of each hole. The front row of holes should be one metre apart from the rear holes.
b: putting in the posts
Place eight 1.5 metre posts in the holes and tamp down with a crowbar to hold the post firmly in an upright position. As you are filling the holes use a spirit level and string line to keep the posts vertical and in a straight line. Make sure that the distance between each post is the same, so that the wooden slats used can be interchangeable with any of the bins.
Make sure that the posts are vertical and in a straight line, and that the distance between each post is the same.
c: Attaching the corrugated iron
Use tech screws to attach the rear and end sides of corrugated iron to the posts. The two inner sheets can be attached either side of the posts but make sure there is enough space on the front inner posts to attach the runners for the slats. To do this the two inner corrugated iron sheets will need to be slightly shorter than one metre.
D: cutting the slats
Measure the distance between the row of posts at the front (the distances should be the same) and cut nine 50mm by 200mm pieces of wood ten millimetres smaller than the distance between the posts.
E: installing the guides for the posts
To hold the slats in place at the front of the compost bin screw two thin strips of wood to the inside sides of the front posts. They gap between each strip of wood should be slightly wider (suggest 5 to 10 mm) than the width of the slats so they can slide in and out easily. Each strip of wood should be around 800 x 20 x 20 mm, though there is room for variation.
Photos of the slats and the strips of wood used to act as guides which were taken when the compost bins were first built.
The compost bins not long after they were built, which was some years ago. The bin of on the left has had two of its slats removed to access the completed compost. The bin in the centre is full of green waste that is in the process of breaking down into compost while the bin on the right is still having green waste added to it. As the widths between the bins are the same the removable slates are interchangeable with any of the bins
Plinth board
When making these compost bins I added a 150 x 25mm plinth board to the rear of the bins to raise the rear wall just that little bit higher. The aim of this higher rear wall was to reduce the risk of green waste falling over the back of the bins when the bins were almost full and green waste was being added. It certainly helped but was not really necessary, so I did not include it in the building instructions above.
steel retaining end posts
Some years after these compost bins were built the wooden strips used to act as guides for the slats rotted out. As I felt I needed to replace them with something more durable I decided to replace them with galvanised steel.
I bought three 75 x 1100mm galvanised steel retaining end posts and cut them in half, attaching the 550 mm lengths to the posts with countersunk screws so that the screws were flush with the surface of the steel. This worked really well as the 50 mm slats slid easily in the 75 mm wide steel posts, much more easily than with the original wooden guides. Though in hindsight a cheaper alternative would have been to use lengths of angle iron.
chopping board
Some time ago I built a chopping board that sits over the top slat of the compost bin that is being filled. It allows me to chop up coarse green waste (such as corn and broad bean stalks) so that when cut they fall directly into the bin. This avoids double handling of coarse green waste as well as providing a clear marker as to which bin is being filled.
TOP: The chopping board in place on top of one of the slats. It was built using some landscape timber offcuts. BOTTOM: The underside of the chopping board showing the sides that hold it in place. The sides could have been made out of a variety of materials including steel, it was just what I had on hand at the time.
