A backer board, or a cement backer board, is a DIYer’s friend. It’s easy to install and comes in handy in various projects. A backer board is also flatter, harder, and less susceptible to warping and rot than plywood. It’s no surprise that even professionals use it for everything from floors to walls.

The one problem you may encounter is cutting your backer board to the desired size. There are two types of backer boards, and both have unique properties. One of them is hard and heavy - a little like concrete - and this usually gives people the most trouble when they try to cut it. The second type is lighter, softer, and more fibrous.

In this guide, we’ll show you how to cut Hardie backer boards to obtain your desired size. But instead of showing one method, we’ll give you 4 options for how to cut backer board, so you can choose whichever suits you best. If you stick around till the end, we’ll also give you tips that make it easier to work with a backer board.

Before You Begin Cutting

One of the first things you learn as a DIYer is that projects can get messy. Depending on the materials you’re using, dust, silica, or even sparks can start flying very easily. Cutting a backer board is no different.

That’s why we recommend that you do it in an open area away from doors and windows. That way, the crystalline silica dust doesn’t go into your home. You’ll also need protective gear - safety goggles and a double cartridge respirator - to keep you safe.

Method 1: The ‘Score and Snap’ for Thinner Sheets

If you’re working with a thinner sheet, you can easily score the board by making a deep groove and snap along the scored line. This method is fairly straightforward, so the only tools you’ll need are:

• A carpenter’s pencil; a regular pencil will dull quickly due to the hard surface
• A straightedge
• A scoring tool or utility knife

To cut the backer board:

1. Lay it on a flat surface -- a concrete floor or work table is ideal. Highlight the desired size using your carpenter’s pencil. It’s important to make your markings easy to see so you may have to run it twice.
2. Using a straightedge, run your utility knife or scoring tool along the line to make a groove. A straightedge helps keep your lines steady.
3. Repeat this step two or three times to make the groove deeper. The deeper the groove, the easier it will be to snap the backer board.
4. Once you have a deep enough groove, lift the board to an upright position and press your knee against the lines. Create as much pressure as needed to snap the piece. 
5. The fiberglass mesh will be intact, so use your utility knife to cut the connecting pieces.

Notes about the score and snap method

This technique is quick and efficient. It’s perfect if you’re looking to make quick cuts, but it may turn out to be quite messy. Additionally, the cuts may not be perfectly precise, and the chances of imprecision go up with shallow grooves. That’s why we often recommend a second method - using a circular saw.

Method 2: Cutting with a Circular Saw

A power tool is exactly what you need for precise cuts in thicker backer concrete boards. Even though the circular saw is often used on wood, it can also be quite effective for making quick clean cuts in a cement board. More importantly, it’s readily available in most DIYers’ workshops.

Before getting started, you’ll need to install a carbide-tipped wood-cutting blade on your circular saw. The backer board can damage your regular blade. If you're shopping for a blade, we recommend something with few teeth. The fewer the teeth, the less the dust.

Some people run into additional problems when they try to cut a straight line with a circular saw. If this is you, don’t worry because we have a step-by-step process that works wonders.

To cut straight lines with a circular saw:

1. Mark the edges where you want to cut with your carpenter’s pencil.
2. Determine the edges of your saw by placing it over the line. Mark the outer edge of the saw along the entire length of your backer board.
3. Place your straight edge along the line you just drew and clamp it down. This way, you can use it to guide your saw without losing track of the line.
4. Simply run the saw along the entire edge until you have two cleanly separated concrete backer board pieces.

Method 3: Using an Angle Grinder

We don’t favor this method because not all DIYers have an angle grinder lying around. Additionally, you’ll need to install a diamond-impregnated cutting wheel; any other wheel will be ruined. We also don’t like the fact that this method kicks up a ton of dust. Even if you’re wearing protective equipment, it can become very difficult to see what you’re doing. 

Finally, there’s also the issue of making straight cuts. If you’ve ever used an angle grinder, you'll know it can be tough to do. 

However, if you’re in a pinch and an angle grinder is the only available tool, you can cut a concrete board with an angle grinder.

Method 4: Cutting Holes

You probably rolled your eyes the second you saw “holes” because you know how tough it can be to cut holes in materials like plywood, let alone a backer board.

But sometimes, it’s inevitable. What’s more, a clean, well-aligned hole cut can make all the difference in your project, separating you from amateur workers.

So how do you cut holes in a backer board? If it’s a small hole, go with a carbide or masonry bit. The bit will go right through, and you can get back to your project.

But if you need a larger hole, the most straightforward solution is a hole-saw. As you can guess, you'll need a carbide tip for that, as well. 

If you don’t have a hole-saw, you can cut out large holes in your backer board using a drill bit. To do this, mark the hole using a carpenter's pencil and drill small holes around it. Then, use a hammer to knock out the centerpiece. With this approach, you’ll have to smooth the rough edges with tile nippers or pliers. 

FAQs About How to Cut Backer Board

How do you cut holes in cement boards?

You can cut holes in a cement board using several tools, depending on what you have on hand or the size of the hole. The best tools for this task include a drill bit, circular saw, portable jigsaw, or saber saw. Each of these needs the right blade or a bit that's strong enough to cut through the cement. It helps to highlight the area you wish to cut with a carpenter's pencil before getting started. 

Can you use a jigsaw to cut cement boards?

Yes, you can cut cement boards with a jigsaw. However, you’ll need the right blade for the job; this will be a metal-cutting blade or a carbide-tipped blade. It’s important to wear appropriate safety gear and make sure the blade is properly fitted into the saw before getting started.

The process will be slow, smooth, and kick up minimal dust. The only downside is that you'll probably get 8 cuts out of the blade before it needs a replacement. This is why it's a good idea to use tools with a tougher blade, like an angle grinder with a diamond-impregnated cutting wheel. 

Is a cement backer board waterproof?

Cement boards are water-resistant, and they’re often used around bathroom areas. However, they’re not waterproof. Some professionals like to waterproof their cement boards by using a barrier or sealant.

Can you cut holes in the HardieBacker cement board?

Yes, you can cut holes in a HardieBacker cement board. To do this, mark the circle on the board and score around the perimeter using your scoring tool. Also, make several scores with different starting points around the hole. When finished, the board will look like a well-sliced pizza.

To knock out the hole, place supports under the board on either side and strike the hole’s center with a hammer. You can then remove extra pieces by hand.

Final Cut

Whether you’re a DIYer or a professional contractor, a backer board will make your work so much easier. If you can find a way to cut it without stress, even better.

In this guide, you've learned exactly how to cut backer board using everything from a utility knife to a hole-saw. This information will come in handy whether you have all the tools you need or you’re just working with a few garage tools.