What is this white chalky paste on the top of the pool tiles (which does not react by bubbling with concentrated muriatic acid)?

[Gary Davis]

What is this white chalky paste on the top of the pool tiles (which does not react by bubbling with concentrated muriatic acid)?

In the past few weeks I've used a few cases of HASA muriatic acid to clean the tiles which bubbled like crazy on the bottom half, presumably calcium carbonate.

The bottom half of the tiles seemed to be calcium carbonate (based on dissolving in acid), but what can this un-reactive white paste be?

And how would you clean off the white paste on top which does not react with muriatic acid?

 

[JamesW]

Scale from evaporation leaves every possible type of scale because as the water dries, every dissolved solid precipitates in every possible combination.

Some types of scale do not react to muriatic acid.

It probably contains calcium carbonate, calcium phosphate, calcium silicate, calcium sulfate etc.

All possible combinations of positive and negative ions.

Calcium, sodium, lithium, magnesium etc.

 

[JamesW]

Any acid that can remove the scale will probably etch the tile.

Maybe some sort of media blasting that is not aggressive to tile.

 

[JamesW]

Salt Blasting Pool Tile Cleaning - Tucson Pool Tile Cleaning and Beed Blasting

Salt Blasting Pool Tile Cleaning What Is Salt Blasting? In a process much like sand blasting, however the air pressure and media are much different.

www.docstucsonpooltilecleaning.com

Here are before and after pics. The material really does an AMAZING job at cleaning tile and I would never use glass media blasting ever now that I know the MaxxStrip stuff exists. I don't think I have the space for the equipment, so I may just pay for the service again even though the guy requires a travel fee to come down to Tucson.

You can't use baking soda to blast calcium, it's too soft.

You need to use a material called kierserite (hydrated magnesium sulfate). It has a Mohs hardness that is perfectly matched to calcium carbonate. It goes under the trade name of MaxxStrip (careful with that search term, it can bring up "unwanted" websites).

 

[ajw22]

Waterline Scale Removal - Further Reading

www.troublefreepool.com

 

[JoyfulNoise]

Salt Blasting Pool Tile Cleaning - Tucson Pool Tile Cleaning and Beed Blasting

Salt Blasting Pool Tile Cleaning What Is Salt Blasting? In a process much like sand blasting, however the air pressure and media are much different.

www.docstucsonpooltilecleaning.com

My thinking has “evolved” on tile cleaning. While I do agree that kierserite (magnesium sulfate) is a good media for getting rid of calcium scale without damaging tile glaze, it’s not good for pool water. The tile cleaners will either claim that it doesn’t dissolve and you can vacuum it to waste (mostly not true) or that it’s a harmless magnesium salt that won’t hurt you or your pool or mess up the chemistry at all (again, mostly not true).

Kierserite most definitely will dissolve into water albeit a bit slowly. Blasters can easily use upwards of 50-75lbs of the stuff cleaning calcium scale. So even if you could get half of it out by vacuuming to waste, you’ll be adding hundreds of ppm of sulfate ions to the water. Not only are sulfates damaging to an SWG cell they will also react with calcium forming calcium sulfate scale which is much harder to remove than carbonate scale. I saw this happen in my own pool and even though I got about 8 years out of my first SWG cell, I believe it could have lasted longer had it not been exposed to two rounds of kierserite blasting.

So, while it is a good cleaning media, I would only ever use it again if I were draining the pool afterwards and refilling. The sulfate load is very high and it will most definitely cause problems.

 

[JamesW]

While I do agree that kieserite (magnesium sulfate) is a good media for getting rid of calcium scale without damaging tile glaze, it’s not good for pool water.

What about using sodium chloride, magnesium carbonate or calcium carbonate salt for blasting?

Sodium chloride (NaCl), also known as salt, halite, or table salt, has a Mohs hardness of 2.0–2.5.

Kieserite Mohs scale hardness 3.5

Calcium carbonate is a soft mineral with a Mohs of 3.

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Mohs scale hardness 3.5–4.5

Maybe use diamonds as a blasting media for tough scale?

Also, who is this Moe dude anyway who gets to decide how hard things are?

 

[JamesW]

You have many Cations (Positive) and Anions (Negative) in pool water.

Positive Cations: Sodium, potassium, magnesium, lithium, aluminum, calcium etc.

Negative Anions: Sulfate, carbonate, hydroxide, bicarbonate, chloride, bromide, silicate, phosphate etc.

The total charges will zero out.

A Calcium ion is +2 and it will combine with (1) -2 ion like carbonate or (2) -1 ions like chloride.

If you take a pot of pool water and boil off all of the water, you will end up with scale that is a combination of every type of ionic compound possible.

Evaporation will do the same thing.

As the water evaporates, every dissolved solid is left behind.

As the tile gets wet again, some of the more soluble salts, like sodium chloride, will redissolve.

So, the scale that is left is a combination of the least soluble compounds like calcium carbonate, calcium silicate, calcium phosphate, calcium sulfate etc.

If the scale was primarily calcium carbonate, then hydrochloric acid would dissolve it.

Hydrofluoric acid would probably work, but it is way too dangerous and it will probably etch the tile.

Sodium hydroxide might work, but that is uncertain and lye is very hazardous.

Media blasting will probably work but there are downsides to media getting into the water.

The media has to be in a very narrow range to be effective without scratching or damaging the tile.

Tile can be scratched, cracked, chipped, spalled etc. by excessive hardness, excessive particle size, excessive velocity etc.

Maybe you can find a blasting company that can capture most of the blast media before it hits the water?

 

[JoyfulNoise]

Most pool tile cleaners use a combination of chemical and mechanical cleaning techniques. If they are skillful and careful, they know how to test small areas and adjust flow and pressure to get the quickest cut possible without damaging the tile. Morons that just want to get paid and go will crank the pressure up super high, cause scratches and damage, and then try to hide it by wiping the tiles with WD-40 afterwards to make them look shiny and clean. I’ve had experience with both types of “professionals” … so just make sure if you do hire someone that they can back up their work with references from happy customers.

 

[JamesW]

I’ve had experience with both types of “professionals” … so just make sure if you do hire someone that they can back up their work with references from happy customers.

How about this company?