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Use Durock™ Primer-Sealer, a low VOC, high-solids acrylic primer, for sealing the concrete and wood subfloor prior to application of Durock™ self-leveling underlayment. Proper use of Durock™ Primer-Sealer effectively seals the subfloor and prevents formation of pinholes, domes and craters in self-leveling underlayment due to upward migration of the air bubbles from the subfloor. Floors to be primed must be dry, structurally sound and clean. Remove any dirt, tar, wax, oil, grease, latex compounds, sealers, curing compounds, release agents, asphalt, adhesives, paint, chemicals, loose topping, joint compounds from drywall installation or any other contaminant that might interfere with development of good bond.

Apply Durock™ Primer-Sealer in a two-step application. For the first application, dilute 1 part of Durock™ Primer-Sealer to 4 parts of water. Mix the diluted solution with a paddle mixer at slow speed for approximately 1 minute. Next, apply primer solution to the subfloor at a coverage rate of approximately 200-300 sq. ft./gal. using a soft push broom. Apply evenly and do not puddle. The actual coverage of the primer will depend upon the nature and porosity of the subfloor. High absorption concrete will require more primer. Allow the first coat to dry for a minimum of 1 hour prior to the application of the second coat.

For the second application, dilute 1 part Durock™ Primer-Sealer to 1 part of water. Mix gently with a paddle mixer at slow speed for approximately 1 minute. Next, apply the primer solution to the subfloor using a soft push broom. Apply the primer evenly and do not puddle. The coverage rate of the diluted primer is approximately 300 sq. ft./gal. Again, the actual coverage of the primer will depend upon the nature and porosity of the subfloor. Allow the second coat to dry to a clear thin film for a minimum of 3 hours and a maximum of 16 hours before recoating will be necessary. High air relative humidity and/or low subfloor temperature may necessitate a longer drying time. Primer must be completely dry before application of the self-leveling underlayment. Extremely porous concrete subfloors may require an additional application.

For primer application, the temperature of Durock™ Primer-Sealer, the subfloor and the room must be maintained between 50°F and 95°F for a period of 72 hours before and after application.