17
Cracks
Provide joints
either here or
here
Avoiding Cracking Wall Finishes
If a clean
fi
nish with no tile, etc. is desired, joints in the
non-combustible board and the transition to gypsum
board will require special attention if future cracking
is to be controlled. Be aware that temperatures on the
non-combustible wall surface above the appliance can
exceed 200°F (93°C).
Below are some tips on how to best avoid any cracking:
• Allow materials to dry thoroughly before
fi
nishing the
wall. Non-combustible board has the ability to absorb
up to 30 percent of its weight in water and may shrink
as much as 1/8” over a 48” length when drying from
a saturated condition. Running the
fi
replace for an
extended period before
fi
nal
fi
nishing will help drive
out moisture.
• Always pre-drill screw holes through non-combustible
board and use screws with self-milling head.
• Always use mesh tape over joints.
• Always stagger joints in wall board.
Installation Planning
Wall Finish
• Behind joints, double up studs or use studs “on the
fl
at” to add extra support to the joint. Adhesive on
the backside of wall board behind any joints can help
control di
ff
erential movement.
• Use multiple, thinner coats of joint compound and al-
low to dry thoroughly between coats.
• Ensure framing materials are dry.
• After
fi
nishing the wall, introduce heat gradually to
slowly dry any excess moisture rather than drying too
fast.
• Avoid notching non-combustible board or tiles around
corners of window opening and instead provide a joint
that intersects the corner.
• Avoid using lage one-piece slab of material with a
cut-out in the middle as a surround for the
fi
replace.
Expansion above the opening will cause cracking at
inside corners. Provide a joint that intersects the inside
corner to avoid cracking.
