How to Cut Cement Board and Hardie Board

what is a cement board?

Cement board, also known as the concrete board, fiber cement board, or sometimes hardie backer board, is one of the most useful home improvement inventions of the 20th century. ​Cement board is used as a tile backing board in areas of moisture, such as your kitchen or bathroom. 

​Once you learn how to cut cement board, you will be able to update and add walling and tilework to your home. Here is our complete guide on how to ​cut hardie ​board for your next kitchen or bathroom remodel. 

An Overview of Hardie and Cement Board

For starters, lets make sure we're all taking about the same product. Cement board is interchangeably referred to by quite a few names, and it is worth listing those out.

For the sake of this article, cement board is the same product as:

  • Hardie Board
  • Hardie Backer
  • Backer Board
  • CBU (Cementitous backer unit)

​Often easily confused with drywall, cement board is actually quite different, and used for very different purposes.

To the untrained eye, they can be easy to confuse.

  • Cement board looks and feels somewhat like drywall. You can think of it as sort of a cousin to it.
  • The difference is that drywall is made of gypsum covered with paper, and hardie board is made of a combination of cement and reinforcing fibers.
  • This means that unlike materials like drywall, plywood, or green board, there is no organic matter in cement board. Unlike drywall, hardie backer has no gypsum, asbestos, or formaldehyde.
  • This also means cement board will never mold, rot, shrink, or decompose due to the presence of organic materials.

​Cement board is water proof, which means that it will resist water, making it the perfect substrate to sit behind tile.

what is a cement board?

Photo credit: garann on Flickr / CC BY-ND

​If your project actually requires drywall (and not cement board), make sure to read our article on sheetrock vs drywall

​Applications

Now that you know the differences between cement and hardie board vs drywall, lets talk about where is best to use this product.

​Cement Board vs Drywall

Cement board has the great advantage of being totally inorganic. As mentioned earlier, it will not rot, warp, mold, or deteriorate when wet. Obviously, wood is not an ideal material to use in places where there is moisture. Neither is drywall.

​Cement Board vs Greenboard

Even greenboard, which is more durable and hardy than drywall, is not recommended for use in showers and other places where there is constant water usage. For these purposes, cement backer board is perfect. That is why cement board is mainly used as a substrate for tiling.

Since tile is widely used in bathrooms, kitchens, and other places where there is constant moisture, it has become the go-to solution when tiling. ​

​Where to Use

Hardie board is also used as a substrate for manufactured veneer stone, at times. In contrast with more traditional materials like drywall, cement board won’t soak in moisture from the mortar under the veneer stone like drywall will. It offers considerably more strength when compared to drywall.

Cement board provides builders with the easy-install equivalent of a concrete subfloor. It is a very hard, very flat surface. Tile and other materials can easily be laid on it with no concern for the presence of moisture on the substrate. While perfect for tile, professional builders often use cement board for other kinds of floors, countertops, backsplashes, and even walls.

Now that we've covered what cement board and hardie board is, and when to use it, lets review the various ​types and sizes that cement board comes to us in.

​Types and Sizes

​There are two basic types of hardie board​. One is hard and heavy like concrete, and the other is softer and lighter.

Cement backer board comes in several thicknesses much like drywall. Hardie board is generally made in thicknesses of 1/4”, 7/16”, 1/2”, and 5/8”. You'll use the thinner boards in areas like countertops, and the thicker boards behind shower and kitchen walls. 

Cement board, or hardie board, usually comes in one of two sizes: 3'x5' and 4'x8'.

​It’s relatively inexpensive for most DIY jobs around the house. For example, a 3'x5' sheet of 1/4” backer board runs around $10, and the same size in the 1/2” thickness runs around $14.

​​How to Cut Cement Board and Hardie Board

​No matter what, whenever you install cement board, you're going to have a variety of cuts to make. And, there are a variety of different ways to cut ​this type of board, ranging from very easy to very precise.

The best way for cutting hardie board will depend on the tools you have at your disposal, how much time you have, and how precise you need to be. We'll go through each of the most common ways ​for cutting ​cement board below. 

​Note: If you're researching how to cut durock, you can follow the same process. Durock is simply a brand of ​cement board.

​Score and Snap Method

The simplest way to cut concrete wallboard or cement backer board is not to use power tools at all. Similar to the way drywall is cut, it is possible to score the cement board and snap it along that scoreline. It is possible to use a drywall knife to score cement board sometimes. But, it will wear down the blade and take some effort.

A better option is to pick up a carbide-tipped score knife. These tools have a very durable scoring tip which can be used to easily score cement board.

the better option on how to cut cement board is to use a carbide-tipped score knife
  1. Begin by laying your cement board out on a flat surface and mark the line where you’d like to score the board. You can do this with a carpenter’s pencil or use a chalk line.
  2. When it’s time to make the cut, set a straightedge across your sheet. Use a level, yardstick, or a leftover piece of scrap lumber. 
  3. Kneel on one end to ensure the straightedge does not move, and firmly draw the scoring tool along the line.
  4. Holding the tool against the straightedge, you can use it as a guide to ensure a perfectly straight score line.
  5. Repeat the movement three or four times to get a nice, deep score cut into your cement board.
  6. Once you have a sufficient score groove, stand up the cement board. Press with your knee and pull. The cement board should snap cleanly along your score line.

Cement board has fiber inside it for structural strength, so you can use a utility knife to cut through this mesh to separate your two pieces. Using a rasp, you can easily smooth the rough snapped edge.

​With a ​Circular Saw

how to cut cement board using circular saw

​Scoring and snapping can be tricky, especially with thicker cement boards. Not only is it difficult to hold a straight line for the entire cut, but cutting by hand takes a long time if you're cutting a lot of cement boards. 

When scoring and snapping aren’t ideal, it is possible to use power tools to cut your fiber cement backer board. ​We'll review several power saws that you can use, starting with the circular saw. 

A word of caution: cutting hardibacker board ​with a saw produces a fine silica dust that is crystalline in structure. That means the dust has sharp edges and will irritate eyes and lungs. Always wear a high quality respirator and goggles when cutting ​cement board. It’s a good idea to make your cuts outdoors, clear of open doors and windows.

​Again, you should always wear a respirator and goggles when cutting cement board. ​This is dangerous​, so make sure to read the safety instructions for your circular saw and follow them to a tee.

For simple straight cuts, you can fit your circular saw with a carbide-tipped wood blade, and use slow, even pressure when you make the cut. The best way to cut hardie board using this method is to use a blade with the fewest teeth you can find.

When you’re cutting wood, you typically want more teeth in your blade so to make for a cleaner cut. But, when cutting hardie board, more teeth in the blade isn't necessary, and will just make more dust. A carbide-tipped blade with as few as six teeth will cut cement backer board smoothly and quickly.

​With a ​​Jigsaw

​If you’re not cutting a straight line, it is possible to use a jigsaw with a carbide-grit or a metal-cutting blade installed. Cutting curves is much easier with a jigsaw, and the preferred option in the case to a circular saw. 

This method will be slow to cut, and produces a little dust. ​After several cuts, you’ll probably need to replace your blade. Still, if you need to cut a smooth curve, the jigsaw is probably the best way to cut hardibacker board for you.

​Don't forget about a cord free jigsaw option either. If you have one that is powerful enough, this can make the project go a little faster, and make it a lot more convenient. 

​The Best Jigsaw

​We've put together a comprehensive review, where we found the very best ​jigsaw on the market​.

​Using an Angle Grinder​ or Tile Saw

It is also possible to cut hardibacker board with an angle grinder which has been fit with a diamond cutting wheel. However, the angle grinder makes a lot of dust, and is a little more difficult to control than a circular saw.

You really only want to use this method for fast cuts, as your lines won't be as straight as with other methods. 

If you have a wet saw for cutting tile, you could use this for cutting your hardie board, as the abrasive blade is constantly bathed in water, resulting in a clean cut with no dust. You might not find it worthwhile to get out your tile saw for this, but if you have a lot of cuts to make it might be worthwhile.

This method probably produces the least amount of dust out of all of the ones listed. 

​The Best Tile Saw

​We've put together a comprehensive review, where we found the very best ​​tile saw on the market​.

​How to Cut Circular Holes in Cement Board

When installing cement board around a toilet, faucet, or other pipe fitting, you may find you need to cut a circular hole in your cement board. Similar to cutting circles in wood, there are a few tricks available for those who need to do this.

If the hole is small enough, the simplest solution to cutting a hole into cement board is to use a carbide-tipped hole saw and a drill. ​

Related: How to Drill Into Tile

drill holes along the edge of the circle on cement board
  1. First, draw the outline of your hole on your cement backer board with a compass. Or, you could trace a pipe fitting or other circular object of the proper size.
  2. Using a 1/4” masonry bit and a cordless drill, drill a bunch of holes along the edge of this circle. Think of making a perforated “dotted line” along the edge, so drill as close to the other holes as you can. 
  3. Once this is done, using a hammer, lightly tap on the center of your circle.
  4. After a few taps, the cement board should snap along your dotted line.
  5. From here, you can finish the cut with a utility knife and smooth out the rough edges with nippers.

We mentioned it above, but a jigsaw is also the perfect power saw to use for cutting a circle in cement board.

Related: What is a Jigsaw Used For?

Conclusion

​When you are considering ​the best way to cut hardie board or cement board, first evaluate and ensure you are using the proper substrate.

Cutting cement board depends greatly on what tools you have, how accurate you need to be, and how fast you want to go. While power saws make it a lot easier, it is possible to cut hardie board by hand.

Either way, follow the steps we've outlined in this guide for how to cut fiber cement board and hardie board. And, remember to follow all safety instructions!

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