Cement Board: What It Is & When to Use

Cement board is the most common building material used under tile installed on floors, walls, countertops and backsplashes. It's purpose is to support the tile which needs a level surface to avoid cracking. That's why this material is also called backer board or cement backer board.

Man installing shower floor tile on top of cement backer board ... — Installing shower floor tile on top of cement backer board …

You'll find cement board in building supply stores, typically near the drywall. It's slightly more expensive that drywall but worth the investment as you don't want to have to replace cracked tiles. The boards come in 3 x 5 ft sheets (about $10 per sheet) that work well for bathtub surrounds and showers.

What is Cement Board Made Of?

The boards are made of cement, water, silica, limestone flour and fiberglass for increased strength. Unlike wood or drywall (paper faced), cement backer board doesn't have an organic materials or “food” which makes it resistant to mold, rot or decomposition. The core isn't waterproof but it can get wet without falling apart (what happens with wet drywall).

It's still important to try to keep these boards, and the materials behind/underneath it dry so it's common to brush a waterproofing membrane on top of the board when used in wet areas like bathrooms (showers, bathtub surrounds and floors).

One of the most common water problems my handyman company dealt with were floors next to the bathtub from kids splashing water over the edge, so it's best to take all the precautions you can.

Laying out cement backer board before installing ... — Laying out cement backer board before installing …

Working With Cement Backer Board

Cement board is much heavier than drywall, varying based on the manufacturer. Here's a great comparison chart from JamesHardie (their board is called HardieBacker). This covers the three most popular cement backer board products 1/4 inch (here is the complete comparison of 1/4 and 1/2 manufacturers).

Wondering why it's important to research building materials? One warning about using cement backer board is that it leaves abrasive sandy crumbs so you have to be careful when working around tubs and showers. In the table below, you'll see that HardieBacker doesn't contain glass fibers which makes it non-abrasive.

Cutting cement backer board is similar to drywall (scoring and snapping) but harder because the material is more sense. They say a picture is worth a thousand words so I wonder how many words a video is worth?