expanding polyurethane foam to address long crack in old gunite pool?

[rhthompson]

Anybody have experience using expanding polyurethane foam to fill large voids below an in-ground pool?

I suspect there are some sizable voids in the earth below my 40 year old gunite pool which is perched above the edge of a steep slop where there was some grading during construction, There had clearly been some settling over the years by the time I bought the place; I have been thinking (hoping) it had finally stabilized, but apparently not. Two years ago a hairline crack started in the bottom and it has grown to several feet long. It has leaked and i've had it patched with pool putty a few times, which helps for a while.

Anybody know anyone in the east Tennessee area who could (1) advise whether injecting foam might help, and (2) do the injection?

thanks

 

[rhthompson]

PS: how do you detect voids below a pool? Some kind of ground penetrating radar?

 

[ajw22]

Polyurethene foam will not stabilize a pool structure that is cracking.

There are a bunch of Youtube videos showing concrete staples being used to repair gunite cracks.

If the staple repairs are done properly with quality materials and an experienced crew it should hold stronger then the surrounding gunite.

There are a few different crack repair techniques and concrete staples will be stronger then just an epoxy injection crack repair.

 

[Bperry]

Anybody have experience using expanding polyurethane foam to fill large voids below an in-ground pool?

I suspect there are some sizable voids in the earth below my 40 year old gunite pool which is perched above the edge of a steep slop where there was some grading during construction, There had clearly been some settling over the years by the time I bought the place; I have been thinking (hoping) it had finally stabilized, but apparently not. Two years ago a hairline crack started in the bottom and it has grown to several feet long. It has leaked and i've had it patched with pool putty a few times, which helps for a while.

Anybody know anyone in the east Tennessee area who could (1) advise whether injecting foam might help, and (2) do the injection?

thanks

MasterPro services does foam injection locally for patios, foundations, etc but I doubt they’d try it on a pool and I wouldn’t expect it to do anything even if they did. They wanted about $6k to lift up my sunken pool deck. Slab jackets will inject construction grout (ie concrete) under a slab as well. That was slightly cheaper than the foam injection. Installing staples was way cheaper than $6k,, but if the soil is moving then I wouldn’t waste money on repairs until you find the source of the movement. (It’s likely a water leak of high water table.)

 

[proavia]

You may need a structural engineer to evaluate any possible fix.

 

[rhthompson]

MasterPro services does foam injection locally for patios, foundations, etc but I doubt they’d try it on a pool and I wouldn’t expect it to do anything even if they did. They wanted about $6k to lift up my sunken pool deck. Slab jackets will inject construction grout (ie concrete) under a slab as well. That was slightly cheaper than the foam injection. Installing staples was way cheaper than $6k,, but if the soil is moving then I wouldn’t waste money on repairs until you find the source of the movement. (It’s likely a water leak of high water table.)

Thanks Bperry -- I agree, staples alone will not fix this if there is insufficient soil support underneath the pool. Fortifying and stabilizing that support is what I am seeking advice on. I had slabjacking done on parts of my deck several years ago, and i am wondering if something similar is available for under the pool shell itself.

 

[rhthompson]

You may need a structural engineer to evaluate any possible fix.

I think you are right. I have gotten the name of one here that comes recommended.

 

[proavia]

I think you are right. I have gotten the name of one here that comes recommended.

Being on a slope and you suspecting movement probably requires mitigating the reason for the movement and better supporting the pool shell to prevent future movement.

 

[JoyfulNoise]

Draining the pool and doing core samples is the only way to know if there are voids under the pool. If there is significant loss of soil under the pool, slurry or polyjacking will do nothing. A pool is a massive structure with upwards of 100,000lbs of water weight. You may need piers installed to stabilize the pool but that would require cutting significant access holes into the bottom and drilling down to a more solid surface. Then building up the piers out of reinforced concrete.

I wouldn’t consider any fixes until you get an evaluation from a structural/geotechnical engineer. They may need to do some core samples to determine what’s going on with the soil under the pool.

Good luck.

 

[ajw22]

Here is an example of how piers were done to stabilize a pool…

Need urgent help with cracking/leaking pool on a hillside in Austin, TX!

We did hire an engineer and he wants us to make a hole from the center of the pool to the bottom of the outside wall but I am not sure who I hire to do that?!? He said this will give us a good cross section of the construction thru the crack. ... Any ideas on who I would hire to make the hole...

www.troublefreepool.com

 

[rhthompson]

Polyurethene foam will not stabilize a pool structure that is cracking.

There are a bunch of Youtube videos showing concrete staples being used to repair gunite cracks.

If the staple repairs are done properly with quality materials and an experienced crew it should hold stronger then the surrounding gunite.

There are a few different crack repair techniques and concrete staples will be stronger then just an epoxy injection crack repair.

Draining the pool and doing core samples is the only way to know if there are voids under the pool. If there is significant loss of soil under the pool, slurry or polyjacking will do nothing. A pool is a massive structure with upwards of 100,000lbs of water weight. You may need piers installed to stabilize the pool but that would require cutting significant access holes into the bottom and drilling down to a more solid surface. Then building up the piers out of reinforced concrete.

I wouldn’t consider any fixes until you get an evaluation from a structural/geotechnical engineer. They may need to do some core samples to determine what’s going on with the soil under the pool.

Good luck.

Ouch! But thanks

 

[rhthompson]

Here is an example of how piers were done to stabilize a pool…

Need urgent help with cracking/leaking pool on a hillside in Austin, TX!

We did hire an engineer and he wants us to make a hole from the center of the pool to the bottom of the outside wall but I am not sure who I hire to do that?!? He said this will give us a good cross section of the construction thru the crack. ... Any ideas on who I would hire to make the hole...

www.troublefreepool.com

Oh my God. But thanks

 

[rhthompson]

recap: 40 year old gunite in-ground pool at edge of steep downward slope / settling had clearly occurred when I bought the house in 2007 / things seemed stable until two years ago when a crack appeared in bottom of pool / crack has been growing / pool has leaked but temporarily fixed with underwater pool putty, but crack grows and leak resumes.

followup: a geotech guy has looked at the pool crack and the slope. He thinks the slope looks stable. He suspects a void under the pool. He will probably suggest draining the pool and using ground penetrating radar to look for void underneath. If void is located, consult with structural engineer and with pool builder who recently built a pool for the CEO of the geotech company. Possible fix: drill holes in bottom of pool and inject cementatious slurry until pressure readings indicate void is filled. But JoyfulNoise and ajw 22 have indicated earlier on this thread that if void is large, slurry will not fix the problem. Ajw22 showed solution of putting piers below the pool into bedrock, but that looks like such a major operation and I suspect any bedrock is pretty far down.

one question: downside of just going ahead and draining the pool for radar and leaving it unfilled until fix is decided upon? With pool being at edge of downslope, and assuming a void, I wonder if hydrostatic pressure lifting the shell is a likely problem. Is weathering damage to surface of empty pool a big problem? Probably will need to be replastered anyway.

 

[ajw22]

If you drain the pool for the radar survey and then will leave it empty either open hydrostatic drains in the bottom of the pool, if you have them, or drill 2 to 3 holes in the bottom of the pool to relieve any water pressure.

The holes can be filled with hydraulic cement before you refill the pool.

Any major invasive repair will require a replaster.

 

[rhthompson]

If you drain the pool for the radar survey and then will leave it empty either open hydrostatic drains in the bottom of the pool, if you have them, or drill 2 to 3 holes in the bottom of the pool to relieve any water pressure.

The holes can be filled with hydraulic cement before you refill the pool.

Any major invasive repair will require a replaster.

thank you ajw22. Related question: with crack still growing, presumably due to weight of filled pool, might going ahead and draining the pool and leaving it empty for a while carry a lower risk of damage than waiting to drain it?

 

[ajw22]

thank you ajw22. Related question: with crack still growing, presumably due to weight of filled pool, might going ahead and draining the pool and leaving it empty for a while carry a lower risk of damage than waiting to drain it?

Nobody knows.

What are you going to say if you drain the pool and the crack continues to grow.

Right now everyone is guessing and no one knows why your pool is cracking.