Flush-Cutting Fiber-Cement Siding

Installers look for an easy way to cut fiber-cement siding in place for a window flashing retrofit. October 27, 2009

I am looking at a job cutting HardiPlank siding in place above windows and doors in order to install flashing that was left off. I have researched methods and found a tool called Multimaster by Fein that seems to meet my needs for flush, precise cutting, but haven't found any testimony of real experience doing so with this siding. I have 25 windows and doors to flash and I would appreciate any feedback you might have on the subject.

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor P:
If you could find a blade for HardiPlank there is no doubt the multi-master will cut it. I think they have some sort of carbide blade that would probably work, but I would double check that. Their flush cut blades are prohibitively expensive. We're talking upwards of $40 each. You could also use a 4 1/2" grinder with a thin cut-off wheel that would probably work fine. Since you don't have to worry about cutting through the flashing, cutting depth shouldn't be a problem. Itís definitely less expensive, but somewhat dustier.

From contributor K:
I recently purchased a Multimaster for a job where I need to cut out the baseboard to install casework. It was very easy to cut but not very fast. If you have 25 windows to do I would suggest a battery saw and a fixture designed to track the saw on to do most of the cutting. Then you could use the Multimaster to complete the ends of the cuts. Also you would need to do some research on the best Multimaster blade to use. If I remember correctly, that siding is made with some cement in it, correct? If so you will need the carbide grit blade design to cut it.

From contributor A:
The Fein tools are great, but the accessories are very costly. They have some cutters for grinding grout between tiles. I would think this would cut fiber cement. Likewise I would consider using a conventional grinder for doing 95% of the cutting. I have a nice small 4" Makita grinder that is light and small enough to do detail work. The typical 4 1/2" are heavier and more awkward. In body shops they call them detailers.

From contributor S:
James Hardie siding is made from cellulose and Portland cement. Just about any type of cutting tool can be used to cut it, even a utility knife however the problem comes from the dust generated during the cutting and blade life. The Portland is very hard on the tooling so itís recommended that you use carbide blades in the saw or diamond wheels on the grinder. If it were my job I would buy a saw blade specific to cutting Hardie board and use a circ saw with a vacuum attachment. Of all the options available this one will generate the least amount of dust and user fatigue. Iím curious as to your method of cutting and installing the flashing. The nature of your question leads me to believe that this task is somewhat foreign to you and i may be able to offer some insight as to some proper flashing and siding techniques.

From contributor J:
Bosch makes a great flush cutting reciprocal saw. We have several and use them for cutting baseboards when installing wall units in existing applications. I am sure it will do what you want!

From the original questioner:
Thanks for all of the advice. I still haven't heard from anyone who has tried to cut HardiPlank with a Multimaster, so I am thinking it is not a good idea. I have flashed many windows but never after a bonehead has finished a house without flashing first! I think the sidehead grinder idea will probably be what I end up with, though I'm not excited about the dust.

From contributor S:
One way to eliminate cutting or at least keep it to a minimum would be to remove the entire piece above the window, flash the window and then replace the siding. If any cutting needs to be done (to allow for the added flashing) than it can be done on the workbench with a pair of siding shears (zero dust). Shears can be rented from most tool rental shops.

From contributor K:
To answer your question directly, you assume correctly. I don't think the Multimaster is a good choice for long cuts. I don't think they cut at a speed that would be productive. As a result you will wear out a lot of blades or simply spend too much time doing the work. I have never cut HardiPlank but I don't expect it to cut faster than solid wood.

From the original questioner:
Yeah, you guys are right. I probably have to remove the siding. Itís a bummer because it's caulked and painted and I wanted to avoid the time and expense of touching up, but I guess my customer and I will have to bite the bullet. I have a set of shears, having done a few HardiPlank siding jobs (not my favorite material, despite its durability and longevity).

From contributor S:
Remove the panel and install your flashing, then cut your siding, install it and use stainless 18 gauge braid on the piece above it to hold it in place. Set your gun so the nail does not countersink.