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) of new 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 adjust calcium levels! We begin adjusting calcium as the water is filling. In doing so, our customers and their pools have proven that plaster dust can be prevented entirely. The Orenda Startup is the result of hard-working people in the field trying hard to prevent problems that almost always occur. Here's a video showing the difference between the pool being filled while adding calcium, vs. the spa that was filled without adding anything to it:
Why does plaster damage occur?
Doing the Orenda calcium startup can prevent many plaster problems. The three biggest reasons plaster damage occurs (according to the National Plasterers Council) are:
- Alkalinity is too low...specifically carbonate alkalinity
- Calcium hardness is too low
- Lack of a quality scale and metal sequest or chelant in the water
Another way to explain items (1) and (2) is the LSI of your tap water is too low. It is critical to know more than just calcium hardness, alkalinity and pH of the tap water prior to filling a freshly surfaced pool. You MUST know the fill water's temperature! Ground water in the Northeastern United States is between 50-60ºF, depending on location and time of year. That's pretty cold, and it makes a dramatic difference on the LSI of that fill water. Cold water can cause etching. Are you testing the fill water before putting it in the pool?
Low-LSI water causes plaster dust and other problems
Plaster dust, as you may already know, is carbonated calcium hydroxide. It forms when aggressive water takes calcium hydroxide from the surface--which is still trying to cure, by the way--and draws the calcium into solution so the water can find LSI balance on its own. When that happens, carbonate ions in the water (or dissolved carbon dioxide) 'carbonate' the calcium hydroxide (Ca(OH)2), leaving behind calcium carbonate (CaCO3) and water. That calcium carbonate is in the form of white dust, which we refer to as plaster dust. And it's a nuisance for pool startups. Here's a video explaining how plaster dust is formed:
Many people think plaster dust is the problem; when in fact, plaster dust is merely a symptom of a more long-term problem. The loss of calcium hydroxide is permanent structural weakening of the surface, and it almost always comes back to bite down the road.
Our habits make startups worse
Water always strives to find LSI balance on its own. So when doing a new startup the traditional way, you may have noticed the pH tends to spike really high, and the calcium hardness "drifts up" every day for the first week or more. Have you ever wondered why that happens? Everything happens for a reason.
Low-LSI water is aggressively looking for calcium saturation, and the most soluble form of calcium available is the calcium hydroxide in the surface, which has a high pH of 12.6-12.8. When it is drawn into the water, the pH spikes and calcium slowly 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 to a super high pH on startup takes 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 interfering with our chances for success.
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 Calcium Startup
For startups, follow the Orenda Startup Guide, or watch some of our videos showing different ways to do it. Basically, it's a procedure that goes like this:
- Test the fill water, and input results in the Orenda LSI Calculator App (available on iOS and Android)
- Use the Orenda App to figure out where you want your startup chemistry to be, and tap Get Dosage
- Add the 'purge dose' of SC-1000 to the pool, either in the main drain, or down the Orenda Startup Barrel hose, and some of it in the pre-dissolving calcium solution (in the barrel or in the buckets) to chelate calcium prior to adding it to the pool.
- Add prescribed amount of pre-dissolved, chelated calcium as the water is filling. Add sodium bicarb the next day.
- Continue with NPC startup guidelines from there.
We are often asked about the acid startup practice. This is also called a "hot start" or "zero alkalinity startup". These startups are highly aggressive to cementitious surfaces, and they have been used as an exposure technique. Sure, it may look great in the short term, but an acid startup aggressively leeches calcium hydroxide from the surface; valuable calcium that belongs in the surface. The loss of material to water creates etching, which makes the surface rough and pitted.
The acid startup should only be used as a last resort if there are problems. When done right, the Orenda startup feeds the water so it doesn't feed on your fresh coat of plaster, and therefore you should not get plaster dust.
Either feed the water the calcium saturation (LSI) balance it needs, or it will find it 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. Someone on the job needs to take ownership of the startup and ensure that calcium is properly fed in a timely manner. Is it the pool builder? Plaster applicator? Service tech? We don't really care who does it, provided it gets done and everyone is on the same page. Communication between all parties is important.
Plaster dust is a choice. We suggest you choose to avoid it.
1 National Plasterers Council. (2018). Technical Manual (9th ed.)., §8.7, pp. 23-25.