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Allthunbs 12-08-2010 06:11 PM

most efficient way to cut poured concrete floor

I'm in the process of installing a new DWV system for my home. I've laid everythhing out and today started _trying_ to cut the concrete. I'm using an 1/8" abrasive disk specifically for concrete. It ain't workin'!

I'm looking at diamond blades but they run $18 for a Vermont American Skil suitable for reinforced concrete to $70 for a Bosch equivalent. What do you recommend and why?

Thanks for all the help.

Bondo 12-08-2010 06:17 PM

Ayuh,... What are ya turnin' these blades with, 'n what diameter,..??

A 14" demosaw really don't care whether you use a carborundon, or diamond blade....

TheEplumber 12-08-2010 06:40 PM

199 Attachment(s)
Demo saw is about the best IMO. Rent one with a water feed and concrete blade. You'll pay rent on the saw and wear on the blade.

Homerepairguy 12-08-2010 07:47 PM

Are you cutting a "new" hole in the middle of the slab or a notch adjoining an existing hole? That info might help the pros answer your question better.

Don't know if this is a good way to cut the concrete but what comes to mind is to drill 1/2" holes around the perimeter of the hole using a hammer drill. (A "hammer" drill is a MUST unless you have tons of time.) Then chip out the concrete using a small electric jack hammer or by hand using hammer and cold chisel. --- You might hit rebars while drilling so don't force it too much. After chipping out the hole, cut any rebars or wire mesh using whatever you have.


Work4living 12-09-2010 12:16 AM

Check your area for a concrete cutting company. Usually around $150.00 for 70' of cut. They have all the equipment. Much cleaner, plus you'll pay at least half that in rental equipment.

Allthunbs 12-09-2010 04:56 AM

Bondo: I'm using a 15A 7.25" circular saw. I can't find carborundum anywhere.

Homerepairguy: I'm extending an existing hole but I have about 80' of cuts to do. I'm putting in a completely new DWV system. Replacing a septic system on the back of the house with a municipal sewer connection at the front of the house. It's too far to run the sewer out the back.

There's just too much to do to start drilling holes. I have several hammerdrills and it's just too big for that kind of work. I've so far cut about 3' and only hit concrete. No mesh or rebar. Typical for construction here. _No_ building codes but you're responsible if your work doesn't stand up.

Work4living: there are no "local" concrete cutting companies. Equipment like that is too expensive for a collection of small villages so when something like this comes along, one improvises. Equipment rental companies are wayyyyyy too pricey. They start by doubling the price of the nearest competition. Companies pay but individuals can't. The competition is at least 1 hour away so they charge a good chunk of folding cash for the privilege of using their equipment and don't you dare scratch it.

Thanks for the suggestions. Hope this makes the picture clearer.

Work4living 12-09-2010 05:37 AM

Well then I guess you are using what you can. Only other option I can suggest is your old friends Sledgehammer & Manual Labor. If you don't have any wire or bar then dig under the concrete in the direction of your trench. Once thee is a hollow void then hit the slab on its edge the concrete will break off in pieces. You can always clean the edges with a saw later before you replace the concrete.

Bondo 12-09-2010 06:00 AM


I'm using a 15A 7.25" circular saw. I can't find carborundum anywhere
Equipment rental companies are wayyyyyy too pricey.
Ayuh,... The 7" saw is your Problem,... The Fiber discs Are carborundum discs...

Either man up, 'n Rent the proper tool, or keep doin' what your doin'...
80' in a few hours with the proper tool, or several Weeks the way yer goin'...

COLDIRON 12-09-2010 06:14 AM

Ya got to rent a Demo from HD. or you'll be there a couple years. Pay Up. Your still saving major bucks doing it yourself.

TheEplumber 12-09-2010 08:39 AM

199 Attachment(s)

Originally Posted by Bondo (Post 548426)
Ayuh,... The 7" saw is your Problem,... The Fiber discs Are carborundum discs...

Either man up, 'n Rent the proper tool, or keep doin' what your doin'...
80' in a few hours with the proper tool, or several Weeks the way yer goin'...

you will trash that saw. Thats what 150 bones plus or minus?

Allthunbs 12-16-2010 04:55 AM

Ok, I hope this kind of summary is accepted here. Another forum I frequent doesn't appreciate such tombs.

A summary of our experiences on the search for the "most efficient way to cut poured concrete floor."

I havexxxx had two 7 1/4" circular saws. A PorterCable 423 MAG left hander and a Skil 5170. Too bad too, the PorterCable was the only left hander I've seen in a long while.

First attempt: PorterCable with an abrasive/fiber (carborundum) concrete disk 7" x 1/8". Pushed like heck for several hours and actually managed a 1 1/4" deep cut about 2 feet long. Lots of dust, dust mask, face shield, then safety glasses kept getting covered with dust. House got down to about 55 degrees Fahrenheit and I was still sweating like a ______! I had so much dust on me I was almost made of concrete.

Second attempt: learned from first attempt! Porter Cable - managed to find a segmented diamond blade. There are three kinds of diamond blades, continuous for ceramics and porcelains, "patched" where the diamond is applied in a hundred or so patches all around the blade, and, segmented where the blade is cut into segments and the diamonds applied in patches to those segments. Whatever the package says, make sure it says for use on cured concrete, potentially with reinforcing steel bars (rebar.)

On this one, I enlisted the help of my wife. We hooked up the shop vac and we dug a Chapman sprayer out of the garden shed. That it be a Chapman sprayer isn't important. That it is a garden sprayer is important. You want to keep a _small_ amount of water going on the blade. Not enough to wet the surroundings but enough to keep the blade cool and lubricated. The downside to this is that the concrete dust creates a slurry that cakes up underneath the saw and along the cut. It has to be scraped up periodically and the environs kept clean. It also has to be dug out of the saw. It gets jammed up in the blade guard and can stop the blade dead.

The blade cut counter-clockwise. My wife kept the outside of the blade wet with the sprayer. I was on the other side of the blade where the motor is. She wet where the blade started to enter the concrete, i.e. on the back edge of the blade. The vacuum nozzle was applied to the blade where it exited the concrete, or on the front edge of the blade.

This actually worked quite nicely. Yes, there was some dust but it was manageable. I kept a box fan with a 5 micron furnace filter running in the background and that helped too.

We managed to cut some 50 feet like this before the PorterCable bit the dust. Now, before you cry about the loss of an expensive piece of equipment; I almost cried harder when my brother-in-law almost cut his leg off when the safety guard stuck. I cleaned and lubricated it and it worked flawlessly, until the next time I ran it through a piece of wood and the guard stuck again. It was almost destined for the dust bin at that time. I'm glad I held onto it for this project. It seemed a fitting end for a dangerous tool.

Third attempt: on the demise of the PorterCable I turned to the "almost indestructible" Skil 5170. I had burned out a Craftsman circular saw, you know the type, expensive with all the bells and whistles except you can't get parts for it. The Skil was the cheapest thing I could find and even that was discounted "on sale."

We repeated the same operation. Except this saw was a right hander. The blade was on the opposite side.

I found with the left handed PorterCable I could push with the right hand on the front "handle" and keep the saw relatively straight. The diamond blade doesn't cut much of a kerf so it seems that I'm always fighting, keeping it from binding. The more tired I got the more it seemed to bind.

With the right hand saw I had to switch to the left hand but I couldn't quite duplicate the action. Also the Skil being a really cheap saw, didn't have the fancy padding that the PorterCable did so I had to wrap a thick glove around the front knob. I tired even faster especially since I'm not using my dominant hand.

Well, the inevitable happened and the Skil swallowed enough concrete dust that it quit too. This one I did cry over. But all is not lost, I figure a good cleaning, new bearings and brushes and it should be as good as new.

Now, I went looking for a replacement saw and there was nothing worth while that I could find for $30 or less. However, I did find a fellow who knew what he was talking about. He described exactly what I was finding and he told me why and what to do about it. It seems that no matter how careful you are, the concrete dust gets sucked into the motor and fouls the bearings and the brushes. An aid in preventing this is to wrap the motor intake in a nylon stocking. It was too late for me but maybe it isn't for you. Also let the saw keep cool. When it gets warm, give it a break.

Fourth attempt: well we had to bite the bullet and go and rent a saw. In my original attempt to find a concrete saw small enough to get into the basement was futile. The rental companies I saw on the 'net rented the gas jobs and the only electric for floor use was a 420 lb monster that I couldn't even get down the basement steps.

Then I stumbled across two: A Makita 4112H which seems to have some neat stuff specifically for concrete "Rotation of cut is away from operator to avoid accidents. Soft-Start for safety and control. Makita's exclusive Super Joint System protects the operator if the wheel snags." That was an interesting one for me but it was not available when I called the rental place. He did have a Hilti DCH300.

The Hilti was big and heavy but it could do the job. First, this thing is unwieldy. You held on to the two handles and the trigger is in the hand hold but takes up the entire hand hold. This allows you to change hand positions while cutting, but, to release the trigger you almost have to let go of the handle. I wasn't thrilled about that part. Next there are two little wheels that the saw rests on while cutting. You put the saw on these two wheels, turn it on and plunge into the concrete. You now pull the saw toward you. So far, so good. but you're bent over trying to control this thing and it's very powerful. I tried on my knees and quickly gave up on that idea. You also can't switch hands on the hand positions. You have one operating position and it gets painful.

Unlike the Makita the Hilti doesn't have snag prevention so when this one snags, make sure you're not in line with the blade. When it jumps out of the concrete, remember you can't turn the blade off easily, especially when the saw is airborne. This happened to me several times.

I never thought fatigue was important when I was younger but now that I'm past 60, and one operation later, it is more important. This saw is a handful. Don't be afraid of it, you can do it but get a good nights sleep and keep your wits about you.

I also found out that saws labelled for concrete use have sealed motors and bearings.

I also found out that, if you're married, the Hilti has quite an additional expense. This was tough. My wife works alongside me throughout this renovation and to create additional work for her does not make me happy. The dust it created went everywhere. There is a vacuum port but it got only about 90% of the dust and the other 10% went into places you couldn't imagine. Closing a sealing doors didn't help. Even wetting the blade didn't help much. Remember, we're coming up on Christmas and a woman wants her home to be a showplace as only she can make it. I'm now doing the fetching and carrying but she still has to do the cleaning. Thank heavens I can do some of the cooking to take some of the load off of her.

On the plus side, I was using a 7 1/4" diamond blade on my saws and only cut in about 1 1/2". This one had a 12" diamond blade and it cut completely through the concrete. Removal of the concrete with my blade included a hand sledge and cold chisel but with the 12" a few whacks with the sledge hammer broke it up completely and was easy (comparatively speaking) to lift out. Don't get me wrong, it's still work, just easier work.

If you're in an empty house and you don't need to worry about how dirty it gets, the big concrete saws are best. The 400 pounder is the easiest to use if you have a way to get it to the job site without killing yourself. Failing that, the electric hand jobs are OK but you're going to tire quickly trying to hang on to the dragon's tail. The home circular saw method is practical and easier to keep water and dust under control but figure it as a "one use" tool and allow yourself days where you thought hours would do.

I'll track this so any comments, suggestions or things I've missed would be appreciated.

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