Expanding In-ground Concrete Kidney Shaped Pool (Baja Shelf, Rounding Off Caved In Portion)

[kidney-pool]

Pool History and Remodel Requirement
Hi all, I live in the Phoenix, AZ area, currently looking at our pool remodel options. The pool in question is an in-ground concrete pool, likely 30+ years old. The pool surface had been chipped out but has been left emptied for a few years. With it left out for so long and given the age of the pool, I would look at all new plumbing to be redone. The pool pitches into the center, with the deepest part about 5.5', the shallowest around 4.25'. Optionally, I look 1) to decrease the depth of the pool, 2) add a Baja shelf, and 3) reshape portion of the kidney-shaped pool to remove the caved in portion (sort of rounding it off).

Proposed Solution
A contractor came out to evaluate the structure of the pool, despite some cracks along the bottom of the pool, he said there are no cracks along the vertical walls, so it is structurally okay. He proposed with the requirements, he can cut out the caved in side of the kidney-shaped pool and extend it out, same thing with then Baja shelf. Additionally, he can fill in the bottom of the pool with about 6" of concrete and rebar, so it will reduce the depth, plus it will add strength to where the cracks are at the bottom. He said after cutting out the side of the pool, they will shotcrete the side and tie that in with the existing beam bond.

Concerns

1. I do not how feasible that is, but researching about pool renovation and expansion using shotcrete, it seems it is a standard practice (reference: https://shotcrete.org/wp-content/uploads/2020/05/2019Spr_Drakeley.pdf).
2. My other concern is with pool finishes, would he old concrete and the new shotcrete cause issues with bonding?

I want to see what does the rest of this community think and have experienced?

 

[ajw22]

Welcome to TFP.

It all sounds very feasible if the builder knows what he is doing.

A bonding coat should be applied to the old gunite for the palster to have good adherence.

@AQUA~HOLICS may have thoughts.

 

[AQUA~HOLICS]

How was the evaluation of the shell performed? Visual, mechanical or both? The contractors comment regarding the structure being OK due to no cracking on the vertical walls, yet the shell has cracks on the floor, contradicts itself in my opinion.
The crack with the weed growing in the middle of it needs to be corrected, but first the reason for the crack needs to be determined.
Building over the crack with out the proper correction will only delay the situation from coming back again.

Building a Baja shelf and decreasing the depth is very common in remodeling of older pools, specific steps are to be followed in order to maintain the structural integrity of the shell, this includes how the Shotcrete is applied to the existing shell and its slump. Rebuilding the rebar cage also has specific requirements to be followed.

The new Shotcrete and old concrete if installed correctly and prepped prior to plaster installation should have no effect on the overall condition. With the amount of reconstruction being done I personally would request to have Shotcrete used and no concrete, this may increase the overall cost but in the long run it will be a far superior shell.

 

[kidney-pool]

Thank you for all the feedback.

The evaluation of the shell was only performed visually. What additional prep work can be done prior to filling in the pool to decrease the depth?

I will request for Shotcrete to be used to fill the bottom of the pool. Would the addition of rebar and Shotcrete along the bottom of the pool be sufficient to remediate the issues of the crack?

Please advise if there is anything I should ask the contractor to perform prior to any work being commenced. Also, let me know if there is anything I can do or test myself so to call out potential issues for the contractor.

Thanks.

 

[AQUA~HOLICS]

Finding the reason for the crack in the bottom of the pool is the first priority. Ground movement, improper mixture/application of Shotcrete or rebar cage are only a few reasons that may be present. Building on top will not always be sufficient, especially if ground movement was the cause.
I would ask to have the floor crack exposed to see the extent of damage, then a proper plan can be developed to prevent further damage prior to covering over for the depth of pool water you are requesting.
Can you provide more information on what the “caved in side” means?

 

[ajw22]

Please advise if there is anything I should ask the contractor to perform prior to any work being commenced. Also, let me know if there is anything I can do or test myself so to call out potential issues for the contractor.

You more have to dig into exactly how the contractor intends to fix the problems. Some things will not be known until he digs further into the structure.

• How will the old rebar be tied the new rebar?
• How much rebar will be installed and what will be the size and spacing of it?
• Why did the structure fail? Was it a rebar problem or a gunite quality problem or both?
• Will an engineer be reviewing the repairs or is the contractor going by the seat of his pants?
• What engineering specifications are being followed?
• What specific products will be used?

I said before it all sounds very feasible if the builder knows what he is doing. Only by digging into the details can you determine if the builder knows what he is doing. If you do not have the expertise to judge what he is saying then hire an expert who works for you to advise you.

Yeah, that costs money but it will cost you more if the pool cracks again in a few years and you need to do it over.

 

[kidney-pool]

Thanks @AQUA~HOLICS and @ajw22.

Expanding the "caved in side” is an attempt to make the pool more rectangular, essentially changing the kidney shape to more of a round shape. I used to have a rectangular pool, inviting friends and family over for a game of pool volleyball was fun, that was one the reasons for the reshaping -- another reason is by reshaping the pool it will give it more of a modern look.

Really thankful all the feedback. I will have to work with the contractor to dig into the finer details of the remodel/repair. We are not working with any engineers right now, but would appreciate if there are any good references the community here can point me to.

 

[AQUA~HOLICS]

I use this firm for all my engineering needs.