27
Planning Wall Finish
Cracking Wall Finishes
We recommend installing the optional HeatShift
System to reduce the wall temperatures and minimize
the possibility of cracking wall fi nishes. See Appendix
D - HeatShift System pages 79–98.
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.
Shrinkage and diff erential movement of the framing
and non-combustible wall board can transmit cracking
through to tiles, etc.
Be aware that temperatures on the non-combustible
wall surface above the appliance can exceed 200°F.
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 for the type of board used.
• Always use mesh tape over joints.
• Always stagger joints in wall board.
• 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 diff 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 large, 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 in-
side corners. Provide a joint that intersects the inside
corner to avoid cracking.
Cracks
Provide joints
either here or
here
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