What is Backer Board & Where Do You Use It?

The term backer board reminds me of when I started my handyman business. There were hundreds of construction that weren't easy to decipher. Backer board is moisture resistant so it's used to support tile installations, both walls and flooring. It's name doesn't tell you much about the role it plays and unlike drywall which we see every day, backer board is never seen.

Backer board is ideal in “wet areas” which are vulnerable to water because it resists moisture and swelling.

Your most important tile projects are in bathrooms. You always want to install backer board behind showers and the walls surrounding bathtubs. Backer board is also used under floor tile when there's a wood sub-floor. This includes bathroom floors and any other tile flooring in your house, what builders call the “wet areas”. And if you're building a new house or remodeling a kitchen, you'll also want to put backer board behind the backsplash.

Let me share the bathroom project where I learned about backer boards. One of my handyman technicians started to finish a new walk-in shower in a lovely 1700s home in Newfields, New Hampshire. We ran into a scheduling conflict so another technician went out to finish the job. The phone call I got wasn't fun because the new technician ranted for a while about the walls not being finished with backer board. He told me the only acceptable solution was to replace the moisture resistant drywall (known as green board) already installed with backer board!

This was a big job and a loyal, repeat customer, so I approved and paid for the upgrade. It wasn't part of the original estimate but I learned a valuable lesson about bathrooms and backer board.

What is Backer Board Made Of?

Backer board is also known as cement board. Unlike drywall that contains some wood, concrete backer board doesn't have any organic material. This means it's less likely to rot, decompose or support the growth of mold. Backer board is made from cement, water, silica, limestone flour, and reinforcing fibers like fiberglass for strength.

Where Do You Use Backer Board?

Where there's water and tile, you'll want to use cement board even though it costs a little (not much really) more than drywall. That means you should expect to find/use it in (here are tile tips for DIY):

Cement backer board can be nailed or screwed just like drywall. It comes in smaller 3 x 5 ft sheets (drywall comes in 4 x 8 ft sheets). And like drywall, cement board comes in different thicknesses for different applications:

Walls and ceilings – need at least 1/2″ thick boards or 5/8″ inch. The boards should be nailed or screwed into the wall studs or joists.
Tile kitchen countertops – should use 1/4″ or thicker backer board on top of 3/4″ exterior-grade plywood.
Kitchen backsplashes – can be installed over 1/4″ backer board (preferred) or over clean, level drywall since sinks are not considered wet areas.
Flooring – requires the use of 1/4″ or thicker cement backer board over a plywood sub-floor that's 5/8″. An exterior-grade plywood is preferable as the layers are glued together with a waterproof adhesive that prevents them from delaminating due to exposure to water.

Builders install tile in what are called “wet areas”. These include entry ways, mudrooms and laundry rooms … in addition to the kitchen and bathrooms. Tile is also a good idea where you have other exterior doors. There's nothing worse than having to refinish wood floors near a patio door, because of the water and mud tracked indoors from the backyard. You don't have to tile the entire room – you can do tile for 18 to 24 inches along that wall or just around the patio doors similar to what you expect around a fireplace.