I don't understand why your zap is thickening. I live in Florida and leave my ZAP opened and on the shelf in my workshop for as much as a year. I don't even put the cap on the Zap a Gap. It is just as good as the day I opened it. I did have one bottle of thin Zap thicken after a little over a year but I had never even opened it. I buy my Zap from Tower Hobbies because I believe that their stock is fresher than that in any hobby shop. I usually buy 5 bottles 2 oz Zap a Gap and 2 bottles of 2 oz thin Zap at a time. To have only one bottle thicken in over 20 years of modeling attests to the quality of ZAP. That's my $1.98 cents worth. Ron