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Frequently Asked Questions
Gain answers to our most frequently asked questions about pool refinishing and water chemistry.
NPC White Papers for Pool Owners
The Importance of Water Testing
Interior Finish Tolerances – “Smoothness,” “Levelness,” “Thickness,” and “Mottling”
Why is White Cement Used in Swimming Pool Plastering?
What Happened to my Pools Interior Finish?
Is my Pool Supposed to be “Waterproof” or “Watertight”?
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Frequently Asked Questions
What is the best type of chlorine for my pool?
What do Polymeric additive and Pozzolonic admixes do?
Polymeric additives modify the cement matrix, or sometimes form a co-matrix with cement. Pozzolanic admixtures combine with the calcium hydroxide in cement (the weakest compound in the cement binder) to form a stronger cement compound. Both polymeric and pozzolanic materials enhance the durability and lifespan of the finish by making it less susceptible to aggressive pool water chemistry and pool chemicals.
Why are additive and admixtures used?
Additives and admixtures are used to increase the ability of the plastering technicians to create the optimum finish. They are also used to increase the strength and durability of finishes. Additives or admixtures can alter the physical and chemical composition of the finish, making them more resistant to chemical attack from aggressive pool water chemistry and pool chemicals. Incorporating these into the mix design, can increase the overall durability and lifespan of your finish.
Is it important to maintain the water in a balanced condition, as per industry standards?
Ongoing maintenance of proper water chemistry and ongoing proper care of the finish will ensure that your finish achieves the manufacturers expected maximum lifespan. When pool water is in a ‘balanced’ condition, it is neither ‘plating’ (causing a calcium scale to form) or ‘aggressive’ (causing calcium to be leached out of the finish), your pool will likely achieve its’ anticipated lifespan without issue. Good water balance is needed to help the sanitizer keep the water safe for swimmers.
What recommendations are there to maximize the life expectancy of my new finish?
Cementitious-based finishes are very durable products, but certain conditions can cause premature deterioration, and potentially failure. Installing a high-performance finish, or adding a durability-enhancing additive and/or admixture to the finish can help reduce the rate of chemical deterioration and increase the lifespan of the finish.
What factors affect the lifespan of my finish?
The type of finish chosen, proper installation, proper initial start-up, ongoing maintenance of proper water chemistry and ongoing proper care of the finish, will ensure that your finish achieves the manufacturers expected maximum lifespan. Ask an NPC member in your region of the country for specific information on the finish of your choice.
When is the right time to refinish my pool?
For aesthetics reasons, or to upgrade your pool, anytime is the right time. Otherwise, a pool generally needs to be resurfaced when the surface is no longer comfortable for use, or has become pitted and rough. An NPC member in your region can advise you of the various types of swimming pool finishes available, and can assist you in selecting the finish that best meets your needs.
I've begun to notice small rust colored spots. What are these spots?
1.) Iron fertilizer used on the grass or other plants nearby the pool
2.) A new wrought iron fence, or other metal work being done nearby the pool
3.) B-B’s, nails, screws, bobby pins, or other small metallic objects
Each of the above issues can be the cause of small rust spots. The in-floors, pool cleaner, and/or circulation returns frequently move these small objects, so even one small metal object, or iron-containing material, can cause numerous rust spots before it is removed from the pool.
Generally, small metal rust spots can be easily sanded off underwater using a piece of wet/dry sand paper, diamond disc, or other abrasive pad. A professional can often remove rust spots chemically, by pouring ascorbic acid or other such rust removal chemical (for swimming pools usage) directly onto the rust spot (follow manufacturer directions). If the spots are not removed after implementing one of these processes, then the issue may not be on the surface. There may be some impurity within the finish, or there may be a structural reinforcement issue, in which case your Builder or Plasterer should be contacted.
Do you have an SOP that relates to pool plastering in cold temperatures and what is the recommended temp to plaster an unground pool in NJ.
5.3 Cold Weather
It is important that the cementitious binder continue to hydrate and strengthen. The placement of an interior finish in cold weather is considered an acceptable practice, as long as, the daily average mean temperature (the daily average of the highest high and the lowest low, from midnight to midnight) is above 40oF (4oC) and the substrate is not frozen. Optionally, special precautions can be taken to protect the material from freezing. Once the finish coating has reached final set, the temperature of the coating should not be allowed to freeze before the pool is filled. Cementitious materials will resume hydrating and continue to gain strength when the temperature of the coating rises above 40oF (4oC). Cementitious materials continue to hydrate underwater, and achieve a significant portion of their ultimate strength underwater, during the first three months after installation.
My finish is old and in need of replacement. What are my options?
There are four main types of finishes: plaster, polished ,quartz, and exposed pebble aggregate, each having their own unique properties and characteristics. Each of these types of finishes comes in a variety of colors. Many of these products incorporate special additives and/or admixtures, such as pozzolanic or polymeric materials that can enhance the finishing ability and the long-term durability of these surfaces.
My pool plaster is approximately two years old. For the first 18 months the white plaster looked fine, but now is slowly turning blue, blue/green and black. What is this?
This is likely due to some type of metal staining. The most common metal stains are copper or iron. Try sanding a small area with a piece of #80 grit wet/dry sand paper, diamond disc, or abrasive pad, and see if the stains lessens, or is removed. A professional might try a few chemical tests as well, to see if a certain chemical lessens or removes the staining. The most common sources of metals are from:
1.) Fill water (well water or trucked-in water)
2.) Corrosive pool water (can attack heat exchanger and/or other metal components)
3.) Ionization systems (anode deterioration)
4) Copper-based algaecides
5.) Metal pipes
6.) Iron-based fertilizers
My plastering company recently advised me that a problem in my pool surface was attributed to low carbonate alkalinity. What is “Carbonate Alkalinity?”
Carbonate alkalinity is also known as the corrected or adjusted total alkalinity. The three most important water chemistry parameters necessary to have “balanced” water are pH, carbonate alkalinity (adjusted total alkalinity), and calcium hardness in their correct ranges.
Test kits determine the total alkalinity, but it is the carbonate alkalinity that is used to calculate the water balance. This is done by taking approximately 1/3 of the cyanuric acid (or ‘stabilizer’) content, and subtracting it from the tested total alkalinity. Remember, only carbonate alkalinity can be used to calculate the Saturation Index, which determines whether your water is in a balanced condition.
If the total alkalinity is 100 ppm, and the cyanuric acid level is 100 ppm, then the adjusted carbonate alkalinity is: 100 ppm (total alkalinity) – 33 ppm (cyanuric acid) = 76 ppm carbonate alkalinity.
When I turn the light on in my pool I see waviness and unevenness across the surface of the finish. Is this normal?
Swimming pool plastering is a hand-crafted finish. The finish is produced by ‘free hand’, meaning it is not molded or pre-formed. There will always be some waviness or unevenness associated with hand-crafted finishes. The National Plasterers Council Technical Manual (9th edition) states: “Observation , using the swimming pool light at night, or other sources of light that shine across the surface, instead of upon the surface, are not considered a fair representation of the surfaces true appearance. Certain angles of light will grossly exaggerate imperfections and/or the waviness across the surface finish.” Basically, some fluctuations and waviness are inherent to the application, and as such, are considered normal. However, if certain inconsistencies are readily apparent under normal daylight viewing conditions, then the builder or plastering company should be contacted for evaluation.
I have a 20'x40' swimming pool and have always enjoyed the smoothness and appearance of "white plaster". Now it's time to re-plaster and many (including my poolman) have said that the white plaster available today is not as good as that used 10+ years ago. In other words, I should not expect the replaster job to last as long as the old one. Many recommended I consider "PebbleTech" or white plaster with some (quartz?) additive. What can you tell me about the durability of today's white pool plaster? Also, are there "grades" of plaster, with the higher priced grades being more durable?
Lots of people say that the plaster of today does not last as long as it used to. There are a few things that could have merit on the subject. My own opinion is it may be a combination of things. First, the chemicals we use today for maintenance are different and more powerful like the chlorine tablets, salt systems, and gas chlorine (which may not be in use now). Second, some have said the aggregates/sands have changed. The procuring of aggregates with the transportation costs and the sheer amount needed to satisfy the worlds current building rate have led manufacturers to seek sands/stones in locations closer to where they are used. The aggregates test out at the same hardness so I do not put much credibility in that reason. Third, I think the client expectations for their swimming pools have changed. They are no longer thought of as a swimming hole for the kids. They have become focal points and artistic perceptions of very skilled architects and homeowners. Whatever the reason we do have an answer.
Standard white plaster will do what it is supposed to. It will be watertight and serve its function for that 10 to 15 years depending on maintenance. But pebble finishes, properly installed and maintained, will last 20 to 30 years or more. It is the most durable finish our industry has to offer. For those that do not like the textured finish there are plaster additives, quartz, quartz/ marble blends, and polished finishes that deliver a smooth finish with a more durable surface then regular plaster. They are considered high performance finishes. Just remember any time a pigment is added there will be modeling and marbling that will occur. This is considered cosmetic not structural.
Over the years replasterers have used axes, hammers, and all other imaginable tools to remove existing swimming pool plaster prior to replastering. I'm sure that is NOT good for the pool! What approach do you recommend to remove the plaster that gives good results and limits trauma to the swimming pool?
There are a few ways to prep the existing surface. You can sandblast then use a manufactured bonding agent to bond the old surface to the new one. Some water blast with a high pressure washer then bondcoat. Some use the small chipping guns and jackhammers to remove the old plaster to the original shell. Some use a water jetting machine that strips it down using 40,000 psi water pressure. All are considered fine as long as any loose, peeling, hollow areas are removed and there is a course, rough surface that will provide mechanical/and or chemical bond.