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 building materials maker USG (NYSE: USG) fell 13% today after the company reported weaker than expected earnings.

So what: Revenue rose 8% in the quarter to $825 million but was short of the $845 million analysts had expected. Net loss improved to $57 million from $70 million a year ago and after adjusting for a one-time charge was $0.15 per share, but this also was short of the estimated loss of $0.12 from analysts.

Now what: The building market is still in rough shape despite some improvements in recent years. The growing revenue number is one of the positive signs coming out of the company, but after it's reported another net loss I don't see any catalysts for the stock going forward. If cost reductions pull up earnings in coming quarters the investment thesis may change, but I'm not buying shares until I see more positive numbers than what USG reported today.

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