Installing Moisture Sensitive Materials Over Fresh SLC

Comment

Comment by Stephen on January 26, 2011 at 8:10pm

"Finally, be cautious when considering installing a vapor barrier over an underlayment. If there is a moisture issue in the concrete where an underlayment is installed, slapping a moisture vapor barrier on the top of it is about like putting the underlayment in a swimming pool. If the underlayment isn’t meant for this type of moisture exposure, it will eventually degrade under these conditions"

 

Well gall darn I totally missed T.Schneider's reply to my blog post. I like the answers.

 

As far as Melissa's reply, this is an intersting point about putting patch and underlayments under vapor retarders as this is what we are told to do allot. In many instances we cannot put them over retarders like 6mil plastic and the like. And bonding to trowel on retarders like MVP4 could be an huge issue. It's confusing to say the least.

 

On another recent thread on the Wagner Rapid Rh. I did do CaCl tests on top of the MVP4...and plastic just for my curiousity of course How else is someone supposed to know what emissions are coming through, even though thery may be influenced by the topping?

Comment by Melissa Alliston on January 26, 2011 at 12:44pm

A little late to this party, but there are some interesting comments to add regarding the drying properties of different underlayments. As Stephen points out, they are not all equal. This applies not only to performance characteristics (compressive strength, etc.), but also to drying times. In fact, most underlayment manufacturers have a range of underlayment products that feature an equal range of drying times. Some products will use 100% of their mix water for chemical hydration (such as ARDEX Feather Finish or ARDEX K 55 Rapid), while others use varying combinations of chemical hydration and evaporation. The more evaporation is needed, the more the drying time of the underlayment will vary with ambient conditions, because evaporation is dependent on temperature and humidity. Where more evaporation is needed, the thickness of the underlayment installation can also affect the drying time, i.e. the thicker it is, the longer it will need to dry.

Why have varying dry times? Economy. It costs money to speed a product up, and if the jobsite has a time frame that allows for a slower dry, there are often viable options that can save a little money without sacrificing the quality of the installation, such as choosing ARDEX V 1200 over ARDEX K 15 where the job schedule allows a few days of drying time before the flooring has to go down. It all depends on what’s needed on the job.

Finally, be cautious when considering installing a vapor barrier over an underlayment. If there is a moisture issue in the concrete where an underlayment is installed, slapping a moisture vapor barrier on the top of it is about like putting the underlayment in a swimming pool. If the underlayment isn’t meant for this type of moisture exposure, it will eventually degrade under these conditions. If calcium chloride testing is used on the concrete (as opposed to relative humidity testing), the risk is even greater, as calcium chloride testing is a very superficial test. Concrete is always damper below than it is above. Even if you come in under the 3 or 5 lb. mark today, this number will tend to increase once the barrier or flooring is installed as the moisture in the slab redistributes.

Comment by T. Schneider on September 27, 2010 at 12:32pm

Hi, I am T. Schneider with ARDEX Engineered Cements. We manufacture a wide variety of high-performance underlayments and toppings, including both self-leveling and trowel-grade materials. Further to Mr. Higgins comment, I would like to add that calcium chloride testing cannot be conducted over installed underlayments and toppings per a recent change to ASTM F1869, which states that calcium chloride kits are not to be used over lightweight concrete, gypsum, coatings or underlayments.

Relative humidity testing (ASTM F2170) can be conducted after underlayments and toppings are installed, but keep in mind that in most cases, the underlayment or topping would have to be removed prior to installation of a moisture remediation system. Also, if a moisture remediation system is already installed beneath the underlayment or topping, the drilling required for the relative humidity test probes would puncture and compromise the system.

Mr. Higgins also mentions that a self-leveler should not contribute free moisture to the flooring installation. I can confirm that with ARDEX products, provided they are mixed and installed in accordance with our written recommendations, it is actually chemically impossible for them to contribute free moisture. This is because once the material has sufficiently cured, all remaining mix water is chemically bound into the cement matrix.

Comment by Bob Higgins on April 14, 2009 at 3:09pm

The moisture testing for SLC is a bit misleading. Most if not ALL of them contain some cellulosic materials and other materials that can actually exaggerate the readings. Much of this moisture is not "free" moisture, some is chemically bound to a certain extent. As long as the manufacturers recommendations are followed, if there is no contributing moisture from underneath, any decent quality SLC, properly mixed, proportioned and placed; should present no problem to even the most moisture sensitive flooring materials