# Cutting Concrete Slab for New Door



## MikeinBurien (Nov 12, 2005)

Hi Folks,

I'm replacing a sliding door in the downstairs area and while the new door fits the hole perfectly along the perimeter, the new door requires 3" of clearance on the inside and the old door only needed 2 1/4".

Here's the rub: The original door was set just outside the slab of the floor and in order for the new door to fit I need to cut about 3/4" off the concrete about 1" deep and about 72" wide.

I'd like to know the best way to approach this that will result in a nice clean edge. I was thinking about using one of those masonry cut off blades in my circular saw, but I suspect the concrete is harder than masonry.

Any ideas?

MikeinBurien


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## send_it_all (Apr 30, 2007)

That blade will work, but it will probably take a few of them to make that cut...they go fast. (Im assuming you are talking about the black colored carborundum blades). A diamond blade in your saw would work better, but you might not be able to cut all the way into the corners due to hitting the framing...if Im picturing it right. If you have a 4 1/2" angle grinder, you can put a diamond blade on that to get closer to the corners. Hope this helps


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## MikeinBurien (Nov 12, 2005)

Thanks Send-it-All. 

You're seeing it exactly right. The concrete needs to be cut along the 72" between frame studs and as I get to the frame with a circular saw it will bump and the cut will be short - at both ends! I was thinking about getting the diamond blade to make life a bit easier, but don't have a grinder for the final 5" or so at each end. I'll give some thought to the grinder and see what I can come up with. If I could at least score down make a 1/4", then I might be able to chisel the rest.

Thoughts?


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## AtlanticWBConst. (May 12, 2006)

MikeinBurien said:


> Thanks Send-it-All.
> 
> You're seeing it exactly right. The concrete needs to be cut along the 72" between frame studs and as I get to the frame with a circular saw it will bump and the cut will be short - at both ends! I was thinking about getting the diamond blade to make life a bit easier, but don't have a grinder for the final 5" or so at each end. I'll give some thought to the grinder and see what I can come up with. If I could at least score down make a 1/4", then I might be able to chisel the rest.
> 
> Thoughts?


Now you have an excuse to buy a nice grinder.... :yes:


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## AtlanticWBConst. (May 12, 2006)

If you can't get your hands on a grinder, you can try to cold chisel that last 5" as well. You may make a little mess. 

The important thing is to be able to get the door in place. 

You can go back and clean up the area with some new quick setting cement...


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## MikeinBurien (Nov 12, 2005)

Folks - The project is done!

One guy at Home Depot tried to convince me to rent the giant water cooled concrete saw for $85/4-hours, but another guy said that the diamond blade and even the cheap masonry carborundum blades would work fine.

I ended up buying a nice Bosch 7" blade with cooler slots for my Milwaukee circular saw. And... a decent Makita grinder which happened to come with a "Free" diamond blade.

The diamond blade on the circular saw made quick work of the 1" deep x 72" long cut. Did it in about 1/4" increments to reduce strain on the saw. Total time for that part - about 5 minutes max. Lots of dust!

The Makita grinder also made quick work of the last 4" at each end - no problem. Another 2 or 3 minutes max. 

I then had to cold chisel the piece of concrete outside the cut and that took about 15-20 minutes. Then used the grinder with the diamond blade to do some clean up. 

The door is in and it looks perfect. A little bit of finish work inside and out and we're done. 

Thanks all! :thumbup: 

MikeinBurien


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## MikeinBurien (Nov 12, 2005)

One last comment - there seemed to be an interest in how old the concrete was from the Home Depot guys. After I told the first guy it was 50 years, he then said it would be too hard to work with the diamond blade on my circular saw.

Don't hesitate to use a diamond blade for relatively small cuts in old concrete. Mine was even reinforced with rocks! Cut right through them and there's almost no wear on the blade. 

Now I have a nice blade and a grinder for about the same price I would have paid for the rental.

Sweet!


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## send_it_all (Apr 30, 2007)

Glad it worked out.


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## Longtooth (Apr 28, 2007)

way to go mike. :drink:


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## AtlanticWBConst. (May 12, 2006)

MikeinBurien said:


> ...... Total time for that part - about 5 minutes max. *Lots of dust*!
> ....The door is in and it looks perfect. A little bit of finish work inside and out and we're done.
> Thanks all! :thumbup:
> MikeinBurien


Tip to reduce all the dust: Use a pressurized pump spray filled with water. While your cutting, a second person sprays the blade and cutting location. (Also keeps the blade cool)

Example of a pressurized pump sprayer:

http://www.solousa.com/store/flypage/handheld_sprayers/lcs-1g_handheld_sprayer.html


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