I’ve made these with my trusty craft cotton and a 4.5 mm hook. Instructions below use US crochet terminology and uses standard crochet abbreviations.
1. Chain 4, and join into a circle.
2. Ch 3 (counts as first dc), 2 dc into ring, ch 2, *3 dc, ch 2; repeat from * 2 times more. Join into the top of ch 3 with a sl st.
3. Sl st into the next ch 2 space.
4. Ch 3 (counts as 1st dc), 2 dc, ch 2, 3 dc into same ch space. Ch 1. *(3 dc, ch 2, 3 dc) in next space, ch 1; repeat from * 2 times more. Join into top of ch 3 with a sl st.
5. Ch 1, sc 1 in same stitch. Ch 1, miss a stitch, sc 1, ch 1. This will bring you to the corner space. Work sc 1, ch 2, sc 1, ch 1 into corner.
6. *Sc 1 in dc, ch 1, miss next dc, sc 1 in next dc, ch 1, miss ch 1 space; repeat from * as you continue around each side, working (sc 1, ch 2, sc 1, ch 1) into corner spaces. (you are basically working sc 1, ch 1, around working 2 scs and an extra ch in the corner)
7. Don’t join with a slip stitch into the top of the 1st sc as it is too bulky. Instead work your slip stitch into the next ch 1 space after the 1st sc.
8. This round you are working your sc into the ch spaces from the previous round. So ch 1, work sc into same space, ch 1, sc 1 in next sp, ch 1; (sc 1, ch 2, sc 1, ch 1) into corner. Carry on around the other sides continuing the pattern sc 1, ch 1, working your sc into the ch spaces from the previous row and working the corners as set. As before at the end of the round join by working a slip stitch into the ch space after the 1st sc.
9. Repeat last row once more. I think that 3 rounds of moss stitch is enough for a coaster.
10. To finish don’t join with a slip stitch but cut yarn and pull through the stitch.
11. Thread through a needle and push the needle from front to back through the top 2 loops of the next ch st.
12. Sew back into the end stitch, and tighten loop to the same tension as the other surrounding stitches.
13. This way you shouldn’t be able to tell it apart from the surrounding stitches.
14. Fasten off at the back.
And that’s it. Go and make yourself a cup of whatever you fancy, rest it upon your new mat and admire.
Want a bigger mat; just make your granny square bigger and work more rounds of moss stitch.