While there are several methods for creating a double border on a mosaic crochet project, this method is the one I most prefer. There are benefits of some of the other methods as well, but it's a matter of personal preference. Some people like the Slip Stitch Start method because it gives a good structure to the border. I personally like the Front Post Stitch Start method better though. One reason is that it's easier to see where to make your border stitches with the front post method. Another reason is it saves time because it skips the step of having to make slip stitches around the project, which also saves a bit on yarn.
In order to be able to start your border with front post stitches you need to have a chain space near the edge of each row of your mosaic projects. For this reason, most of my mosaic patterns include a chain space next to the border stitch on each end of each row. This post will show how to create a solid border. Feel free to customize your project with a pattern in the border, or even a different stitch such as linen stitch for the border rows. That's a subject for another post.
To begin the border, turn your work so the back side is facing you. You can start with the front facing, but it’s easier to see your stitches and makes a cleaner border if you start with the back side.
Round 1: With your border color attach yarn with a standing fpsc (front post single crochet) around the chain in your foundation row that lines up with the chains along the border. This should be the next to last chain of the foundation. Work a fpsc around the chain at the end of each row, including the last row.
When you reach the corner, chain 2 and turn your work 90 degrees so the top of the blanket is facing you.
Work a sc (single crochet) in the front loop only of each stitch across the row, stopping at the stitch before the chain at the other end of the row.
Chain 2 to create the 2nd corner. Turn again to work down the next side and work a fpsc around the chain at the end of each row. When you get to the end, chain 2 to create the 3rd corner. Turn again to work across the bottom of the blanket. Work a sc in the front loop only of each stitch across and stop when you reach the fpsc that started the round. Chain 2 to create the 4th corner and either slip stitch to the first fpsc or invisible join to the first fpsc.
Round 2: Chain 1. Scblo (sc in the back loop only) in the same stitch as join. Tip: It may be helpful to place a stitch marker in this first sc so it's easier to see when you complete the round.
*Scblo in each stitch across. When you reach the chain-2 corner, sc in the first chain (in the actual chain, not in the ch-2 space).
Chain 2. Sc in the second chain of the corner ch-2 (in the actual chain, not in the ch-2 space). ** Repeat from * to ** until you reach the beginning of the round. Either slip stitch to the first sc or invisible join to the first sc.
Round 3: Repeat Round 2. You’ll notice you’ll have to sc an additional stitch each round after the last corner before the join. Fasten off after round 3. (If you choose to work more border rounds repeat round 2. Just be sure to work the same number of rounds for the front and back so the stitches line up properly in the joining round.)
Turn your blanket so the front is facing you. Before working the front layer of the border tie the yarn ends in a knot in pairs. You can then trim the ends short – about 1-2 inches long is plenty.
For the front border, repeat rounds 1-3 of the back, working the fpsc stitches around the chains at the row ends under the stitch from the back layer. Do not fasten off at the end of round 3.
Tip: I find it easier if I gently hold the back border down out of the way while I work the front border.
Joining round: Chain 1. Holding the front and back border layers together so the stitches align, sc in the back loops of both layers to join. When you get to the corners sc into the 1st chain, chain 1, sc into the 2nd chain. Make sure the trimmed yarn ends from the sides are enclosed between the border layers as you stitch. Fasten off and join the round with an invisible stitch. Alternatively, you can join with a slip stitch to the first sc of the joining round and then fasten off. Weave in yarn end.