Dimitris Pikrodimitris took out a mortgage four years ago when he was drawing an annual income of 27,000 euros ($36,720).
But the economy quickly sank into a debt crisis, forcing Greeks to tighten their belts and driving the insurance agent's wages down to just 6,500 euros last year.
"I have difficulty even making basic expenses. I haven't paid the loan for the last two years," Pikrodimitris told AFP.
The number of defaulting debtors like Pikrodimitris is growing in Greece, and experts are warning that the situation could blow up and smash hopes the country can finally emerge from a crippling six-year recession this year.
Greece's central bank said that non-performing loans -- loans for which debtors have failed to make payments for more than 90 days -- are currently worth 77 billion euros.
"Managing non-performing loans is a key challenge for banks," Yannis Stournaras, a former finance minister who is now the Bank of Greece chief, told parliament last month.
Repayment has stalled on around 30 percent of mortgages and business loans, and around 50 percent of consumer loans, says Victor Tsiafoutis, a lawyer offering guidance to debtors at Athens-based consumer group Ekpizo.
"This is a bomb that is going to blow (and cause) a breakdown in the bank system," Tsiafoutis said. "Imagine a default of 70 billion euros. Who is going to pay this money?"
Greece's central bank said the rate of non-performing loans has risen to 33.5 percent at the end of March from 32 percent last year.