GingerK

I think you have been given some very good advice. One thing that I do, is mark the seam of each block on the border. So if my blocks are supposed to finish at 12 inches, I will have marks at 12 1/4, 12, 12 and so on until the last at 12 1/4. If the blocks have a lot of HST's I will even go so far as to mark the center of each block. I find it is the best way for me.

You have been talking a lot about borders, but what about your binding? I made a baby quilt that ended up with a tsunami of waves on the borders. I was soooo frustrated because it was a gift. I ended up taking off the binding and letting the quilt just sit for a few days. I then re-pinned my binding on before sewing, and had a whopping 5 inches extra!! Guess I was stretching the body of the quilt while I was sewing on the binding.

Barb2018

I stay stitch the edges of my border pieces with a small stitch about 1/8-inch from the edge. I've never had a wavy border.

cashs_mom

I often do this also. It seems to make things stay flat and square and helps the bindings go on well and easily.

GingerK

Agreed about stay stitching around the top. It is also very helpful to the longarmer, because it keeps any seams on the edges from coming apart.

I had one other thought--if you piece your border, do you use a straight seam or a diagonal seam? If you use a diagonal seam, the border will be more prone to stretching.

Onebyone

I use straight seams when piecing a border and my binding too. I rarely use solids for borders or binding, so the seam isn't noticeable at all.

Snooze2978

As I didn't want to put a nail into my plaster walls, I used velcro on both the top and bottom corners. Seems to work well for me. Occasionally I'll find my bottom ends have loosened the velcro so I just press it back to the wall and it's good for more time.

Stitchnripper

This is what I do. For me it works consistently for non wavy borders. I am not an expert but this technique is great in my experience.

Still Sew N

I had not thought about the binding. It is very possible I am stretching the quilt while putting on the binding. That makes sense. My quilts are nice and flat and then after washing, drying, I have been getting waves. Thank you!

Still Sew N

Thank you all for your great suggestions! I will try them and hopefully get a cure. Thank you!!

GingerK

There is one (or maybe two or a combination) that hasn't been mentioned. You said you prewashed all your fabric. But if you are using 80/20 batting and are not doing dense quilting, the batting might be shrinking a bit while the fabric is not. So many variables.