Subfloor Preparation

All subfloors must be structurally sound, stable and solid. If there is any question about the structural soundness of the subfloor, consult with the engineer on the project or request the services of a professional structural engineer. Shot blasting is not required for most applications.

Subfloors must be clean and free of dirt, tar, wax, oil, grease, latex compounds, sealers, curing compounds, release agents, asphalt, water-soluble adhesives, paint, chemicals, loose old cementitious products, joint compounds from drywall installation or any other contaminant that might prevent proper bonding of underlayments to concrete. Seal off floor drains before starting to pour underlayment to prevent drain pipes from clogging.

A weak or degraded concrete surface layer must be removed mechanically to provide a solid base. To decide whether mechanical preparation of substrate is required or not, the concrete substrate must be thoroughly assessed for its quality over the entire pour area. Simple visual appearance of concrete substrate as strong and solid does not necessarily guarantee that hte concrete substrate is free of impurities and has the right tensile strength.

Concrete exhibiting signs of laitance (a layer of weak material on the concrete surface either visible or invisible), scaling, spalling, crumbling or delamination must be mechanically removed to achieve a solid and clean substrate. Prior to installation of the underlayment, remove weak or degraded concrete (as described above) with hammer, chisel or other simple means. It is not required to mechanically profile the concrete subfloor with methods such as shot blasting, scarifying or diamond grinding.

Concrete subfloors receiving cementitious underlayment systems must be cured properly (generally for a minimum of 28 days) prior to underlayment installation. Subfloor moisture vapor emission rate (MVER) exceeding 5 lbs./1,000 sq. ft./24 hours per ASTM F1869 must be treated with USG Durock Brand RH-100 Moisture Vapor Reducer or an appropriate moisture mitigation system that either limits the flooring system's moisture vapor exposure to acceptable levels or completely stops the vapor transmission through the top of the subfloor. USG Durock ProFlow self-leveling underlayment is not a vapor barrier. Transmission of excessive moisture vapors from the concrete subfloor through USG Durock ProFlow self-leveling underlayment can interfere with floor-covering adhesives and compromise their performance. Apply USG Durock RH-100 Moisture Vapor Reducer or an industry-recognized moisture mitigation system per manufacturer recommendations to achieve an MVER value of 5 lbs./1,000 sq. ft./24 hours or less. Ensure compatibility of the moisture mitigation system with the Durock ProFlow self-leveling underlayment by a test application in small areas. If sand broadcasting is not required during the installation of the moisture mitigation system, the surface must be primerd with a USG Durock Brand primer prior to application of Durock Brand self-leveling underlayments. Contact USG Technical Service (800 874-4968) for further information regarding suitable moisture mitigation products and systems for use with USG Durock ProFlow self-leveling underlayment.

Cracks in the existing concrete subfloor must be inspected to determine if the crack is due to typical concrete "shrink" or if it is a result of a structural movement. In the case of the latter, remediation of the crack must be addressed or eventually the crack will telegraph through USG Durock ProFlow self-leveling underlayment. Repair all existing cracks in old and new concrete to minimize and control their ability to telegraph through the layer of USG Durock ProFlow self-leveling underlayment. Remove the weak concrete along the legnth of the cracks by chiseling or other suitable means. Remove accumulated dust and debris from the crack cavities using a vacuum or other suitable means. Remove accumulated dust and debris from the crack cavities using a vacuum or other suitable means. Various cracks present in the concrete subfloor, including shrinkage cracks, must be filled with a suitable commercially available crack-fill epoxy adhesive designed for concrete flooring applications. To ensure superior resistance to crack growth, use injection epoxy crack-repair techniques per industry guidelines to repair cracks that are active or deep. Note that repair of existing cracks in the concrete subfloor only subdues but does not completely prevent their ability to telegraph through USG Durock ProFlow self-leveling underlayment. Growth of existing cracks or formation of new cracks in the concrete subfloor can lead to cracks telegraphing through USG Durock ProFlow self-leveling underlayment. Respect existing expansion and control joints. See Notes/Limitations, pg. 5, #9.

To minimize the effect of gypsum expansion and cracking on outside corners, use USG Levelrock Perimeter Isolation Strip. See USG Levelrock Brand Perimeter Isolation Strip Submittal (IG1874) for further details.

Fill deep areas and holes prior to final application. Contact USG for further information.

USG Durock ProFlow self-leveling underlayment can be applied with metal lath over engineer-approved, APA-Rated exterior glue plywood or oriented strand board (OSB) (i.e., APA-Rated Exterior or Exposure 1 panels) wood subfloors following the Tile Council of North America's F185-14 specificaiton at a minimum 1/2 in. depth. Subfloor must be properly prepared and primed with USG Durock Brand Primer-Sealer or 3E Primer. See Notes/Limitations, pg. 6, #22 for subfloor deflections.

For the application of USG Durock ProFlow self-leveling underlayment over existing floor coverings on concrete subfloors such as ceramic tile, vinyl composition tile (VCT), cement terrazzo and thin cutback adhesive, the surface needs to be well bonded, sound and clean.

Tiles that exhibit a bubbled surface or that are debonding from the substrate are not suitable surfaces for receiving presanded floor underlayments. These floor-covering surfaces need to be removed and the substrate inspected for potential water damage. If water damage is detected, the source of the moisture needs to be identified and addressed. These areas should be checked for Moisture Vapor Emission Rate (MVER) using the ASTM F1869-11 test method (see above). Depending on the MVER ratings, the subfloor may need to be treated with USG Durock Brand RH-100 Moisture Vapor Reducer.

Contact USG for applications over vinyl asbetsos tile (VAT).

USG Durock ProFlow self-leveling underlayment can be installed over non-water-soluble adhesives on concrete only. The adhesive residue must first be tested to make certain it is non-water-soluble. Any water-soluble adhesive residues must be mechanically removed down to clean concrete. Non-water-soluble adhesive residues should be prepared to a thin, well-bonded residue using the "wet-scraping" technique as recommended by the Resilient Floor Covering Institute (rfci.com) to remove thick areas and adhesive buildup, as well as any areas that are weak or not well bonded to the concrete. Any existing patches below the adhesive must be completely removed.

USG Durock ProFlow self-leveling underlayment will set within two hours under normal conditions. Light foot traffic can occur after this time; normal trade traffic can resume the next day. After USG Durock ProFlow self-leveling underlayment is firmly set (typically two hours after the pour), provide adequate ventilation to ensure uniform drying of the installed underlayment, which typically occurs within two to five days at 1/4 in. thickness. High ambient humidity and higher thicknesses will delay the drying process. Protect floors from heavy trade traffic loads (i.e. loaded drywall carts, heavy tool cabinets, etc.) with plywood. This may cause the protected areas to take longer to dry. Check for dryness in these areas before installing floor coverings.

USG Durock ProFlow self-leveling underlayment can be used as a wear surface with a tested decorative coating system. Coating systems must be tested for adhesion to USG Durock ProFlow self-leveling underlayment. The bond test and performance of coatings are the responsibility of the coating manufacturer. Contact USG for further information regarding decorative coating options.

Priming

Use USG Durock Primer-Sealer or 3E Primer for preparing the concrete, wood or gypsum subfloor prior to application of USG Durock ProFlow self-leveling underlayment. Proper use of USG Durock Primer-Sealer or 3E Primer enhances the bond of the underlayment and effectively seals the subfloor and prevents formation of pinholes, domes and craters in USG Durock ProFlow self-leveling underlayment due to the upward migration of air bubbles from the subfloor. Refer to USG Durock Brand Primer-Sealer submittal (CB519) or USG Durock Brand 3E Primer submittal (CB658) at usg.com for installation instructions and application rates.

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, water-soluble adhesives, paint, chemicals, loose topping, joint compounds from drywall installation or any other contaminant that might interfere with development of good bond.

For primer application, the temperature of USG Durock primer, the subfloor and the room must be maintained between 50°F and 95°F for a period of 48 hours before and after application.

Barrel Mixing

When opening bags use engineering controls, including local exhaust, to reduce exposure to dust. Wear NIOSH-reommended respirator if needed. It is important that the mixing water for the total number of bags to be mixed is in the barrel prior to adding the dry material.

Determine the number of bages needed. Add 3.6 to 4.8 quarts (3.4 to 4.5 liters) of cool, clean potable water for each bag (50 lbs.) of USG Durock ProFlow self-leveling underlayment powder to the dry mixing barrel. Next, slowly add one bag to the barrel while mixing. Mix for 30 seconds, making sure that all material is wetted out thoroughly. Slowly add the second and any additional bags to the mixing barrel while continuing to mix. Make sure the barrel sides are thoroughly scraped free of dry powder and that there is no unmixed material on the bottom of the barrel. Mix for an additional 90 seconds and ensure the material is uniform and lump free.

Perform a slump test on the material before application. See Test Procedures for instructions.

Do not add additional water until the two-minute mixing cycle has been completed. Do not overwater the material. If additional water is required, add no more that 0.4 quarts per bag and mix for 30 seconds or until mix is uniform. Do not overmix (more than three minutes), as this may induce air into the material.

The presence of bleed water on the surface and/or material segregation (settling of sand) indicates overwatering. Adjusts the amount of water added to the mix to prevent bleed water and material segregation.

Slump Test

Set Plexiglas sheet on a level, stable surface, away from foot traffic. Ensure that the 1 in. x 2 in. cylinder is clean and dry. Place the cylinder in the middle of the Plexiglas sheet. Pour the USG Durock ProFlow slurry into the cylinder, slightly overfilling it. Screed off the excess material from the top of the poured cylinder, away from the Plexiglas sheet. Lift the cylinder up smoothly to form the patty. Do not shake any excess slurry from the cylinder. Wait one minute and measure the patty in two directions ninety degrees apart and calculate the average of the two measurements +/- 1/8 in. Ensure that the average patty diameter is within the 6 in. to 6-3/4 in. range.

Application

During application and until the USG Durock ProFlow self-leveling underlayment is firmly set (typically the first two hours immediately following the pour), close all doors, windows and other openings in the building and turn off HVAC systems to prevent air drafts. Protect installation areas from direct sunlight exposure for at least 24 hours. Thereafter, the HVAC system can resume, as well as the use of doors, windows and other openings.

Subfloor, room temperature and the USG Durock ProFlow self-leveling underlayment - either mixed or in powdered form - must be between 50°F and 95°F at the time of application and for 72 hours after installation of USG Durock ProFlow self-leveling underlayment. For temperatures above 95°F, follow the American Concrete Institute (ACI) Hot Weather Concrete Guidelines to ensure proper installation. If available water is not cool, chill water to 70°F (21°C).

When uncertain or unknown construction conditions are present on the jobsite, it is recommended to pour a small test area before conducting full installation. The test area must also include finish flooring to establish suitability of the complete system for intended use.

USG Durock ProFlow self-leveling underlayment has a flow time of appoximately 15 minutes at 70°F. At higher temperatures the flow time is shortened; at lower temperatures the flow time is extended. Work as a team to obtain a satisfactory installation. Ensure continuous flow of slurry and promptly spread the USG Durock ProFlow self-leveling underlayment to desired thickness and finish using a gage rake and a smoother. Perform these operations promptly to avoid trapping air bubbles, prevent formation of cold joints and achieve a satisfactory finish surface.

Apply the USG Durock ProFlow self-leveling underlayment in an even ribbon along the short dimension of the room or area to be poured. Maintain a continuous wet edge. If pouring the USG Durock ProFlow self-leveling underlayment against an edge that has been allowed to set, the edge of the previous pour should be treated with USG Durock Primer-Sealer or 3E Primer.

Floor-Covering Installation

• USG Durock ProFlow self-leveling underlayment can be walked on two hours after installation.
• Floor coverings can be installed within two to five days when USG Durock ProFlow self-leveling underlayment is applied at 1/4 in. thickness. Drying time will vary depending on underlayment thickness and ambient climate conditions.
• Check with floor-covering and adhesive manufacturers for installation guidelines and suitability of their manufactured products over USG Durock ProFlow self-leveling underlayment.
• Perform field bond test to determine adhesive/flooring performance over USG Durock ProFlow self-leveling underlayment. Install floor covering with adhesive and perform field bond test approximately 72 hours after installation.
• Follow floor-covering manufacturers' recommendations for surface-sealing requirements. If the floor-covering or adhesive manufacturer requirements are more stringent, their requirements take precedence.

For further details on installation requirements, specifications and the most up-to-date product information, please see usg.com.

Notes/Limitations

1. Do not use in exterior applications.
2. USG Durock ProFlow self-leveling underlayment can be used as a wear surface with a tested decorative, protective coating system. Coating systems must be tested for adhesion to USG Durock ProFlow self-leveling underlayment. The bond test and performance of coatings is the responsibility of the coating manufacturer. Contact USG for further information regarding decorative coating options.
3. Do not install where continuous exposure to moisture is a possibility.
4. Do not install over dimensionally unstable, improperly prepared, weak subfloors.
5. For depths greater than 1 in., contact USG.
6. Do not install over concrete subfloor less than 28 days old. For untreated (without an approved moisture mitigation system) concrete subfloors less than 28 days old, contact USG.
7. For below-grade applications, contact USG.
8. Do not use over sound mats.
9. Do not use over expansion or isolation joints. Continue all movement joints in the concrete slab up through the layer of underlayment. In areas where the expansion or isolation joints are not present in the floor or where the concrete slab has developed systematic cracks in response to slab movement, consult with an engineer on the project or request services of a professional structural engineer to provide such joints as part of the system in accordance with engineering requirements and industry standards.
10. Existing cracks in the new and old concrete must be repaired with an appropriate crack-repair material in accordance with industry recommendations prior to installation of the underlayment. Note that repair of existing cracks in the concrete subfloor only subdues but does not completely prevent their ability to telegraph through USG Durock ProFlow self-leveling underlayment. Growth of existing cracks of formation of new cracks in the concrete subfloor can lead to cracks telegraphing through the poured underlayment.
11. When the MVER exceeds 5 lbs./1,000 sq. ft./ 24 hours treat the concrete subfloor with USG Durock RH-100 Moisture Vapor Reducer in all areas of use where potential for moisture problems may exist. USG Durock ProFlow self-leveling underlayment is not a vapor or moisture barrier. Transmission of excessive water vapors or moisture from the concrete subfloor through the USG Durock ProFlow self-leveling underlayment can interfere with floor-covering adhesives and compromise their performance.
12. For on-grade applications, use USG Durock RH-100 Moisture Vapor Reducer over concrete. Moisture mitigation system may not be needed if a vapor retarder is installed below the concrete slab in accordance to industry specifications and practice (ASTM E1745, ASTM E1993 and ASTM E1693) and the MVER value of the concrete slab is below 5 lbs./1,000 sq. ft./24 hours.
13. Do not use acid etching as a method of cleaning and preparing the concrete subfloor.
14. Do not use oil-based sweeping compounds to clean and prepare the concrete subfloor. Use of such sweeping compounds leaves an oil film on the surface of the concrte that will interfere with the underlayment's bond development. Use vacuum, compressed air or a dry broom to remove the dust and debris and prepare the subfloor for USG Durock ProFlow self-leveling underlayment application.
15. Do not use adhesive-removing chemicals or solvents to eliminate contaminants from the concrete subfloor. Use of such chemicals can transport oil, grease and other contaminants further into the concrete pores. These chemicals can be released back to the surface at a later time to interfere with the floor-covering adhesives, thus compromising the bond performance with USG Durock ProFlow self-leveling underlayment. Mechanically removing the water-soluble adhesives, asphalt, coal-tar based adhesives and other oil-based contaminants is the sole recommended method of preparing the subfloor for application of USG Durock ProFlow self-leveling underlayment.
16. Contact USG for applications of USG Durock gypsum-based cements self-leveling underlayments over asbestos tiles. Do not mechanically remove organic adhesives, asphalt, coal-tar-based adhesives or other materials containing asbestos.
17. Do not overwater or overmix.
18. Do not add any chemical additives or polymers to USG Durock ProFlow self-leveling underlayment.
19. Do not use wet curing or curing compounds.
20. Do not mix with other cementitious products or self-leveling materials.
21. Do not apply USG Durock ProFlow self-leveling underlayment over wood subfloor without metal lath. Differential or excessive movement of the wood subfloor may lead to development of cracks in USG Durock ProFlow self-leveling underlayment at the wood subfloor joints and adjacent areas.
22. Structure shall be designed to so deflection does not exceed L/420 from combined dead and live loads and L/360 from live loads. Certain floor coverings such as marble, limestone, travertine and wood may have more restrictive deflection limits. Consult the appropriate floor-covering manufacturer.
23. Existing gypsum underlayments must be solid with no cracks and dust free. Gypsum underlayment must be sealed with USG Durock Primer-Sealer or 3E Primer. First test surface hardness by scratching existing underlayment with a coin. If surface can be gouged, do not use USG Durock ProFlow self-leveling underlayment and consult USG for alternative repair methods.