Cracks in new concrete

[garagejournal9]

I just had 1400 sq feet of concrete patio done last month, with color concrete, stamped. The contractor did the work on a very hot day, and then when I asked him if I should spray water on the concrete, he said no.

We had 105+ days for a week right after that, and looks like the concrete has not cured well. Right away nearly half of the controlled joints had long cracks, and cracks started appearing (and getting longer) on the concrete surface (see the pictures).

It also seems like the top layer of the concrete is not very strong, as I dropped a screwdriver from 3 feet height and it chipped the concrete.

The contractor says this is normal (no surprise there ). Is that correct? He says he will put a quick patching, and once the concrete is sealed, the cracks won't be visible at all.

What do you guys think? Thanks for your advice.

 

[bobscogin]

Could you elaborate on the control and/or expansion joints? Layout, spacing, method, etc. Also, there appears to be de-lamination of the surface. Was there a lot of bleed water on the surface during finishing?

Bob

 

[garagejournal9]

Thanks Bob. They used what looked like a string to create the control joints. The joints are about 6 feet apart, then 1 foot apart, then 6 feet and so on (Please see the picture).

Also, please pardon my ignorance, but what is "de-lamination of the surface"?

 

[bobscogin]

Those look like cosmetic grooves rather than control joints. Control joints are usually saw cut and should be at least as deep as 25% of the slab thickness. De-lamination is when the top surface of the concrete peels or blisters from improper finishing techniques. Looking at the last photo you posted, I may have mistaken the surface texture variations in the stamped surface for "blisters".

Bob

 

[dcs Inc]

It looked to me as it that was a cold joint. Was this done with 2 pours?

Never mind. Looks like they took some color hardener and mixed it with water then troweled it on a crack to hide it.

Those tooled joints may serve OK for control joints if they were deep enough. Bob's got it right for the depth, at least 1/4 the thickness of the slab. I like the look of tooled joints and would install these verses saw cutting. Once placed and the concrete had dried enough to walk on, I would then use my portable cut off saw and deepen the joints.

The problem I have found with sawed crack control cuts is it is very critical on the timing to install these. Concrete cracks from the bottom up and sometimes the random cracks are already developed on the bottom of the slab and those saw cuts you are installing are only decorative.

 

[bobscogin]

The problem I have found with sawed crack control cuts is it is very critical on the timing to install these.

Yup, if you didn't plan for saw cut control joints from the start, it's too late. Saw and operator must be ready to saw at a moment's notice. As soon as the concrete is set sufficiently to walk on and support the saw, make the cuts.

Bob

 

[joes169]

Those look like cosmetic grooves rather than control joints. Control joints are usually saw cut and should be at least as deep as 25% of the slab thickness.
Bob

I've been pouring concrete for 25+ years, and I have no idea where you gather this info from. Those tooled control joints look deep enough to me. It really doesn't matter if they saw joints in your area or not, properly tooled control joints have been a far more effective approach at controlling random cracking for decades.......

 

[bobscogin]

I've been pouring concrete for 25+ years, and I have no idea where you gather this info from. Those tooled control joints look deep enough to me. It really doesn't matter if they saw joints in your area or not, properly tooled control joints have been a far more effective approach at controlling random cracking for decades.......

Reference -Joints in Concrete Construction, ACI 224.3R, American Concrete Institute.

Bob

 

[joes169]

Reference -Joints in Concrete Construction, ACI 224.3R, American Concrete Institute.

Bob

Yes, I understand the 25% depth for control joints, it's extremely elementary, although ultra-early saws are showing that number isn't always necessary.

What I'm questioning is the rest of the quote. Those joints look deep enough to me, and as straight as they are, I'll bet they used a longer airplane jointer or similar to cut them in. Air plain jointers are generally 1.5" deep.

Also, tooled joints are perfectly acceptable when placed correctly, and even have a number of advantages over sawn joints......

 

[Spudland_Dave]

I just had 1400 sq feet of concrete patio done last month, with color concrete, stamped. The contractor did the work on a very hot day, and then when I asked him if I should spray water on the concrete, he said no.

We had 105+ days for a week right after that, and looks like the concrete has not cured well. Right away nearly half of the controlled joints had long cracks, and cracks started appearing (and getting longer) on the concrete surface (see the pictures).

I think you got a bigger issue... My concrete guy told me the same thing...DONT SPRAY WATER ON IT...it was early July when we poured my 1500 sq/ft for the garage, not 105 degrees, but it was very warm that week. He had told me that modern concrete has many chemicals and additives to make the concrete behave how they want it to, so watering the top on a hot day does more damage then good. Specifically he said the surface is VERY hot because of the sun and the exothermic reaction within the concrete...spraying ice cold water on it will shock the surface and create spider web cracks all over the surface...Made sense to me (Called my dad to verify, which he did) and I followed his advice, My slab is BEAUTIFUL. Not even a hairline crack anywhere...I have dropped my Estwing hammer off my scaffold and it didn't even make a mark where it landed. I wouldn't blame not watering the slab...

 

[dcs Inc]

Wow..... The spider cracks as you call them are caused by the concrete not being able to shrink properly during the drying process. This is often caused by the installer applying water to the surface to increase surface paste during the finishing process. The added moisture causes the shrink cracks. Most of the time these are only cosmetic but sometimes if too much water is mixed into the surface paste it weakens the finish. Concrete shrinks as it dries and adding the moisture during the finishing expands the surface paste to the point it creates the small voids during the "exothermic" reaction of drying and shrinking.

If you do a little online research you will find that it is imperative to keep the concrete moist to delay the hydration process. Some do it chemically, some do it by keeping the surface wet. It is silly to think applying water on the concrete will damage it. I bet if you did a core sample your concrete would test low on compressive strength due to the excessively fast hydration.

 

[ConCretin]

Going back to the OP's questions, there are several issues here;

Based on the photos, I don't think you got an acceptable slab. There are clear indications of de lamination. This problem usually occurs in hot weather when the slab surface sets up quickly before bleed water can dissipate. If it is extensive, you'll likely lose much of the surface.

Check the surface by dragging a chain over it. You'll hear a distinct change in tone as the chain passes over de laminated sections. There is no fix for this on a decorative finish other than to rip it out and replace it.

The second issue is crack control. Control joints can be grooved or sawn but they should be 1/4 if the slab thickness. The crack in your photo looks pretty bad so I'm going to assume there are not adequate control joints. Again, there is no fix for this now.

Finally we have the issue of curing. Improper curing will make the shrinkage problem worse and affect it's durability. Concrete MUST be properly cured to ensure adequate mix water for hydration remains in the concrete to allow the concrete to reach design strength. Your slab wasn't cured and given the weather conditions, it's likely that it is under strength.

Spraying cold water on a hot slab isn't a good idea but there are other ways to cure concrete such as a moisture retaining cover.

It's obviously tough to offer an opinion based on a few photos but I wouldn't accept the slab or some half assed repairs. Decorative concrete is tough to do and I don't think your contractor was up to the job. If my guys did that slab, I'd rip it out and replace it myself.

Sorry but that's how I see it.

 

[bigbadktm]

Having dealt with concrete and concrete coatings for the past 13 years, I can tell you from hands on experience that there is no repair for a slab crack. You can cover it or hide it, but it will re-crack. For him to tell you that once it is sealed that you won't even be able to see the crack, is a flat out lie.

Concrete moves throughout the day with the weather conditions. Certain times of day the crack will be hairline that you may not even see it, other times it stands out like crazy. This just happened to me on the last job I was on, doing a clean and reseal. I was looking for cracks to caulk before painting and didn't see any, by the time I had reached a certain area, I found the cracks I was looking for.

In short, don't ever believe anybody that tells you they have a repair for cracks.

 

[dcs Inc]

I tell people we "treat" cracks, we don't repair them. Saying that, I have found using Elite Crete Systems Epoxy crack fill really "glues" the crack back together. Now the problem becomes when what ever created the crack show it's ugly head again (most all the time a simple weather change), the stresses that caused the original crack could/will either open the original or create a new one. So what do you do? You saw cut a new stress relief line really close to the original random crack. I cut them deep so as to make sure you will recontrol the crack.

 

[garagejournal9]

Thanks for all the feedback!

I called the ready-mix concrete company my contractor had used, and inquired about what exactly was ordered by my contractor. It turns out that he ordered the concrete with a slump of 5, which is marginal at best (4 or less is desirable). So the concrete was already somewhat watery. On top of that, he added 40 gallons of water on arrival (to 16 cubic yards of concrete), making the slump to 7.5 - WAY too watery. The water to cement ratio was 0.59, making both the ratio as well as the slump too high to make acceptable concrete.

It turns out that he clearly violated the ASTM C 94 standard. According to the ready-mix quality control guy, he should have requested plasticizer instead of adding so much extra water. Plasticizers are cheap ($1-3 per cubic yard), so it is really surprising that he cut corners there.

Now I also understand why he asked me not to spray water, as he know he already had put in too much water to begin with. So we ended up with too much water during pouring, and too less water during curing.

Just to gather some conclusive evidence, I have asked the concrete quality control guy to come by tomorrow and do some Schmidt hammer testing, so that I can clearly show that the slab is weak. (For those who do not know this, the test is free, and non-destructive).

Then the fun will begin when I break this to the contractor...

 

[gatchel]

Thanks for posting the details. I didn't know about the testing. Keep us posted on the results.

 

[ConCretin]

Now I also understand why he asked me not to spray water, as he know he already had put in too much water to begin with. So we ended up with too much water during pouring, and too less water during curing.

First of all, good luck in your discussions with your contractor. You have some legitimate concerns and I hope you can reach an acceptable conclusion.

Secondly, let me clarify something for you. Mix water and curing water are entirely different. Adding water during curing does nothing to alter the water/cement ratio of the concrete. It's just a barrier against evaporation.

Don't mean to nit pick, just want you to have your facts straight in upcoming discussions.

 

[fwillison]

Sorry to HiJack the thread a bit, but I've been told you can't cut control joints in a post-tensioned slab (presumably due to the risk of cutting a cable).
Should I ask for tooled joints or some other substitute.
It's a big slab (44x60), and it's on clay soil.

Fred
Tulsa

 

[ConCretin]

Sorry to HiJack the thread a bit, but I've been told you can't cut control joints in a post-tensioned slab (presumably due to the risk of cutting a cable).
Should I ask for tooled joints or some other substitute.
It's a big slab (44x60), and it's on clay soil.

Interesting question. We don't do a lot of residential PT slabs - mostly thicker elevated slabs where CJs aren't used - but I'll take a run at your question anyway. Others might know better though.

I'm not sure if CJs are even necessary. You might get random shrinkage cracks during the time the concrete sets before the post tensioning is applied but they would be pulled tightly together once it is.

If you want to avoid random cracks entirely, you could make sure the cables are secured low enough to ensure they aren't cut.

 

[Eric Commarato]

I'm going to step out on a limb here. In my opinion, these cracks look more substantial than shrinkage. What was the subgrade preparation? How did the contractor prepare the soil below the slab? You may have a little settlement issue due to the type of fill and compaction of the soil below the new slab. I know down here in Mississippi we have expansive soils that really move when they dry out or get wet. When I built my house many years ago, I had my dirt contractor excavate below my driveway 2'-0" and install compacted red sand material. I also put a bunch of steel in the drive way. Most all other contractors at that time skimped on sub-grade preparation and only put "fiber" in the slab for reinforcing..."fiber" was the new wonder additive to concrete mixes. My drive way looks pretty much like the day I put it in, where everybody else's in the neighboor has 1"-2" open cracks. Most homeowners have just torn out their driveways and put new ones in. I've been a practicing architect here for 28 years, and though I'm not a structural engineer, or a soils engineer, I'm just throwing out this theory as a thought. I know for a patio it probably isn't reasonable to have a soil boring and recommendation from a soils engineer on subgrade preparation, but I would keep an eye on the cracking and see if it worsens. Also, lots of contractor's won't place a vapor barrier between the soil and the concrete, but even a cheap 6 mil poly vapor barrier is important because even on a hot day, the ground can **** the water out of a newly poured concrete slab depriving it of water essential to the curing process. As per earlier posts, regarding "watering" the slab, here during a really hot summer, lots of contractors will cover a new pour with burlap bags and place a lawn sprinkler on the slab to minimize thermal cracking...not sure if this really works or not.

Hope this helps...

 

[garagejournal9]

I have the Schmidt Hammer test results:

The compression strength of the patio ranged from just 1500 PSI to 2200 PSI. COmpare this to my existing patio right next to it, which scored 4000 to 4500 PSI.

As expected, the contractor is balking at the idea of redoing the work. His excuse is that everyone adds extra water into the concrete preparation, and 1500 PSI is just fine.

The work is clearly not acceptable to me, so let's see how we resolve this. I will keep you posted.

Thanks for your replies so far, I learned quite a bit already.

 

[garagejournal9]

Quick question: The contractor now says he will overlay a top layer of strong bond concrete to make the concrete stronger. Is there such a thing?

 

[LegacyIndustrial]

Absolutely not. A weak foundation means a weak everything!

 

[bczygan]

Do you still have all his money in your pocket?
Do you have a contract with specifications for the concrete work?

 

[fnieto]

Two kinds of concrete... the kind that crack and the kind that a going to crack.

 

[nolimits76]

Quick question: The contractor now says he will overlay a top layer of strong bond concrete to make the concrete stronger. Is there such a thing?

To partially steal a George Stait lyric...is there ocean front property in Arizona?

The fix is to demo out and repour. If your temps are still high and you have subsoil conditions in the area, it might be worthwhile to over-excavate and use a compacted backfill of some sort to ensure a solid foundation as recommended by another user.

Do you still have all his money in your pocket?
Do you have a contract with specifications for the concrete work?

This is a good question. Doubtful most homeowners will have the forethought, or experience, to request or put them in a contract format. Even if they did, most will not know what to request.

My company works for the DOT performing bridge and roadway work. We have firm concrete specifications that materials must meet, as well as how it must be poured, cured, finished, etc. Concrete mixes must be submitted for approval. Material is tested on a frequency basis starting when the first truck arrives on-site. We verify slump, moisture content, etc. Also, we take core samples to send to the lab to verify strength requirements. The DOT mimicks our operations. In the event any of the cores fail, we run the risk of having to rip the concrete and redo the job. **** happens, but 99.9% of the time it's right.

Assuming you don't have a detailed contract, I think the stance you should take is that it's substandard work not to your satisfaction. Your greatest power to resolve the matter is NOT to pay him further, if he hasn't already been paid in full. If you find yourself in a stale mate, perhaps doing a peer review would provide resolve. It involves using (3) other contractors/experts in the same field to evaluate the work and provide a written opinion.

If he still disagrees, it might be worth a trip to small claims court. Assuming the peer review was in your favor, it would seem simple enough to present...along with pictures and assume a fairly easy victory.

Two kinds of concrete... the kind that crack and the kind that a going to crack.

Yes, but looking at the work I would agree this looks substandard.

 

[CNGsaves]

All the signs point to you got boondoggled !!

Painful reality is that it needs jackhammered out and start over. Go get two quotes from bona fide concrete installers to rip it out and fix.

How much money involved ?? Did you have contract?? Sure hope the company was legit and had insurance . . . if not, you may be paying twice and taking the schmuck to Small Claims court.

What's current status?? Any more pics of delamination or cracks you can post??

 

[ConcreteConnection]

There are so many factors that can cause your concrete to crack.

It looks like your contractor wasn't able to avoid some of them.

I hope he is able to fix the problem or replace the work with new material.

 

[boostme]

The OP hasnt logged in since 9.18.2013... I too want to know how it was handled and what was done!