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ponch37300 11-27-2008 02:40 PM

cutting hardi board
What is the best way to cut hardi backer board? Also what is the best way to cut cement backer? Thanks

Nestor_Kelebay 11-27-2008 04:06 PM

I guess that depends a lot on your definition of "best".

You're SUPPOSED to be able to cut cement board much like drywall; you just score through the fiberglass mesh on one side, snap along the score line and then cut through the mesh on the other side. The first time I did it that way (using a laminate knife to score the cement board with), I decided that would be the last time I'd do it that way because of the very rough cut edge I got.

So, that was the fastest and easiest way, but I didn't consider the results acceptable.

Since then I'd cut either with a circular saw fitted with a masonary blade or a hand grinder fitted with a THIN metal grinding blade that will handle the High RPM's. You can get these at most welding stores.

And, of course you can cut holes in both with a jig saw fitted with a "RemGrit" blade, which you should be able to find in the tiling tools section of your local Home Depot. You can cut straight lines that way too, but the hand grinder cuts a straight line faster, and the circular cuts a straightER line than either if it's guided by a straight edge.

Hardibacker is surprisingly abrasive on metal tools. I think that's because of the amount of silica sand in it. If you use any metal blades or drill bits to cut or drill holes in the stuff, plan on throwing them out afterwards cuz they'll dull very quickly cutting Hardibacker.

jerryh3 11-27-2008 05:56 PM

For 1/2" I use a 4" grinder with a diamond blade. 1/4" you can usually score and snap easily with a good utility blade. For small holes, I have a diamond grit hole saw, and for other cutouts I use a diamond grit jigsaw blade.

JazMan 11-28-2008 05:13 PM

Most people try to cut Hardie as common sense and experience cutting other products would tell us. WRONG! Hardie is cut by scoring the surface, then snapping up, not down. :thumbsup:

If you're using a 4" side grinder with a diamond blade, you can set the sheet on a wooden pallet, then score or cut through with the grinder. HOWEVER, this produces lost of dust and Hardie is not good for your health. (silica and other bad things). When I cut any CBU with a grinder, I do it outside near the approach of the garage with a fan blowing from behind me. This blows most of the dust outside if the wind isn't working against me. :thumbsup:


Dan V. 11-28-2008 07:57 PM

Score and snap for straight cuts, Rotozip with cement cutting bit for curves and circles. Any rough edges, just lightly rasp.

AtlanticWBConst. 11-29-2008 07:47 AM

Manufactures of cementitious boards, do not regularly suggest using a power tool to cut their products, due to the amount of airborn dust produced. Generally, a carbide-tipped knife, is the best method for manual cutting of the boards.

I still prefer to use a skill saw with carbide tipped blade, that gets tossed when done with the installation.
I also use a carbide-dusted jig saw blade (tile cutting blade) for off-angle, or circular cuts.

As stated, the key point to using a power tool, when cutting any cementitious board, is good ventilation. I always use safety glassess and the appropriate type mask/filter. Lastly, I also use a portable filtration system, if cutting indoors.

Silicaa dust is not good for your respiratory track.

Be forwarned that there are dangers to the production of silica dust. Please familarize yourself with some information at the following links:

SSGMEADER 02-12-2009 12:27 PM

I pretty much do what Dan V and Atlantic do. Score and snap rotozip if needed but like Atlantic says silica is BAD for you. make sure you wear a respirator or at bare minimum a filter mask. Also someone commented that hardiboard will wreck most power tool blades and such. he is correct. For shower stems and valves I ussually use a carbide tip hole bit 3/4'-1" and that doesnt tend to throw the dust all over the place at a nice slower speed it wil mostly fall to the floor.

cbyrd 02-12-2009 01:23 PM

I have one of these I got on ebay.. Great for cutting hardibacker ... No dust..

ponch37300 02-23-2009 12:57 PM

Cbyrd, I just ordered one of those from ebay, got it shipped for 103 bucks brand new. I cut some 1/4" hardi and it went threw it like butter with almost no dust! It leaves nice straight cuts and can even do off angle cuts also. It says it will cut 1/2 hardi also. They are 279.00 brand new and I got a great deal and am amazed how well these work. Anyone in the tile business or even just doing your own house, for 100 bucks they make this job easy. Thanks for that link Cbyrd!

amakarevic 04-11-2011 09:24 PM

what kind of hole bits would you use for drilling holes in hardie backer ? can you use the same ones as for wood?

Bud Cline 04-11-2011 09:40 PM


...can you use the same ones as for wood?
Yes but it is hard on them. Hardibacker is a fiber-cement product. Carbide tipped tools are probably best.:)

BMS98 04-12-2011 03:02 PM

circular saw with inexpensive blade you don't mind dulling/ruining. Jigsaw for curves, circles, etc. It's abrasive, but it's not that hard to cut. Wear a dust mask. Don't breathe the dust.

JazMan 04-13-2011 01:53 PM


circular saw
I would NEVER do that.:no:


amakarevic 04-13-2011 01:58 PM

i found out that what helps A LOT is, after creasing it with a utility knife, you just kind of make a small incision at the beginning of the cut line with a saw, any kind of saw, hand saw, drywall saw etc., and that helps TREMENDOUSLY in folding over the crease, upwards rather than downwards, as was instructed above.

condoremodel 04-14-2011 01:29 PM


I am in the process of renovating my condo and I've bought books and watched Youtube over and over again and I must say it did help!

Laying flooring is not my strong point because it is a lot of back breaking work but I am close to the end I will post a pic when I'm finished.

I am a single mom on mat leave juggling a 8month old, a condo reno and school (part time).

I came across this site and I was really impressed they had movies and articles of DIY projects.... I think I will tackle the kitchen next but I think I will need my dad's help for this one!!


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