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concrete patio hairline crack
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posted
My monolithic concrete patio (19'x 16') was poured on footers 12" wide, 36" deep on 3 sides (fourth side next to house), with 4"of concrete poured on 4" of stone, and wire reinforced. After excavation, the concrete was poured the 1st week of May,2005. The middle of Dec.2005 I noticed hairline cracks running through 3 of the four quarters (where patio scoured, not with relief cuts). The contractor said that the cracks are surface cracks and won't effect the integrity of the patio. His solution is to seal the patio "to keep water out". I live in the eastern part of PA and winters are usually very cold with freeze thaw cycles happening throughout the winter. I have several questions.
1.Was it proper to have no relief cuts in the patio?
2.Will merely sealing the patio provide patio integrity and longevity?
3.Has anyone heard of the concrete sealers that penetrate 4" to 6" into the concrete thus strengthening the patio?
4.The concrete sealers that I reasearched are...Hydra Loc manufactured by Endur-O-Seal, RadonSeal plus manufactured by RadonSeal Mitigation & Waterproofing Concrete Sealer Co., V-Seal 101 and V-Seal 102 manufactured by TARA.
HELP.
 
Posts: 2 | Registered: 15 January 2006Reply With QuoteReport This Post
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What you have there, according to your description, is a 19 x 16 patio supported on 3 sides by a foundation, with no support under the fourth side. This configuration almost guarantees cracking, because the 4" slab acnnot span nearly those distamces, and will settle and naturally crack. It would have been better to omit the foundation entirely. It serves no purpose. Control joints in a slab that big are also a good idea,

A slab on ground should not rest on any foundation, and if it does for some reason, it should be thickened gradually to 8 inch thickness at the foundation. If this is not done, cracking is inevitable.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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I believe the side of the patio that does not have a footer is tied into the foundation of the house. The slab was poured in the 1st step to add a 3 season room. I thought this method was standard practice. Will pouring another inch or two on top of the existing pad plus cutting in control joints be a possible fix for the patio?
 
Posts: 2 | Registered: 15 January 2006Reply With QuoteReport This Post
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Standard practice for a slab-on-ground floor is to float it inside the foundation, not rest it on top of the foundation. If for some reason it must rest on the foundation, then the edges should be 8 inches thick, and should taper off to the standard 4-inch thickness over a distance of three feet.

Tying a slab into an existing fundation is also incorrect.

All the practices you described will virtually guarantee cracking, and that's what's happening.

As far as "repairing" the cracks, I can't help. My expertise is in specifying the proper way to do things, not in trying to compensate for poor practice. Perhaps someone who works evey day with concrete might comment.

But thr problem is, the work was done incorrectly in the first place, and the real cure for that is removal and replacement in the correct manner. Sorry.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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What you are describing is fairly normal surface cracks. The weight of the slab causes the soil underneath to settle and the cracks are a normal byproduct of the soil settling. (I was a warranty superintendent for a number of years) The reason to seal the slab is not to strengthen it. The sealer will keep water from going down into the cracks which might create additional soil instability, and result in worse cracks. If the cracking becomes widespread or severe, they can come back and pour a 2" cap over the slab which should eliminate any further issues.
 
Posts: 38 | Registered: 30 November 2005Reply With QuoteReport This Post
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Great idea...add 2 inches MORE weight to a slab that is already settling from its own weight.

The problem, without seeing the actual conditions, is very likely exactly what I have described, and unfortunatley, the cure is exactly what I have suggested also.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
Picture of lmelso
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If this topic is still up for discussion, I would like to interject my 2 cents. I did the tried and true method of concrete patios w/ a 16x25 monolithic patio, in Bucks County PA. This method always works, and there are other ways, but they overkill in my experience. Theoretically, you could place 4" thick slab over a grass yard and it will last a lifetime. It's not the right way, but it would work. It's friggin concrete! Yes, you'll get cracking, it's not styrofoam. So Mr. Hetzel, you make some valid points, but I question you working know. of concrete. Anyway, my patio has 12" wide foundation all 3 sides, 36" deep, and the 4-5" slab portion that is against the house is "tied" in to my houses 10" thick foundation (basement) wall every 2 feet w/ 1/2" dia. rebar along the 25' width of the patio (we drilled 5/8"x4" holes in the basement foundation). There is 4-6" of stone under the slab portion, and there is 1/2" rebar throughout the foundation, along w/ 6x6 wiremesh through the slab and also down in the foundation. The edges of the slab that meet the foundation are "chamfered" which just thickens the slab all around the perimeter. I forgot to mention, 4" of top soil was excavated and the area was compacted and compacted again after the stone was placed before the wire and rebar and conc. poured. We used 3500 psi concrete and I specifically wanted only 1 control joint in the middle 12.5 feet going 16 feet out b/c I think too many look ugly and they usually don't work anyway. So all that and guess what? I have some small hairline cracks, so what? All concrete patios crack! I want to meet the genius that has developed the crackless patio. Some will say fibermesh, bull, I've seen it crack too! It is an uncontrollable act. The whole job was $2500, and it was 1/6 the cost of an all wood deck, 1/10 of a composite, and someday, I can build over it, and not have to worry about pouring foundations or piers later. Lord knows how your yard looks after the f-ing mess of the backhoe, the concrete truck, and then grading. I wanted a patio, and I knew someday I want to put an addition on it, so I spent the measly extra $3/ sqft. and be done w/ it. So don't worry DOSELF, you did it correctly, it is just the people out there that think concrete is rocket science. I didn't seal mine b/c it looks "wet" after you do it. It's just preference. I think the sealers are b.s. They cant span a crack like the tar waterproofing sealer on basement walls, so what is their purpose? Let's remember people, what the **** supports bridges? Concrete underwater! And to all the patio haters that have decks, concrete supports them! I'm done!
 
Posts: 3 | Registered: 06 March 2006Reply With QuoteReport This Post
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The fact remains that the proper way to build a slab on ground is NOT to support it on the walls. The proof of the pudding is that the previous poster used reinforcing steel in addition to mesh, thickened the slab at the walls, and STILL got cracks, which were rationalized by claiming that ALL concrete cracks.

Well, it is true that all concrete cracks, but properly designed, mixed and installed concrete does NOT always crack visibly.

I stand by my opinion. The cracks were caused by improperly supporting the slab on the perimeter walls.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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WinkWhat we have here is the age old standoff between those who sit at drafting boards and those who actually go out and slog around in the mud and the 100 degree weather for a living! It never ends!
 
Posts: 38 | Registered: 30 November 2005Reply With QuoteReport This Post
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If concrete is poured in a configuration such as that shown in the posted link, cracks are almost guaranteed. The concrete should be gradually tapered to at least a double thickness. The sharp angle shown is much too sharp.

Also, there is a big difference between a carefully engineered reinforced concrete structure, and a simple slab on ground with nothing in it but mesh. A slab on ground ideally should not be supported on the perimeter walls, but should "float:" within them. If it must be supported on walls, such as at garage doors, then it should be thickened to at least 8 inches, tapering to 4 inches over at least 4 feet, and the thichened part should have at least double mesh, if not reinforcing bars.


Architect (NY) and Home Designer (PA)
 
Posts: 2870 | Location: Tobyhanna, PA | Registered: 24 October 2005Reply With QuoteReport This Post
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