ASK THE EXPERTS QUESTION I was wondering if there are any “industry guidelines” or commonly- accepted standards to go by concern- ing moisture in subfloors. The reason I am asking is that I have read the CCT and RH ASTMs and understand the 5 lb. and 75% RH thresholds, but the information I see when I research manufacturer data is widespread and seems like there is no universally- accepted criteria. It almost seems like some of the guidelines are hand-me- downs that people tend to follow, but there is not concrete data to support the guidelines (no pun intended), maybe just a lack of research. I was considering purchasing the latest TCNA Handbook to see if there were any guidelines in there – that’s pret- ty universally accepted, so maybe their guidelines – if any – would be considered an industry standard. If I had wood flooring in one room and tile in the other room and I get MVER of 7 lbs. in the wood room and 12 lbs. in the tile room, is there a grey area where it might be ok, or is it an exact science where anything over say 5 lbs. for wood, and 10 lbs. for tile is generally not recommend- ed? Thanks for your help on this! It’s a challenging subject matter! ANSWER The effect of moisture on floor covering is a huge problem across the United States. There are a lot of variables that affect the per- formance of different types of floor covering in the presence of moisture. Ceramic, porcelain and stone tiles – for most part – handle moisture better than other floor covering surfaces. There are thousands of setting products that are affected by dif- fering amounts of moisture in a variety of ways. Using the infor- mation you have received from a calcium chloride test (CCT), and relative humidity (RH) test in con- cert with technical data from your setting material provider is para- mount for a successful installation. In general, most setting manufac- turers’ products perform well with readings of 3 lbs./1,000sf/ 24 hours in a calcium chloride test, or read- ings less than 75% using a rela- tive humidity test. Some manufac- turers have systems that include waterproof membrane, and spe- cific thin-set mortars that are war- ranted up to 12 lbs./1,000 and 90% relative humidity. My advice to you is to make sure you are Sponsored by 20 TileLetter | September 2017