Lately we have had a lot of questions about tile installation, especially from Do It Yourself homeowner flooring projects. To help other consumers that have the same questions, we will start posting some of the e–mails we get online.

Is it overkill to apply RedGard over Hardie backer board? I want to make sure the niches and corners in my shower are sealed before I tile with stone tile. If I don't use RedGard will the thinset and grout be enough to ensure waterproofing? Also, I have a thinset that is NOT polymer modified thinset. I understand this can be used directly on the cement backer board, but if I use Red Guard I must use a polymer modified thinset. Is this correct?

Thank you for your question about your tile installation. Hardie backerboard will not seal out moisture completely, nor will thinset or grout. Although it will hold up under wet conditions it will allow some moisture to pass through. Applying RedGard will block out moisture and yes, you would then need to use a polymer modified thinset.

If you want to use a backer board with a built in moisture barrier than you should use DensShield by Georgia-Pacific. The panels are completely waterproof, and are very light and easy to work with, requiring only a razor knife to score and snap to fit. Here is a link to the product.

http://www.gp.com/build/product.aspx?pid=4684

Please let me know if you have any other questions. Good luck!

Michael Prachniak
CEO, Tile and Mosaic Artisan, Tile Productions

TileProductions.com