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Old 03-22-2015, 06:03 AM   #1
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Fresh concrete slab pour. Need to cut wider deeper joint lines


We just poured a concrete slab 7 feet wide by 12 feet long. We pulled joint lines across the slab every 16.75 inches in order to visually match the 1.5" spacer lines of adjacent rows of 16x16 pavers. The pic below should help illustrate the intended look.

Obviously the joint lines we pulled across the slab are only about an 1/8" wide, but they do carry the lines across visually.

In hindsight, we should have just laid the forms to insure the full 1.5" separation, rather than have to deal with fixing it after the fact, but we ran out of time to form this section of the job before the concrete truck arrived.

So, my question is, what would be the best approach to cut the 1.5" lines across? They need to be atleast an inch deep and will be filled in with 89/10 (same as pavers) or with mondo grass.



In the above pic, the dark area at the top right is the front porch. The section below that is the area I'm talking about. To achieve that, we poured a single slab rather than 9 slabs as it would appear in the pic.

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Last edited by vestaviascott; 03-22-2015 at 06:27 AM.
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Old 03-22-2015, 06:09 AM   #2
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Fresh concrete slab pour. Need to cut wider deeper joint lines


Here's my proposed solution, but I'm open to better ways:

1) chalk the lines from the square pavers over to the slab.

2*) Using a Circular saw with a masonry blade, cut across the chalk lines, 1.25" deep. Use a 2x10 laid across the slab as a guide for the saw.

3) Continue step 2 cutting down into the existing joint that we made into the concrete.

4) Repeat steps 2-3 until we can easily chisel the mix out of the spacer lines.

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Last edited by vestaviascott; 03-22-2015 at 06:11 AM.
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Old 03-22-2015, 06:25 AM   #3
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Fresh concrete slab pour. Need to cut wider deeper joint lines


Use a 7-1/4 diamond blade not a masonery abrasive blade.
They wear out to fast and your depth will be way off from end to end of cut.
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Old 03-22-2015, 06:44 AM   #4
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Fresh concrete slab pour. Need to cut wider deeper joint lines


Thanks Joe. I appreciate that. Any additional info or suggestions? Do you think the 3 cuts will be enough to loosen the mix for easy chisel force?

Its raining pretty steady here now and started raining shortly after the mix was set. We covered it with plastic. Its still less than 24 hours old.

I'm the homeowner and I'm no expert with concrete but I'd expect it would be much easier to cut now than later and with less risk of cracks due to the moisture still in the mix. Is that correct?
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Old 03-22-2015, 06:56 AM   #5
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Fresh concrete slab pour. Need to cut wider deeper joint lines


I'll let the full time concrete guys ansewer those questions.
I can think of several reasons your idea is not going to work out.
I would have done it as a stamped slab not cut in the lines like that, but let's see what they say.
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Old 03-22-2015, 07:29 AM   #6
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Fresh concrete slab pour. Need to cut wider deeper joint lines


too late to be using a 'green' conc blade which is very close in specs to an asphalt dia blade,,, IF i were you, i'd wait 7days,,, in the meantime, find a cured conc dia blade,,, cut your outside lines to the depth you wish & 1 or 2 cuts inside them,,, after that its a chipping gun & chisel,,, you want the new joint to be 1 1/2" wide to match, correct ?

bear in mind this is based on atl/birmingham/key west nas/hgwy/etc experience w/conc paving but it should be applicable to backyard conc too
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Old 03-22-2015, 07:42 AM   #7
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Fresh concrete slab pour. Need to cut wider deeper joint lines


Quote:
Originally Posted by stadry View Post
too late to be using a 'green' conc blade which is very close in specs to an asphalt dia blade,,, IF i were you, i'd wait 7days,,,
Thanks. What happens to the concrete after 7 days?

Quote:
in the meantime, find a cured conc dia blade,,, cut your outside lines to the depth you wish & 1 or 2 cuts inside them,,, after that its a chipping gun & chisel,,, you want the new joint to be 1 1/2" wide to match, correct ?
Yes, 1.5" wide to match the space between the 16x16 pavers (and to look like a separate slab rather than part of the actual slab it is).

Thanks for your suggestions and experience.

Last edited by vestaviascott; 03-22-2015 at 07:48 AM.
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Old 03-22-2015, 07:51 AM   #8
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Fresh concrete slab pour. Need to cut wider deeper joint lines


What happens to the concrete after 7 days? it gets harder + its not as abrasive which's why you need a different spec diamond blade,,, see if you can find a 12" elec saw to rent,,, more h/p = faster cutting,,, using a worm-drive circle saw will require 4 or 5 cuts each sequentially deeper which will be a large pita to say nothing of the strain on your knees & back
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Old 03-22-2015, 07:59 AM   #9
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Fresh concrete slab pour. Need to cut wider deeper joint lines


OK, more powerful saw makes sense. I'm with you there. But I'm a bit confused on what you are suggesting for timing...

When you said, "in the meantime" I took that to mean, do it now. So, you are suggesting to do nothing now, wait 7 days and make all the cuts then? Or make the cuts now and wait 7 days to chisel them out?
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Old 03-22-2015, 08:02 AM   #10
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Fresh concrete slab pour. Need to cut wider deeper joint lines


wait & cut later,,, MUCH easier to sawcut cured conc than cutting green
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Old 03-22-2015, 08:04 AM   #11
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Fresh concrete slab pour. Need to cut wider deeper joint lines


OK, thanks for the help. I understand better now. I'd have never thought that cured concrete would be easier to cut than green. Its counter-intuitive but that's why I came here to seek advice
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Old 03-22-2015, 06:34 PM   #12
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Fresh concrete slab pour. Need to cut wider deeper joint lines


Just so you know what you might be getting into, I would plan on spending hundreds of dollars on diamond blades & on circular saws. You're looking to cut hundreds of feet of relief joints, if I understand correctly. You're going to need to volunteer a ton of time to it as well. As a professional who values his time, I'd honestly consider tearing it all out and making sure I had the dimensional lumber strips in place before I re-poured.............
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Old 03-22-2015, 08:49 PM   #13
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Fresh concrete slab pour. Need to cut wider deeper joint lines


normally that would be true as both jo & i use pro equip,,, however, 1 can usually buy a decent bevel drive skilsaw for under $75 2 most pawn shops sawcuttin's measured by the inch/foot so 100' @ 2" deep = 200" ',,, most decent blades should last for 7,500" ' unless you beat the **** out of them the point made about time is certainly relevant but diy'ers rarely consider such costs i have no idea why not,,, my father always said go do what you do best & charge for it then you'll have enough $ to hire a pro, more time to work, &, when you do get off work, you can enjoy your family a bit before going back to work the 1st wife never understood that as her family always worked 40hrs 5d per wk,,, 70-80hrs was unheard of but they never owned their own biz.

1 other advantage is dble-barrel'd - if the work goes to hell, you can blame him & escape your bride's wrath ( unlike my bride, nagzilla, who has an elephant's memory ! )
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Old 03-23-2015, 06:36 AM   #14
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Fresh concrete slab pour. Need to cut wider deeper joint lines


I hope you don't have neighbors. The noise and dust would drive them crazy. Is it possible to replace the pavers instead do cutting all of those lines. Seems to me it would never match. Aside from all of the cutting, it seems like you would have to round over each side of each joint.
Good luck
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Old 03-23-2015, 07:03 AM   #15
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Fresh concrete slab pour. Need to cut wider deeper joint lines


perhaps dusty but no more noisy than a week whacker or back pack blower,,, this helps w/dust & ease of cutting: http://www.amazon.com/Pearl-Abrasive.../dp/B00006ANSG

they're kind of an industry standard for decorative conc work & most of us own 'em,,, CAUTION: you'll also need good kneepads, straight edge for a fence, good 20a extension cord, & a good 20a gfci,,, depending on how many spare eyes you have, also suggest safety glasses,,, you can always buy hearing aids when you get older unless you're safety conscious now

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