Repair advice on old pool

[Conifer]

There's a pool in the old house we're renovating. It's about 45 years old, hasn't been used for 7 or 8 years. It loses water, but we're not sure from where. As you can see in this picture, in the shallow end around the steps, there's a crack that someone in the past attempted to repair. There's also a crack in the tiles on the far end of the shallow part, but higher. Those cracks don't extend to the deeper part of the pool. There's also some cracking on the floor of the shallow end, that also appear to have been patched at some point.
I live in a very remote area of South America. There is one trustworthy contractor here, but I don't think he has much pool experience. He suggests basically building a new pool inside this one, with concrete and rebar, and shoring up one side wall by digging it out and adding another one of concrete. He's very good with concrete, so that's his solution to many things. I'd like to avoid that expense. I'm thinking about pulling out the tiles where there are cracks and filling in with concrete, then covering with liquid pool membrane. And just covering the cracks in the floor with that as well.
I don't mind if I have to redo this every season, as long as it costs me less than about 15% of the big job.
Any advice?

 

[Texas Splash]

Welcome to TFP! One thing for sure, there is a leak down low at that current waterline. Maybe even the main drain if there is one installed. If there is a leak behind some of the tiles near the bottom, pulling them away from the gunite shell may be the only way to confirm. It would be good if you could pump-out that green water to inspect for a drain if installed and inspect it. I suppose one option would be to remove some of the lower tiles at a certain height, fill in any cracks in the gunite shell to prevent further leaking, then simply apply a plaster coating of your choosing for cosmetic purposes. Another option, however it may not be ideal in your remote area, would be to have a vinyl liner made for that shape of pool and just use it that way. But let's give others time to review your situation to get more ideas. Thanks for posting.

 

[Conifer]

Thanks for the answer! I know for sure that there is no leak on the bottom, as the water does not drain away once it gets below the level of that "bath ring".
I can get a vinyl liner made 600km away, but it's over $140 m2, much more than I want to pay.
If I did pull out the tiles and patch with plaster, is there a special kind of plaster I need to use? BTW, I'm pretty sure that's concrete, not gunite. I've never seen gunite used here.

 

[Texas Splash]

If I did pull out the tiles and patch with plaster, is there a special kind of plaster I need to use?

I'd prefer tp defer that question to someone in the field like @Poolbreh. Let's see what he might recommend.

 

[duraleigh]

What is "liquid pool membrane"?

 

[Poolbreh]

Not knowing the typical building process for your area makes it hard to comment. My initial thought is using anchors if anchors aren’t available in your area I’ve seen videos using rebar as anchors like large staples. Hydraulic cement is used on anchors and crack and finished with plaster. It’s hard finding a company where I live to do it right. Most company’s want to kick the bucket down the road and plaster over it, inevitably it fails. You will have to remove those tiles to expose the depth of the crack behind it, my guess is you will have to do a full renovation where you are the contractor. Any liquid membrane will fail prematurely you will want to stick with plaster, tile, vinyl. I personally would do the bottom in tile with an epoxy grout unless you have a good plaster company near by.

 

[Conifer]

What is "liquid pool membrane"?

Something like this.

 

[Conifer]

Not knowing the typical building process for your area makes it hard to comment. My initial thought is using anchors if anchors aren’t available in your area I’ve seen videos using rebar as anchors like large staples. Hydraulic cement is used on anchors and crack and finished with plaster. It’s hard finding a company where I live to do it right. Most company’s want to kick the bucket down the road and plaster over it, inevitably it fails. You will have to remove those tiles to expose the depth of the crack behind it, my guess is you will have to do a full renovation where you are the contractor. Any liquid membrane will fail prematurely you will want to stick with plaster, tile, vinyl. I personally would do the bottom in tile with an epoxy grout unless you have a good plaster company near by.

From what I can tell, a hole was dug. Brick walls were made inside on the verticals (on the floor, I don't know). Those walls were covered with some kind of plaster, cement or concrete, and then tiles. I highly doubt that any kind of rebar or anchors were used - I just had to replace a flat concrete roof on the house that was built without any kind of rebar, so I doubt they used it on the pool.
I'm sure it's a mess and not up to today's standards or even those of 40 years ago. Consider that it was built in remotest Argentina by a guy who took some pretty shocking shortcuts on the house.
I just need it to work for a couple of years without investing too much money!

 

[Poolbreh]

If there isn’t rebar it’s not worth fixing, any cracks will reoccur with any shifting of the pool. You will need to either start over or convert to vinyl imo.