Armstrong World Industries (NYSE:AWI) is about to see a large chunk of its equity change hands. The company announced last week that two of its major shareholders, The Armstrong World Industries, Asbestos Personal Injury Settlement Trust and Armor TPG Holdings,are floating a combined 6 million shares of the company's stock common stock in an underwritten secondary public issue. The price is $51.00 per share. 

The company did not provide the reasons why the Trust and Armor TPG Holdings are selling their stakes. It did not respond to requests from The Motley Fool for more information.

In the press release announcing the offering, Armstrong pointed out that it will receive no proceeds from the sale, as it is not a selling party.

The joint book running managers of the issue are Citigroup and the Securities arm of Deutsche Bank. The offering is expected to close "on or about" Wednesday. 

Currently, Armstrong has just over 54 million shares outstanding, and its stock's last closing price was $50.52 per share.