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How To Cut Hardie Board Siding

James Hardie fiber cement siding is one of the most popular siding materials for new home builders.  This material is a hard mix of cement, silicate, and wood fibers; properly installed Hardie boards can last over fifty years.  At TrueBlue, we work almost exclusively with Hardie boards for this reason. If you want to learn how to cut Hardie board yourself, we have some tips and tricks to make the job easier.

However, if you’re looking to do some DIY with Hardie boards, you’ll need to be careful.  Due to the composite nature of fiber cement, cutting the boards can produce a cloud of thick dust laden with silicate particles; this dust can be extremely harmful if inhaled, so you’ll need proper respiratory protection for this project.  A dust mask respirator and protective eyewear are necessary to prevent bodily injury; if these materials are unavailable to you, consider getting the aid of a professional for your board-cutting needs.

Cutting Hardie Board Siding: The Score and Snap Method

The most popular and least messy way to cut Hardie boards is actually quite simple: the score and snap method.  With this method, you won’t need any power tools, and the dust created will be minimal.  However, we always suggest cutting Hardie boards outside whenever possible.  For the score and snap method, you’ll ideally want to use a carbide-tipped scoring knife; these are generally used for scoring cement backboards.  The carbide tip is much stronger than your average utility knife; if you don’t have a carbide knife, you can use a regular utility knife, though you should expect your knife blade to take some damage.

The step-by-step process for the score and snap method is as follows:

  1. Using a straightedge, mark out the line where you want the board to be cut.  This method works best for long, straight cuts.
  2. Following the line you just marked, score the board with your knife.  You may need to make several passes with the knife before the cuts are deep enough to be snapped.
  3. Hold the board against an elevated surface (a sawhorse, your knee, a table edge, etc) and apply downward pressure on both ends. With enough pressure, the board should snap cleanly along the scoreline.


How To Cut Fiber Cement with Power Tools or Saws

If you’re planning to do a large project or have thicker pieces such as trim boards, you may want to opt for a proper power tool or saw for the job.  Several tool options will work for this, though each one will require specialized blades; a simple wood-cutting saw or tool will not be sufficient for this job.

Using Electric Shears

There are specific electric shears on the market that are designed to cut fiber cement boards; these can be expensive, though they work quickly and produce very little dust, and can handle some curved shapes.  The shears may not be wide enough to cut through Hardie trim boards, however.

  1. Measure and outline your desired shape on the board.
  2. Line the jaws of your shear up with the edge of your shape.
  3. Turn on the tool, and follow the marked lines on your board.  Be sure to keep the edge of the shear pressed firmly against the board for a clean cut.


Using a Jigsaw or Circle Saw

A jigsaw can be a useful tool for cutting Hardie board, especially if you don’t have specialized fiber cement tools around.  You can use course wood blades for this, though your blade will wear out after only a few cuts.  Specialty diamond blades are available for jigsaws, so this is recommended.  The jigsaw works best for irregular shapes or curves.

The circle saw method is not the most efficient way to cut siding; it will require specialty fiber-cement or diamond grit blades and will produce a lot of dust.  If you choose this method, be sure to do your cuts outside and do NOT forgo your respirator.

  1. Measure and mark your cut line.
  2. Line up the edge of the saw with the beginning of your cut line.
  3. Turn on the saw and cut slowly for the best accuracy.
  4. Replace blades regularly and remember your respirator.

Installing or Replacing Fiber Cement Boards

If you’ve successfully cut down your Hardie boards, be sure to read our blog on Hardie board installation.  If you’ve decided to save yourself the trouble of cutting and installing the boards on your own, consider reaching out to us at True Blue Roofing and Siding for help.  Our expert team has all the tools and expertise to make your Hardie board installation a breeze.  Contact us today by phone or by using our online form.



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