22. But first we have to make our backing strips. These need to be twice the width of the steam a seam, so 1 ½ inches wide. I don’t worry about length – I just cut a couple across the width of the fabric then trimmed them as I went – to lazy to do the maths ! But if you prefer to calculate how many you need in advance, go for it ! You need a backing strip for every joint between the blocks and then long strips to cover the joints in the rows later on. My strips are in the same fabric as my backing. It’s a fairly soft, thin unbleached cotton. Try and use something soft and fine or it will get really stiff.