MOISTURE TESTING OF CONCRETE SUB FLOORSConcrete sub floors should always be tested for moisture content before commencing floor preparation or installation of new floor coverings. Testing should not be restricted to the ground floor but to all levels of a building where floor coverings are to be installed because the subfloor may have an unacceptable moisture level or be "wet" because moisture has "wicked" up piers, columns or walls.
A concrete sub floors may be "wet" because:
- It is a new slab and the water used in the mix to allow the concrete to be pumped and troweled has not fully evaporated to the atmosphere or been converted to help cure the concrete.
- It may also be a slab without a plastic moisture membrane which may allow moisture in
the ground to penetrate the slab and allow its moisture content to rise and be above the recommended level.Australian Standard AS1884-1985 Floor Coverings- Resilient Sheet and Tiles Laying and Maintenance Practices, sets out the methods of testing for sub floor moisture and the acceptable levels. Copies of this document may be purchased from the Standards Association Of Australia in your capital city.
As a "rule of thumb", its has been found that under average conditions with good ventilation, a 100 mm thick slab of normal concrete, drying from one face only will take approximately five months to dry to a moisture level to allow floorcoverings to be installed. The application of a vapour barrier or water based epoxy moisture barrier will reduce the waiting time before
installation can commence.A concrete sub floor can be accurately checked to determine its moisture content using an Hair Hygrometer Test or an Electrical Resistance Meter.
- An Hair Hygrometer Test Meter involves the use of an accurately calibrated meter which calculates the humidity level in a sealed area and the level may be read from the dial on the instrument. The Hygrometer is laid on the concrete sub floor and sealed to the slab for at least 16 hours allowing it to determine the amount of moisture vapour being omitted by the slab.
- An Electrical Resistance Meter determines the resistance in the slab to the flow of electricity and is calibrated to determine the percentage of moisture content and the results are shown on the instrument dial as the moisture level contained in the slab. The test is carried out by driving two nails into the slab approximately 100mm apart and then placing two probes in contact with the nails and immediately being able to read the percentage of moisture contained in the slab. The Electrical Resistance Meter test is the method most often used because a moisture content reading is quickly available.
An Acceptable Sub-floor
Australian Standard 1884-1985 Appendix A.5.3 states that a sub floor is not sufficiently dry if the moisture content exceeds 5.5 percent. A concrete sub floor must comply with the relevant Australian Standards before commencement of the application of floor preparation materials such as cementitious compounds, primers, adhesives or floorcoverings because the installation may fail. The failure may result in the floor preparation materials or the floor coverings bubbling severely which may cause a possible tripping or safety issue or be unsightly requiring expensive repairs or replacement.Further information on floor coatings, sub floor preparation and sealers may be obtained from our information folder "Floor Coatings" or
At : www.rlapolymer.com.au
Contact us at: info@rlapolymers.com.auIssued: September 2004