Open time, sometimes called flash time, describes the amount of time that you want the freshly troweled adhesive to remain open to the elements before you start installing floor covering. There is a good reason why open time needs to be followed: Many water-based adhesives need a little time to start evaporating and letting some of the water out before you start installing flooring. Moisture-curing adhesives need to be exposed to atmospheric humidity to get the reaction started. Again, if you start installing before allowing for the recommended open or flash time, you run the risk of a delayed curing time, which can lead to placement problems and long-term performance issues.
Oriented strand board (OSB) is a problem for resilient and wood flooring installations because of the nature of its construction. Traditional OSB is made from large chips of wood that will swell when exposed to humidity and moisture, causing the texture of the chip structure to show through on resilient floors. According to the Engineered Wood Association, OSB is only suitable as a substrate for stretch-in carpet, which isolates the texture of the OSB from the flooring with a layer of carpet pad. The association goes on to recommend applying a 1/4" (6 mm) layer of underlayment over the OSB for installation of resilient and wood flooring. The main thing to remember about traditional OSB is that it is very absorptive and swells when exposed to moisture (such as rain). This swelling is not good for floor installation. Having said that, there are new OSB products out there that are “engineered” materials, making them different from traditional chip/strand OSB. Some of these new engineered OSB boards have much better moisture resistance and can handle water contact without a change in dimensional properties.
The following example illustrates this process, with Keraflex Super thin-set mortar, a 1/4" x
1/4" x 1/4" (6 x 6 x 6 mm) trowel for installing
Mapeheat Membrane, plus filling the
membrane and installing the tiles with a
1/2" x 1/2" x 1/2" (12 x 12 x 12 mm) trowel.*
In this example the total floorspace requiring
coverage is 250 square feet (23.2 m2). To
determine how many bags of Keraflex Super is needed to install tile over Mapeheat
Membrane, we need to add the amounts from three separate calculations:
a) Installation of Mapeheat Membrane with a 1/4" x 1/4" x 1/4" (6 x 6 x 6 mm) trowel (with Keraflex Super):
At the per-bag minimum coverage of 100 sq. ft. (9.29 m2),
b) Filling of Mapeheat Membrane (with Keraflex Super)
At the per-bag minimum coverage of 60 sq. ft. (5.57 m2),
c) Installation of tiles (with Keraflex Super)
At the per-bag minimum coverage of 50 sq. ft. (4.65 m2),
Total = 12 bags of Keraflex Super
For additional helpful tips and product information, visit www.mapei.ca or contact MAPEI’s Technical Services Product Support Team.
* Note that the amounts of coverage for each recommended trowel are available on the Technical Data Sheets of MAPEI's thin-set mortars.
When going over membranes, check the Technical Data Sheet of the thin-set mortar for proper water ratios, as
additional water may be required.
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