Do You Need Cement Board Under Bathroom Tile?

When renovating a bathroom, many homeowners ask a fundamental question: Do you really need cement board under bathroom tile?

The short answer: Yes, in most cases — especially in wet areas. Below, we’ll break down when, why, and where it’s needed — and what can go wrong if you skip it.

When Is Cement Board Under Bathroom Tile Absolutely Necessary?

Cement board (also called backer board) is a rigid panel made from cement and reinforcing fibers. It's designed to:

• Resist moisture and mold

• Provide a stable, non-flexing surface

• Ensure strong adhesion and long-lasting tile installs

Unlike drywall, including moisture-resistant green board, cement board does not break down when wet — making it the preferred base for tile in bathrooms.

Where You Definitely Need It

Shower and Bathtub Walls

If you're tiling around a tub or inside a shower, cement board under bathroom tile is non-negotiable. These areas are exposed to constant moisture. Even with waterproofing, drywall will eventually fail.

Bathroom Floors with Wood Subfloors

If your subfloor is plywood or OSB, tile needs a solid, moisture-resistant base. Cement board keeps the floor from flexing and prevents cracking in grout and tile.

Behind Freestanding Tubs and Wall Niches

Even if there's no direct water spray, condensation or slow leaks can build up. Cement board gives long-term peace of mind.

When You Might Not Need Cement Board

Concrete Subfloors

If you’re tiling over a solid concrete slab, you don’t need cement board. The slab is already stable and moisture-resistant. Just make sure it's level and clean.

Using Waterproof Foam Panels

Materials like Kerdi-Board or Wedi Board can replace cement board. They're lighter, fully waterproof, and easier to cut — but more expensive. They’re a great option for high-end or custom builds.

Common Mistakes to Avoid

1. Tiling over drywall in the shower Even green board will eventually fail. Moisture seeps in and causes mold or tile failure.
   

2. Skipping waterproofing Cement board is water-resistant, not waterproof. Use a membrane like RedGard or a sheet membrane in wet zones.
   

3. Incorrect installation Cement board must be fastened with alkaline-resistant screws and installed over a bed of thin-set mortar. Gaps should be taped with fiberglass mesh and mudded with thin-set.

   
   
   
   

What Happens If You Skip Cement Board Under Bathroom Tile?

• Cracked tiles and grout lines from subfloor movement

• Mold and rot behind the walls or floor

• Delamination and early failure of the tile

• Costly water damage and repairs

Trying to save time or money by skipping cement board often leads to much bigger issues later on.

Final Verdict: Is Cement Board Under Bathroom Tile Necessary?

Yes, if you’re tiling over a wood subfloor or applying tile in wet areas like shower walls or tub surrounds. No, only if you're tiling over a solid concrete slab or using specialized waterproof panels.

When in doubt — use cement board under bathroom tile. It’s affordable, durable, and gives your project the long-term integrity it deserves.

Need Professional Tile Installation in the Chicago Area?

If you're planning a bathroom remodel and want it done properly — from surface prep to final tilework — reach out to Tools and Hands. We serve Chicago’s Northwest Suburbs and ensure every project is built on a solid foundation — including what’s under your tile.