For a few years I’ve been researching and also working with factories on the best way to make a crochet bikini comfortable to use in the pool or while swimming in the ocean, and here is my conclusion and the best ways to do it.
Elastic under SC row:
After you finish your project, cut a skinny elastic 4 cm shorter than the piece you’re going to apply it to, stitch both ends together and place behind your bikini piece. Start a new crochet row and go around the piece using the single crochet stitch to cover the elastic. This way you will have a strong bikini that stays when you dive or swim in the ocean or pool.
DC row with elastic:
This solution works really well and once the elastic is stretched after been used for a while, you can easily replace for a new one. Make a 1 DC 1 SC skip 1 around legs and waist. Pass the skinny elastic through it. Its a strong finish and your can use colorful elastic to match your work.
Silicon Elastic SC row:
After you finish your crochet bikini, start a row with a silicon elastic string, make a SC row with the elastic silicon around both leg holes and waist and finish with a strong knot. After you finish this row, make another row on top, with the same yarn used to make the bikini, to cover the elastic string.
Sew skinny elastic under the bikini:
After you finish your bikini, make another SC row around legs and waist to finish your work nicely. Use 3mm elastic to sew with the sewing machine inside your bikini. Note that you need to use the zig zag stitch to keep any elasticity of your crochet piece, and also the same color of your work. This is a good solution if you have many orders and need to make them fast.
Silicon skinny elastic :
This is the same elastic used for underwear, cut it a bit shorter than the crochet piece, even waist or leg hole, make a strong knot at the end and start a SC row to cover it. This is also a fast solution.
From this 5 ways of finishing a bikini, the ones I choose are the first 2, and the reason why is because the skinny elastic is more durable in chlorine water then the silicon, the silicon gets dry and brake after 1 year of using it, even though the 3 solution with the silicon elastic give your work an even finish then the skinny elastic because you need to pull the elastic while you are covering it with SC.