Rough Work PhaseStep 15 of 27
Install Cement Backer Board
Backer board provides a stable, water-resistant substrate for tile installation. Proper installation is critical for a lasting shower.
Quick Summary
Time Needed
4-8 hours
Cost
$150 - $400
Difficulty
Intermediate
Why Backer Board Matters
Tile needs a dimensionally stable substrate that won't swell, warp, or deteriorate from moisture. Drywall and plywood fail these requirements in wet areas. Cement backer board provides the rigid, water-resistant surface that tile requires. Combined with proper waterproofing, it ensures your shower lasts for decades.
Backer Board Options
| Type | Cost | Pros | Cons |
|---|---|---|---|
| Cement Board Hardiebacker, Durock | $10-15/sheet | Affordable, rigid, proven | Heavy, dusty to cut |
| Foam Board Kerdi-Board, GoBoard | $30-50/sheet | Lightweight, waterproof | Expensive, less rigid |
| Fiber Cement PermaBase, Fiberock | $12-18/sheet | Lighter than cement | Still needs waterproofing |
Important: No backer board is fully waterproof on its own. All require a waterproofing membrane (like RedGard or Kerdi) over the surface before tiling.
Tools & Materials
Tools
- • Cement board scoring tool
- • Utility knife with extra blades
- • Jigsaw or angle grinder (for cutouts)
- • Drill/driver
- • T-square or drywall square
- • Tape measure
- • Safety glasses & N95 mask
- • Margin trowel
Materials
- • Cement backer board (1/2" for walls)
- • Cement board screws (1-5/8")
- • Alkali-resistant mesh tape
- • Thinset mortar
- • Waterproof membrane (RedGard, Kerdi)
- • Vapor barrier (for exterior walls)
Step-by-Step Installation
1
Prepare the Area
- Verify all rough plumbing and electrical are complete
- Ensure studs are plumb and flat (max 1/8" deviation)
- Install vapor barrier on exterior walls (code requirement in many areas)
- Ensure blocking is installed for fixtures and grab bars
2
Measure and Cut Panels
Score and snap method:
- Mark cut line with straightedge
- Score deeply with cement board knife (multiple passes)
- Snap board along scored line
- Score backing paper and snap clean
For cutouts:
- Use carbide hole saw for pipe holes (1/4" larger than pipe)
- Use jigsaw with cement board blade for irregular shapes
- Wear N95 mask—silica dust is hazardous
3
Install Panels
- Start at bottom, working up
- Leave 1/4" gap from tub/shower pan (prevents wicking)
- Leave 1/8" gap between panels
- Stagger joints from row to row (like brickwork)
- Smooth side out for tiling
- Use cement board screws every 8" on studs (1/2" from edges)
- Keep screws flush—don't overdrive
Pro tip: For horizontal joints, center them on studs for solid backing. For vertical joints, don't line up with corners or door frames.
4
Tape and Mud Seams
- Apply thin layer of thinset over all seams
- Embed alkali-resistant mesh tape (not paper tape!)
- Apply another thin coat of thinset over tape
- Feather edges smooth
- Treat inside corners with tape and thinset (or corner bead)
- Let cure 24 hours before waterproofing
5
Apply Waterproofing
After thinset cures, apply waterproof membrane over entire surface:
- Liquid membrane (RedGard): Roll on 2 coats, let dry between coats
- Sheet membrane (Kerdi): Apply with unmodified thinset
- Cover entire wet area including curb and niche
- Extend waterproofing 6" beyond direct water exposure
Common Mistakes to Avoid
- ✗Using drywall screws instead of cement board screws (they rust)
- ✗Resting board directly on tub/pan (moisture wicks up)
- ✗Using paper drywall tape instead of alkali-resistant mesh
- ✗Skipping waterproof membrane (backer board is NOT waterproof)
- ✗Overdriving screws (creates weak spots)
- ✗Not wearing proper dust protection when cutting
Frequently Asked Questions
What type of backer board is best for showers?
Cement board (Hardiebacker, Durock) is the most common and affordable option. Foam board (Kerdi-Board, GoBoard) is lighter and fully waterproof but more expensive. All require proper waterproofing—no backer board is fully waterproof on its own.
Can I use drywall in a bathroom?
Regular drywall should never be used in wet areas like showers or tub surrounds. Green board (moisture-resistant drywall) is only suitable for bathroom walls away from direct water exposure. Always use cement board or tile backer board in shower and tub areas.
How far should backer board be from the shower pan?
Leave a 1/4" gap between the bottom of the backer board and the shower pan or tub flange. This prevents wicking moisture up into the wall. The gap will be covered by tile and caulk.