Understitching curved edges for neat, comfortable facings

A well-made facing gives a neckline, armhole or opening a clean finish without adding the weight of a full lining. The difference between a facing that lies flat and one that rolls, flips or shows from the outside often comes down to one small construction step: understitching.

This technique secures the seam allowance to the facing on the inside of the garment. When the piece is turned right side out, the stitching gently encourages the facing to sit underneath the garment edge. It is especially useful on curves, where fabric has to spread, compress and turn smoothly.

Whether you are sewing a lightweight summer top for Brisbane or a layered knit for a cooler Melbourne wardrobe, careful pressing and accurate stitching make a noticeable difference. The method is beginner-friendly, but a few practical adjustments will help you get a professional result.

Why understitching changes a facing

After stitching the facing to the garment, the seam allowance naturally wants to roll towards the outer layer. Understitching anchors that allowance to the facing, keeping the raw edge hidden and helping the finished edge turn towards the inside. It is usually sewn a few millimetres from the seam line, through the facing and both seam allowances.

The stitching does not normally reach the garment body. Stop just short of corners, shoulder seams or other bulky intersections, then use a pressing tool or a few hand stitches to settle those areas. On a neckline or armhole, the line may look slightly curved rather than perfectly parallel to the edge, and that is exactly what you want.

A simple project such as the Love Notions Allie Top offers a useful setting for practising this finish. A relatively uncomplicated top lets you concentrate on controlling the curve instead of managing several complicated construction details at once.

Gather tools and prepare the edge

Before sewing, check that the facing has been interfaced appropriately and that its seam allowance matches the garment. A facing that is too narrow may be difficult to understitch, while one that is very wide can feel heavy around the neck. Transfer notches accurately, particularly at the centre front and centre back, because they help distribute the curve evenly.

Choose a fine or medium universal needle according to the fabric, a thread that blends with the facing, and a stitch length around 2.5 to 3 mm. A small iron, tailor’s ham and sharp fabric scissors are valuable for curved areas. If the fabric is slippery, use extra pins or clips, but remove them before the presser foot reaches them.

Interfacing affects the behaviour of the whole edge, so it is worth testing scraps first. This guide to choosing collar interfacing is also relevant to facings, especially when deciding between a soft fusible, a stable woven option or a lightweight knit interfacing. Australian fabric shops and online retailers can vary in stock, so buying a small sample or checking the fibre content before ordering saves frustration.

Sew the curve without puckers

Place the facing and garment right sides together, matching the neckline or armhole seam. Align the notches and shoulder seams, then pin with the facing uppermost if that gives you better visibility. Sew slowly around the curve, keeping the seam allowance consistent. Avoid stretching either layer; even a slight pull can create ripples once the edge is turned.

For a tight curve, take a few stitches, stop with the needle down, and gently reposition the fabric. Do not force the edge around the presser foot. If the seam allowance is wider than the pattern recommends, trim it down before understitching, leaving enough fabric to support the seam. Grading one layer slightly narrower than the other also reduces bulk.

Once the facing seam is sewn, press the seam allowance towards the facing before stitching. This preliminary pressing makes the understitching line easier to control. Sew from the facing side, catching the facing and seam allowances but keeping the garment layer out of the stitching. Aim for 2–3 mm from the seam, or as close as your machine allows without drifting into the garment.

For a very shallow neckline or narrow armhole, you may only be able to understitch part of the curve. Sew as far as possible from each end, then press the remaining section carefully. A garment such as the Love Notions Gemma Tank is a good example of the kind of warm-weather style where a tidy armhole finish matters: there is little fabric to disguise a bulky or uneven edge.

Press, clip and turn cleanly

After understitching, trim the seam allowance with pinking shears or small snips where the curve is tight. Clip perpendicular to the seam without cutting through the stitching. On an inward curve, small clips allow the seam allowance to spread; on an outward curve, remove tiny wedges if the fabric is particularly full. Space the clips more closely around sharper sections.

Press the seam over a tailor’s ham, following the curve instead of flattening it on a straight ironing board. Use the iron to set the stitches rather than dragging it across the fabric. Let the piece cool before turning, as warm fabric can relax back into an unwanted shape.

Turn the facing to the inside and use a blunt point turner to ease the edge into place. Avoid sharp scissors or a knitting needle, which can push through the seam. If the garment fabric keeps rolling to the outside, press from the facing side and gently roll the seam a fraction towards the inside before cooling it.

The same patience used for a curved seam is useful in other precise crafts. If you enjoy making objects as well as garments, careful craft projects can reinforce the habit of marking, shaping and checking each stage before committing to the next one.

Troubleshoot common facing problems

A facing that shows from the outside usually needs more understitching, closer trimming or a slightly wider seam allowance. Check that the facing was cut accurately and that the interfacing has not stretched the edge. If the facing rolls out after washing, secure it at shoulder seams with a small slip stitch or a discreet thread tack.

Puckers often come from stretching the curve while sewing, using stitches that are too short, or failing to clip an inward curve. Unpick only the affected section if possible, ease the fabric back into shape and resew with a steady feed. Pressing alone will not remove a stretched seam permanently.

If the edge looks angular, the curve may have been clipped too little or the seam may have been sewn unevenly. Mark the seam line on the facing before joining it if visibility is poor. A washable fabric marker can be particularly useful on pale cottons and linens, which are popular choices for Australian summer sewing.

For makers who enjoy applying the same shaping principles to larger projects, surfboard shaping plans show how measured curves and controlled trimming affect the final outline. The scale is different, but the lesson is familiar: smooth results come from small, deliberate corrections rather than forcing a material into place.

A reliable finishing routine

Use this sequence whenever you are working on a curved neckline, armhole, pocket opening or waist facing:

• Check the facing pattern piece against the garment before cutting.
• Test the interfacing and stitch settings on a fabric scrap.
• Sew the joining seam without stretching either layer.
• Trim and clip the curve before turning it right side out.
• Understitch from the facing side as close to the seam as practical.
• Press over a curved surface, then tack the facing at key seams if needed.

The quick guide below can help identify where to focus when a finish is not lying flat.

Problem	Likely cause	Useful correction
Facing rolls to the outside	No understitching or insufficient pressing	Stitch the seam allowance to the facing and press the edge inward
Small puckers	Curve was stretched or not clipped	Unpick the worst area, clip carefully and resew slowly
Bulky neckline	Seam allowances are too wide or ungraded	Trim, grade and reduce bulk at intersections
Uneven edge	Inconsistent seam allowance	Mark the seam line and use a slower machine speed
Facing shifts during wear	It is unsecured at key points	Add discreet tacks at shoulder or side seams

With practice, understitching becomes a quiet but dependable part of garment construction. It is particularly worthwhile on sleeveless tops, summer dresses and lightweight layers, where the inside edge may be seen during movement. In Australia’s varied climate, from humid Darwin to breezy Hobart, a neat facing helps handmade clothes remain comfortable, washable and polished.