How To Cut Hardie Board Siding

Hardie Board siding is slightly trickier to cut than wood. The material is primarily composed of cement, so it is dense and produces a lot of harmful dust when you cut it with a saw. So, using the appropriate tools and take precautions to manage the risks associated with fiber cement sawdust is crucial. 

How Do You Cut Hardie Board Siding Correctly?

Cut Hardie Board siding with a power saw and a fiber cement blade or a diamond blade, facing the material opposite the blade’s cutting direction, and work outdoors or use a vacuum system to avoid harmful dust. Alternatively, cut Hardie Board with siding shears or by scoring (with a utility knife) and snapping it. 

Cutting Tool To Use	How to Cut Properly
Siding shears	Use a metal ruler to guide the blade for a straight cut
Utility knife	Score it first before snapping the workpiece
Power saws	Need dust collection attachments to get rid of the harmful sawdust that accumulates

Method 1: Siding Shears

Siding shears are designed specifically for cutting fiber cement board (also called Hardie Board siding). 

Stationary shears are mounted to a frame and resemble a guillotine whose blade cuts the siding in a downward slicing motion. These cutting tools are available in manual or electrically-powered models (which are more expensive)

Hand-held shears have scissor-like blades and are more commonly used than the stationary type (due to their lower cost and portability). These shears attach to the body of a power drill (either cordless or corded). 

The primary benefit of siding shears is the lack of dust generated when cutting fiber cement. This simplifies the process as you don’t need to set up a vacuum system as you would when using a power saw.

Step 1: Measure The Piece And Mark If Necessary 

Measure the Hardie Board to the required size.

Mark the intended cut line on the board [pencil?].

Step 2: Position The Board In Preparation For Cutting

If you plan to use hand-held shears, position the siding on a suitably stable work surface. Make sure there is sufficient free space underneath the board for the blade to move.

The blades of hand-held shears cut upward, so place the front side of the Hardie Board facing downward. Cutting into the front of the workpiece produces the neatest results (if tearing or chipping occurs, it will be on the side where the blade exits).  

If the piece of Hardie siding is large and unwieldy, it is advantageous to secure it to the cutting table with clamps. 

When using the guillotine-style stationary shears, lay the piece of fiber cement on the tool’s cutting table. 

As the blade of this cutting tool slices in a downward direction, orient the workpiece with the front side facing upward.

Step 3: Execute The Cut 

Now the fiber cement workpiece is ready to cut. 

Using the hand-held shears, start cutting slowly and carefully along the marked line. For added accuracy and straightness, use a metal ruler (square) to guide the blade as it cuts. 

If you have stationary shears, lower the blade down firmly to slice through the board. 

Method 2: Utility Knife (Score-And-Snap)

Another method for cutting fiber cement siding involves two stages. Firstly, one scores the material with a utility knife (or a carbide scoring knife), which is almost the same as cutting a vinyl siding. The second stage entails snapping the board along the scored weak point. Snap it just like how you cut MDF boards.

Step 1: Measure And Mark

Measure the Hardie Board and mark where you plan to cut.

Step 2: Position The Board Appropriately

Situate the board on a stable, evenly flat cutting surface. 

Remember to lay the piece of fiber cement facing skyward because the knife blade cuts downward (obviously!)

Clamping the fiber cement to the work surface adds extra stability but, in most cases, you can achieve satisfactory results without clamps. 

Step 3: Line Up A Ruler For A Cutting Guide

For a cutting guide, put a metal ruler or square on the workpiece and align it precisely with the marked line (on the waste side of the marking).

Step 4: Scoring Cut

Perform the scoring cut by drawing the knife blade along the guide.

It is ideal to make each pass of the blade in one continuous motion from one end of the board to the other.

Press the blade gently for the first cut and apply more pressure with subsequent passes.

Step 5: Snap The Workpiece 

Now execute the final stage of the procedure by snapping the piece of Hardie Board. 

Place the board with the score line along the edge of the work surface. Lean on the workpiece with one hand, then grab the waste side in the other hand and snap it off with a brisk, powerful downward motion.

If you want to see this method in action, check this helpful video out. 

Method 3: Power Saw

Power saws are ideal if you need to cut a large quantity of Hardie Board siding fast. 

A primary factor to consider when cutting fiber cement with a power saw is the harmful dust that is produced. It is always advisable to wear a respirator mask, even when working outdoors. If you are cutting Hardie Board indoors, it is also crucial to have a way to remove the sawdust as it accumulates.

Step 1: Select A Power Saw

The types of power saws that are suitable for cutting Hardie Board siding include:

• Circular saws
• Miter saws
• Jig saws

Dust collection attachments for circular saws, miter saws, and jig saws are also widely available, affordable, and easy to set up. 

Choose a circular saw for making straight cuts in Hardie Board.

Miter saws are an excellent choice for cutting fiber cement if you need to make short, straight cuts (at various angles). The dust hoods and removal hoses for these mounted power saws are also simple and relatively cheap to use.

Jigsaws are also effective for making straight and angled cuts in fiber cement boards and cutting tough plexiglass. There are also excellent cordless jigsaws that enable a high level of precision cutting.

Step 2: Choose An Appropriate Saw Blade

Choosing an appropriate power or circular saw blade for Hardie Board is critical for success.

Only use cement siding blades specially designed for sawing through this material. You can cut this material with blades that you usually use for your cedar wood projects, but the teeth will get blunted quickly (and might break off).

Special fiber cement siding blades are available for circular saws, miter saws, and jigsaws. These blades are segmented, with have a small number of large teeth to minimize the accumulation of sawdust. Fiber cement blades are also significantly more durable than those for sawing wood.

Diablo produces the optimal fiber cement saw blade called the HardieBlade®. This blade (or cutting disc) is available for circular and miter saws. The edge of the HardieBlade® is made from super-strong polycrystalline diamond. Diablo claims it produces roughly 50% less dust and lasts three times longer than other fiber cement blades. 

Diablo also produces a high-quality jigsaw blade for cutting fiber cement. The blade is carbide-tipped and has extra-large teeth, enabling it to cut through cement board neatly without creating excess dust or becoming blunted.

Step 3: Measure And Mark 

Once you have selected a power saw and blade, you can measure the cement board to the required size.

Next, mark the intended cut on the workpiece with a carpenter’s pencil or a marker pen.

Step 4: Position The Board Correctly

Place the board on a workbench or suitably stable, flat surface. If you intend to use a mounted circular or jig saw, lay the piece of cement siding on the tool’s cutting table.

Follow the golden rule of orienting the workpiece with the front side facing opposite the cutting motion of the saw blade. So, for instance, lay the fiber cement facing downward when using a circular saw because the tool’s blade cuts in an upward (clockwise) direction. 

The benefit of positioning the workpiece in this way is that the neatest part of the cut is on the side where the saw blade teeth enter the board. In contrast, the side where the blade exits the workpiece often looks untidier (as the teeth push inner fibers outwards as they cut through the board).

Finally, ensure the board rests against the cutting fence or guide if the saw has one of these components.

Step 5: Stabilize The Board 

When working with hand-held power saws, it might be worth providing additional stability to the workpiece by clamping it to the cutting surface.  

Step 6: Set-Up A Guideboard If Necessary

If you need to make long, straight cuts with a hand-held power saw that does not have a fence or cutting guide, consider using a homemade or commercially-manufactured guideboard. 

Step 7: Wear Personal Protective Equipment

Taking health and safety precautions is essential when using power saws to cut fiber cement. Put on protective eyewear, cut-proof gloves, and a respirator mask before cutting the material. 

Step 8: Execute The Cut

With the board set up at its cutting station, it is time to execute the cut. 

First, activate the vacuum or dust removal system. 

Then switch on the saw and start cutting the piece of Hardie Board. It is critical to sawing the cement board in a slow, controlled fashion, so you minimize the safety risks and maximize the neatness of the cut.

Conclusion

You can cut cement board safely and successfully with siding shears, or by performing the score-and-snap method with a utility knife. Another way to cut Hardie Board is to use a circular, jig, or miter saw fitted with a fiber cement blade and a dust removal system (if you are working indoors).