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Discussion Starter · #1 ·
Hello All,

Quick intro: I'm a GC and have a C-20 that still holds his licenses but am now into property management.

We put a pool in our backyard at the end of 2013. There was a lot of immediate efflorescence. Concrete contractor acid washed it. Shortly after, the concrete coping spalled in 1 area and is now showing rust stains in other areas. There are lots of fine cracks in the coping sections that go all the way through. No cracking at the expansion joints. The concrete guy cut out 3 of the sections and exposed the rebar which is clean in some areas and rusted in others. While he was hammering away at it, I put a 1/2 bit on his hilti and gave it a shot. Seemed a little soft to me. Concrete guy is saying he used a 6 sack mix.

What do you think went wrong?
What kind of pressure does a 6 sack mix produce? 5000psi?
Should I push for all new coping?
Other than a compression test on the concrete, is there anything else a lab can do for me?
Any advice?

Thanks,
Dave
 

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Your concrete contractor induced corrosion onto your rebar by acid washing the surface. Lowered the PH of the concrete and now the rebar is corroding within the concrete structure causing the spalling and rust stains. You now have a major problem. When the PH of concrete is below 9 then all sorts of problems start to happen. Cement paste starts to weaken and fall apart. Looks like you will have a lot of repairs to make and some may not show up later on down the road.
 

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Discussion Starter · #3 · (Edited)
Your concrete contractor induced corrosion onto your rebar by acid washing the surface. Lowered the PH of the concrete and now the rebar is corroding within the concrete structure causing the spalling and rust stains. You now have a major problem. When the PH of concrete is below 9 then all sorts of problems start to happen. Cement paste starts to weaken and fall apart. Looks like you will have a lot of repairs to make and some may not show up later on down the road.
Thanks for responding.

The section that saplled happened before the acid wash for efflorescence. The rusting areas that are bleeding through happened after the acid wash. If the contractor has a problem with replacing the coping, is there a chemical test I can have done? If so, should I ask for a PH test?

I called a structural engineer that I've worked with in the past and he said the rebar should be at least 1 1/2 inches below the horizontal surface. The rebar is at 1 1/4. I don't believe that this is the problem. What do you think?
 

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For one, acid washing is not the prescribed method for removing effloresces. This should be removed with a dry stiff brush. By washing it, the salts which migrated through the concrete was just pushed back into the concrete substrate from where they came from. Not sure why some people think acid washing is a fix all. At times it can be a problem creator. If the spalling was already present then of course you have had a corrosion issue with the rebar from the beginning. Yes, the rebar does need proper coverage and a 1/4" could be enough to allow some of that to happen. Since there was effloresces present that is telling me that your having a lot of moisture vapor emission going on and there is a high salt concentration. The salts can and will increase the corrosion activity, thus causing the rebar to corrode, swell and increasing inner stress of the concrete to the point of cracking and spalling. You best fix is to excavate all problem areas, remove the rust to a clean metal "might need to abrasive blast the area" and apply a rust inhibitive primer and then repair the concrete. A polymer modified concrete repair material might work best to replace the damaged concrete. That's the best I can do without seeing the problem first hand. Good luck. You may not be able to stop it, but you can slow it down.
 

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Not disagreeing with the certified inspector, all good points

What area are you in? Do you have 'winter'? Freezing temps? I ask, since I am in an area with freezing temps, all exposed concrete here is required to be air entrained to prevent spalling.

But to answer your question, I would push for new coping to be installed
 

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Chris Johnson said:
Not disagreeing with the certified inspector, all good points What area are you in? Do you have 'winter'? Freezing temps? I ask, since I am in an area with freezing temps, all exposed concrete here is required to be air entrained to prevent spalling. But to answer your question, I would push for new coping to be installed
That is a very good point Chris as I had not thought about a freeze thaw cycle occurring. This would be a very valid question to ask.

And yes some pictures would really help to paint that picture.
 

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Discussion Starter · #8 ·
Th coping was poured during the winter months. Although we're in Northern California, it was a very cold winter for us and below 32* on many occasions. I don't recall if temps fell to below 32* during the pour or while it was curing.

I'll try to load pics now.
 

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I lived in Napa and mornings in the winter could be 29f, but not long. Air wasn't used there

Did a project in Shasta and air was in the concrete
 

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Discussion Starter · #11 ·
I lived in Napa and mornings in the winter could be 29f, but not long. Air wasn't used there

Did a project in Shasta and air was in the concrete
I'm in Martinez and the air temps dropped below 32 on several occasions last winter. I remeber because we lost lots of new landscape due to freezing.
 

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I was in Lafayette for a year, temps drop but usually by 9:00 it was above freezing

I'm wondering if they wet the mix or splashed to much water on because they let it get to far before finish and we're wetting it a lot to get cream up
 

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I'm out of guesses haha

Looking at your pics...rip it out and redo it, no repair is going to look good

If you know the ready mix company that supplied, have the rep come and see, get his opinion
 

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Discussion Starter · #15 ·
Thanks. Wrote an email to the Pool Builder last night saying I want it all replaced. I'll let you know what he says.

By the way, I failed to mention that the pool uses salt and an electrical cell to chlorinate the water. The water once chlorinated tastes no more salty than a tear drop.
 

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Salt water should not be an issue, I too have a electronic cell for salt water on my pool which is gunite and a concrete cap, mind you, my pool is 50 years old, shouldn't make a difference though. You need to monitor your levels as the salt has been known to damage concrete pools, salt can damage concrete, and anywhere the salt water can make contact with the rebar, well salt water and steel...we know where that leads to.

I take it the pool builder did a complete package, all concrete work, set up including the salt water system? If so, he knows the risks and should know how to make sure everything is done proper
 

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Discussion Starter · #17 ·
Salt water should not be an issue, I too have a electronic cell for salt water on my pool which is gunite and a concrete cap, mind you, my pool is 50 years old, shouldn't make a difference though. You need to monitor your levels as the salt has been known to damage concrete pools, salt can damage concrete, and anywhere the salt water can make contact with the rebar, well salt water and steel...we know where that leads to.

I take it the pool builder did a complete package, all concrete work, set up including the salt water system? If so, he knows the risks and should know how to make sure everything is done proper
Thanks for the comments on the salt water. I too didn't think it was an issue but thought I'd mention it to give out the complete equation.
 

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My guess is that it had too much water in it when poured and was also overworked.

Next time ask to see the loading ticket to see what kind of mix you got.
 

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My guess is that it had too much water in it when poured and was also overworked.

Next time ask to see the loading ticket to see what kind of mix you got.
In my experience that is almost always the first issue to look at.

You said it was poured in winter too though, low temps slow down the cure a ton, freezing temps during the cure are just a problem waiting to happen.
 
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