Specification

Panel Micro-Cracking Durock cement board is formulated to develop fine micro-cracking (also called as multiple-cracking) in the
panel. The micro-cracking process helps to evenly relieve the stored strain energy in the product due to
handling and installation, external loads, and/or panel restrained movement. The presence of micro-cracks in
the panel should not be considered a product defect.
Installation A. Install cement board with ends and edges closely abutted, but not forced together. Stagger end joints in
successive courses.
B. For flooring applications over a wood-based substrate, laminate
Durock to subfloor using Type 1 organic
adhesive or latex-modified thin-set mortar suitable for bonding cement board. Fasten to subfloor with 1-1/4"
Durock
™
brand tile backer screws for wood framing (or equivalent) or 1-1/2" hot-dipped galvanized roofing
nails spaced 8" o.c. in both directions with perimeter fasteners at least 3/8" and less than 5/8" from ends and
edges. Drive nails and screws so that bottoms of heads are flush with panel surface to ensure firm panel contact
with sub floor. Do not overdrive fasteners. Prefill joints with tile-setting mortar or adhesive and then immediately
embed
Durock
™
brand tile backer tape and level joints.
C. For wall application, fasten
Durock panels to framing with specified fasteners. Drive fasteners into field of
panels first, working toward ends and edges. Hold panels in firm contact with framing while driving fasteners.
Space fasteners maximum 8" o.c. for walls, 6" o.c. for ceilings, with perimeter fasteners at least 3/8" and less
than 5/8" from ends and edges. Drive nails and screws so that bottoms of heads are flush with panel surface
to ensure firm panel contact with framing. Do not overdrive fasteners. Approved fasteners include:
Durock tile
backer screws for steel framing (or equivalent), 1-1/4" and 1-5/8" for 14- to 20-gauge steel framing;
Durock
tile backer screws for wood framing (or equivalent), 1-1/4", 1-5/8", and 2-1/4" for wood framing. Nails (1-1/2"
hot-dipped galvanized roofing nails). Prefill joints with tile-setting mortar or adhesive and then immediately
embed
Durock tile backer tape and level joints.
D. Cement board should be cut to size with a knife and straight edge. A power saw should be used only if it is
equipped with a dust-collection device. Installer should wear NIOSH/MSHA-approved dust mask.
E. If waterproofing is desired, use
Durock
™
brand tile membrane. See USG literature piece CB492 for Durock tile
membrane product information.
Refer to current United States Gypsum Company literature piece SA932 for complete installation information,
including good design practices. For technical assistance, call USG Technical Service at 800 USG.4YOU
(874.4968).
Limitations 1. Designed for positive or negative uniform loads up to 60 psf. For complete information on the use of
Durock
panels in exterior systems, consult uniform load table on page 3 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. Maximum dead load for ceiling system is 7.5 psf.
5. Steel framing must be 20-gauge equivalent or heavier.
6. Do not use drywall screws or drywall nails. Do not use drywall joint tape.
7. Do not use 1/4"
Durock cement board for wall or ceiling applications.
8. Do not use
Durock cement board with vinyl flooring.
9.
Durock cement board is not designed for use as a structural panel.
10. In locations close to saltwater or other challenging environments, design
professionals should consider the use of stainless steel fasteners.