How thick can the USG Durock™ Brand Self-Leveling Underlayment be poured in a single lift? Can I pour deeper using pea gravel?
USG Durock™ Brand Self-Leveling Underlayments can be installed from featheredge to a thickness of 2-in. in a single lift. Thicker applications of up to 5 in. can be accomplished with the addition of clean 3/8-in. Surface Saturated Dry (SSD) pea gravel with no standing water. For these pours, the recommended technique is to apply pea gravel to the deep section within ¼-in. of the final grade. Make an initial pour of the USG Durock™ Brand Self-Leveling Underlayment into the gravel and using a garden rake, thoroughly mix the underlayment and pea gravel together. Allow to dry for 24 hours. Prime with USG Durock™ Brand Primer-Sealer as directed in Priming. Complete application by capping with a minimum of ¼-in. of the USG Durock™ Brand Self-Leveling Underlayment.
At SSD, the pea gravel aggregate is wet, thus requiring a reduction in the amount of water in the mixture to prevent overwatering. Ensure there is no bleeding or material segregation (settling of sand) in the final mixture. Use only clean and chemically stable aggregate. Do not use limestone aggregate or other types of potentially reactive aggregate.