I usually coat the cardboard first with white glue and let it dry. Especially on very thin cardboard.

It sounds like too much water is involved, and the moisture is saturating the original box.  If you are soaking your paper strips in the adhesive, don't.  Just brush some adhesive onto one side of the paper and apply it to the box and smooth it down, and repeat.

Sue

I'm not really sure about this, I'm just throwing some ideas out there.

Somehow, I am thinking the problem is caused by moisture.

I don't know what that kind of box that is, so I am wondering if it's thin, if it's absorbing the moisture from the adhesive, and the stresses of drying is causing the distortion.

Mostly, water in PM is good, as it works to help bond the fibers together, but with a project like yours, less may be better.

It's possible that the gravy-like consistency of your adhesive is too thick, and is holding too much water.  But if the base box is thin, there may be invisible stresses from its manufacture that are also causing problems.

I would thin down the glue so it's more like watery eggwhite, and try that.

Another idea comes to mind, but I'm not sure it's workable:  Find some wood or styrofoam that would fit inside the box to help the box keep its shape as it's drying.  I would work on either the sides or the bottom first, and let it firm up (if not dry completely), then do the other.  You may not need to do it this way, it's just a thought.

The only other thing I can think of is to get some shellac (real shellac, not synthetic), which is alcohol-based and non-toxic, and coat the bankers box with that, let it dry (doesn't take too long with shellac), and then start applying your PM.

If you find something that works, please post here and let us know, okay?

Sue

I am happy to report that I was able to get the lid of the bankers box that warped into its original shape by putting in on top of the box, putting more paste on half of the lid, and then pressing it down on the other half that didn't have paste on it with a weight. It worked perfectly! I am so happy I don't need to throw anything out.

I have been using julie tretakoff advice, except since I don't have any white glue I have just been brushing the paste on the cardboard first, letting it dry - and then papier-maching over it. It seems not to be warping now.

Thanks so much for your helpful advice guys! I am sure I'll be harassing you for more of it in the future.