I am a DIY who is redoing a bathroom countertop. I am using 5/8 exterior plywood and plan to use thinset mortar between the plywood and 1/2" Hardibacker board(In case you are wondering, I used the 1/2" instead of 1/4" because I needed the solidity and needed to raise my sink up a bit to the level of a backsplash). I used a spiral saw to cut out the shape of my sink on the plywood, but found that even with a so-called cement board bit the spiral saw will not cut the Hardibacker board. The instructions say to use a circular saw with a carbide blade to cut the Hardibacker, and I have one, but am not sure how to cut such a round hole with a circular saw. Do I just make a zillion straight cuts and eventually get rid of all the material bit by bit? Seems like there should be a better way. Help!
I'm not the expert, but have you tried a carbide tipped scoring knife? Use the plywood cutout as a template and score the hell out of the Hardibacker on both sides & carefully punch out the cutout with a hammer. Or, once it is well scored, your spiral saw might work better.
You can use a jigsaw to cut Hardibacker with. The blade won't last long but you could get cut around the corners - then do straights with circ. saw. There is a circ. saw blade for Hardibacker - it only has a few teeth - it works well.
Use a carbide tipped scoring knife to score the shape of the sink in the board, and use your circular saw to cut an x with the ends meeting the inside of where you scored,then the 4 pieces will come out easily and neatly. A cheap cut off blade works much better and lasts much longer than the more expensive carbide circular saw blade with hardibacker. 1/4" hardibacker, when combined with the subfloor, gives slightly more solidity than 1/2".
Ditto Rob's method - I just finished installing 50 sheets of the stuff and I cut every piece with a 4" grinder running a continuous rim diamond blade. Wear eye and dust protection - this work is best done outside and it helps to have a slight breeze to clear the air around you. We cut the small radii with a diamond hole saw / coring bit and use the grinder to link the tangents of the cores.
Still spreading your trash around the site without leaving your name or address?
That is the coward's way to do things, though, so we should not come to expect too much from you.
Not until you check yourself into a detox facility. Fix yourself up, learn some manners, and we will be happy to have you back in the forum--doing something constructive with your life instead of being a pain in the ass to the forum and probably everybody around you.
Thanks to all for the suggestions. I tried the first reccomendation and scored the hell out of the Hardibacker weith a carbide tip scoring blade and then used the cement board bit with a spiral saw and it worked very well. Seems like injuring the top and bottom layer of the board was neccessary before the spiral saw would work(?) Lots of toxic dust, though. Wonder if I have shortened my life by a couple of years!! Thanks again for all the info.
For anyone planning on cutting alot of Hardibacker I recommend getting the Makita saw made for cutting fiber cement. I got the 4 inch saw and chucked a diamond wheel in it. Works great and virtually dust free cutting. For round or other odd shaped cuts, I use my grinder...that is dusty!