Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Continental Building Products Inc (NYSE:CBPX) fell as much as 10% today after a major shareholder announced a share offering.

So what: An affiliate of Lone Star Funds, the company's largest shareholder, said it would sell 5 million shares in an underwritten offering likely to close next week. If the full overallotment is exercised, the sale could reach 5.75 million shares, just over a quarter of the fund's stake in the company.  

Now what: It's never a good sign when a major shareholder sells a stake in a company, and in this case Lone Star owns over 50% of Continental Building Products. There wasn't a reason given for the sale, but it's clear that the investors are no longer bullish on the company. I don't think this is a reason to completely abandon your investment thesis, but it may be time to reevaluate given the fact that a major investor is starting to sell out.

From the market's perspective, this will also increase the number of shares being traded significantly, which could cause some downward pressure on shares in the near term.