Cracks in gunite/shotcrete

[SwimmingBevo]

Hi Pool Pros,

Have a pool under construction in Austin and have a thread on it...but wanted to start this one for the thread title to see if any experienced builders have dealt with this issue. I noticed these cracks today and informed my PB. The gunite/shotcrete was done almost two months ago. The upper portion is a three-foot wall that was formed to be above water level, for looks across back of pool and to and hold our two three-foot water shears.

I showed this pic to my future pool maintenance person who passed it to a PB he knows who said I need to send it to the national shotcrete association to make sure the proper fix is done. I told my PB who is a good guy and he believes he has it under control as he said the cracks were much smaller and only now visible because they’ve cut into them to repair them. The other PB said standard procedure is something like cutting three feet on either side back into the rebar and the re applying the gunite/shotcrete.

How concerned should I be and should I reach out to any association?

Appreciate any thoughts.

 

[JoyfulNoise]

2 months?? Typically a gunite shell is given 21-28 days to cure. What’s the delay??

More important than fixing the shell (which is typically done with staples and epoxy cement fill) is WHY did this happen? Was a proper soil analysis done before the dig? Do you have expansive clay soil? Some soil types need remediation and extra fill done before the shotcrete to ensure the stability of the shell.

If it cracked now, there’s a high probability you will develop another crack when this pool is filled with over 100,000 lbs of water in it.

A soil analysis and discussion with a geological engineer familiar with your area is a good place to start.

 

[SwimmingBevo]

2 months?? Typically a gunite shell is given 21-28 days to cure. What’s the delay??

More important than fixing the shell (which is typically done with staples and epoxy cement fill) is WHY did this happen? Was a proper soil analysis done before the dig? Do you have expansive clay soil? Some soil types need remediation and extra fill done before the shotcrete to ensure the stability of the shell.

If it cracked now, there’s a high probability you will develop another crack when this pool is filled with over 100,000 lbs of water in it.

A soil analysis and discussion with a geological engineer familiar with your area is a good place to start.

Thanks for the reply...we are on a bed of limestone in our area and excavation was entirely all rock and not much dirt...I’m not sure about soil analysis and will check.

The delay was weather and removing an infloor system we didn’t realize was being done and had to be removed as we didn’t like having that many moving parts in the pool. PB is also installing stone decking in areas that extend beyond pool that needed to be finished first for house build.

I will I’ll bring you questions up to him. Appreciate it.

 

[PoolguyinCT]

You must be referencing ASA.

American shotcrete association, defect diagnosis is not part of their mission.

Hopefully for you MinerJason comments on this, he knows more about concrete placement than anybody I have seen post here..

Your situation is a paid consultant’s jobs, asa can route you to a relevant contact.




@minerjason
#minerjason
- guess who the only votin asa pool industry member is?? Yup our buddy...

OP save you a few minutes.
Answer:

We are not able to advise you on the structural integrity of a remodel of a spa or any other structure and would suggest you consult with a local engineer who is familiar with pools and spas. Shotcrete is often used to overlay or patch structures and the success of such overlays and patches is highly dependent upon the quality of the surface preparation prior to the application of the shotcrete. With respect to referrals of independent professionals, we would suggest that you use the directory of Corporate Members in the ASA Buyers Guide.

 

[SwimmingBevo]

You must be referencing ASA.

American shotcrete association, defect diagnosis is not part of their mission.

Hopefully for you MinerJason comments on this, he knows more about concrete placement than anybody I have seen post here..

Your situation is a paid consultant’s jobs, asa can route you to a relevant contact.




@minerjason
#minerjason
- guess who the only votin asa pool industry member is?? Yup our buddy...

OP save you a few minutes.
Answer:

We are not able to advise you on the structural integrity of a remodel of a spa or any other structure and would suggest you consult with a local engineer who is familiar with pools and spas. Shotcrete is often used to overlay or patch structures and the success of such overlays and patches is highly dependent upon the quality of the surface preparation prior to the application of the shotcrete. With respect to referrals of independent professionals, we would suggest that you use the directory of Corporate Members in the ASA Buyers Guide.

Thank you very much for this comment. I will look up this directory for a consultant.

 

[PoolguyinCT]

Good luck buddy, I’m looking forward to watching this one.

 

[CMorrow]

Good luck with this. Hopefully, there's a satisfactory solution.

 

[blakeusa]

Cracks are best fixed with concrete staples and epoxy as noted above. The staples or splices offer lateral strength.

However if it was me I would tear it out and re shoot that section

IMO it will crack again even if very fine. And that will crack your top coat of plaster or pebble.

Not that it is not structurally sound just expansion and contraction.

Maybe it's a 2 to 3k fix now.

 

[SwimmingBevo]

Good luck buddy, I’m looking forward to watching this one.

Thanks, I just emailed the ASA and hope to hear back soon. I’ll be letting my PB know I’d like to hear from them before we do anything. Really appreciate your post. Hoping I don’t get anymore gray hair from this one.

 

[SwimmingBevo]

Cracks are best fixed with concrete staples and epoxy as noted above. The staples or splices offer lateral strength.

However if it was me I would tear it out and re shoot that section

IMO it will crack again even if very fine. And that will crack your top coat of plaster or pebble.

Not that it is not structurally sound just expansion and contraction.

Maybe it's a 2 to 3k fix now.

I am no expert but this sounds like would I would do too...will pass along these thoughts and thank you.

 

[JamesW]

Do you know the concrete thickness and psi rating?

What was the rebar diameter and spacing?

Did you have an engineer design the pool?

Can you see the cracks from the back?

Do the cracks go across the floor?

Is there a bond beam?

 

[SwimmingBevo]

Do you know the concrete thickness and psi rating?

What was the rebar diameter and spacing?

Did you have an engineer design the pool?

Can you see the cracks from the back?

Do the cracks go across the floor?

Is there a bond beam?

Thanks for the post...I’ll be asking these questions.

 

[RoyR]

Do you have a picture of the rebar before the gunite?

 

[SwimmingBevo]

Do you have a picture of the rebar before the gunite?

Here are a couple...

 

[JamesW]

How much gap is there between the rebar and the plywood?

Are the sheers supposed to be where the pvc pipe is and where the rebar dips down?

Where are the sheers in the concrete?

It looks like there is pvc pipe running vertically through the concrete wall.

Assuming a 1.5" pvc pipe, that creates a 1.9" tunnel lengthwise through the concrete.

At the cove, it looks like the rebar is resting on the horizontal pipe. It looks like there is no room to get enough concrete there.

Where are the cracks in relation to the rebar pictures?

I suspect that the concrete was made too thin in general and the pipes interfered with getting consistent thickness everywhere.

PVC pipes should only penetrate the concrete perpendicularly. They should not be embedded in the wall lengthwise.

Plumbing pipes should never be embedded in the gunite/shotcrete swimming pool shell because the pipe creates a thin structural section at the pipe location where cracking can develop.

http://rci-online.org/wp-content/uploads/2016-bes-holmer-phifer.pdf

 

[SwimmingBevo]

How much gap is there between the rebar and the plywood?

Are the sheers supposed to be where the pvc pipe is and where the rebar dips down?

Where are the sheers in the concrete?

It looks like there is pvc pipe running vertically through the concrete wall.

Assuming a 1.5" pvc pipe, that creates a 1.9" tunnel lengthwise through the concrete.

At the cove, it looks like the rebar is resting on the horizontal pipe. It looks like there is no room to get enough concrete there.

Where are the cracks in relation to the rebar pictures?

I suspect that the concrete was made too thin in general and the pipes interfered with getting consistent thickness everywhere.

PVC pipes should only penetrate the concrete perpendicularly. They should not be embedded in the wall lengthwise.

Thanks for the questions. Will be asking these but can answer some. The cracks are too the right of the second sheer. You are correct, they are where the rebar bends down at the top of that back wall...here is another pic...I just noticed what looks like a crack at the pool bottom I will be reviewing as well that runs across the pool near the second sheer.

 

[JamesW]

There's a pipe to the right of the second crack that's not in the rebar pictures. When was that put in?

 

[SwimmingBevo]

There's a pipe to the right of the second crack that's not in the rebar pictures. When was that put in?

That was put in after shotcrete dried and we decided we did not want an infloor system...so that’s one of the returns that was added and they patched/covered all the infloor.

 

[MinerJason]

You must be referencing ASA.

American shotcrete association, defect diagnosis is not part of their mission.

Hopefully for you MinerJason comments on this, he knows more about concrete placement than anybody I have seen post here..

Your situation is a paid consultant’s jobs, asa can route you to a relevant contact.


@minerjason
#minerjason
- guess who the only votin asa pool industry member is?? Yup our buddy...

OP save you a few minutes.
Answer:

We are not able to advise you on the structural integrity of a remodel of a spa or any other structure and would suggest you consult with a local engineer who is familiar with pools and spas. Shotcrete is often used to overlay or patch structures and the success of such overlays and patches is highly dependent upon the quality of the surface preparation prior to the application of the shotcrete. With respect to referrals of independent professionals, we would suggest that you use the directory of Corporate Members in the ASA Buyers Guide.

Thanks Ray, but I think you may give me too much credit. My work with shotcrete is in a much different application, where we design it to crack under dynamic loads, and have special rock bolts behind the shotcrete that share the loads in dynamic situations. I totally agree that a local paid independent consultant is likely the best way to determine the specifics of this situation. Even if I specialized in pool shotcrete rather than underground shotcrete, I'd need to be able to see the ground conditions for myself and gather a lot more information than the OP is likely able to give us in order to determine the cause. And without having at least an idea of the cause, there's really no way to select the appropriate remediation strategy.

Do you know the concrete thickness and psi rating?

What was the rebar diameter and spacing?

Did you have an engineer design the pool?

Can you see the cracks from the back?

Do the cracks go across the floor?

Is there a bond beam?

All good, relevant questions. To add to this list, I'd also want to know the following:

What types and quantities of admixes were used, if any? And were they added at the batch plant or at the nozzle?

What was the weather like during the shoot and for the week following (temps and general humidity levels)?

When was it first watered and how often was it watered, particularly during the first week?

Assuming it was wet mix shotcrete, how far away was the batch plant, and how long did it take between loading and the start of the shoot for each truck?

Were there any delays during the shoot?

Did the batch plant use chilled water?

What was the moisture level of the soil/rock during the dig?

Do you have any photos of the dig before the gravel and rebar were added? Were there any indications of geological structures in the walls or floor?

It may be that a few cores need to be taken and tested to determine true thickness and strength of the shotcrete.

 

[SwimmingBevo]

Thanks Ray, but I think you may give me too much credit. My work with shotcrete is in a much different application, where we design it to crack under dynamic loads, and have special rock bolts behind the shotcrete that share the loads in dynamic situations. I totally agree that a local paid independent consultant is likely the best way to determine the specifics of this situation. Even if I specialized in pool shotcrete rather than underground shotcrete, I'd need to be able to see the ground conditions for myself and gather a lot more information than the OP is likely able to give us in order to determine the cause. And without having at least an idea of the cause, there's really no way to select the appropriate remediation strategy.



All good, relevant questions. To add to this list, I'd also want to know the following:

What types and quantities of admixes were used, if any? And were they added at the batch plant or at the nozzle?

What was the weather like during the shoot and for the week following (temps and general humidity levels)?

When was it first watered and how often was it watered, particularly during the first week?

Assuming it was wet mix shotcrete, how far away was the batch plant, and how long did it take between loading and the start of the shoot for each truck?

Were there any delays during the shoot?

Did the batch plant use chilled water?

What was the moisture level of the soil/rock during the dig?

Do you have any photos of the dig before the gravel and rebar were added? Were there any indications of geological structures in the walls or floor?

It may be that a few cores need to be taken and tested to determine true thickness and strength of the shotcrete.

Thank you very much for commenting on this post. And you are correct, I cannot answer most of these questions. Through ASA I foiund a Texas base gunite company that I have just contacted to see if they can help consult on this project. I will keep this thread updated with progress as we make it and again, thanks everyone for their input. I hope I can find someone who knows about this in my area and is available to consult.