Expert: Stephen Hayes - 3/13/2010

Question
I have a new home that the basement floor quickly developed large cracks and some heaving.  The heaving has subsided but the cracks still have some small vertical displacement.  I am finishing a basement bath and want to use ceramic tile to finish.  I have looked at the isolation membrane but am concerned that it seems to only provide protection for horizontal movement, not any vertical.  I had thought about using cement board over the membrane but am concerned about the overall thickness.

Any suggestions?

Answer
Hi David;You need to find out the reason for the heaving, subsiding, and cracking, and then to properly solve their cause(s). Being in a basement, I am assuming the subfloor is concrete.  If there is a crawl space, under the concrete, use a flashlight to be sure the ground, in that crawl space, has been fully covered with a plastic type moisture barrier.  If the subfloor is a concrete slab, then you should have the slab tested to see if you have a moisture problem, such as any proper ground cover being installed before the foundation was poured.  Perhaps the concrete was poured too late or too soon, perhaps the concrete had too much moisture.  Concrete is absorbent, and always moves, and moisture in concrete is the greatest cause of floor covering installation failures.  You need to find the source of that original problem and fully solve it.
Finding the source and solving it is not cheap, so you should check your homeowner's policy to see if it is covered, and, if the builder of the home is still around and solvent, you need to bring that builder into the mix.

Testing for moisture in concrete has been done by methods that never gave true results, so ASTM, a Company headquartered in Washington, DC and in Philadelphia, who establishes testing standards for, just about, everything that you and I use, has recently established the new concrete testing method which entails drilling 3/4 inch wide holes, down into the concrete 40% of the thickness of the concrete, inserting a moisture barrier along the interior sides of those drill holes, then inserting a capsule that is designed to read moisture content, leaving those capsules undisturbed for 72 hours, then, with a proper meter, read the moisture content taken from the capsules (the capsules remain in the drill holes and after the testing, a concrete filler is applied to level the concrete and forever entomb the capsules), and if a moisture problem is found, it has to be solved by the builder or a knowledgeable contractor.  Remember that all of the old moisture testing methods have been superceded by this new moisture test, which is know as ASTM-F2170.  You can purchase the written test method from the website, <astm/org>.  Wagner Electronics makes the capsules and the meter that reads them.  I think they are in Oregon.  I believe the testing calls for drilling 3 holes for the first 1000 sq. ft., and then one hole for each additional 1000 sq. ft.  Another thing you can do is contact a local restoration company such as ServPro and have them take photos of the concrete with one of those new infrared cameras.  Note that those cameras, which themselves are very expensive, only show if there is a moisture problem on the surface or just below the surface.  Those cameras cannot provide information if the moisture problem is up to 40% of the thickness from the surface of the concrete.

Cement backerboard usually should not be used over concrete.  You would need a level concrete subfloor topped with an acceptable underlayment.  Note that installation specifications from various manufacturers of the same products, such as ceramic tile, vary, so once you have chosen the tile, BEFORE you purchase, obtain the name of the EXACT manufacturer of the tile.  'Google' that manufacturer and visit their website.  On that website will be free, downloadable installation specifications which you should obtain and read thoroughly.  They detail lots of important information including acceptable underlayments, along with proper methods of the installation of the tiles.  Also, on that website, there is contact information, which is usually an 800#.  Call the number and speak with their technical services people to ask any needed questions you may have.  Don't take information from a dealer, installer, or from someone 'who knows all about concrete and ceramic tiles'.  Get the correct information from the correct source, the EXACT manufacturer of the tiles you plan to use, who has done extensive testing of product, installation, and maintenance, before bringing product to market.

If you find you can use a cement type backerboard, visit the website, <hardibacker.com>, which is the website of the California based James Hardi Company.  They make premium backerboards.  Call their 800# and speak with their technical services people to find out which one of their products they would suggest you use.  Also call 1-888-300-4422.  That is the number for the Florida based Mapei Company who makes some of the best adhesives in the world, including mortar adhesives needed for the installation of ceramic.  Follow the prompts to the technical services department for U. S. sales and ask which one of their adhesives they would suggest that you use for your product, and what trowel size you will need for the application of the adhesive.  

If you have any other questions, please feel free to get back to me.

Cordially,

John Michaels