My personal preference, and its just that-Mine- is to use silicone as an adhesive for most things. Its flexibility when cured just works, especially for items that might tend to "breathe" a bit with temp changes. That being said, PVC can be tough to adhere to. And mosaic while it is tough, theres always a risk when dropping from any height due to the grout and so on.

I agree with wacky

I love your squirrel feeder. I'd like to make one someday.
That's terrible that the pieces fell off. :(
I'm thinking glue would work too. I'm wondering if that primer they make for PVC would be helpful too( ??? )

Thanks for your input. I do want to do another one and I will indeed try the silicone adhesive.
It is going to be affixed to a tree - it is not designed to sit on the ground. Just haven't gotten it up yet.

What a cool feeder!

There are a number of PVC cement products out there that would work. I just saw an ad for something called Quick & Easy Performance Plus, saying its eco-friendly, which means it should be safe for the squirrels and any other little critter that comes in contact with it. It's from a company with the first name Bond...I think. If it is not thick enough to act as a grout, wait until the PVC cement dries, fill seams with grout and then seal the grout with a good water seal product.

Hope this helps. Your squirrels should be thanking you!