We have to assume that the base was at one time separate from the building , in which case , the idea that Hans put forward has much merit .
I would modify the approach advocated , slightly , by inserting a chisel into a corner of the junction between the building and base , apply MEK locally around the chisel , and gently—gently now— prise apart . Given a bit of luck and a following wind , you may see a crack appear. ATTACK,
immediately with a drop or two more MEK . Prise gently . Look , I said gently , you broke it now . Let the MEK set and bung gravel around the base.
Or persevere with the MEK treatment—outdoors unless you are a MEK junkie , it really does work . I have dismantled plastic kits in this manner to salvage them . I also am addicted to MEK . Excuse me while I sniff . AAAHHHH BYEEeeee…
With apologies to Hans , it really does work .