Installing tile or stone on a concrete floor can be a great way to upgrade the look and feel of a space. However, it’s important to use the right materials and techniques to ensure success. One key question that often comes up is whether you need to install cement backer board on concrete before laying tile. Here’s a detailed look at the pros and cons of using backer board over concrete, along with recommendations from flooring experts.
What is Cement Backer Board?
Cement backer board, also known as cement board or Wonderboard, is a stiff tile backing material made of Portland cement and fiberglass mesh. It was designed as an alternative to traditional tile backer boards like greenboard (drywall) and plywood.
Backer board is water-resistant and designed to provide a stable, rigid surface for installing tile or stone. It helps prevent cracks and damage from moisture exposure. Backer board comes in 1/4-inch and 1/2-inch thicknesses and is installed similarly to drywall, using screws or nails.
Unlike drywall, backer board will not soften or deteriorate when exposed to water. This makes it ideal for wet areas like bathrooms, kitchens, and laundry rooms. The cement formulation also provides excellent adhesion for mortar and tile.
Pros of Installing Cement Backer Board on Concrete
Here are some potential benefits of using backer board over a concrete subfloor:
Provides a Smooth, Uniform Surface
Freshly poured and older concrete floors often have slight imperfections and variations in height. These can telegraph through to the finished tile installation and cause lippage (uneven tile surfaces).
Cement backer board creates a smooth, consistent substrate that allows for a flat tile installation. The backer board joints are easily sanded down to create a seamless underlayment.
Prevents Cracking Issues
Concrete naturally cracks over time due to settlement, shrinkage, expansion and contraction. If tile is installed directly over concrete, inherent slab cracks will transfer through to the tile surface. This can lead to cracking grout lines and tiles over time.
Installing a cleavage membrane like backer board on top of the concrete acts as a crack isolation layer. It effectively bridges any cracks, preventing them from transmitting up through the tile layer.
Provides Better Adhesion for Thin-Set Mortar
Mortar bonds best to porous, rigid surfaces. Concrete slabs are typically polished smooth during the finishing process. This can make it more difficult for thin-set mortar to adhere properly, increasing the risk of cracked or de-bonded tiles.
The fibrous, cementitious surface of backer board offers an ideal bonding surface for thin-set mortar. It allows the mortar to key into the surface better, creating a stronger bond.
Adds Warmth Underneath Tile Floors
Concrete is inherently cold to the touch and tends to draw heat away from a space. In home or bathroom settings, installing tile directly over concrete can result in a cold floor surface.
A layer of cement backer board helps insulate the tile and provides a warmer surface underfoot. This makes it more comfortable for extended wear.
Allows for Thinner Tile Installations
Backer board is available in 1/4-inch sheets. Using thin backer allows tile installations with smaller overall thicknesses. This may be beneficial when tying into existing floor elevations or thresholds.
Provides Moisture Protection
Excess moisture from underlying concrete can cause issues with tile bonding and grout. Backer board creates a protective layer that impedes moisture transmission from below. This provides added protection and prevents efflorescence or discoloration.
Cons of Using Backer Board on Concrete
There are also some downsides to consider when using backer board on concrete:
Adds Overall Height to Floor
The 1/4-inch or 1/2-inch thickness of the backer board adds overall height to the new flooring. Transition areas, existing door jambs or adjacent floor finishes may need to be adjusted to account for the change in floor level.
Increases Costs Somewhat
Backer board is more expensive than many alternative tile underlayments like plywood or cementitious pre-slopes. The backer material, along with associated fasteners and labor to install it, increases project costs.
Can Create More Dust and Debris
Cutting and fastening backer board produces gypsum and cementitious dust. Additional cleanup and containment is needed compared to working directly atop a concrete subfloor.
May Require Additional Sound Dampening
Backer board generally provides less sound insulation than a directly adhered tile system over concrete. In multi-family units, additional sound attenuation mats may be recommended under the backer to achieve required IIC (impact sound transmission) ratings.
Not Necessary for Every Application
If the concrete slab is new, properly finished, and free of existing cracks, backer board may be redundant. In some situations, tiles can be successfully bonded directly to concrete.
Expert Recommendations
Flooring experts generally recommend installing cement backer board in residential settings as a good practice:
- Sal DiBlasi, author and industry advisor, states, “I recommend cement backer units (CBUs) for most ceramic and stone tile installations over concrete. A cleavage membrane provides crack isolation and a good bonding surface for the mortar.”
- The National Tile Contractors Association’s (NTCA) Reference Manual advises, “Cement backerboard should be specified for tile installations over concrete to allow for movement of the subfloor.”
- Tile installer Bryan McKay (TubTile.com) notes, “I always use cement board on concrete floors before tiling. It creates a strong underlayment that handles movement and imperfections in the slab.”
However, experts indicate backer board may not be required in some scenarios:
- For new construction with proper concrete specifications and finishing, the Tile Council of North America’s Handbook recommends, “If done correctly, most tiles can be installed directly over concrete.”
- The Ceramic Tile Education Foundation’s (CTEF) Certified Installer Program teaches, “On smooth steel troweled concrete less than 2 years old, tile can often be installed directly with no underlayment.”
- Master tile setter John Bridge writes, “My choice is to bond directly to perfect concrete with no history of moisture or structural cracks.”
Should You Use Cement Backer Board on Concrete?
Based on the above considerations, here are some guidelines for deciding whether or not to use backer board:
Recommended Cases for Backer Board:
- Existing or older concrete with unknown slab quality or cracking
- Polished or slick concrete finishes lacking texture
- Underfloor radiant heat installations
- Areas prone to moisture like basements, bathrooms or laundry rooms
- Multi-family dwellings needing sound insulation
May be Optional Cases for Backer Board:
- New construction projects with proper concrete specifications
- High-quality slabs that are properly finished and cured
- Residential floors without noise concerns
- Low-moisture areas like living rooms or bedrooms
Consider Alternatives like Self-Leveling Underlayments
- As an alternative to backer board, using a self-leveling underlayment can also help correct minor variations or repairs in concrete. This adds minimal thickness while still providing a smooth finish.
Consult Manufacturers’ Recommendations
- Be sure to check tile and mortar manufacturers’ instructions to see if they require or recommend using backer board over concrete. Some warranties may be contingent on proper underlayment materials.
Perform Bond Tests First
- In select cases, consider bonding a few tile samples directly to the concrete in an inconspicuous area. Check adhesion after they fully cure. If properly bonded, it may be feasible to install without backer board.
How to Install Cement Backer Board on Concrete
If you decide to use backer board on a concrete floor, here are some tips for proper installation:
Select the Right Thickness
- For floors, use 1/2-inch backer board to add rigidity and prevent flexing. 1/4-inch boards are more prone to cracking underfoot.
Check Floor Flatness
- Grind, patch or level any significant dips or flaws in the concrete subfloor first. The backer board will only span minor variations up to 1/8 inch.
Clean and Prime the Concrete
- Remove any coatings or debris so mortar bonds directly to concrete. Apply a primer/sealer to increase adhesion.
Mark Your Layout
- Map out the backer board layout and snap chalk lines to guide the placement. Stagger joints similarly to drywall.
Mix Mortar and Apply
- Use unmodified thin-set mortar and a 1/4-inch square-notched trowel. Key a thin layer into the concrete first as a slurry coat.
Fasten the Boards
- Screw or nail boards every 8 inches along edges and every 12 inches throughout the field. Ring shank nails provide the best holding power.
Tape and Finish Seams
- Cover all joints with fiberglass mesh tape and skim with mortar to embed tape. Feather edges slightly. Allow to fully cure before tiling.
Plan Transitions
- Account for the added height around existing transitions or thresholds. Use tapered edging or transitional pieces to bridge any height differences.
With proper planning and installation, cement backer board can provide an excellent foundation for durable, long-lasting tile floors over concrete slabs. Be sure to follow all manufacturer instructions and building code requirements in your area.
Frequently Asked Questions
Is backer board necessary for tile on concrete?
Backer board is recommended for most residential tile projects over concrete to prevent cracks, add insulation, and improve mortar bonds. In some cases, it may be deemed optional, but it’s generally considered a good practice for home installations.
What can I use instead of backer board?
Alternatives like plywood underlayment, cork, or rubber membranes can be used. For thin builds, self-leveling underlayments help correct concrete without adding as much height. Always check manufacturer limits on suitable substrates.
Can I install tile directly over concrete?
Installing tile directly over concrete is only recommended if it’s a new, properly finished slab without existing cracks or moisture issues. Adhesion testing is advisable to verify tiles will bond adequately without backer board.
Does backer board help with cracking?
Yes, backer board acts as a cleavage membrane that helps absorb movement and prevent inherent concrete cracks from transferring through to the tile layer. This helps minimize cracking grout lines.
Can I use drywall instead of backer board?
Drywall should not be used as an underlayment for tile floors due to its tendency to soften and deteriorate when exposed to moisture. Cement backer board or other concrete-based substrates are required.
Conclusion
Installing cement backer board before tiling over a concrete floor comes with a range of benefits forbothperformance and longevity. While added costs are modest, the crack prevention, comfort, and stability backer board provides are compelling reasons to use it in areas prone to moisture or cracking. With proper planning for height transitions and seam finishing, it can offer a smooth, consistent foundation for beautiful, durable tile floors.