When laying hardie backer I was told to make my joints as tight as possible, so I imagine I'll run into this often.

Currently I have a standard 6' board that just barely doesn't fit inside the lip of the tub (I'm leaving a 1/4" gap below per hardie board's instructions).

What is the best way to shave off a piece of hardy board so I can make a tight fit?


I am not saying this is the cleanest or the most practical but I will just tell you what I do... Angle grinder with diamond blade. I cut these pieces only outside and I wear proper goggles and mask. It is one of the only times that I overdo safety.

This is the only way I can get a clean small cut in HB. If I use a knife it will take a few scores, then I bend it and since the bent area is small, the break won't be even at all.

  • Turns out the compressor I had was underrated for my angle grinder so I used a carbide blade with my oscillating saw and it worked beautifully and left a better edge than I could score / cut. Turns out anything over an 1/8 inch is easy to cut with a jigsaw and carbide blade. – virtualxtc Mar 17 '14 at 4:36

You can use one of those cheese grater looking rasps most people use for drywall. They're called serrated contour planes.

Something like the Stanley Surform Pocket Plane or Stanley Surform Plane-Type

Those tools will be quicker/easier and make less of a mess than using a power saw. Or at least a more controlled mess. You can also use a utility knife with a sharp blade but the rasps are easier to use and safer.

  • small cuts on hardieboard are hard and I don't think a rasp would do it. – DMoore Mar 10 '14 at 18:02
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    @DMoore It works to shave off a little off the edge. I've done it. Also works on cement board too. – OrganicLawnDIY Mar 10 '14 at 18:16
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    I have tried it too and my rasping isn't even over the course of 6 feet because it takes so much effort. Maybe your rasp is better than mine. – DMoore Mar 10 '14 at 18:18
  • Wow -thanks!! I'll consider this, but since I already have an angle grinder I'm going use that first. – virtualxtc Mar 12 '14 at 8:50
  • @virtualxtc The best thing is to get the cut right the first time. Power tools make a big mess. I like to lay the panel where it's going to go (usually upside down) and mark the panel. It's faster and more accurate than using a tape measure. Then score and snap. There might be some high spots which are easy to clean up with a rasp or sharp utility knife on the opposite edge but since you marked the board upside down you'll have factory edge to factory edge in most situations. – OrganicLawnDIY Mar 12 '14 at 16:00

we used a tub saw with an old blade.(NO WATER) cut out doors. use face mask and eye protection as it makes clouds of dust. draw size and cut free hand a the guide seemed to bind. cuts like butter!! even a perfect bevel.

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