Start-up Chemistry for Plaster Pools

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O

onBalance

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Jul 25, 2011
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The effects of four different chemical startup procedures were studied.

the “Acid” startup – where enough acid was added to lower the pH to 4.5 and alkalinity to zero - about 3 gals. of acid per 10,000 gallons of water
the “pH-Neutral” startup – which equates to about one gallon of acid is added to about 10,000 gallons of water
the “Traditional” startup - where the water is maintained with CSI balanced water; near zero or (0.0) CSI
the "Bicarb" start-up - where the tap water is pre-treated with sodium bicarbonate to raise the TA to 300 ppm and the CSI is about +0.6 to +1.0

Two different methods were used to analyze and determine what chemical startup provided the best protection for a new plaster surface. One method was microscopy (40X magnification) to examine the plaster surface. The other analysis was performed by determining the calcium increase of the water that the plaster coupons were submerged in.

Well made, high quality plaster coupons were formed and placed in water after 24 hours of drying in moderate temperatures. Several coupons were each (separately) placed in water where conditions duplicated the “Bicarb” startup. The second set of coupons were placed in typical balanced water (simulating a “Traditional” startup), the third set were placed in moderately aggressive water (an SI of –0.8, similar to the so-called “pH Neutral” startup), and the fourth set were placed in water that simulated an “Acid” startup (which equals a very aggressive –4.0 SI).

After three days, the coupons were removed and the calcium level in each water tank was tested. The Bicarb startup water had a zero to 2 ppm increase in calcium, the Traditional start water had an average calcium increase of 7 to 10 ppm, the pH Neutral (moderately aggressive) startup water had a 15 to 20 ppm calcium average increase, and the Acid (or zero alkalinity) startup process had an average calcium increase of 60 to 80 ppm. When the Acid startup process was extended for an additional four days, the results indicated a calcium loss of about 120 ppm! This is significant because an increase in calcium (in the water) indicates a loss of calcium from the plaster, and increased porosity of the surface. As can be seen from these results, the bicarb startup program had the least amount of calcium loss, preserving the high surface density which provides the best protection for the plaster surface.

When 40X magnification was used to examine the plaster surface, we found that the Acid startup coupons were slightly etched, with the thin layer of cream (cement) missing, the aggregate exposed, and the surface uniformly rough. On other hand, the Bicarb startup coupons were very smooth, with the cement cream layer still intact and the aggregate not exposed. The other two methods fell in between the Acid and Bicarb results, with the Traditional startup coupons showing just a slight effect of exposed aggregate, and the pH Neutral startup coupons just a little more exposed than the Traditional. This microscopic examination was consistent with, and confirmed the results found by using the “calcium increase” analysis method.

As can be seen, the results obtained by this study shows that the Acid startup is the most detrimental method and causes irreparable harm to a new plaster surface. While the Acid startup may dissolve plaster dust and help the surface look good for a few months, it should be understood that this etched and more porous plaster surface will deteriorate and stain earlier and easier. The Bicarb method, on the other hand, is an improvement on the industry standard Traditional method.

For instructions on Bicarb Start-up, see this post: The Bicarb Start-up and Why it Works

Also see this post: aggressive-water-versus-improper-pool-plastering-t51900.html

For proper plastering practices, see this post: ten-guidelines-for-quality-pool-plaster-t42957.html
 
Great question JamesW. I probably don't have a good answer, but I will try.

My guess is that if the pH is kept under 8.0, and no alkaline chemical is added (like bleach, cal hypo, and soda ash) and only acidic sanitizer are used until the TA is lowered somewhat, then that seems to help keep calcium in solution. When the pH is under 8.0, more than 99 percent of the alkalinity is in the bicarbonate form. But once the pH rises to 8.4 and above, carbonate alkalinity becomes more prevalent, which leads to likely calcium carbonate scaling. I have observed scaling when the TA and CH is very low (50 ppm), but with a very high pH (over 9). If an alkaline chemical is added to the pool water, that can cause a precipitation (of scale) reaction to occur where the chemical is added even though the pH is below 8.0. Additionally, the chemical can sink to the bottom and create scale there. I assume Chemgeek may comment on this.

I stumbled across this high alkalinity (Bicarb) concept 30 years ago. I had an area of service that the tap water came from wells underground. The TA was 300 ppm and the CH was about 200 to 250 ppm. I observed that no plaster dust formed or developed on new plaster pools. I also noted that dark colored or black plaster remained very black even after several years time. Because of the high TA of the well water, the TA remained on the high side permanently. But as long as I didn't add any alkaline chemicals, scaling didn't become a problem.

In my soft tap water areas, a lot of plaster dust always developed. And black pools became lighter, kind of gray and mottled.

In several experiments a few years ago, I also made black plaster coupons and put them through a Bicarb start-up process. The coupons remained very black, and using a microscope for observations, no scale was detected.

To answer Richard's question, my answer is to wait about three weeks, and then start lowering the TA significantly with acid. Just use trichlor (like TFP reccommends) or dichlor for chlorination until the TA is lowered.
 
We usually don't see scaling until the saturation index gets to around +0.7 and especially +1.0 (an exception is in hot water as with spas where sometimes we see scaling at +0.3 or so). So the water is probably just super-saturated and perhaps if there is any precipitation at all, it is at the pool surface where some calcium hydroxide gets converted to calcium carbonate which if done in place doesn't look like scale but instead is just plaster becoming harder. That is, the purpose of the higher bicarbonate in the water is to encourage that conversion.

Also, the saturation index isn't always quite that high when using the bicarbonate method since the "rule" for it is that the sum of TA and CH is 500 and the pH is kept around 7.8 to 8.2. With cool pool water at 70ºF or below, the saturation index will vary from 0.13 to 0.51 with a TA of 50 and CH of 450, to varying from 0.56 to 0.94 with a TA of 200 and CH of 300, to varying from 0.15 to 0.53 with a TA of 450 and a CH of 50. So there is a lot of variation here that is very dependent on the starting CH which then determines the TA from adding additional bicarbonate. The peak saturation index is when the TA and CH are both in the 200-300 ppm range.

It may be the case that the saturation index need not be much higher than 0.7 when the pH is 8.2 and it all may work out just as well, but so long as there aren't problems with the procedure even as the saturation index approaches +1.0, then it's OK as it is relatively short-term.
 
The results of this study mentioned above (and several others that I have performed) demonstrate that if the CSI is kept at a slightly positive number during the first month of new plaster, there is no calcium loss from the plaster (which increases the CH of the water). Therefore, it is best to increase the CH level to at least 200-250 ppm once the pH is stable in the new pool water (should only take about one week), even if the Bicarb start-up is not used. After the CH has been increased, then the process of lowering of the TA can begin (if needed) about two to three weeks later. This program ensures that the CSI is never negative during this critical time of a new plaster (including quartz) pool.

If this program is followed closely, then there will be no "natural" increasing of the calcium level or the alkalinity during the first few months, unless the plastering workmanship and cement materials have been compromised. The hardening and hydration (curing) of quality pool plaster does not "naturally" release calcuim and alkaline materials from the plaster. I strongly recommend not allowing the water to be "aggressive" at any time during the first two months. Afterwards, the CSI of the water can vary between a slightly negative number and a slightly positive number. New plaster is more vulnerable to aggressive water during the first month (especially the first two weeks) than afterwards.

While new plaster may be more vulnerable to aggressive water attack during the first few weeks, it is not true that the plaster is soft and can be "dented" or "marred" by auto pool cleaners or brushing. Once a plaster is full of water, the plaster surface is "brick" hard. What is often misunderstood, is that the wheels of cleaners can "pack down" plaster dust (if any) on the plaster surface, create a raised layer of hardened "plaster dust" that results in tracks around the pool and can look like the cleaner indented the plaster surface. That is why builders do not want a cleaner installed too early. The important thing is to wait until the plaster dust is gone, or vigorously brush the pool after the cleaner has been running each day until the plaster dust is no longer present.
 
If you're having a new pool built how would you go about a bi-carb startup? How could you pre-treat the fill water with bi-carb? Can you purchase it trucked in that way? I'm sure PB's are not up to speed with methods like this and will just do whatever startup they have been doing.
 
I assure you that the Bicarb start-up is the best way to chemically start-up a plaster pool. Adding Bicarb to a tank (truck) of water would be an easy way of doing a Bicarb start-up, but also would be expensive. The Poolhelp link you provided does explain how to do one properly and for less money. Many PB's do not know about a Bicarb start-up, but more and more are learning about it.
 
My tap water has TA of 220 and CH of 20. So the sum of those is already 240. However, adding to get alkalinity to make up the entire difference to get to a sum or 500 seems crazy. Can't I add calcium chloride in the same manner to get to the total of 500. Given that the TFP guidelines are CH of 250-350, it seems that pre-treating the fill water to raise CH to 250 or in my case to 260 should work just as well as trying to add baking soda. It is heck to lower the TA over time, you know. And my pool has a constant spillover at the spa so high TA really drive pH to un swim-able levels.
 

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Oops! I saw and responded to your other post before this one. It sure seems odd that the tap water TA is so high and the CH is so low.
But yes, it may be okay to try what you want to do, but with a slight modification. I let's communicate on your other post.
 
onBalance said:
the “Acid” startup – where enough acid was added to lower the pH to 4.5 and alkalinity to zero - about 3 gals. of acid per 10,000 gallons of water
Click to expand...
It takes around 2 gallons of acid per 10,000 gallons to lower the TA by 100 ppm so where does the 3 gallon figure come from? Does it assume a needed amount to react with calcium hydroxide?
 
One of the companies I was looking at for a replaster, in their quartz surface startup, says they will use 4 gallons of acid per 10,000 gallons of pool water. Starting TA is about 220. Couldn't you remove alkalinity with carbon filtration?
 
Chem geek,
Yes, you are right on both counts. I should have clarified that.
And as anonapersona stated, most companies will add at least 3 to 4 gallons of acid per 10,000 gallons of water. And I wanted my experiment to be similar and represent what occurs in practice.

It is my understanding that carbon filtration will not remove alkalinity from water.
 
I have an activated carbon filter at our sink for tap water (my wife doesn't like the taste of our "raw" tap water) and it does not change the TA of the water by a measurable degree (i.e < 5 ppm). It does lower the pH slightly and it removes chlorine and monochloramine and a lot of other chemicals.
 
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