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All concrete will shrink and crack, as Mike says–I would not worry about hairline cracks.
An article in FHB about a year ago started a barrage of letters from engineer types supporting rebar in foundations, footings and slabs, and just as many letters from “we’ve done it this way forever” types saying rebar just adds expense. My entry in this fray was too late to get published…
I don’t lose any sleep over the hairline cracks in my foundation and slabs–but I’ve also got rebar in there to keep them from expanding or shifting!
Thor Matteson,
Structural Engineer, CA
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what dumn ass would not put rebar in a poured wall.
Or mesh in a slab. Your just asking for it. was the outside of the poured walls waterproofed, with a french drain. If not you should have your butt kicked
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Greg, Hairline cracks are quite common and are seldom a structural problem. In resisting the lateral pressures a foundation experiences, I believe that rebar is absolutely the most cost effective insurance. In regard to basement slabs, the perimeter walls will prevent the cracks from "widening". I believe wire is a moot point. If there is settlement in your subgrade wire will offer little resistance
Slabs on grade; once again,rebar with proper spacing and fiber mesh. (The proof is in the jackhamer) Wire mesh ends up at the very bottom of the slab all too often,rendering it ineffective. It really costs (actual) little more to do it right. Regards, Rick
*Greg, the questions Ryan asked are important.Concrete will often give hairline cracks. In most cases, they are nothing to worry about. Rebar probably should have been used in the back wall but here in CT I don't think it is code. Don't worryabout the fiber mesh. It isn't needed in a regular basement. In a garage I like it.My only concern is, which area of CT you live. Don't answer this. In some areas (Hartford) the soil is mostly clay. I have seen cases where excavators have backfilled with clay which retains water. Even with a perimitter drain, the force caused by this cracked the foundation. THe backfill should be gravel.
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I have found hairline cracks in my basement floor and my foundation walls. The walls were poured last Nov. and the floor was done 3 weeks later. The temp in Conn. was running 40- 60 degree range which for Conn. was great. The foundation walls are 10 inch thick 3500psi mix, no rebar in them. The walls are 48 long by 30 wide the two hairline cracks are one on each side almost right in the middle of the span. There is no water since the foundation is at the top of a hill sitting on ledge. Floor has developed hairline cracks running from the the center lally columns ( there are five columns) towards the walls. The concrete floor is 4000psi that is 4 inchs thick. The lally columns sit on the floor underneath the is 12 inch x 6inch footing that runs right down the center of the foundation. The footings that run the perimeter are all 24 inchX 12 inch. I have footing drains but underneath this all is ledge and 3 inchs of 3/4 inch gravel. the question is how do I stop and seal these cracks. 2nd question will they pose a problem later on. Oh last input they have appeared once the heat was put on 2 months ago.
Thanks for the help
Greg.
*greg, I just want to make sure I understand what you see.Are you saying that there are hairline cracks radiating outward from each or some of the lally columns? Or are there just random cracks that don't seem to have a real pattern?was there rewire or fiber in the slab?If there is no rebar in the walls, is there rebar in the footings for the columns?And do you know what type of soil you are one?
*There is no mesh or rebar anywhere, the cracks are random around some columns but not others. Like I said they seem to apperar once the heat was on. The house was not set until 2 months after the walls and floor were poured. The foundation and footings sit on 2-3 inchs of gravel. I was planning on putting in a pre-cast foundation walls but that fell thru, but I but the gravel down for that. Underneath the gravel is solid ledge covering almost the whole perimeter of the foundation. Greg
*It's the nature of the beast. Forgedaboutit. Hairline cracks are part of the mix, if you ain't got 'em you just haven't looked close enough.
*All concrete will shrink and crack, as Mike says--I would not worry about hairline cracks.An article in FHB about a year ago started a barrage of letters from engineer types supporting rebar in foundations, footings and slabs, and just as many letters from "we've done it this way forever" types saying rebar just adds expense. My entry in this fray was too late to get published...I don't lose any sleep over the hairline cracks in my foundation and slabs--but I've also got rebar in there to keep them from expanding or shifting!Thor Matteson,Structural Engineer, CA