rebar in pool structure

[morning dipper]

be happy to swap info with anyone about corrosion issues/structural issues in rebar/concrete pools.
My newbuild (form poured reinforced concrete) has a couple of microcracks (hairline 0.2- 0.3 mm) on one wall ( 8.5m long 1.65h - that's the wall not the cracks). This wall is above ground (exposed) while the other sides are inground. The visiting structural engineer said not uncommon micro cracks; not structural. Water seeps through one, while the other has self sealed.
It seeps because waterproof membrane applied inside under tiles is not doing its job. Membrane has no elasticity to allow for movement on concrete support. Concrete moves membrane follows, and cannot bridge cracks. Work is planned to strip tiles and redo membrane correctly on the one wall.
Given that many pools are concrete and rebar construction and concrete does have a tendency to microcrack (shrinkage from new, thermal etc) what are the longterm risks that pool water 1) gets into contact with rebar and 2) corrodes rebar.
Am i dealing with a rogue pool, or is minor seepage acceptable/the norm on a concrete pool.
Any thoughts much appreciated
Patrick

 

[HermanTX]

Microcracks in gunite is common. Plaster is what makes the structure waterproof and seals the gunite.
Show photos of the issue.
Maybe @AQUA~HOLICS can provide some guidance. Any additional information you can provide with how a pool structure is designed in France would be helpful.

 

[AQUA~HOLICS]

Long term risk of water being in contact with the steel cage is possible failure of the steel cage and loss of strength in that area.

Micro Cracks are common in Shotcrete vessels but are an indication of improper hydration during curing and can be avoided if properly hydrated during the first 28 days or so depending on the weather conditions.

In my opinion, no water seepage is normal in a swimming pool vessel.

 

[Bperry]

be happy to swap info with anyone about corrosion issues/structural issues in rebar/concrete pools.
My newbuild (form poured reinforced concrete) has a couple of microcracks (hairline 0.2- 0.3 mm) on one wall ( 8.5m long 1.65h - that's the wall not the cracks). This wall is above ground (exposed) while the other sides are inground. The visiting structural engineer said not uncommon micro cracks; not structural. Water seeps through one, while the other has self sealed.
It seeps because waterproof membrane applied inside under tiles is not doing its job. Membrane has no elasticity to allow for movement on concrete support. Concrete moves membrane follows, and cannot bridge cracks. Work is planned to strip tiles and redo membrane correctly on the one wall.
Given that many pools are concrete and rebar construction and concrete does have a tendency to microcrack (shrinkage from new, thermal etc) what are the longterm risks that pool water 1) gets into contact with rebar and 2) corrodes rebar.
Am i dealing with a rogue pool, or is minor seepage acceptable/the norm on a concrete pool.
Any thoughts much appreciated
Patrick

Zero seepage is the only acceptable option.

 

[morning dipper]

Hi all and thanks for your thoughts. I agree about zero seepage, but was curious about % of gunite/plaster pools that actually achieved zero seepage, and how many pools actually get to structural difficulty via corrosion. Are US pool builders regularly delivering non seep pools?
This pool is poured concrete (in fact pumped as above road level). Traditional steel reinforcing with 2in cover is placed in formwork and pool is cast in 3 pours: 1) floor, 2) bulk of walls, 3) final pour to join walls and minimise shrinkage problems.
Concrete is local code pool grade concrete for constant immersion.
Inside is waterproofed with a Sika product - in our case Sika 121; 2 component cementitious tanking product.
Inside of pool is then tiled.
Long wall shows what is described as shrinkage crack (hairline) and seeping cold joint (between pours).
Sika product should have prevented water traversing walls, but Sika 121 is not 'elastic' like Sika 155 for example or Mapelastic, and so cracks crack waterproofing too, rendering it useless.
Solution is to empty pool, remove tiles, and apply appropriate waterproofing, then retile. Big job, but PB is taking responsibility.
Big wall (8.5m) is being repaired like this, while other shorter walls (max 5m - pool rectangular with one corner rounded inwards ) with no cold joints are deemed less at risk, so with no repairs.
My concern is towards long term viability of pool with zero corrosion using salt water.
This thread started life as a chemical one, wondering if non salt water ie no swg would offer a less aggressive environment for the rebar.
My thanks to this great site, and its contributors.

 

[setsailsoon]

My experience is very similar to Aqua~holics. Micro-cracks are common because concrete is not properly hydrated during first 28 days of curing. For industrial applications we keep concrete wet with spray and/or burlap for 30 days. Concrete is not waterproof so water will soak through it. But it happens at a very slow rate because even though there are a lot of pours in it they are very tiny. Seeps indicate a crack (not not the normal tiny pours that all concrete has) has connected with other cracks to make a path through the concrete. Plaster and other internal coatings are waterproof so they stop water from soaking through. You can also waterproof the concrete before adding plaster but modern plasters don't require this. I like to waterproof anyway. Belt and suspenders are good in cases where your pants falling down is expensive. Pool shell repair fits that category as your builder is discovering.

I'll leave it to our expert resident chemists to comment on corrosion of rebar in salt vs non-salt pool structures. @JoyfulNoise over to you! My guess is that he will say to make sure your "sealing" coating has good integrity and you shouldn't have to worry. I've built a lot of rebar reenforced concrete dock structures that were exposed to ocean salt water that's about 10 x saltier than pool water so I doubt it's a problem. I just build my second salt water pool and they don't require anything special from a code requirement.

Chris

 

[Bperry]

Hi all and thanks for your thoughts. I agree about zero seepage, but was curious about % of gunite/plaster pools that actually achieved zero seepage, and how many pools actually get to structural difficulty via corrosion. Are US pool builders regularly delivering non seep pools?
This pool is poured concrete (in fact pumped as above road level). Traditional steel reinforcing with 2in cover is placed in formwork and pool is cast in 3 pours: 1) floor, 2) bulk of walls, 3) final pour to join walls and minimise shrinkage problems.
Concrete is local code pool grade concrete for constant immersion.
Inside is waterproofed with a Sika product - in our case Sika 121; 2 component cementitious tanking product.
Inside of pool is then tiled.
Long wall shows what is described as shrinkage crack (hairline) and seeping cold joint (between pours).
Sika product should have prevented water traversing walls, but Sika 121 is not 'elastic' like Sika 155 for example or Mapelastic, and so cracks crack waterproofing too, rendering it useless.
Solution is to empty pool, remove tiles, and apply appropriate waterproofing, then retile. Big job, but PB is taking responsibility.
Big wall (8.5m) is being repaired like this, while other shorter walls (max 5m - pool rectangular with one corner rounded inwards ) with no cold joints are deemed less at risk, so with no repairs.
My concern is towards long term viability of pool with zero corrosion using salt water.
This thread started life as a chemical one, wondering if non salt water ie no swg would offer a less aggressive environment for the rebar.
My thanks to this great site, and its contributors.

Water getting to the rebar (whether it has some salt in it or not) will corrode it. US builders quite regularly achieve 100% waterproof. I just spent a lot of time and sweat (and $$) repairing concrete pool that had been leaking for some time.

 

[morning dipper]

shotcrete pools here (France) are a bit niche. Polyester, yes or concrete, poured and generally tiled.
Your shotcrete pools are then plastered, which I understand gives the finish and waterproofs them.
Be interested to know about this plaster, thickness application elasticity etc. Can you give any names links for some reading.
Considered using a plaster system available here, but seemed a nightmare. Very picky (like overly impractical) on time to get pool full of water once applied, or risk colour variations. Ditched and went tile route.

 

[Bperry]

shotcrete pools here (France) are a bit niche. Polyester, yes or concrete, poured and generally tiled.
Your shotcrete pools are then plastered, which I understand gives the finish and waterproofs them.
Be interested to know about this plaster, thickness application elasticity etc. Can you give any names links for some reading.
Considered using a plaster system available here, but seemed a nightmare. Very picky (like overly impractical) on time to get pool full of water once applied, or risk colour variations. Ditched and went tile route.

Diamondbrite is quite common. Plaster is a cement based product and so is not elastic. If the shell has cracks opening and closing, nothing except a vinyl liner will seal that. Plaster goes down >10mm thick and is hand troweled so there are variations in color and texture depending on the skill of the applicator.

 

[setsailsoon]

shotcrete pools here (France) are a bit niche. Polyester, yes or concrete, poured and generally tiled.
Your shotcrete pools are then plastered, which I understand gives the finish and waterproofs them.
Be interested to know about this plaster, thickness application elasticity etc. Can you give any names links for some reading.
Considered using a plaster system available here, but seemed a nightmare. Very picky (like overly impractical) on time to get pool full of water once applied, or risk colour variations. Ditched and went tile route.

Very common in Florida is a brand named Florida Stucco. They're all very similar with base being white plaster and various different amounts of dye and pebbles added to improve surface appearance. All the different brands have additives to enhance bond to raw concrete and surface appearance. They also prescribe application requirements and initial cure period requirements. I found there's a combination of science, art, and talent that's required for successful outcomes. I'd never let a contractor do this that I haven't watched in progress. For gunite, I also feel the same. If you can't do it this way in France I wouldn't try it. That said there are many pools in Europe that sure look like they have plaster finishes. So I'm guessing somebody over there must know how and have experience.

Chris