In order to get cob walls plumb and flat, trimming and cutting is a major step in the building process.
To build a cob wall, I will place a new layer of cob onto my wall, knead the individual cobs together a bit with my hands, and then stomp on top and kick the sides a bit. At this point, the excess cob is already hanging over the edge of the wall. Now is the time to start trimming.
What do you trim with?
When I first started building with cob I was taught to trim my walls with a simple hand saw. Many times people would cut out larger teeth and call it a “cob saw.” I think this tool does not deserve the name though.
The hand saw typically has small teeth that quickly dull from cutting through cob. The handle is uncomfortable and not ergonomic for hours of potential cutting work. The blade itself is short and you either have to stand at the level you are cutting at or bend down very far. A good way to make your back sore! The blade is also too flexible and will sometimes just contour to the organic shape of your wall making it more difficult to get the wall straight.
Solution? The Hay Saw!
The best tool that I can possibly recommend to anyone for trimming their cob walls is an antique tool called a hay saw (or sometimes called a hay knife). This tool is simply amazing for the job and is 10 times better than any hand saw!
My friend, Jamie Tyree, over at the Baleyree Shire is the one who first recommended this tool to me. He described it as like “cutting through cob like butter.” He showed me two in his barn that he picked up at a flea market, and I immediately went out to buy my own.
You can find hay saws in antique shops or on eBay for between $20-$40 a piece.
The hay saw blade is usually about 3 feet in length, stiff metal, and has two handles. It cuts through cob very well, makes a clean edge, and is very comfortable for heavy use.