13
Planning
Wall Finish
Plan the Wall Finish
Non-Combustible Materials Specifications
Non-combustible materials are those which will not
ignite and burn. Such materials are those consisting
entirely of steel, iron, brick, tile, concrete, slate, glass
or plasters, or any combination thereof.
Materials that are reported as passing ASTM E 136,
Standard Test Method for Behavior of Materials in a
Vertical Tube Furnace
at 750 °C shall be considered
non-combustible materials.
Combustible Materials Specifications
Materials made of or surfaced with wood, compressed
paper, plant
fi
bers, plastics, or other material that
can ignite and burn, whether
fl
ame proofed or not,
or plastered or unplastered shall be considered
combustible materials.
Cracking Wall Finishes
If a clean
fi
nish with no tile, etc. is desired, joints in the
gypsum board will require special attention if future
cracking is to be controlled.
Shrinkage and di
ff
erential movement of the framing
and wall board can transmit cracking through to tiles,
etc.
Be aware that temperatures on the wall surface above
the appliance can exceed 185
°
F. Although safe, this is
too hot for many many materials and
fi
nishes. Choose
materials that will withstand these temperatures.
Cracks
Provide joints
either here or
here
Below are some tips on how to best avoid any cracking:
• Allow materials to dry thoroughly before
fi
nishing the
wall. Some materials, such as cement board has the
ability to absorb up to 30 percent of its weight in wa-
ter 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. Moisture is the leading
cause of material shrinkage!
• Always pre-drill screw holes through cement board
and use screws with self-milling head.
• 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 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 cement 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.
