Concrete pad sinking/sunk

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Northern cannonball

Northern cannonball

Bronze Supporter
Sep 12, 2021
147
Toronto, Canada
Pool Size
9250
Surface
Vinyl
Chlorine
Salt Water Generator
Hey everyone,
Pool is coming up to two years old and I've noticed the concrete pad has sunk toward one end. Some pictures below. Half the nature 2 vessel is off the ground and you can see the slant from left to right on the pad. The return line from the heater has also dropped to pretty much rest on top of the gas line. I added a couple of shims under the right side of the heater to reduce any of the weight and to level it out a bit more. Wondering what solutions I should be exploring. The pad itself is not cracked and I've shoved as much dirt as possible around the base.
Thanks in advance.
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I think your options are mudjacking the slab by injecting foam under it to lift or level it, or pull all the equipment off the slab and redo the slab on a better prepared base, or live with it and adjust the plumbing as required.
 
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You could probably lever that up with a 4x4x10', and pack soil under it. Worth a shot anyway. Use a fulcrum and a lever. It will probably continue to sink if it was poured on fill, might have to adjust it for several years.
 
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Thanks ajw22 & RLP. If it gets much worse I'll likely redo the slab or explore ways to lift it and back fill. If I live with it for the near future, how hard is it to replumb some of those lines? Are we in pool builder territory or can a student of TFP tackle it themselves? ;)
 
Hi everyone,
After the long winter it appears the slab has sunk another 1/2" or so. I plan on getting the issue remediated as soon as I can before pool season arrives. Armed with the advice in this thread and a few youtube videos, I plan on using a bottle jack to lift the slab so that it is even. Similar to this vid
Lifting Concrete Slab. Once I have it up, what materials would you recommend I try and back fill with? I've read sand, gravel and / or soil but wanted to check here before I attempt anything. I figure this may be an exercise I have to repeat every few years, but it seems like the least expensive option. Thanks!
 
Northern cannonball said:
Hi everyone,
After the long winter it appears the slab has sunk another 1/2" or so. I plan on getting the issue remediated as soon as I can before pool season arrives. Armed with the advice in this thread and a few youtube videos, I plan on using a bottle jack to lift the slab so that it is even. Similar to this vid
Lifting Concrete Slab. Once I have it up, what materials would you recommend I try and back fill with? I've read sand, gravel and / or soil but wanted to check here before I attempt anything. I figure this may be an exercise I have to repeat every few years, but it seems like the least expensive option. Thanks!
Click to expand...
I did about 1/3 of my pool deck that sunk 6+ inches and put up a video on youtube of it with a tool I built. Since you just have one end of a small slab, i think the bottle jack will work fine.

It looks like the pad is right on the edge of a downward slope? What kind of soil is it? Is there a drainage problem there or you think its just built on a bad spot?

I’m a fan of construction grout for this. We have critters that dig in the ground and eat or nest with the foam stuff. You can lift it up, shim it level, and dig out and remove any soft soil/debris and then form it out with some boards(they make cheap cedar fence boards that work well for us down here at home centers). If you can find a funnel with at least an inch diameter opening, you can place the funnel in the corner of your form near the joint and pour in as much grout as itll let you and it should fill up the cavity underneath the slab. You just have to work quickly cause its hydraulic cement so mix it a little wet.
 
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Bperry said:
I did about 1/3 of my pool deck that sunk 6+ inches and put up a video on youtube of it with a tool I built. Since you just have one end of a small slab, i think the bottle jack will work fine.

It looks like the pad is right on the edge of a downward slope? What kind of soil is it? Is there a drainage problem there or you think its just built on a bad spot?

I’m a fan of construction grout for this. We have critters that dig in the ground and eat or nest with the foam stuff. You can lift it up, shim it level, and dig out and remove any soft soil/debris and then form it out with some boards(they make cheap cedar fence boards that work well for us down here at home centers). If you can find a funnel with at least an inch diameter opening, you can place the funnel in the corner of your form near the joint and pour in as much grout as itll let you and it should fill up the cavity underneath the slab. You just have to work quickly cause its hydraulic cement so mix it a little wet.
Click to expand...
Hi @Bperry , thanks for the response. To answer your questions, the pad is on a slope and the soil is clay. The area drains well.

I'll check out construction grout. So I believe my steps are as follows (a few questions also ;))
  1. Dig out an area under (right edge) and place a couple of pieces of lumber for the jack to sit on and between the jack and pad.
  2. Jack up the pad so it is level
  3. Remove soft soil/debris
  4. Shim it when it is level. What should i use for shimming? Add some wood shims vertically where the jack is and move the jack?
  5. place a fence board at edge of raised pad, where it is lifted. Support it with a couple of stakes in front.
  6. Pour the construction grout into the cavity. Since I added a board where the opening is, where would I pour the cement? And also do I just leave the shims in there with the concrete?
  7. once the concrete dries remove the board/form and cross fingers it doesn't sink anymore
Would love to see your video on youtube if you could provide the link. thanks again for your help.
 

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Northern cannonball said:
Hi @Bperry , thanks for the response. To answer your questions, the pad is on a slope and the soil is clay. The area drains well.

I'll check out construction grout. So I believe my steps are as follows (a few questions also ;))
  1. Dig out an area under (right edge) and place a couple of pieces of lumber for the jack to sit on and between the jack and pad.
  2. Jack up the pad so it is level
  3. Remove soft soil/debris
  4. Shim it when it is level. What should i use for shimming? Add some wood shims vertically where the jack is and move the jack?
  5. place a fence board at edge of raised pad, where it is lifted. Support it with a couple of stakes in front.
  6. Pour the construction grout into the cavity. Since I added a board where the opening is, where would I pour the cement? And also do I just leave the shims in there with the concrete?
  7. once the concrete dries remove the board/form and cross fingers it doesn't sink anymore
Would love to see your video on youtube if you could provide the link. thanks again for your help.
Click to expand...
I would use something that doesnt degrade for the shims and just leave them in there to be encased in the grout. But otherwise sounds like the plan.

Youll have to be creative with filling it. Perhaps drill a hole in your fence board or cut a notch in your existing slab and use that as a fill hole?
 
Bperry said:
I would use something that doesnt degrade for the shims and just leave them in there to be encased in the grout. But otherwise sounds like the plan.

Youll have to be creative with filling it. Perhaps drill a hole in your fence board or cut a notch in your existing slab and use that as a fill hole?
Click to expand...
Awesome! Thank you. Now I have yet another spring project ;)... this one seems kinda fun though
 
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