Operating Guide

1. Designed for positive or negative uniform loads up to 60 psf. For complete information on
the use of USG Durock® Brand panels in exterior systems, consult uniform load table on
Page 4 for applicable positive or negative uniform loads on wall systems.
2. Wall applications: Maximum stud spacing: 16" o.c. (24" o.c. for cavity shaft wall assembly).
Framing shall be designed (based on stud properties alone) not to exceed L/360 deflection
for tile and thin brick, L/240 for direct-applied exterior finish systems. Maximum fastener
spacing: 8" o.c. for wood and steel framing; 6" o.c. for ceiling applications.
3. Floor applications: Maximum joist spacing 24" o.c. The subfloor system should be designed
with a minimum deflection limit of L/360 for the span. Some finish materials may require a
more rigid subassembly (such as large format tile and natural stone products). In these cases,
follow the manufacturer’s minimum requirements. The subfloor should be APA Span-Rated
Plywood or OSB with an Exposure 1 classification or better with tongue and groove or back
blocked at the unsupported edges.
4. In exterior applications, USG Durock® cement board should not be left uncovered for a
period of time exceeding 90 days. Discoloration or staining may occur due to exposure to
the elements which will not aect performance of the panel.
5. Brittle coatings, such as epoxy coatings, are not recommended for use with USG Durock®
cement board. USG Durock® cement board is intended for use with tile, thin brick and
exterior stucco coatings only.
6. Maximum dead load for ceiling system is 7.5 psf.
7. Steel framing must be 20-gauge equivalent or heavier.
8. Do not use drywall screws or drywall nails. Do not use drywall joint tape.
9. Do not use 1/4" USG Durock® cement board for wall or ceiling applications.
10. Do not use USG Durock® cement board with vinyl flooring.
11. USG Durock® cement board is not designed for use as a structural panel.
12. Maximum installed weight of the finish system should not exceed 15 psf.
13. USG Durock® cement board panels should not be used in areas where they are exposed
to temperatures that exceed 200°F.
14. In locations close to salt water or other challenging environments, design professionals
should consider the use of stainless steel fasteners.
15. Do not use lightweight setting-type joint compounds or ready-mix joint compounds directly
over USG Durock® cement board.
Property Unit of Measure ASTM Test
Method
5/8" USG Durock®
Brand Cement Board
1/2" Cement
Board
1/4"
Underlayment
Flexural strength
psi C947 > 480 > 750 > 1000
Indentation strength
psi D2394 > 1250 > 1250 > 1250
Shear bond strength
psi ANSI A118.4 > 50 > 50 > 50
Water absorption
% by wt. 24 hrs. C473 15 15 15
Nail-pull resistance
lb. (0.375" head diameter,
wet or dry)
C473 > 90 > 90 —
Weight
psf C473 3 2.4 < 1.9
Freeze/thaw
resistance
procedure B, number of
cycles with no deterioration
C666 100 100 100
Mold resistance
— G21
D3273
Rating 0,
No growth
10/10
Rating 0,
No growth
10/10
Rating 0,
No growth
10/10
Noncombustibility
Pass/Fail E136 Pass Pass Pass
Surface-burning
characteristics
flame/smoke E84 0/0 0/0 0/0
Thermal
“R”/k value C518 .49/1.27 0.39/1.27 —
Standard method for
evaluating ceramic
floor tile installation
systems
Passes cycles 1-6 C627 Light commercial Light
commercial
Light
commercial
Minimum bending
radius
ft. (requires special
framing details available
upon request)
— 6 6 —
LIMITATIONS
TECHNICAL DATA