7.5″ circular saw for cutting ‘crete
I have a section of cracked concrete floor in my garage to cut out. It’s keeping my garage door from sitting flush and therefore allows rainwater and sometimes mice to get in.
My plan is to cut a section of about 1 foot by 9 feet out, build a form, put some wire mesh down, and then repour.
For the cutting, can I accomplish this with a dry cut mansonry saw in my Makita 7.5″ circular saw? How thick is the concrete usually? I guess I can’t cut it if it’s deeper than 3-3.5″.
I’m fine with renting a bigger saw if I have to. If I can do it with my saw, I don’t have a problem with buying the blade (vs paying for wear and tear on the rental).
The other advantage would be that I’m comfortable using my saw. I’m not sure how comfortable I would be with a much larger saw. I have vivid memories of my dad coming home from an accident on the job where he almost cut his thumb off…and this was after working residential construction for 15 years. Handsaws, tablesaws, miter saws don’t bother me. That handheld powersaw does for some odd reason.
Replies
Dry cutting with a diamond blade in a circular saw can be done...but you're limited by the depth-of-cut, just like when cutting wood.
One other consideration is that you'll make multiple passes, and the deeper you go the more friction heat you can get, thus an inexperienced user may end up overheating the blade and getting blade wobble. This can sometimes cause the blade to jam in the kerf. Not a huge problem...just an observation.
Best bet would be to rent a rig. This will give you a full-depth cut, though you will still have to make multiple passes, and the rental rig performs better than a homemade setup.
Watch out for rebar.
And consider yourself warned...after dry cutting 12" you'll be in a whiteout. You'll be amazed at how much dust is produced, so tarp off or plastic off all you can because the dust will go EVERYWHERE.
A wet cutting rig would be a nice choice.
A good 7" diamond blade is going to run you $60-$70. Subtract that from the cost of a rental, add in the ease of use of a rental and the face that it'll cut full-depth, relish the idea of a wet-cutting rental which will minimize dust, and rental may very well be the way to go.
do yer self a favor, rent a "quickie saw" chainsaw motor with a 12'' diamond blade...have a kid or some cheap help, spray a hose lightly as ya cut, goggles, hearing protection, and mask for both of you.
A sledg hammer, a flat shovel ( here's where the cheap help really shines) and a bunch of cold beer.
A half day tops..probly no rebar, but there likely is remesh, have bolt cutters handy.
You would probly kill your circ.saw. and they dont like water, and that means more dust..
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
Right on.
Even some of the hand held concrete demo saws yer talking about will accept a garden hose for wet cutting. The Husquanva I've rented in the past does any way. They look a little intimidating (those saws, not the rental guys) but they're not much to handle. Just go easy.
Probably the best choice for the application anywho.... those full on walk-behind wet saws ain't so good for tight spaces like a garage.
Down here many of the houses with concrete slabs have post-tension cables embedded in the concrete. You might check your slab, cuz if you hit a cable it will get interesting.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
How dangerous are these cables? It's not something that will snap and lash back at me, is it? I'm all for hiring a pro to do this if there is a real chance of getting seriously hurt.
The cables are not particularly dangerous. But what happens is, you cut it and release the tension, it tries to shrink, and somewhere it will blow out a chunk in the floor slab. A friend at work had it happen in her house, but in this case the socket went bad on it's own (a very rare case) and she noticed a hump under the bedroom carpet.
You may not even have cables in the slab. Depends on the foundation practices in your part of the country.
Whenever you are asked if you can do a job, tell'em "Certainly, I can!" Then get busy and find out how to do it. T. Roosevelt
If your rental place doesn't know what a quickie saw is... tell them "partner saw".
This is REALLY the way to go if you can ventilate the area (chain saw motor fumes get to me). Some of these saws even have water setups built into the machine (I don't like 'em, but for a novice, it might be helpful).
This job will be cut in half (pun intended) with one of these babies. I use my circ saw to cut where I can't get ventilation... and it is a real bear. I have rented an electric model... but they don't really do any better than my circ (except for depth of cut).
BTW... pay the cost for the diamond blade if your tool rental charges extra for it. The composite/friction blade will do it... but the cut time is long. A diamond blade will cut about 8-10 times faster (at least it seems that way).
Most 7 1/4 saws will only cut about 2.5 inches, & I hope the slab is thicker than that, and 20+ feet of cured crete can be a real beeoch on a saw designed for a little softer fare. Rent something made for the task at hand and preferably with a wet cut blade.You'd be amazed at the dust made from a dry cut. The young/ low cost help is also a wonderful way to allow you to drink beer after the cut and during the clean up.
Foir just that much buy one of the cheap $10 diamond blades (one diamod chip every 1/8 inch or so), chuck in your saw, run slow trickle out of garden hose in front of blade - try to use a double insulated saw with a FRONT sawdust chute, that way the water comes out that way, my choice for this abuse is an old Craftsman contractor grade saw. Way I do it the water flow is at a speed that the stuff out of the chute is the viscosity of heavy cream.
Cut 15 feet of 12 YO concrete last week that way, with a blade that had cut about 10 feet previously, so you will get at least 25-30 ft of cutting out of the cheapo diamond blade. Speed is about 4-5 inches per minute, keep your pressure on the blade HIGH ( I sit on a pad and put my foot against the handle) and do a full depth (about 2.8" deep) cut in one pass. A sledge then breaks it out clean, with usually some undercut breakout on the sides, but clean edges.