Pool builders, plaster applicators and service techs know that a pool startup can be a real pain. Plaster dust is just the tip of the iceberg. For residential pools especially, most pools have water filling them within hours of finishing the plaster. That means the tap water and its chemistry is immensely important in the curing process (hydration) new pool plaster.
According to the National Plasterer’s Council (NPC) Technical Manual:1
"Acidic water aggressively attacks and dissolves cementitious surface materials. Water that is low in hardness, or soft water, can cause leaching of certain compounds of the cement, especially calcium hydroxide [Ca(OH)2]." - pg. 23
At Orenda we believe--through undeniable field evidence--that urgency matters in water chemistry balance. We do not wait for the pool to be full to try and balance the LSI! We begin adjusting calcium as the water is filling, unless there is 300+ ppm of calcium in the source water already (in which case we adjust alkalinity instead). In doing so, our customers and their pools have proven that plaster dust can be prevented entirely.
The Orenda Startup™ is the result of smart, hard-working people in the field trying hard to prevent problems that almost always occur. Here's a video from Blue Moon Pools showing the difference between the pool being filled while adding calcium, vs. the spa that was filled without adding anything to it:
Risks of 'just filling the pool' without testing and adjusting chemistry
Doing an LSI-focused startup can prevent many plaster problems, by preventing the loss of an important substance called Calcium Hydroxide (Ca(OH)2) from the cement as it cures. Calcium hydroxide is very basic (high pH of 12.6) and forms when water (H2O) mixes with Calcium Oxide (CaO) in the surface, in a process called hydration, which looks like this:
CaO + H2O → Ca(OH)2
Calcium Oxide + Water → Calcium Hydroxide
If you start up pools with cementitious finishes (like plaster, pebble, quartz, etc.), have you ever wondered why the pH is always off-the-charts high when the pool is full? And even after adding acid, when you return the next day, the pH is sky high again? The pH spike during startup happens for a reason. You're losing calcium hydroxide. So you show up to the pool when it's full, and the pH is sky high. Want to take a guess where the LSI is?
The LSI is perfect.
When it is drawn into the water, calcium hydroxide spikes the pH, and the calcium hardness level drifts up until the water finds 0.00 LSI on its own. The water then stops attacking the surface, because it has found balance. But we, in an effort to comply with textbook range chemistry, see a super high pH and do what?
Adding acid takes that perfectly-balanced water and makes it aggressive again. So the pattern repeats itself. Water gets hungry ("hangry" might be a better word to describe it) and takes more calcium hydroxide. Calcium drifts up again, and pH spikes again. We show up the next day and add acid again. The process repeats. See how this goes? Our habits are actually making the problem worse. It's a self-fulfilling prophecy.
This is why it is so paramount to test the fill water! We must know what the water chemistry ahead of time so we can act accordingly. Test for water temperature, pH, total alkalinity, and calcium hardness especially.
So, let's cover the risks of just filling the pool, disregarding the tap water chemistry. First of all, unless you are blessed with amazing tap water that is already LSI balanced, you will almost certainly lose some calcium. This loss of calcium will convert into plaster dust (which we will cover in a moment), and you will be brushing for days. It will also cost you a lot of acid to fight a constantly rising pH. The water chemistry will bounce up and down, and will be difficult to nail down for at least a few days (and you will be spending money on all the pH and alkalinity adjustment chemicals like sodium bicarb and muriatic acid). But the real risks are long term. Once calcium is stolen from the surface, it will not be put back. There are going to be microscopic cracks and voids in the cement, and the integrity of the surface will never be as strong as it could have been. This leads to many issues down the road, which is a conversation for another article entirely.
Low-LSI water causes Plaster Dust
Plaster dust is just carbonated calcium hydroxide. It forms when aggressive water steals calcium hydroxide from the surface–which is still trying to cure–and draws it into solution. As mentioned earlier, this happens so the water can find LSI balance on its own. So the pH rapidly rises near the surface, because Calcium Hydroxide's pH is an astounding 12.6, which is super basic. That high pH converts bicarbonate ions into carbonate ions (CO3) in the water. These carbonates and/or dissolved carbon dioxide (CO2) then bind to calcium and 'carbonate' it into calcium carbonate (CaCO3). The reaction looks like this:
Ca(OH)2 + CO2 → CaCO3 + H2O
Calcium Hydroxide + Carbon Dioxide → Calcium Carbonate (dust) + Water
This calcium carbonate looks like white dust, which we refer to as plaster dust. And it's a nuisance for pool startups. Most people think plaster dust is the problem; when in fact, plaster dust is merely a symptom of the real problem: the loss of calcium hydroxide. It is a permanent structural weakening of the surface, and almost always comes back to bite down the road. Here's a video explaining how plaster dust is formed:
Traditional Startup Methods
NPC 30-Day Startup
The industry standard startup protocol is the National Plasterers Council's 30-Day Startup. This process is loaded with great information, like not using wheeled vacuum cleaners (which can leave lines) and not adding salt until after 28 days. This startup card is a step-by-step guide for anyone to start up a pool, which makes it a valuable tool to pool builders and service techs in the field. But the NPC takes it a step further, and serves the industry by offering startup certification courses. These courses are loaded with great information and are quite an education in themselves. Test kit do's and don'ts, the importance of testing tap water, and an understanding of how plaster hydrates and cures. We strongly recommend taking the NPC Startup Course if you have not already, even if you choose to do our Orenda Startup™. The knowledge and expertise shared in the NPC startup course is invaluable.
There is another traditional way to start up a pool, called a hot start, or a zero alkalinity startup. This basically doubles down on the acid strategy, and gets the pH down so low (below 4.3) that there is zero alkalinity in the water at all. By getting below 4.3, the pool's water takes longer to recover and reach LSI balance on its own. In the process, it takes a lot of calcium from the brand new surface...but hey, it sure makes the pool look fresh and clean. It can actually make the pool appear darker than it was originally. There are plenty of downsides to hot starts, and we at Orenda do not recommend them. We have an entire article devoted to hot starts and other exposure techniques for new plaster and pebble surfaces.
That being said, as a means of cleaning up a bad exposure process (like puddle rings, streaking, and other unsightly spots in the pool), a far less aggressive acid bath has a purpose. Rather than dropping the pH to zero alkalinity (below 4.3), this method takes the pH down to about 6.5 for a few days, and serves as more of a cosmetic cleanup of the surface, rather than a 'scorch-the-earth' hot start. Hopefully this isn't needed in your pool either, but it's a reliable option for cleaning up a messy surface.
What's the proper thing to do when you see a spiked pH? It's to recognize why the pH spiked in the first place. Measure the LSI using the Orenda LSI Calculator App, and find out what chemistry is needed to correct the LSI. Chances are, you need to add calcium.
The Orenda Startup™
For startups, you can follow our Orenda Startup Guide, or watch some of our videos showing different ways to do it. Our startup method is derived from a few facts that we learned from the NPC and industry textbooks about how plaster hydrates and cures, as well as how water chemistry interacts with a curing surface.
The objective is simple: prevent the loss of calcium hydroxide.
We prevent the loss of calcium hydroxide from the start, by feeding the water the LSI saturation it craves, as the pool fills. The key is to get the LSI within a desired range (+0.20 to +0.50) as quickly as possible. Usually that means adding calcium chloride with SC-1000 as the pool is filling, and sodium bicarb the next day. We generally want between 400-500 combined parts-per-million between calcium hardness and alkalinity.
Why do we need SC-1000? Because it allows for the rapid addition of calcium, as it is a scale inhibitor and chelating agent. Without SC-1000, adding calcium so quickly can cause calcium to fall out of solution and make a mess.
The following day, we adjust the other factor (either alkalinity, or calcium, whichever one you did not add as the pool was filling), and purge the pool with CV-600 enzymes.
Other Pool Plaster Problems
We have written about several other plaster issues on our blog. Check out some of our other articles here:
- Understanding calcium nodules
- Calcite crystals vs. Scale
- Weepers, Efflorescence and other Concrete Pool Shell Problems
Either give water the (LSI) balance it craves, or it will find balance on its own. The first several weeks are the most vulnerable for plaster, so protecting it while it cures is essential for the lifespan of the surface. Plaster dust is a choice, and we choose to prevent it.
1 National Plasterers Council. (2018). Technical Manual (9th ed.)., §8.7, pp. 23-25.