My house was flooded by Tropical Storm Allison in June 2001. Carpet was installed throughout the house except in the bathroom and kitchen areas. My wife and I decided to extended the house 12’ (length) * 24’ (width) to included a master bathroom and increase our sons room. The renovations to the house were completed in 2002, which included laying tiles throughout the house instead of carpet. In 2003 – 2004, we began to see certain spots in the original part of the house where the grout began to bubble up. The grout bubbling affect has not occurred in the tiles that were laid in the new addition of house as of 5/10/2009. Our assumption is that due to new building codes, the contractors laid down a moisture barrier tarp before pouring the concrete to create the fountain of the new extension to the house. My wife and I have tried using acid tile cleaners, simple green, and even regrouted the affected areas to know avail. We were wondering if any of the members of This Old House has encountered this particular problem or would know of a company / product(s) that would be able to solve our problem?