# Hairline cracks in shop floor



## mpt1123 (Mar 20, 2008)

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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## JD3lta (Nov 22, 2009)

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


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## Kent Whitten (Mar 24, 2006)

Could be a few things.

How big is the shop?
Did you put control joints in?
What was the condition of the base before you put concrete on?
What slump was the concrete?


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## 6stringmason (May 20, 2005)

Theres two for sures about concrete. It will crack, and its heavy.


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## Cole82 (Nov 22, 2008)

6stringmason said:


> 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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## CarpenterRN (Dec 3, 2009)

mpt1123 said:


> 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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## [email protected] (Sep 25, 2009)

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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## genecarp (Mar 16, 2008)

Waste of time, if the floor was done correctly, these are normal hairlines and are not a problem, GMOD


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## mpt1123 (Mar 20, 2008)

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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## JD3lta (Nov 22, 2009)

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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## 6stringmason (May 20, 2005)

I'd rather have little hairline cracks than discoloration where I put in different concrete or caulk.


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## Tscarborough (Feb 25, 2006)

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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## scrapecc (May 11, 2009)

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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## CarpenterRN (Dec 3, 2009)

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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## JD3lta (Nov 22, 2009)

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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## ContrBob (Dec 11, 2009)

*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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## Tscarborough (Feb 25, 2006)

It is also crap. Spend the 6 bucks a tube for a good one like NP1.


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## Rio (Oct 13, 2009)

genecarp said:


> Waste of time, if the floor was done correctly, these are normal hairlines and are not a problem, GMOD


This sums it up along with with the comments that anything you do will highlight the crack(s).


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## neolitic (Apr 20, 2006)

mpt1123 said:


> 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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## parkers5150 (Dec 5, 2008)

take a 4 inch grinder w/ diamond blade, open up the the cracks into a random stone pattern, acid stain, grout the cracks and seal. looks awsome and looks like you planned it


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## ARealplumber (Aug 11, 2009)

Here is my experience with concrete. The concrete guy is lazy so he adds a crap load of water to the mix and that makes it flow easier for them. This weakens the mix and causes more shrinking. Uneven compaction of the base material is also another cause of cracks. Uneven copaction will give you different expansion and contraction rates. The weather conditions at the time of the pour can also contribute to cracking and improper finishing. So if you lay concrete one of these things are gonna get ya. I have a pet peave about front porches cracking.....on my home I compacted the dirt for the porch and did it in an even pattern,added the 6x6 wire and then applied rebar every 24". We used 3500# mix and I was there to assure the lazy mofos didn't add water. The result...after 15 years.....a front porch that has a couple tiny tiny surface cracks that you hafta get down on your hands and knees to see. I'm very pleased with the results compared to alot of porches I see.


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## mudpad (Dec 26, 2008)

I have been pouring large slabs for many years and I have only found one to way positively prevent cracks.

DON"T POUR IT!


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## CONCRETE MIKE (Jan 11, 2010)

mpt1123 said:


> 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.


 If u want to repair the cracks , saw cut the cracks to open them up clean the area and fill with epoxy, mm80 will work.


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## CONCRETE MIKE (Jan 11, 2010)

Tscarborough said:


> 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.


 That is the correct thing to do.:thumbsup:


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## CONCRETE MIKE (Jan 11, 2010)

Saw cut cracks like Tscarborough said, and fill with epoxy, mm 80 or another compatible epoxy, but remember that it will look like a patch. If the cracks are hair line, walk away and leave it alone, if they open at a latter date then fill.


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## genecarp (Mar 16, 2008)

quote=CONCRETE MIKE;848165]Saw cut cracks like Tscarborough said, and fill with epoxy, mm 80 or another compatible epoxy, but remember that it will look like a patch. If the cracks are hair line, walk away and leave it alone, if they open at a latter date then fill.[/quote]


I like the looks of the MM80 Mike, i went to there website, the colormatching service and product selection looks top notch, and they will do small orders, thanks, GMOD:clap:


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## silvertree (Jul 22, 2007)

Really, you can't be sure what caused cracks half the time.


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## DavidC (Feb 16, 2008)

If you poured the slab it's a normal condition of the material. If anyone else poured, it cracked because he's a hack. :>)

Good Luck
Dave


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## jlhaslip (Dec 31, 2009)

Cracks are only an issue when they separate. Until then, don't sweat the small stuff.


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## CONCRETE MIKE (Jan 11, 2010)

DavidC said:


> If you poured the slab it's a normal condition of the material. If anyone else poured, it cracked because he's a hack. :>)
> 
> Good Luck
> Dave


I am sorry, all concrete will crack, just where is the question? If u use the correct base,correct placement of the concrete(not to exceed 7" slump with super plastizer) unless it is a high performance concrete like microcillica or latex, correct placement of joints (pre cracks), correct placement of expanshion material, correct placement of wire or fiber,correct cure, it can still odd crack!! If you read any aci books or have been to any portland concrete seminars u will learn that.I have placed more concrete than the average person has walked on is his or her life and seen one thing, it all cracks!! Thats why u ask the pro's (concrete finishers-engineer)


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## DavidC (Feb 16, 2008)

CONCRETE MIKE said:


> I am sorry, all concrete will crack, just where is the question? If u use the correct base,correct placement of the concrete(not to exceed 7" slump with super plastizer) unless it is a high performance concrete like microcillica or latex, correct placement of joints (pre cracks), correct placement of expanshion material, correct placement of wire or fiber,correct cure, it can still odd crack!! If you read any aci books or have been to any portland concrete seminars u will learn that.I have placed more concrete than the average person has walked on is his or her life and seen one thing, it all cracks!! Thats why u ask the pro's (concrete finishers-engineer)


Relax Mike. Humor was implied, apparently not delivered. Maybe it will be on the next post.

Good Luck
Dave


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## CONCRETE MIKE (Jan 11, 2010)

DavidC said:


> Relax Mike. Humor was implied, apparently not delivered. Maybe it will be on the next post.
> 
> Good Luck
> Dave


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## bytor (Jan 23, 2010)

Yup...


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## scrapecc (May 11, 2009)

CONCRETE MIKE said:


> I am sorry, all concrete will crack, just where is the question? If u use the correct base,correct placement of the concrete(not to exceed 7" slump with super plastizer) unless it is a high performance concrete like microcillica or latex, correct placement of joints (pre cracks), correct placement of expanshion material, correct placement of wire or fiber,correct cure, it can still odd crack!! If you read any aci books or have been to any portland concrete seminars u will learn that.I have placed more concrete than the average person has walked on is his or her life and seen one thing, it all cracks!! Thats why u ask the pro's (concrete finishers-engineer)


 When you say portland concrete seminar, do you mean PCA?


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