Another thought is the grain of the backing fabric. Less stretch with the lengthwize grain.
Libby Lehman puts a narrower sleeve on the bottom of the quilt in which she adds a rod. She sews one end shut so that it can't be hung upside down.

Margo had it right (as usual). I almost exclusively make wall quilts. I use an 80% cotton/20% poly batting, only one layer unless I particularly want the quilting to puff up. If I do, then I add a wool layer on top. Wool alone is not adequate for a wall quilt. I have tried other battings and they just don't seem to stay as straight.

I preshrink/prewash all my fabrics, which makes a difference too, especially if you live in a damp climate. And then I wash and block my quilt after it is quilted and before I put the binding on, square it up, and then apply the binding, which I have also pre-washed. Also, hanging it with a strip of wood or dowel all the way across in the rod pocket supports it so it doesn't sag.

Also, something that can affect it is if you cut your quilt with the straight of the grain. A little off one way or another can make it wave in time. This does not apply for applique, that can be cut off grain without affecting the way the quilt hangs, however.

A little trick you may want to try is something that drapery makers sometimes use...loosening the binding and hiding some small flat drapery weights or a chain across the lower edge, then sewing it back, could help fix an already completed, wavy quilt.

Cheers,
BJ

Another suggestion for batting for wall hangings is to use felt instead of a regular batting. This is what Leah Day uses in her quilts. I haven't tried this yet since I don't make many wall hangings, but this is definitely what I plan for my next one.

tnx everybody, i will iron the quilt and stiff it as a brick with starch, the next one i will use heavier bading, on this one i used the syntetic most light one, i thought may be it will be easy to quilt with this beding....
about the border, i try to use the method on the book modern quilt - did any body have an experience with it, i find it nice but i need to get use to it.

I think mine are just not stiff enough. I am very careful with measuring but I usually only use one layer of batting and I have started using wool so that is probably the reason. Of course, if I quilted it to death I guess it would hang without waves--can't wave if you are dead. OK--maybe I am a little punchy working with those HSTs.

Wavy wall quilts can be the result of a lot of factors. You need a really sturdy batting, and sometimes two layers of it! A single layer of polyester or wool is just not strong enough.
Your quilting needs to be a consistent density all over the quilt.
Your borders have to be the same length and width as the center of the quilt. Too long will cause "friendly" borders (waving at you!) or too short will cause cupping.

After your quilt is complete, it should be blocked and thoroughly dried flat before hanging it on the wall.

Hope those tips help.

My quilts get wavy after being on the wall for a while and I think it is probably the weight of the quilt causing it. I will be interested to see what others think.

My amateur opinion is that maybe you are stretching the fabric as you quilt? All I can think of is to wash the quilt and block it, then let it dry on it's own. Spray starch the heck out of it and steam iron it into submission..... Maybe?

Good luck. I should take my own advice. My earlier quilts looked just like yours.

hi there,
few months ago, i have asked how do you squeeze the all quilt in the area of the sewing machine...., ok, now i did quilt the quilt by domestic sewing machine, and when i finished it, binding it...i hanged it on the wall...i am so sad, i tried to make it as strait as possible but the quilt is wavy from the wall, dont know what to do to correct it, i did some quilts before, all of them are wavy - please help. tnx