How to rescue a crotch seam
Short answer: The crotch seam moves more than any other seam. Sew it with zigzag in two rows, and start and finish well inside intact fabric. Sew from the inside, so the seam lies flat against the skin.
Why the crotch seam goes first
Every time you sit down, the crotch stretches several centimetres, and that happens hundreds of times a day. No other seam in a wardrobe is stretched so often and so far. That is why the crotch seam often gives up first, long before the rest of the garment is worn.
What you need
You need a sewing machine with zigzag or a needle, a thread in roughly the garment's colour, scissors and a few pins. A thread that can stretch is preferable. Ordinary thread also works if you leave it a little slack.
Look at the seam first
Turn the garment inside out and find the spot where the seam has opened. See how far it is open and where it is whole again. Check the fabric beside it too: if it is worn thin, sewing together will not hold, and a piece of thin fabric must go behind it first.
How to sew the seam
Turn the garment inside out. Sew a zigzag with a little slack in the thread tension along the old seam, starting and finishing three centimetres inside the intact seam. The overlap spreads the pull, so the seam does not open at the transition. Keep the stitch small and even, and do not pull the fabric.
Sew two rows
Repeat the zigzag two millimetres beside the first row. That gives a reserve if one row gives way, and the crotch gets a seam that is stronger than before. Two rows take only a few extra minutes and help the repair withstand the many movements this seam meets every day.
From the inside, not the outside
Always sew from the inside. The seam should lie flat against the skin without being hard or sticking out. If it lies thick, it can chafe, and the garment becomes uncomfortable to wear. Press the seam flat with your fingers before you sew, and check afterwards that it lies evenly.
If the gusset is loose
In panties the gusset is often sewn to only one end on purpose. Do not sew it down at both ends if it was originally free. See how the original seam lies and follow it. You can see the range at bamboo panties and inner shorts.
Which underwear it suits
The method suits panties, underpants and shorts with a crotch seam, where the same seam moves all day. You can see the range at bamboo underpants for men, bamboo panties and inner shorts. If the fabric around the seam is worn thin, a replacement is usually better than another repair.
How to make the repair last
Wash the garment on a gentle cycle and avoid high dryer heat, so thread and fabric last longer. Check the seam after the first few washes, and sew again if it begins to open. A repair in whole fabric lasts as long as the rest of the garment.
Frequently asked questions
Can you use straight stitches
No. Straight stitches in the crotch open again within a week, because the seam cannot follow the stretch of the fabric. Use zigzag and leave the thread a little slack.
Should you sew from the outside or the inside
The inside. The seam should lie flat against the skin, and a repair from the outside often shows and turns hard. Always sew from within and press the seam flat first.
How long does the repair last
In whole fabric, as long as the rest of the garment. If the fabric around the seam is worn thin, the repair will not hold, and finding a replacement is better.
You can find the full range at Bamboo-Clothing.com.
