No. A loan is only considered a tax deductible mortgage if the loan is secured by the property and "perfected" -- that is, it must be written in such a way that you could be foreclosed if you defaulted, and it must be recorded as a lien against the property with the local authorities, usually the county clerk. A loan that is not secured by the home and recorded as a lien is not deductible even if it is used to buy or build a house or pay off a previous mortgage.
