Spanish cement company Cementos Portland Valderrivas majority owned by FCC, has approached Blackstone over the refinancing of 345 million euros ($436.36 million) of debt, a source close to the matter said on Friday.

Cementos Portland's debt was granted by the U.S. fund's investment vehicle GSO in 2012 to acquire U.S. affiliate Giant Cement and is due in 2018, when it will be possible to convert it into shares.

The refinancing of Cementos Portland is one strand of a complex tangle of debt centring on the builder and service provider FCC, which is planning a 1 billion euro capital hike to pay down its own massive debt pile.

Cementos Portland, 79 percent-owned by FCC, declined to comment.

FCC and Cementos Portland, like all Spanish builders, amassed huge amounts of debt during Spain's construction boom but were then stuck with tumbling profits and loans they could not pay after the bubble burst in 2008.

FCC's capital hike was cleared last week after the builder's main shareholder, a vehicle controlled by Spanish businesswoman Esther Koplowitz, reached an accord to refinance 1 billion euros of its own debt.

The loss-making cement manufacturer, which has a net debt of 1.29 billion euros, said in July it also intended to renegotiate a syndicated loan of 965 million euros contracted with a group of lender that includes U.S. fund Apollo.