It’s not overly simplistic to say one Australian investor, and perhaps one fund manager, stands between the success or failure of the $16.8 billion Cemex bid for Rinker.

Cemex is the third biggest cement group in the world and Mexico’s biggest private company. Its $16.8 billion bid for Rinker is the biggest deal in the building products industry worldwide and Australia’s biggest real offer (discounting the private equity shuffle at Coles Myer).

Rinker gets 80% of its earnings from the US and its shares have been weakened by the downturn in the US housing market but many local investors have misread Rinker’s exposure to this market: it does more in the non-housing construction sector in US, although the housing downturn is hurting.

One investor alone has been taking advantage of the weaker price to build up a stake in Rinker — Perpetual, which owns more than 93 million shares.

Because that holding is equal to 10.32% of Rinker’s issued shares, Perpetual can either make or break the offer: Cemex needs 100% of Rinker’s shares to fully consolidate the company here and in the US, cut costs and start using all the cashflow and earnings to pay down debt.

It’s a unique position for an Australian fund manager in such a big takeover. Perpetual’s high profile Australian investment boss, John Sevior, has already been critical of Coles Myer’s rejection of the private equity deal of $17 billion ($15.25 a share). So what will he do?

On the face of it it’s a standard takeover battle, but it’s interesting for one very important point: if Rinker is taken over, will that mean the end of our building products industry, where we have led the world for years in technology and an ability to create new businesses?

Boral is struggling having slashed its 2007 earnings. If Cemex is successful, will Hanson be far behind in trying to grab Boral for its US businesses?

James Hardie is takeover-proof, no-one wants its asbestos claims problems.