Although SnO is insoluble in water, it is amphoteric, dissolving in base and acid. "Stannic acid" refers to hydrated tin (IV) oxide, SnO, which is also called "stannic oxide."
Tin oxides dissolve in acids. Halogen acids attack SnO to give hexahalostannates, such as [SnI]. One report describes reacting a sample in refluxing HI for many hours.
:SnO + 6 HI → HSnI + 2 HO
Similarly, SnO dissolves in sulfuric acid to give the sulfate:
:SnO + 2 HSO → Sn(SO) + 2 HO
The latter compound can add additional hydrogen sulfate ligands to give hexahydrogensulfatostannic acid. 
SnO dissolves in strong bases to give "stannates," with the nominal formula NaSnO. Dissolving the solidified SnO/NaOH melt in water gives Na[Sn(OH)], "preparing salt," which is used in the dye industry.