I’ve only made 3 coasters and 1 placemat so far but that’s enough to let you know how it was done. They were made using the same stitch as the vintage phone case, they’re nice and thick and seem quite robust so far. As always I’m using English crochet terms so look at the conversion chart for the American equivalents.
I’ve used quite a thin recycled grey cotton doubled up so that it’s ~dk/worsted weight and a 4mm hook.
row 1. Chain 50
row 2. chain 3, turn, tr in 3rd chain from hook, *skip one stitch, dc and then tr both into the next stitch*
* repeat to the end of the row and just 1dc in the last stitch of the row.
row 3. chain 2, turn, tr into the dc at the end of the last row (the 3rd chain/stitch from the hook), *skip one stitch, dc then tr both into the next stitch*
* repeat to the end of the row ending with 1 dc in last stitch of the row.
Repeat row 3 until the piece is as big as you would like the placemat – I completed 30 rows in total.
Do not fasten off but turn the work 90 degrees and continue in the direction you are going – dc all around the edge with 3dc in each corner. Fasten off and weave in ends.
Follow the same instructions as for the placemat but to begin chain 14 and I completed 12 rows but you should add or subtract a few to make them square. Finish by dc-ing all around the edge as for the placemat.