How do I cut cement board?

[Rich Engelhardt]

Hello,
I have to put up some cement board around a bathtub.
We've removed the old drywall and remnants of the old cement board that were there, and are down to the bare studs.
I have a Rotozip with the masonry wheel - which worked well BTW - for cutting into the old cement board.
Do I just use that or is there a better way, such as a masonry blade for a circular saw?
I'm probalby going to need to make only 5 - 36" cuts at most.

[Keel McDonald]

Rich,

For cutting the cement boards just mark the the lines with a pencil, score both sides with a utility knife and snap the board to size (much like drywall). You can also use a carbide-tipped blade with a circular saw to cut or score the boards. Good luck!

[Jake Helmboldt]

Just like Keel said. Don't waste the time and money of using a carbide blade, not to mention dust.

[Dave Bonde]

Keel and Jake are both right - but some of the new cement board is pretty hard to score with a utility knife. You can buy a carbide cutter (works like a utility knife) for about $7.00 that works better than just a knife. They will be with the tile supplies at the big box stores. I would try the utility knife first but if you have trouble I would try the carbide cutter next. Dave

["Gary Brewer"]

Rich: There is a small carbide tipped hand tool made just for scoring concrete backerboard and then you snap it like sheet rock . Putting a board under the edge of the scored snap line can make the snapping easier ( assuming the backerboard is broken across its whole length or width and it is laying on the ground or floor). The tool is very inexpensive and should be available at Home Depot or Lowe's. It works fine and for a few cuts is cheap and easy. I have a 4 1/2 grinder and I put a dry cutting tile blade in it and cut the board outside. The second method creates a lot of dust so it needs to be done outside and wear a mask or hold your breath ( goggles woud also be a good idea ). This is faster, easier and dirtier than the first method. It is useful when you are making a lot of cuts or have a number of cuts to go around something ( usually when installing floor tiling ). It is not worth buying a grinder and blade for one small job but if you have a grinder a blade purchase is worth it if you were going to do more tile work another time. Also the grinder produces a smoother more precise cut than snapping.
FYI there are two manufacturers of concrete backerboard that I know of, Wonderboard and Durock. Durock has tapered edges like sheet rock and I like that better for taping the seams. It also seems better made. There are also special noncorosive screws made just for concrete backer board. If you use them make sure you screw them flush with the surface and not proud of it. You can predrill or tap them in partway with a happer and then screw in. I am not a pro but have done alot of tile jobs for myself, my son and friends. ( Durock has a nice installation pamphlet that covers all the aspects of installing concrete backerboard. ) (I don't have a rotozip but if it works for you there is nothing wrong with using it. Probably outside also. )
Gary

[Mike Parzych]

Rich -

I've used an abrasive blade - about $6-7 - to cut Durock, which I think you're referring to. Real dusty, but it works. Don't know if you've seen it, but Denshield is becoming more popular as a tile backer. Much lighter and doesn't crumble like Durock. You can use a drywall screw sinking bit to take the screws down below surface level easily, and it cuts just like drywall.

[Lou Morrissette]

I used the carbide scoring tool I bought at HD and it worked very well. For stopped or inside cuts I used my jig saw with a Remington abrasive blade. It worked ok but use a mask for the very irritating dust.

Lou

[Cliff Rohrabacher]

Utility knife - carbide scorer.
Both work

[Brad Hammond]

however ya cut it.... wear a mask! that stuff is crazy dusty.

[Mark Singer]

dust mask!

[Brad Hammond]

ha! yeah......or respirator. lol you might want to wear a mask too.... sometimes you gotta sneak up on 'em.

[Rich Engelhardt]

Hello,
Thank you all for the info. & suggestions.
I did some searching on the web also.
Seems like scoring/breaking is the preferred method, with a special jig saw blade being used for cutouts. I'll probably pick up a RotoZip blade for the cutouts - might as well get some use out of the tool.

Re: The dust.
Yup! It's a mess of it! This is for around an old tub, and cutting away the existing cement board - with the RotoZip masonry wheel - created a dust cloud like I've never seen - instantly.
I hate to have to spend "tool money" on one,,but a decent respirator is on my "to buy immediately - if not sooner" list.

[Jeremy Gibson]

I've done the utility knife scoring before on my first bathtub surround project and it works...but the blade dulled immediately and was a little more work to score down to the embedded fiberglass mesh. I'm getting ready for demo of my second bathroom remodel and this time I bought the carbide scorer. I'm hopeful it will score a little faster than just a utility knife.

I have a few cutouts I'll need to do with my job. I think I've been going on the assumption I'd use my 4 1/2" angel grinder with a tile blade (must buy one), dust mask or resperater (good excuse to buy one), safety glasses and a full face shield. I've gone through the pain and expense of a "foreign object" in my eye once before and don't want to go through it again. Maybe I should try the line "but honey, my little B&D jigsaw is too underpowered to go through this backerboard. I need to get that new Bosch jigsaw on my Amazon list!"

Good luck on your project - post pics when you're done!

[Matt Calder]

All,

I sided my shop with cement fiberboard siding, I know it is not the topic of discussion but I thought I would add to the collective knowledge.

When cutting the siding I used a tool that is essentially the same as the electric snippers made by a number of tool makers (Milwaukee has one for sure). These are completely dust free as they work like scissors. I am sure they would work as well for fiberboard panels as they do for fiberboard siding. They cut clean and one can do convex curves easily (concave to a limit of about a 4 inch radius).

The snippers I got were sold specifically for fiberboard but I can't see how they differ from regular electric snippers. If you are going to be cutting a lot of the stuff, and might need to cut curves it is the way to go.


Matt

[Mark Hubler]

I cut my cement board using an angle grinder and a harbor freight diamond blade. Light score on both sides - work great! For holes, I made overlapping straight cuts (octagon to make a circle), and made an X across the hole - on both side; easy to break out the pieces (I drilled a small hole to use as a reference).

This is a very dusty process, so as others have said, use a good dust mask.

[Garay Holland]

We used 230 4x8 ft sheets of Durock in our present project so we had a LOT of cutting to do. Started out trying the scoring and breaking and it might work for some but we soon saw we were having far too many snapped corners and ragged edges. In the end we went to a diamond blade for our 4 1/2" Dewalt side grinder. YES, it makes a lot of dust, and we used resperators but we found it cleaner cuts and faster work to mark with felt tip and do full cut with the diamond blade.

As for other (than Durock and Wonderboard)backer boards we ran several test as to durability under exposure to water. Nother esle even came close. We left one sheet of Durock sumerged in water for a month - let it dry for a couple days and put it up with no noticable effect. Of the two mentioned, we preferred the Durock. It even worked better in cases where we wanted to make curved walls. Our kitchen counter surround has Durock as a plaster base. We were able to make two curved corners which we covered with 4' width of 1/2" Durock on 3' radius curve. Worked like a dream.

Garay

[Rich Engelhardt]

Hello Garay,
Thanks for the info on the Durock. I don't want to have to redo this job, so even though it's a rental house, I'll use something that won't ever need replaced - well,,at least in my lifetime.

[Jim O'Dell]

I used the carbide scoring knife and it worked well. BUT!!!! That thing is scary sharp. I slipped up over my straight edge and made a deep slice in one finger. The carbide blade, hand powered or motor powered, doesn't care if it's wood, concrete, or flesh. Saw Stop hasn't come up with a version for the hand powered one... yet.:rolleyes: :D Jim.