Subscribe or Renew Membership Subscribe Renew

Cutting Hardibacker

AAA Handyman Services's picture

Ok, I give up. What's the trick to cutting curves and circles in Hardibacker?

When tiling a bathroom floor, I never look forward to the dreaded toilet flange cutout. Here's the tried and true 10 step program I've been using for cutting this stuff:

1) Get out the carbide tipped scoring device
2) Apply a huge ammount of preassure repeatedly scoring the same lines over and over
3) Scrape my knuckes on the Hardibarker
4) Curse
5) Keep scraping
6) Still scraping (I now realize that I am only 1/4 way through this stuff)
7) Audible say "To hell with it!" and get out the hammer
8) Bash the circle out (also causing the bottom area around the flange hole to flake off)
9) Try to fit the piece in the bathroom & realize it's too small
10) Repeat Process starting at step 1

I know there's a better way. I have a set of power shears designed for Hardibacker. They work great...for straight lines. Is there an bit for a router or zip bit out there? A jigsaw blade? Anything? Thanks,


(post #70454, reply #1 of 28)

Jig saw.

(post #70454, reply #2 of 28)

Roto-zip, Jig saw with carbide blade or angle grinder with diamond blade all work

(post #70454, reply #3 of 28)

There's a special bit for Rotozips that cut cement board. Do it outside, it makes a lot of dust.

(post #70454, reply #4 of 28)

That sounds painful and distinctly unfun.
I use a 4 1/2" grinder with a cheap ($15) turbo diamond blade for all my hardibacker cuts. pretty easy for toilet or shower mixer cut outs- score all around with the grinder, then make an X in the middle, all the way through, break out the wedges, and clean up with the grinder.

I make all my straight cuts with the grinder too- I snap a chalk line, score it about 1/2 way with my grinder, and then it breaks easily and cleanly. The dust doesn't bother me too much, I always do the cutting outside.



"When we build, let us think that we build forever.  Let it not be for present delight nor for present use alone." --John Ruskin

"so it goes"


(post #70454, reply #5 of 28)

Zak, that sounds like the ticket. I think I like the idea of the angle grinder more than a rotozip. Rotozip bits have a way of breaking on me, and they get dull pretty quick. But a diamond blade...that will make a nice dust cloud pie out of the flange cutout. Thanks,


(post #70454, reply #6 of 28)

We have been using a grinder and a diamond wheel which works well.  that was up until the last job when we heard about a jig saw blade that has the leading edge coated in (I think it is) carbide bits.  Really similar to those grout saws.  it works unbelievably.  Next to no dust and tons of maneuverability.  It was cheap too.

(post #70454, reply #13 of 28)

The jigsaw blade I used for cutting holes in cementitious siding has a leading edge coated with cobalt bits and fits the description of your blade. It's relatively inexpensive and lasts much longer than the carbide blades. I agree with your assessment of how well it works, and although there is minimal dust, a mask is still a good idea.

(post #70454, reply #18 of 28)

Andy - Rotozip blades break for us too, not just you. But the ones that are designed for cement board are about three or four times the thickness of the drywall needles. The cement board ones hold up well. IIRC they work on tile too, (not as sure about that). 

Don K.

EJG Homes     Renovations - New Construction - Rentals

(post #70454, reply #19 of 28)

IIRC they work on tile too, (not as sure about that). 

Wall tile only.  They do not recommend using them on floor tile.


"I am the master of my fate, I am the captain of my soul."  Invictus, by Henley.

"I am the master of my fate, I am the captain of my soul."  Invictus, by Henley.

(post #70454, reply #7 of 28)

Last week our tile layer asked me what I used to make such clean cuts around the shower mixer valves. I might as well share my answer with you folks too. I used a Makita Drywall cutout tool <> with a Rotozip Duracut™ Bit <>.
I used the circle cutter attacment and the dust hood on the Makita hooked up to my shop vac so the circle was precise and there wasn't airborne dust.

Edited 2/14/2006 3:17 am by Renoun

(post #70454, reply #12 of 28)

Thanks for the tip. I will be using that setup for the smaller finer cutouts that a grinder is too big for.


(post #70454, reply #8 of 28)

.....A bigger carbide tipped hammer with a circle attachment ???


. . .

. . . . . . . .

(post #70454, reply #9 of 28)

Angle grinder with a diamond blade.


Make a series of cuts up to the line and break out the thin 'fingers' of hardies. Use the edge of the grinder wheel to 'sculpt' the hardies back to the final shape. I also put a very small bevel on the back of the cut to make sure no fur, lumps etc get in the way of a clean fit.


Whatever it was.................I didnt do it.


Not an exponent of the DILLIGAF system.

(post #70454, reply #10 of 28)

Hardiboard is real easy to cut using plain old circular and jig saws. Any old blade will do. Use an old circ. for straight cuts if you don't want to gunk up your good one.


DCS Inc.

"Whaddya mean I hurt your feelings, I didn't know you had any feelings."  Dave Mustaine


DCS Inc.

"Whaddya mean I hurt your feelings, I didn't know you had any feelings."  Dave Mustaine


(post #70454, reply #11 of 28)

hole saw

. 2+3=7

(post #70454, reply #14 of 28)

Ditto on the carbide jigsaw blade. No dust cloud.

(post #70454, reply #15 of 28)

Trippo on the Carbide blade on a jig saw.

The one I use has grit on the Leading edge.  I believe it's for cutting tile.  It's really cheap and works extremely well.


I hear, and I forget.  I see, and I remember.  I do, and I understand. - Confucious

Edited 2/15/2006 1:07 pm ET by Max Minimus

(post #70454, reply #16 of 28)

Carbide jigsaw blade for Hardibacker?  Come on.  Regular coarse tooth blade will last an awful long time if you run at slow-moderate speed.  It creates so little dust that I can't imagine using a grinder or other high speed cutter.  It's also fast.

For long straight cuts a circular saw blade specifically for hardibacker is the way to go.  It cuts straight and quick, with a lot of dust.

Shears are the way to go if you do a lot of the stuff.



Beer was created so carpenters wouldn't rule the world.

If I could edit my location it would say I'm now in Reno :-)

(post #70454, reply #17 of 28)

I have installed alot of this hardibacker and use 4 inch angle grinder and it works well i use an old ring for a template and it works great and the dust sucks and a i always wear a mask and cut out side if i can.

(post #70454, reply #20 of 28)

I like a jigsaw run slowly since you can make the cut in the house and not have to worry about dust.  There's nothing wrong with using a grinder, cutout tool, kitchen aid mixer, can opener or what have you, but the jigsaw seems to save time and effort when cutting toilet flange openings.

It does make me cringe a little when using a finish tool on concrete.  :-)


Beer was created so carpenters wouldn't rule the world.

If I could edit my location it would say I'm now in Reno :-)

(post #70454, reply #21 of 28)

I agree - a slow speed jigsaw with a course blade works fine.

(post #70454, reply #22 of 28)

I agree with all the methods mentioned. But I'm surprised no one mentioned shears. I have a set of Kett electric shears that will cut 1/2" Hardibacker that works like a charm, and NO DUST. Obviously you need the other methods sometimes, but the shears are the ticket.

(post #70454, reply #23 of 28)

The Hardibacker install video shows the use of a snapper shears that makes it all too easy to do straight or radius cuts. No dust, no fuss! Our sales rep says they sell for $200 but if you buy enough sheets, they would throw one in. Check with your retailer.

I have wanted one for a while, but am aware they make shears for metal only and some for CBB only. Make certain the one you get is for CBB! 

(post #70454, reply #24 of 28)

All good tips, but suppose I'm wanting to cut out for an outlet box in the middle of a sheet of Hardibacker.  What tool and bit would I use to make that initial penetration through the backerboard, say to make a hole large enough for the tip of my jigsaw blade to fit through?  Thanks.

(post #70454, reply #25 of 28)

A hammer with proper backing is the way.

Spheramid Enterprises Architectural Woodworks

I have irriatable Vowel syndrome.  

(post #70454, reply #26 of 28)

Sphere, can you explain a little better? Which end of the hammer, and what is proper backing? Thanks.

(post #70454, reply #27 of 28)

Lenox makes a carbide grit bit for a sawsall.

(post #70454, reply #28 of 28)

Start the hole by a whack with the hammer face, but hold a 2x4 block a inch or so away from the back..this keeps you from burying the hammer in the soon to be cut out.

Spheramid Enterprises Architectural Woodworks

I have irriatable Vowel syndrome.