Originally Posted by
Holice
I would definitely line the borders so all will be the same thickness. Also if you are putting sashing in I would line that as well. As to leaving edges without foundation. I would trim to 12" so again, all would be the same, otherwise there might be some of the seams bulkier than others due to catching some of the foundation in the seam and some areas just the string. Leaving some areas without foundation can cause difficulty in quiting, both home machine as well as long arm.
I have taught string quilting and always recommending this way to make the entire top consistent.
I would trim to 12 inches. No need to line the sashing. I have used interfacing on t-shirts but not the sashing when making a t-shirt quilt. Differences in the thickness did not matter. When you do appliqué, you will have a difference in thickness there too and that is not an issue. This is just what I would do. A lot of people will have a different opinion. I don't think it will matter much either way. Post pix when you are done!!