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Tips for Cutting Cement Backer Board

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Straight cuts in cement backer board can be made using a circular saw.

I just remodeled one of our bathrooms, which included tiling the floor with 12”x 12” Turkish tumbled marble. It was a fun project to work on (it’s a small room) and the tiles look terrific, but the most important step of the entire job was prepping the subfloor.

After ripping up the old vinyl flooring, I discovered that the subfloor consisted of two layers of ½” plywood; the minimum recommended subfloor thickness for tile is 1¼” So, I had to cover the plywood with ¼” cement backer board, which was set in a bed of thinset mortar and then screwed to the subfloor.

Cement backer board can be cut with a carbide-tipped scoring tool, just score and snap the sheet, similar to cutting drywall. But since I had several cuts to make, I decided to use power tools.

Now the first thing you need to know when cutting backer board is that its dust contains crystalline silica, which can be extremely irritating to your eyes and lungs. So, be sure to wear eye goggles and a dual-cartridge respirator when cutting backer board. Also, always make the cuts outdoors and well away from open windows and doors.


A jigsaw works best for cutting curves.

For straight cuts, use a circular saw fitted with a carbide-tipped woodcutting blade, but here’s a little secret: use a blade with the fewest number of teeth you can find. Ordinarily a blade with more teeth is desirable because it produces a smoother cut, but in this case many teeth would bog down and create clouds of thick dust. A blade with fewer teeth (mine only had six) cuts quickly and produces less dust.

To make curved cuts or circular cutouts in backer board, you have a couple of options. You could drill a series of holes along the cut line and then tap out the waste with a hammer.

While that technique works, it creates quite a mess and leaves a ragged edge. I prefer another approach that is both cleaner and quicker.

When I had to cut a 7” diameter hole in backer board to fit around the toilet drain flange, I used a jigsaw fitted with a metal-cutting blade and made the cut slowly. To be honest, I wasn’t sure the blade would cut the dense, fibrous sheet, but it did so quite easily with a minimal amount of dust.

However, I should mention that by the end of the cut I noticed that all the teeth on the blade had been worn down to mere nubs, so if you have a lot of circular cuts to make, be sure to have plenty of metal-cutting jigsaw blades on hand.



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12 Comments on “Tips for Cutting Cement Backer Board”

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  1. KicHeiniasash Says:
    March 12th, 2010 at 7:33 pm

    Hi, my name is Tim. Just wanted to say hi to the forum, I been creeping around here for a while now, but tend to participate more. Looking forward to make some new friends. Ciao!

    Tim

    NY, NY

  2. Official Comment:

    joe t. Says:
    March 12th, 2010 at 8:38 pm

    Hey Tim, Welcome to DannyLipford.com glad to have you aboard. I’m sure you’ll find lots of useful info, and feel free to comment anytime. Ciao!–Joe T.

  3. john Says:
    April 30th, 2011 at 3:10 pm

    Actually if you use a Carbide grit jigsaw blade it will cut through backer board without damaging the blade. It does make a lot of dust though.

  4. Tony Says:
    January 22nd, 2012 at 2:51 pm

    i need to know the best way to cut and remove installed tile on cement backer board that is screwed down,,,i am tearing out the floor and all the joist but i want the least mess

  5. John Says:
    January 24th, 2012 at 3:40 pm

    Thanks for the tips, but what about cutting small holes for plumbing? I have cpvc water lines so is a 1/2″ keyhole saw the only way to go?

  6. Official Comment:

    Joe T. Says:
    January 24th, 2012 at 4:55 pm

    Hey John, According to professional tile contractor, Jimmy Tiganella, owner of Classic Tile in Oakville, Connecticut, the best way to cut small diameter holes is with a carbide-tipped masonry drill bit. Now Jimmy and other professionals will often use diamond-grit or carbide-grit hole saws, but those tools are pretty expensive. If you don’t have a masonry bit large enough for the hole, try this: Use a small-diameter masonry bit–1/4 inch or so–to drill a series of closely spaced holes around the outline of the larger hole. Then, use a hammer to tap out the center. Here’s one more tip that Jimmy suggested trying: Use a razor knife to score all the way around the hole, then tap out the center with a hammer and flat-blade screwdriver. Thanks for writing, John. Hope you find these suggestions helpful.–Joe T.

  7. Gary Says:
    August 2nd, 2012 at 7:55 pm

    Hi a coustermer of mine wonts cement board on the walls of their basment. How hard is it to attach it to the drywall that’s their to the ceament board? And the drywall is 5/8 thick how thick is the ceament board come in? Becuse they wont some kind of water proof the walls and we could not find any warter proofing paint for drywall. They have 22 wals in their basment. Can You Help

  8. Joe T. Says:
    August 4th, 2012 at 10:02 am

    Hi Gary, You can certainly apply tile backerboard (cement board) over drywall: spread thinset mortar onto the drywall with a notched trowel, then screw on the backerboard. However, the backerboard won’t protect the drywall from moisture that’s coming from the rear of the wall. If the basement walls are wet or moist, the drywall will rot from the back side. If a moisture barrier was installed behind the drywall, as it should have been, then you shouldn’t have any problems. Thanks for writing and good luck!–Joe T.

  9. Andy Waz. Says:
    March 16th, 2013 at 9:46 am

    Thanks for the info Joe!

    I have been asked to take on the task of finishing the tile for some friends of ours who are building a house. Their builders’ tile guy left after prepping and laying one floor.

    I do not call myself a pro, more of a handyman. My “real” job is in the sewer and water construction industry. So tile work is more of a hobby than a job. 1300 sq ft. More than I’ve ever done.

    Just a bit of info for your readers. In my line of work we deal with OSHA a lot and they are making us aware of a respiratory issue known as “Silicosis”. It is a result of inhaling the silica found in cementitious products. Prolonged exposure will result in shortness of breath, cough, and increased risk of TB and other respiratory ailments. Although not a death sentence, it can be very troublesome for years to come. If you Google Silicosis you can find all sorts of articles pertaining to causes and symptoms.

    OSHA’s recommendation is to reduce PEL (Personal Exposure Limits) by using a wet-cutting device, eliminating dust, or using a respirator style mouth and nose mask. (which you accurately describe as a cartridge style mask) Those cheap paper masks, however, do not adequately filter the silica particulate out.

    If you’d like more information, drop me a line. I sat through 8(required)hours of class time learning all about the fun of Lead, Asbestos, and Silicosis, and still have all the literature presented to me by OSHA.

    Stay safe and Happy Tinkering

    Andy

  10. don derosa Says:
    April 15th, 2014 at 5:40 pm

    what about using a 4 inch grinder to cut it and thin set used on shower wall and what is best screw for retaining it

  11. marie Says:
    June 17th, 2014 at 5:14 pm

    hey, how to fix a thin backboard under a counter (bar) fixed on the cabinet. since the cabinet are made in particules, impossible to screw the board on it. I want to put tiles under it to match the tile over the sink. I have to return my cement backboard to the hardware store . thin, but heavy.. too heavy for the particule board to be screwed on. any suggestions ? thanks

  12. nelson Says:
    November 1st, 2014 at 5:02 pm

    Putting cement backer board over drywall deletes the purpose of cement board. Cement breathes allows moisture through and back out. Put it on sheetrock in a wet location it will wick water into the rock, the sheet rock will collapsed taking the tile wall with it. Connect strait to studs with backer it will hold up decades longer.

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