Cement board, also known as fiber cement board or backerboard, is a durable and water-resistant building material commonly used as an underlayment for tile, stone, and other surfaces in wet areas like bathrooms, kitchens, and exterior walls. Installing cement board properly is critical to create a sound, long-lasting substrate for your finished surfaces. In this comprehensive guide, we’ll walk through all the steps and best practices for installing cement board like a pro.
Choose the Right Cement Board for Your Project
There are a few different types of cement board to choose from, each with slightly different properties and ideal uses:
Fiber Cement Board
- Made from Portland cement, sand, and cellulose fibers
- Provides exceptional durability and water resistance
- Can be used for interior and exterior applications
- Brands include HardieBacker, PermaBase, and Durock
Fiberglass Mat-Faced Cement Board
- Faced with fiberglass mesh on both sides
- Extremely water durable and mold resistant
- Ideal for tile substrates and wet areas
- Brands include DensShield, FiberBoard, and GlasRoc
Foam Cement Board
- Cement board laminated with a foam core
- Lightweight and easy to cut
- Provides some insulation value
- Good for walls and some flooring applications
Pick the type of cement board designed for your particular tile or flooring project. Fiber cement boards like HardieBacker are the most versatile and commonly used. Invest in 1/2″ thick boards for maximum durability and stability.
Gather the Right Installation Tools and Materials
Installing cement board requires some specialized tools and materials to do the job correctly:
Tools
- Tape measure
- Level
- Square
- Utility knife
- Circular saw with carbide blade or cement board shears
- Drill with carbide drill bits
- Cement board screws or nails
- Rubber mallet
Materials
- Cement backerboard
- Thin-set mortar for embedding in substrate
- Joint tape for seams
- Drywall screws, backerboard screws, or cement board nails
- Acrylic seam sealant
Make sure to use cement board specific screws and nails so they can fully penetrate the dense material without breaking. Carbide-tipped blades and bits are also a must to cut through cement board cleanly.
Prepare the Subfloor for Installation
Installing over a properly prepared subfloor is key to cement board success:
- The subfloor must be completely clean and free of dirt, oil, and debris
- Level any uneven areas for a flat underlayment surface
- Fill any cracks or gaps in the subfloor with hydraulic cement
- Install underlayment grade plywood if the subfloor is questionable
- The subfloor should meet deflection requirements
Test for subfloor deflection by firmly pressing down in multiple areas – if it flexes more than 1/24 the span, strengthen it before installing cement board.
Proper subfloor prep prevents unevenness, cracks, and other issues down the road.
Plan the Layout and Make Any Cutouts
Planning your cement board layout and making necessary cutouts before installation saves lots of time:
- Map out the layout so joints don’t end up in the middle of your finished tile
- Stagger boards similarly to laying hardwood flooring
- Mark and cut out openings for electrical boxes, plumbing, fixtures, etc.
- Pre-cut boards to fit non-standard spaces as needed
Cut cement board with special shears or a carbide tipped circular saw – don’t use a wood saw as it will gum up. Wear proper eye and dust protection when cutting cement board.
Doing the prep work makes the rest of the installation much smoother.
Attach Cement Board with Adhesive Mortar
Embedding cement board in a mortar bed creates excellent adhesion and stability:
- Mix up a batch of thinset mortar, following product mixing directions
- Apply thinset to the subfloor using a 1/4” x 3/16” V-notched trowel
- Press the cement board into place with tongue and groove edges butted tightly
- Fully embed the board in the mortar using a tapping block or rubber mallet
- Check for full contact and levelness as you work
Applying thinset mortar takes a little extra time upfront but prevents loose boards or popping sounds under flooring.
Fasten with Cement Board Screws
In addition to the mortar bed, cement board must be mechanically fastened to the structure:
- Fasten every 6-8” along studs or joists
- Stagger screws 1” from board edges and 2” from corners
- Sink screws so heads are flush with the board, not countersunk
- For wall applications, make sure boards are supported at top and bottom
Using proper cement board screws prevents the heads from popping over time. They have deep threads and heads designed for maximum holding power.
Apply Joint Tape and Sealant
Filling board joints is important to prevent cracks at seams:
- Bed fiberglass joint tape in thinset mortar along each seam
- Apply multiple thin coats of acrylic seam sealant over tape
- Use mesh corner beads for inside and outside corners
- Let sealant fully dry between application of additional coats
Sealing joints helps minimize cracks but is especially critical for waterproofing steam showers, tub surrounds, and other wet locations.
Make Any Final Cuts and Penetrations
With the main installation complete, finish up with any final trimming or openings:
- Measure and cut boards to fit non-standard spaces
- Trace and cut holes for plumbing and electrical penetrations
- Cut boards around registers, light boxes, etc. with hole saws
- Use acrylic sealant around cut edges and openings
Avoid last minute cuts and holes in finished surfaces by addressing them before you tile or install flooring over the cement board substrate.
Install Tile or Flooring with Modified Thinset
Your cement board underlayment is now ready for the finished surface:
- Use modified thinset specifically formulated for cement board
- Allow proper mortar cure times between layers
- Install tile, stone, or wood flooring per manufacturer guidelines
- Appropriate expansion joints and movement spacing still apply
Cement board provides a durable, stable layer but appropriate finishes must still be installed correctly. With proper prep and planning, you can feel confident your cement board will provide many years of worry-free performance beneath your finished surfaces.
Installing cement board with best practices creates a substrate for tile, stone, and flooring that withstands moisture, movement, and heavy use – especially in wet areas like bathrooms and kitchens. Follow these cement board installation steps carefully and you can take comfort knowing your finished surfaces will stay firmly adhered for years to come.
Frequently Asked Questions About Installing Cement Board
Installing cement board well requires following some specific techniques and procedures. Here are answers to some of the most common questions that come up about working with cement backerboard:
Is any special preparation needed before installing cement board?
Yes, the subfloor must be totally clean and free of debris, oil, wax, grease, dust, and any other contaminants. Fix any subfloor issues like cracks beforehand and make sure it meets deflection requirements.
What tools do I need to cut and install cement board?
You’ll need shears and a carbide blade for cutting. Use cement board specific screws or nails for fastening. Have cement board tape, thinset mortar, and an acrylic sealant on hand for seams and penetrations.
What type of screws should be used to install cement board?
Use specialized cement board screws. They have auger shaped threads to grip tightly and flat head designs that won’t pop through the board surface over time. Make sure not to countersink the screws.
Should cement board seams be taped?
Yes, you must tape cement board joints, otherwise you risk cracking along the seams when the substrate flexes or moves. Embed fiberglass joint tape in thinset mortar along each seam.
How thick should cement backerboard be for floor tile?
Use 1/2″ thick boards for flooring applications. The added thickness and rigidity prevents movement or flexing underfoot after tile is installed.
Can I use drywall screws to install cement backerboard?
No, drywall screws do not provide enough holding power for dense cement board. Over time they can loosen or pop through the surface. Always use specialized cement board screws.
What can I use to seal penetrations in cement board?
An acrylic sealant designed for cement board is ideal to seal around penetrations for plumbing, electrical boxes, and anywhere cement board is cut. This prevents moisture intrusion into those openings.
How long should I let thinset mortar dry before applying joint tape?
Let thinset mortar fully cure for 24 hours before applying cement board joint tape over it. This prevents the tape from sinking into uncured thinset.
Can I tile or install flooring directly over cement backerboard?
Yes, you can install tile, stone, and many flooring types directly over cement board provided you use the appropriate modified thinset adhesives designed specifically for cement board substrates.
How do I cut cement board neatly and accurately?
The best method is to score the board face with a carbide tipped utility knife followed by snapping the board upward to break cleanly along the score line. Use a straightedge as a guide for straight cuts.
Installing cement backerboard like a pro ensures it will provide many years of unbreachable performance beneath finished tile, stone, or wood surfaces, even in wet areas. Follow these techniques for a stable, durable underlayment.
Conclusion
Installing cement board properly is an important process to create a long-lasting, durable substrate for finished surfaces like tile. By using the right materials, preparing the subfloor correctly, fastening boards securely, sealing seams and penetrations, and applying finishes with the proper adhesives, you can achieve many years of reliable performance out of your cement board underlayment. Paying attention to the details in these cement board installation steps will also help prevent cracked grout, loose tiles, mold growth, and other issues resulting from an improper underlayment. If undertaking a cement board installation for the first time, don’t be afraid to reach out to a knowledgeable contractor, installer, or technical advisor for assistance and product recommendations. With care taken to follow best practices, you can look forward to cement board providing a crack-free foundation beneath your beautiful tiled shower, stunning stone floor, or solid hardwood for decades to come.