I've used the Weldwood gel formula before and it is a bit easier to spread evenly on foam. http://www.dap.com/product_details.aspx?product_id=36  It seems to not soak into the foam quite as much as the regular contact adhesive.  Perhaps that would work better for you.  Just one more thought also... You are stirring up the contact adhesive really well right?  It tends to separate over time as it sits.

We use a scrap piece of foam about 2-2.5" wide by 3" or so long.  Dip the end into the contact cement just about 1/8" and remove.  Allow excess to drip off. Turn upside down to allow glue to soak into foam just until it looks like there isn't any sitting on top of the foam.  Using the foam, dab onto pieces that will be glued.  Repeat often.  As the foam scrap gets soaked and starts to bend or flop over with to much glue and pressure, cut off end for a fresh start.  Let the pieces dry just until the glue no longer feel cool. Join pieces, hold for a few seconds.

I prefer the original weldwood simply that the gel doesn't seem to go as far. We glue alot of pieces, so we try to make the supplies last as long as possible. Got to save those $

Julie

ok i was back at it tonight. I had reglued with hot glue, just to hopefully get them to stay. some did some did not, so i went back to the weldwood. at the tackiest time i tried to put it together, and kept trying. it didnt stay at all. then the window was gone.  not sure if it doesnt work because of the other glues under it.  i stirred it, but it is pretty humid here tonight. gonna try with fresh pieces tomorrow. grrrr   thanks for all your support and ideas... i will not give up!!

Are you doing this outside in the heat and humidity? Where do you live? For the most part I've had a workshop studio to work in where we had areas we could glue but they where still inside in a controlled environment. The times I've had to go outside to glue I often would go out and coat the pieces then bring them inside to set up. There is a temp range marked on the can and I know that most the country right now is outside that range so that may be the issue if you are doing this outside. The fumes can be harmful but I think if you coat outside and then can find someplace inside to bring them that is not too small a room and closed in you should be ok. Set up a fan on low to lay them in front of. This is more for fume distribution but can help the drying process.  Be aware though that small pieces can be blown across the room if the fan is on too high.

Are you using a multi-temp glue gun? I have one and use the low setting, you have to move quicker when setting the pieces, but I never had an issue like this......knock on wood!

Tackiest time? It seems to me that it is seems almost dry when it is ready to press to the other piece. It seems crazy that those two almost dry surfaces will stick together. If it is bone dry and hard that is too long, but it won't stick good if you try too early or it is still wet like.  It is hard to describe the right timing.  Maybe you could try some tests at different times to see which one works best for your situation.  

So i am back at it tonight. the humidity was awful, so i had to wait it out. then i think my can of adhesive, which i attempted again yesterday to use, may no longer be good...the can does not close well...so possibly not as effective. i still had many seems coming apart...so tonight i got a new can of the weldwood contact cement..but this time it is the gel. we shall see. Also bought gorilla glue...  i will let you know how it goes.   again, I cant tell you how much i appreciate all the ideas and advise!!!

ok, an hour later and i am positive that it was the can of adhesive that was bad...this new stuff is awesome...however, must.use.outside.!

Don't use the gorilla glue on the foam.  You have to dampen the surface to activate the glue and it foams and expands. It's better for other surfaces.

Julie

Thank you for that!! I was starting to feel desperate and would try anything...I will tuck it away for other household stuff.  i am sure my teenage son will need it for SOMEthing...

Yep I was going to say the same thing Julie did about Gorilla glue.  It can be a great adhesive but better for things that need space filled in when glued.   Glad to hear your new can of contact adhesive is working for you. Yep it can go "bad". Keep the rim of your new can cleaned off so it seal well. Something like acetone can be used to clean it up. You can even peel off old dried adhesive normally if it gets really bad.  While we are on the subject, it might be best for the occasional user if they buy the contact adhesive in the smaller tubes if they can find it. In fact often this is all I can find at hardware stores.