You could try a syringe. Get a wall-paper roller, they're a little plastic roller with a handle that you can find at most paint/wall-paper stores. Find the largest gauge syringe needles you can (try a farm-supply store - they carry bigger ones than most pharmacies). Water down the paste a bit before you put it in the syringe and inject it into the bubble (don't use too much! If you use too much it'll leave bumps.) and go over it with the roller. HTH BGK