Stick with it!
WeldBond, a clear drying PVA glue, is available in 3 different sizes at the Stick. Use it to seal mosaic bases and as an adhesive for any indoor mosaic project. Plus, it's nontoxic, which is nice even if you don't have glue eaters in your family.
Thinset is a light cement adhesive that holds up to water and endures MN winters. Just mix this powder with a little water until it looks like frosting - yum!
Disclaimer: We do not recommend eating your thinset, just admiring it.