I've been using my fair share of thick fabrics lately. The denim shirtdress, the Green with Envy shirtdress and my Sew Grateful Skirt. Needless to say, thick fabrics can a be a beast to maneuver unless you grade and trim your seams. What's all this grading and trimming you say? Here let me show you.
Grading a seam is making all the layers of the seam allowance a different width so that when the whole of the seam is pressed into place it doesn't create a bulky ridge on the right side of the fabric. Having said that, you might wonder where and when to grade. I know I did for a very long time and found that I never graded any seam because I felt that doing so weakened that area of the garment - having made the seam allowances shorter, I had introduced weak areas that could fray easier and then cause a blow out somewhere. But over the years I've come to realize that grading is necessary for a beautiful finish and unless you plan to put your final garment through a lot of serious, rigorous washing a graded seam is just as strong as an ungraded one.
Now the thing to remember is that not all seams are graded. Seams that need to be graded, especially when using a thick fabric, are ones that are pressed to one side or sandwiched inside areas of the garment that you can't even see or get to from the inside (like in a waistband facing). Let me give you an example. I didn't grade the seam allowances for the skirt side seams of my Green with Envy shirtdress. Those are pressed open, like a traditional seam. But I did grade the seam where the pocket lining is connected to the dress because this seam allowance is a) pressed in one direction and b) sandwiched in between layers of the garment. Make sense?
So how do you grade a seam? You'll start by sewing your seam and then its time to trim. Depending on how many layers I'm dealing with I like to trim to 1/8", 1/4", and 1/2". If I've only got two layers of fabric that's going to be pressed to one side, I start by trimming the first layer to 1/2" and leave the other seam allowance at 5/8". If I've got 3 layers of fabric then I would trim the first at 1/4", the second at 1/2" and leave the last at 5/8". Make sense?
This next little trick is probably the best trick of all. It's probably something that you all do anyway too, but it's not something I started doing until a little over a year ago. I feel it makes a huge difference in dealing with bulky fabrics, but also in dealing with any fabric as I do it on every project that I sew now.
This trick is applied to seams that end up intersecting one another. Think setting in a shirt sleeve - you have two (sometimes more) seams in the armscye/bodice area and one seam (sometimes more) in the sleeve. After sewing the intersecting seams together, trim the corners of each seam at an angle (creates an inverted V). I find it especially fabulous in seams like the side seam of a skirt that attaches to a waistband that also has a side seam. Leaving the seams un-trimmed, will create 4 layers of bulk!!! Clipping that little inverted V will leave you with much less bulk. This trick also works on french seams too. Pretty impressive huh?
Now, how's that for working with a bit of heavyweight fabric? Now you can maneuver them like a pro!