180-CL2118.IPI.1 v1.00
August 5, 2020
Page 26
CL2118.IPI.1
CRACKING WALL FINISHES
If a clean finish with no tile, etc. is desired, joints in the cement board and the transition to gypsum board
will require special attention if future cracking is to be controlled. Be aware that temperatures on the
noncombustible wall surface above the appliance can exceed 250°F. Below are some tips on how to best
avoid any cracking:
•
Allow materials to dry thoroughly before finishing the wall. Cement 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 fireplace before final finishing will help drive out moisture.
• Always pre-drill screw holes through cement board and use screws with self-milling head.
• Always use tape over joints.
•
Behind joints, double up studs or use studs “on the flat” to add extra support to the joint. Adhesive on the
backside of wall board behind any joints can help control differential movement.
• Use multiple, thinner coats of joint compound and allow to dry thoroughly between coats.
• Ensure framing materials are dry.
•
After finishing 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 openings, and instead provide a joint that
intersects the corner.
INSTALLATION PLANNING