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Understanding Moisture Vapor Migration

Moisture vapor can act independently of the air since its properties do not depend on the presence of air. It exerts its own pressure, and can move about through air in a space, or move through materials under differences in vapor pressure independently of the air. Moisture vapor flows only from high toward low pressure.
Moisture emmisions from a concrete sub floor can increase when a buildings vapor pressure is reduced by air-conditioning. Vapor movement will then reverse and push outward during the winter when a buildings vapor pressure is increased by the heating system.

Check For Moisture

Failure to properly address a moisture problem can result in damage to any floor covering installation. Concrete sub floors always have moisture present, and it is impossible to tell how much moisture it holds merely by looking at it.
If your installation is over a concrete subfloor Scottdel recommends using the Taylor Tools #625 Calcium Chloride Moisture Test Kit. Taylor recommends that in areas of 2,000 sq. ft. or less you should conduct 3 tests and add one more for each additional 1,000 sq. ft. It takes 60 - 72 hours to perform a moisture test. If you follow Taylor's test procedures you will be issued a FREE and independent report of the test results. They also provide an archival service for test results should you need independent confirmation at a later date.

The Calcium Chloride Moisture Test

measures the quantity of moisture passing through on and below grade concrete sub floors and is measured in LBS. of moisture over a 1,000 sq. ft. area during a 24 hour period.

moisture test
Moisture testing should only be performed when enviromental conditions closely approximate the anticipated in-service conditions. Turn-on any climate control systems during testing to obtain accurate test results.
The installation of a moisture barrier over a concrete slab with test results in the range of 3 - 6 LBS / 1,000 Sq Ft / 24 hrs. is considered acceptable by most wood and laminate manufactuers.

DO NOT PROCEED WITH THE INSTALLATION IF MOISTURE EMMISSIONS EXCEED 6 LBS / 1000 Sq Ft / 24 HOURS, this is an indication the slab is not fully cured or there is a more serious moisture problem. Moisture may come from many different sources, such as:

Installation Procedures & Recommendations

1. Concrete sub floors MUST be allowed to cure for 60 days and moisture testing performed before proceeding with installation over concrete.

2. All sub-floor surfaces must be solid, dry and free of all foreign material.

3. Install the 6 mil moisture barrier in all installations, even if moisture tests do not indicate a moisture problem. Overlap seams by at least 8" with a minium 2" flash up all walls. If the overlap is less than 8" be sure to tape the seams (duct tape works well in these situations).

4. Quiet Step, shall be installed perpendicular to the wood or laminate flooring where possible. Cleanly cut and trim Quiet Step tight and flush with all walls. All seams shall be tightly butted together and taped for a secure seal, once again duct tape works well here.

5. All wood and laminate flooring shall be installed according to the manufacturer's recommendations.

Crawl Spaces

Even wood sub floors over crawl spaces can present moisture problems especially if they are not properly ventilated. Use the moisture barrier it's cheap insurance.
Be sure and check for adequate ventilation of crawl spaces. Most manufacturers have a recommended ratio of ventilation per square foot of crawl space.

QUIET STEP Underlayment Warranty

Scottdel Inc. warrants to the original purchaser that Quiet Step sound absorption underlayment is free from material and manufacturing defects and will maintain it's sound absorption properties in residential installations for a period of (15) fifteen years.

Should a warranty claim arise, it must be submitted to Scottdel Inc. for approval before removal of the installation. Otherwise, the warranty is null & void. Scottdel reserves the right to inspect the laminate flooring and Quiet Step underlayment at the site of installation. Prior to inspection by Scottdel, all documentation must be submitted.

Under this warranty, should Quiet Step underlayment properties cause a product failure, Scottdel's sole obligation is to provide new underlayment of like grade and all reasonable labor and material charges for reinstallation of the affected area only. Scottdel is not responsible for any incidental or consequential damages that are not directly caused by the underlayment. Any implied warranties, including the implied warranty of merchantability and fitness for a particular purpose shall be limited to the express warranties stated above.

Scottdel does not warrant damage due to wear caused by improper installation, water, improper cleaning, negligence, unusual environmental conditions such as extreme heat or cold.


1. Bruce Suprenant, Moisture Movement Through Concrete Slabs; & Bruce Suprenant and Ward Malisch Are Your Slabs Dry Enough For Floor Coverings? from Moisture Problems in Concrete Floors, American Concrete Institute

2. Ramsey & Sleeper, Architectural Graphic Standards, The American Institute of Architects.

3. Taylor Tools #625 Moisture/Alkali Test Kit instructions brochure.

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