Our farm has an old grain bin that we would like to use for storage. It is on a concrete slab. Whatever was used to seal the metal to the concrete many years ago is long gone and now rain runs under the metal and across the floor. One old farmer told us to seal it with tar. Tar??? We can't find any. We've tried to use the expanding foam type of sealant...it doesn't last. The tubes of caulking aren't a wide enough band of sealant. Surely farmers who actually store grain must occasionally reseal these bins. What do they use...or what can we use to refurbish and seal this grain bin so that it can be useful to us?