The present invention is directed to flux compositions and uses thereof. One composition comprises an activator, a medium-viscosity solvent being a polymer, and a high-viscosity solvent being a copolymer containing first monomers and second monomers. Another composition comprises an activator, and a high-viscosity solvent comprising a copolymer containing first monomers and second monomers. Another composition comprises an activator of 6-12 percent by weight of glutaric acid, pimelic acid, tartaric acid, or mixtures thereof, and a medium-viscosity solvent of 88-94 percent by weight comprising a polymer with hydroxyl end groups. Another composition comprises an activator in a liquid state comprising poly(ethylene glycol)-diacid, and a medium-viscosity solvent comprising a polymer with hydroxyl end groups. A soldering method for joining objects is also provided, comprising the steps of applying a flux composition to at least a portion of one or more of the objects, and joining the objects.