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Flowable Hydraulic Cement Underlayment (FHU)/ Self-Leveling Underlayment (SLU) Poured cementitious underlayments can provide a satisfactory surface to receive ceramic tile installation systems that must support design loads with a maximum L/360 deflection. These floors are available in compressive strengths of 3,500 to over 7,000 PSI and are installed in as little as 1/16 in. (2 mm) to as deep as 6 in. (152 mm). Poured cement-based underlayments generally have a density of 120 lbs. per cubic foot. Poured cement-based underlayments are suitable for interior substrates. • F205 and F205A - Flowable Hydraulic Cement Underlayment (FHU)/Self-Leveling Underlayment (SLU) over Concrete • F185 - Flowable Hydraulic Cement Underlayment (FHU)/Self-Leveling Underlayment (SLU) over Wood • RH112 & RH112A - Flowable Hydraulic Cement Underlayment (FHU)/Self-Leveling Underlayment (SLU) over Concrete with Hydronic Tubing RH116 & RH116A - Flowable Hydraulic Cement Underlayment (FHU)/Self-Leveling Underlayment (SLU) Underlayment over Concrete with Electric Radiant Heat • RH123 - Flowable Hydraulic Cement Underlayment (FHU)/Self-Leveling Underlayment (SLU) over Wood with Hydronic Tubing • RH140 - Cementitious Self-Leveling Underlayment over Wood with Electric Radiant Heat Drying of the cement-based underlayment Poured cement-based underlayments are made at the job-site and mixed with pre-blended powder and water. This material generally requires very little dry time, usually 2 - 24 hours, before the final floor can be installed. Check with the manufacturer for required curing times before installing the final flooring system. There are currently nine approved methods in the TCNA Handbook for poured cement-based underlayments in tile installations.

Preparation of the poured cement-based underlayment surface When installed correctly, these underlayments require very little, if any prep at all before installing the final floor system.

MEMBRANES The TCNA Handbook has recommendations for the use of optional membranes prior to installing the tile over poured underlayments. For the purposes of these applications, membrane is as defined by ANSI A118.12 for crack-isolation or ANSI A118.10 for waterproof. Check with the manufacturer for their individual requirements.

NOTE: The tile contractor shall obtain written documentation verifying that the poured cementitious floors have met or exceeded the minimum compressive strength requirements of the project. This information shall be provided to the tile contractor by the general contractor, owner, and builder and/or certified poured-gypsum installer.

NOTE: The requirements of this document exclude patching compounds.

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NTCA Reference Manual | 2024 / 2025

Chapter 3 | Backerboards and Underlayments