I have made a hat SS St. Seemed down the back with mattress st., fine.My question is how do I sew or join seem at the ribbed st. part (How I started the hat for a few rows)??thx, Babette;)
You can continue with mattress stitch. You may be seaming knits to purls, but it will work out fine. Remember that you're doing mattress st in the ladders between sts.
This tutorial helped me a lot when I started seaming: Knitty.com
Along with the videos on this site, of course.