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Discussion Starter · #1 ·
Guys:
I just finished building my shop and I noticed a couple of hairline cracks in the concrete floor. Doesn't appear to be anything but cosmetic at this point. I was thinking of spreading a little dry quikcrete on the floor and sweeping it into the cracks - then mist it with a spray bottle. Is that a waste of time? Would it make the situation worse? Any other recommended solution?
Thanks.
 

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Hydraulic cement would be my guess, it's a good question
 

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Theres two for sures about concrete. It will crack, and its heavy.
no body will steal it and it gets hard.:jester:



If they are hairline cracks it can be from over working the surface with a power trowel. If you can sweep some thing into the crack then it could be from shrinking as it cures. The saw cuts might be two far apart.
 

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Guys:
I just finished building my shop and I noticed a couple of hairline cracks in the concrete floor.
Framerman had some excellent points. All concrete cracks, but you can make it crack where you want with proper joints. If everything was done right as far as using quality concrete with the right WC ratio, a solid base, and proper curing or lack of weather that would dramatically affect the cure, then the cracks are normal. Although, if the slab had joints (I'm guessing it doesn't) in the right places, the cracks would form along those instead. Many slabs in basements and garages aren't jointed and they should be. Just like many will pour the slab directly against the foundation wall with nothing to keep the slab and wall from moving together.

A good trick to jointing garage and basement slabs is to cut through the slab with a trowel and straight-edge while finishing and float over the joint, then your hairline crack will form there. Also, cracks will typically form parallel to each other and the distance between the cracks can give an indication of the slab thickness, i.e. cracks form every 6 feet is about a 3" thick slab, 7 feet is 3.5"
 

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THE GRUNT
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The problem with putting the quickrete in it is that as it shrinks and expands it will open and close. There is no guarantee even with control joints but they do help. My garage here at the house is over sawed and I still got a crack. It's concrete so it'll happen eventually.
 

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Discussion Starter · #9 ·
The pad is 24 x 28 and there's no expansion joint. Like I said, they're more cosmetic than anything. I agree that all concrete cracks. I think the issue is the shop is still relatively new (and clean) and business is slow so I have the time to look for problems that don't exist. When things pick up I'm guessing the minor cracks will be the last thing on my mind. For now, I just need to know if what I was planning will make things worse.
Thanks.
 

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Id still go with the quickcrete brand hydraulic cement it comes in a little tub and its powder form.. you can check it at its website, Ive applied it to foundation cracks, it seems easy enough, or that pavement caulk sealer w/e
 

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If you insist on screwing with it at all, do it right. Cut the joints out a minimum of 1/4x1/4 and then use an epoxy (if the joints are dead) or a polyurethane (if the cracks are live).

edit- If you use the polyurethane, be sure and use bondbreaker tape in the bottom of the joint.
 

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Twisted Cameron
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Just like many will pour the slab directly against the foundation wall with nothing to keep the slab and wall from moving together. Very rarely is someone going to put isolation joint inbetween a basement floor and a foundation wall,
It just usually isn't needed. Circumstances vary between soil types, fill, and base used.

A good trick to jointing garage and basement slabs is to cut through the slab with a trowel and straight-edge while finishing and float over the joint, then your hairline crack will form there. Also, cracks will typically form parallel to each other and the distance between the cracks can give an indication of the slab thickness, i.e. cracks form every 6 feet is about a 3" thick slab, 7 feet is 3.5"[/quote]
Why not do something simple like cut it with a saw? then the joint is hopefully hiding the crack, not leaving a rough edge ugly crack exposed.

Oh and 3 things concrete always does, gets hard, cracks, and changes color.
 

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This is done while finishing. You cut through the slab, then float over it smoothing out your cut. You won't even know it's there until the cracks form. And, only a hairline crack will form, but it will form where you made your cut, provided your joint layout is correct. The cracks will look no different than the OP's, but they will be symmetrical rather than random, like any tooled joint slab. Cutting it with a saw is another step that will require one to come back when the slab is dry.

Just because you say isolating a slab from a foundation wall isn't needed doesn't mean it's the right way to do it. Another example is any tile setter who has poured SLC knows to isolate it from the surrounding walls. The slab and the wall should be able to move independently.

All concrete cracks, but with proper joints, you can make it crack where you want. I am not a concrete contractor, but my credentials include engineering courses in concrete flatwork design and construction, as well as, concrete building design. In addition, I have been ACI (American Concrete Institute) certified for field testing and worked at a geotechnical firm, while in college, doing soil and concrete testing.
 

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Binding against existing structure where there might be movement is never taken lightly, I space walls from houses and false joint them incase of movement. In slabs you can drill into the existing concrete and put rebar and stuff, I didn't know the floor was still green when u got the cracks, you must of left it unattended for awhile cause water and a smooth over could of fixed it
 

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Acrylic crack filler

Masonry compuonds like hydraulic cement will crack again as the floor expands and contracts from changes in season temperatures.

Lowes or Home Depot have a crack filler product in the masonry supply section. It comes in a squeeze bottle and is made by Quickcrete. It is an acrylic or polymer formulation and can expand and contract without cracking.

It is also the same color as cement but can also be painted.
 

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I think the issue is the shop is still relatively new (and clean) and business is slow so I have the time to look for problems that don't exist.
Bingo!
Typical customer. :laughing:
 
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