Why Are Calcium Crystals Forming in Pools?

[onBalance]

Orenda has also had crystals analyzed by a lab and they reported that they were made of calcium carbonate. Then they incorrectly assumed that aggressive water was the culprit without considering the possibility of having poor quality plaster involved.

Unfortunately, Orenda didn't obtain any plaster samples and have it analyzed for its' calcium chloride content and water/cement ratio. The calcium chloride content should not exceed 2% of the weight of the cement portion of pool plaster. Additionally, the water/cement ratio should not be any higher than 0.55% of the weight of cement. If both issues are exceeded, then that is evidence of poor quality and defective plaster that easily deteriorates. Even in balanced water.

If those two issues exceed the acceptable amount, then that is what can result in calcium hydroxide bleeding out of a plaster surface in balanced water and create conditions where calcium carbonate crystals may form.

 

[Akhaines525]

This is a great discussion. My pool was installed in 2014 and only in the last 3-years have I started to get crystals forming over the winter (I live in the Philadelphia Area). My pool tech and myself have tried everything over the last two years and still had crystals this winter. I am really tired of having to scrape or sand the pool surface to get rid of the sharp crystals. Does anyone have a suggestions for removing the crystals after they form? Brushing doesn't help, it has to be a hard scraper or low grit sand paper. I have a salt pool by the way...

 

[VAChuck]

I have both a vinyl and fiberglass pool so I haven't had to deal with this. But I am a cement chemist and found this conversation interesting. Pool plaster is typically a combination of limestone (CaCO3) and white portland cement (Marcite). Funny that plaster is actually calcium sulfate hemihydrate (plaster of paris). Not sure why the industry ever named this stuff "plaster" as calcium sulfate hydrates are soluble in water and would make an awful pool liner.

Portland cement, when it hydrates and hardens always produces Calcium Hydroxide (CH), which can be a major source of efflorescence. Pool plaster and all concrete is porous and it is easy for soluble salts to migrate through the material. In the concrete industry we refer to primary and secondary efflorescence. Primary comes from the material itself (ie the CH in the pool plaster) and secondary comes from the underlying substrate, in this case the earth around the pool. For the salts to move through the material there has to be a moisture drive. This is why it typically shows up above the water line - evaporation of water from the dry surface deposits salt on the surface. The moisture could come from the surrounding earth or from the pool water itself.

One way to get rid of the CH in portland cement hydration is to add a pozzolan into the mix. Pozzolans chemically combine with the CH and and eliminate the potential for efflorescence. One potential pozzolan the pool plasterer should use is Metakaolin. Applications & Benefits – We Supply Metakaolin and Silica Fume : Advanced Cement Technologies, LLC (ACT) This will solve primary efflorescence but not secondary efflorescence, thought it may reduce it because the permeability of the plaster should be reduced.

It is true that to finish a job plasterers may add Calcium Chloride to pool plaster to accelerate the setting time, especially in cold weather. Over adding this inexpensive chemical can cause mottling and other issues due to the increase in calcium. Another safer potential plaster accelerator is Ternal W, a calcium aluminate cement. There are other possibilities for the acceleration of portland cement that are "non chloride".

 

[JoyfulNoise]

I have both a vinyl and fiberglass pool so I haven't had to deal with this. But I am a cement chemist and found this conversation interesting. Pool plaster is typically a combination of limestone (CaCO3) and white portland cement (Marcite). Funny that plaster is actually calcium sulfate hemihydrate (plaster of paris). Not sure why the industry ever named this stuff "plaster" as calcium sulfate hydrates are soluble in water and would make an awful pool liner.

Portland cement, when it hydrates and hardens always produces Calcium Hydroxide (CH), which can be a major source of efflorescence. Pool plaster and all concrete is porous and it is easy for soluble salts to migrate through the material. In the concrete industry we refer to primary and secondary efflorescence. Primary comes from the material itself (ie the CH in the pool plaster) and secondary comes from the underlying substrate, in this case the earth around the pool. For the salts to move through the material there has to be a moisture drive. This is why it typically shows up above the water line - evaporation of water from the dry surface deposits salt on the surface. The moisture could come from the surrounding earth or from the pool water itself.

One way to get rid of the CH in portland cement hydration is to add a pozzolan into the mix. Pozzolans chemically combine with the CH and and eliminate the potential for efflorescence. One potential pozzolan the pool plasterer should use is Metakaolin. Applications & Benefits – We Supply Metakaolin and Silica Fume : Advanced Cement Technologies, LLC (ACT) This will solve primary efflorescence but not secondary efflorescence, thought it may reduce it because the permeability of the plaster should be reduced.

It is true that to finish a job plasterers may add Calcium Chloride to pool plaster to accelerate the setting time, especially in cold weather. Over adding this inexpensive chemical can cause mottling and other issues due to the increase in calcium. Another safer potential plaster accelerator is Ternal W, a calcium aluminate cement. There are other possibilities for the acceleration of portland cement that are "non chloride".

I want them to bring back asbestos as an additive!! Those old pool plasters that used asbestos were indestructible and lasted 25+ years without a fail!!

Thanks for the info. Feel free to chime in on plaster threads to share your in-depth knowledge.

 

[JamesW]

Pool plaster is typically a combination of limestone (CaCO3) and white portland cement (Marcite).

Plaster is Portland cement and an aggregate.

The most common aggregates are marble, quartz and pebble.

The plaster with marble is called Marcite.

 

[JamesW]

I want them to bring back asbestos as an additive!! Those old pool plasters that used asbestos were indestructible and lasted 25+ years without a fail!!

The good old days when everything contained asbestos, lead and VOCs and everyone smoked 2 packs a day.

Everyone ate nothing but red meat, cars had no seatbelts and kids could get real M80s to play with.

 

[JoyfulNoise]

The good old days when everything contained asbestos, lead and VOCs and everyone smoked 2 packs a day.

Everyone ate nothing but red meat, cars had no seatbelts and kids could get real M80s to play with.

Yeah, NOW they tell everyone NOT to eat the paint chips … could have used that little bit of sage advice when I was kid … oh well, YOLO!!

 

[mgtfp]

Everyone ate nothing but red meat, cars had no seatbelts and kids could get real M80s to play with.

... and drank Bourbon or Scotch throughout the day instead of super grande skinny lattes.

 

[SoDel]

I got to say that the explanation about the water in winter does make some sense. At pool closing, (assume) calcium saturation equilibrium is achieved and water is about 65 degrees (F). Water then gets super cold, becomes unsaturated due to increased calcium solubility in the cold and takes calcium from the plaster over the winter and re-establishes equilibrium at the cold water level. Water warms up, calcium comes out of solution, open the pool and find crystals. The only trouble with this theory is the reports of operators who swear they accounted for cold temps in the closing chemistry so this should not have happened.

Next explanation is workmanship and too much CaCl2 in the plaster mix. Also makes sense — although I admit I don’t fully understand.

Is there a way to run some experiments, like plaster a set of mini pools using good workmanship, setup one with water that will not violate saturation index in the cold and one that will, put them in a chiller for six months and see what happens. Do another set with excessive CaCl2 in the plaster and see what happens. If somebody has a large walk-in and wouldn’t mind displacing the beer, might be interesting?

 

[onBalance]

SoDel, as you stated, typical calcium carbonate can precipitate out due to being over-saturated when water warms up.
And of course, that can happen to all pools universally. That type of scaling is well known and is understood on how and why is happens.
This "crystal" problem is somewhat different in the type of scaling and is occurring in newer and recently plastered pools.
I have plans to run some experiments as you mentioned and welcome others to do the same.

 

[grassy1]

I am a pool owner in northern (East Hanover) NJ and have been fighting with this calcium crystal issue for the last few years. The pool was originally built in 2012 The company I use seems to have little knowledge of this issue. Can anyone recommend a company in this area that is experienced with removal and prevention of these crystals. Thanks in advance!

 

[onBalance]

If you are having calcium problem develop every year since 2012, it may not be the result of this "calcium crystals" issue mentioned above. It may simply due to poor pool water balancing. Many pool companies know how to remove and prevent the typical calcium carbonate scale that occurs in many pools. There are many articles on this website that explain how to properly keep pool water balanced.