Collage bumps

[ex-savesthed678.livejournal.com]

I make collages, and I seal them with mod podge. The only problem I have with doing this, is that bumps apear when I put it on the finished product. It's really annoying, to have bumps everywhere.. To put on the pictures I either use a glue stick or tacky glue... I know it could be from missing spots, and leaving them unglued, but I check for unglued spots most of the time and it still happens.

Does anyone know how I can stop this from happening?

Thanks!

P.S:: If you are into making collages these books are really awesome for Ideas:

Creative Collage for crafters
Creative Collage Techniques
The crafters complete guide to collage.