Maintaining Code Compliance When Repairing Gypsum Underlayments

Gypsum Underlayment

When repairing damaged and/or low compressive strength gypsum underlayment, you must maintain the fire rating for the floor/ceiling assembly. After removing the original gypsum underlayment, the replacement product must be listed by name or by UL Type Designation in the UL assembly that describes the floor/ceiling being repaired.

Some gypsum-based repair products claim to be UL Classified and may even have a UL logo on their bag. However, that does not mean the product is listed by name in the UL fire rated assembly being repaired. 

USG Durock™ Brand Tuf-Skim™ Floor Patch and USG Durock™ Quik-Top™ and Multi-Use Self-Leveling Underlayments are listed by UL Type Designation in 130+ UL fire rated assemblies including the most common assemblies L521, L528, L569, L570 and L589. Multifamily floor/ceiling fire ratings can be found in the L500 and M500 series of the UL Fire Resistance Directory. Only USG Durock™ gypsum repair products are listed in an L500 or M500 assembly with insulation in the cavity. (Insulation is required to meet the building code for STC and IIC sound transmission.)

For more information on gypsum underlayment repair and code compliant fire rated UL Design assemblies, see the UL Online Certifications Directory, view the literature below or contact USG.

UL DESIGNATION TYPE LRK
L501, L502, L503, L504, L505, L506, L507, L508, L509, L510, L511, L512, L513, L514, L515, L516, L517, L518, L519, L520, L521, L522, L523, L524, L525, L526, L527, L528, L529, L530, L532, L533, L534, L535, L536, L537, L538, L539, L540, L541, L542, L543, L545, L546, L547, L549, L550, L551, L552, L556, L557, L558, L559, L562, L563, L564, L565, L568, L569, L570, L571, L573, L574, L577, L579, L581, L583, L585, L587, L588, L589, L590, L592, L593, M500, M501, M502, M503, M504, M505, M506, M508, M510, M511, M513, M515, M517*, M521*, M522*.

UL DESIGNATION TYPE HSLRK
L501, L502, L503, L504, L505, L506, L507, L508, L509, L510, L511, L512, L513, L514, L515, L516, L517, L518, L519, L520, L521, L522, L523, L524, L525, L526, L527, L528, L529, L530, L532, L533, L534, L535, L536, L537, L538, L539, L540, L541, L542, L543, L545, L546, L547, L549, L550, L551, L552, L556, L557, L558, L559, L562, L563, L564, L565, L568, L569, L570, L571, L573, L574, L577, L579, L581, L583, L585, L587, L588, L589, L590, L592, L593, M500, M501, M502, M503, M504, M505, M506, M508, M510, M511, M513, M515, M517*, M521*, M522*.

UL DESIGNATION TYPE CSD
L501, L502, L503, L504, L505, L506, L507, L508, L509, L510, L511, L512, L513, L514, L515, L516, L517, L518, L519, L520, L521, L522, L523, L524, L525, L526, L527, L528, L529, L530, L532, L533, L534, L535, L536, L537, L538, L539, L540, L541, L542, L543, L545, L546, L547, L549, L550, L551, L552, L556, L557, L558, L559, L562, L563, L564, L565, L568, L569, L570, L571, L573, L574, L577, L579, L581, L583, L585, L587, L588, L589, L590, L592, L593, M500, M501, M502, M503, M504, M505, M506, M508, M510, M511, M513, M515, M521*.

For the most up-to-date UL Designation Type LRK, HSLRK and CSD, contact your USG representative.

Note: *UL Design requires greater minimum pour depths and compressive strengths and/or additional requirements. See individual UL Designs for specifics.

Type CSD is UL/ULC Classified as a non-combustible material in accordance with ASTM E136 and CAN/ULC-S114.

RESOURCES

Products

USG Durock™ Quik-Top™ Series

7,000-10,000 psi (48.3-68.9 MPa)
Commercial, institutional & rehab construction

USG Durock™ Multi-Use

3,500-4,500 psi (24.1-31.0 MPa)
Wood frame, renovation & light commercial construction, radiant heat installations

USG Durock™ Tuf-Skim™ Floor Patch

• Trowel-able, high early strength
UL Classified for gypsum underlayment repair in fire-rated applications

USG Durock™ Primer-Sealer

 Enhances bond between substrate & underlayment
For use on concrete, wood & gypsum

USG Durock™ Fusion™ Primer

3-component, 36% solids, waterborne-epoxy
For surface consolidation of compromised gypsum underlayments

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