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Question DetailsAsked on 5/17/2015

I had a stamped concrete patio installed and is it normal to see cracks on the surface and along the 4inch depth?

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3 Answers

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Trick question ? Yes it is common, but no it should not be. If properly reinforce, placed on a properly compacted base of suitable material, and cured correctly, it should not crack for typically 5+ years - excepting of course the cracks through the control joints (typically every 3-4 feet apart for 4" slab) which are placed there to control the cracking to the joint line.


If it cracked without load on it and within the first few days to week after placement, then it was most likely not cured correctly - it was allowed to dry out so it shrinkage cracked. MOST concrete contractors either shortcut or plain do not know anything about curing - they think spraying a curing compound on the slab guarantees proper curing, which is not the case. Most also do not properly wet the base and forms before placing the concrete so the moisture is pulled from the concrete into the dry wood and soil. Without proper water the concrete cannot cure properly - especially in the first 7 days, and most particularly in the first 3 days where going dry can almost totally and permanently stop the curing. With few exceptions, concrete should be wet cured for a week at least (more in hot dry or very cold conditions) - meaning constantly wet, either with sprinkler, wet curing blankets or thick straw, or by wetting it several times a day and putting plastic sheeting over it to keep it from evaporating.


Another common reason is they may have added water to make it more workable or to extend the "pour time", which unless the mix at the plant was originally designed to account for this added water, results in weakear concrete and more shrinkage.


Of course, if it was allowed to freeze during the initial 5-7 days of curing that can cause serious cracking too.


If significantly cracked (other than along control joints notched into the concrete for that purpose) patching may make it look OK for now, but will almost certainly recrack the same place in short order, and will NOT restore the structural integrity, so the substandard work should be replaced - at no cost to you.

Answered 2 years ago by LCD

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Thanks LCD. The patio was installed during mild to warm weather last week. It didn't appear the contractor did anything to aid curing. I don't recall any water being used at that stage. The patio was poured about 4 in the afternoon, and the contractors were stamping it until about 9 pm.


I wasn't able to add pic when asking my question.. but can add them to a response see below where the patio meets a retaining wall there appears to be a large crack the whole way through.


I'm reading a lot about control joints. with concrete. I don't know if they were used in this job . I know the contractor cut a 1 inch deep line in several places across the top of the patio. Is that considered a control join?



Spot where patio side meets concrete retaining wall.


Answered 2 years ago by Guest_9548398

0
Votes

If he cut or grooved about 1 inch deep straight lines clear across the patio, at probably 3-5 foot intervals, then yes - those are the crack control joints - an intentional weak spot to cause the natural shrinkage cracks (which yours look like) to occur in a nice straight line rather than wandering randomly, which you can (and should) later caulk with concrete caulk (special latex caulk for concrete that comes in caulk tubes) to keep water and freezing out of the cracks.


The first diagonal crack makes it look like maybe the patio is unreinforced, or that there is poor support under the lower right corner (in the photo) so it cracked from being walked on during the stamping process while not cured yet. The second crack is a very normal one - at a reentrant corner/junction like that there should have been a control joint cut right across to the right across the narrow strip (retaining wall, you said, though looks more like a curb) at that corner, right where the crack would be expected to and did occur.


One thing that REALLY worries me, is stamping 5 hours after the pour - to be able to do that they would have had to have really watered the mix down (which is a no-no), because it should have been too well set to stamp within 1/2-2 hours of the pour depending on temperature and whether there was a wind blowing.


For curing, while the release compound is on it (typically 1 day) it should have been covered with plastic sheeting to keep the moisture level high, typically wetting down the surrounding ground and covering that too to provide a source of high humidity for curing. Then after the release compound is swept off and the excess coloring agent washed off, it should be wet-cured (usually twice daily hosing and recovering with plastic sheet weighted down around edges), then sealed typically about a week after placement, at which time wet curing can end though is a good idea to "feed" it water (without saturating the ground underneath) for at least another week, because without adequate water to complete the hydration process (the water is chemically bound with the cement to provide the bond) the concr4ete will be weaker and more frost susceptible.


Contractor may claim curing compound will replace wet curing - don't believe it - it helps, but the slab will still be losing moisture throught the compound, and to the surrounding air and ground.


Now the tough part - repair or replace ? Certainly if there are cracks like that all over it should be torn out and replaced - and probably the replacement by a contractor who knows what he is doing. If a few random cracks like that and you know that it was reinforced, I would have him (in lieu of tearing out and replacing now) give you an extended warranty for say 6-12 months against further cracking (and keep photos of current cracking), and he fills the current cracks - if all that small probably with concrete caulk, which can be colored to match by mixing with the coloring powder he used and metal troweling into the cracks, using masking tape to protect the adjacent concrete from being smeared with the caulk. Any straight cracks like the second photo which should have had a control joint but did not should be cut with a control joint, then the crack sealed. MIcrocracks too small to caulk can be filled with a needle injector with concrete repair epoxy.

Answered 2 years ago by LCD

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Votes

Two added things - not helping the OP at this point, but using this one as a link to another similar question so wanted to clean up my answer:


1) yes the 1" deep cuts across the patio would be control joints - designed to force shrinkage cracking (which is much worse if concrete is not water cured) to follow the straight joint, rather than wandering across the field like the first photo. Cuts typically 1/4 of slab thickness so 1" deep would be right for your 4" slab.


2) the crack at the apparent curb-to-patio connection occurred where there should have been a control joint or construction joint (with compressible filler) - every angular intersection should generally have a control joint at least one direction, commonly two at 90 degrees to each other - see this article. (Visualize where it would crack if the slab was a greaham cracker or slab of gingerbread and uyou bent it - where those cracks would occur is almost always where you need control joints). Also, field areas should have control joints typically every 12-20 times the slab thickness (up to 30 times in strongly reinforced slabs, which most driveways are not) - so typically every 4-8 feet in the "field" areas in residential thickness slabs.


https://www.concretenetwork.com/concr...

Answered 29 days ago by LCD




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