Plaster is the most common type of pool finish

There is more than one reason why an interior finish could be cracking. First, you need to diagnose which type of cracking has occurred. Closed shrinkage cracks, open shrinkage cracks, and structural movement cracks are each unique, in terms of the cause and remedy. Each type of cracking is defined in the NPC 9th Edition Technical Manual. (Some sections that deal with cracking are given below)

New installations and drained pools: A common appearance of cracking can occur when a cementitious interior finish is wetted prior to being filled. Microscopic shrinkage cracks (micro cracks are present in all hardened plaster, precast, shotcrete, and concrete products) absorb water faster than the overall surface. This results in these micro-cracks becoming visible. The cracks (having the appearance of a road map) appear to be 'highlighted' by the water absorbing into them. Once the water evaporates, or once the pool is filled with water, they are no longer visible. In fact, these micro-cracks actually seal themselves shut with cement hydration material after the pool is full. These cracks are known as 'check cracks' (or closed shrinkage cracks). They are common to all cement and concrete products, and are generally nothing to worry about. However, any cracks that remain open 24-hours after the pool has been filled should be reported to the Pool Builder or Plastering Company.

The following types of cracking are generally in need of some type of repair.

NPC Technical Manual
Cracks in cementitious surface coatings should be classified as to their type, prior to determining the optimum method of repair. Cracks can be classified into one of these three types:

Closed Shrinkage Cracks that develop during application or within the first twenty-four hours after final set.

Open shrinkage cracks that develop during application or within the first twenty-four hours after final set.

Structural movement cracks, tensile stress cracks, and all other cracks, that develop throughout the life of the coating, subsequent to the first twenty-four hours after application.

One of the most common issues in pool plaster is etching deterioration, or 'spot etching.' This can result from aggressive water chemistry: low carbonate alkalinity and elevated cyanuric acid are the main contributors to spot etching. You can calculate how to keep your water chemistry in proper balance using the Langelier Saturation Index (LSI), as seen on the NPC Start-Up Procedures Card, which is offered here. Section 7.6.1.1 of the NPC 8^th Edition Technical Manual explains in detail what an “aggressive chemical attack” is and what it means for your plaster's health.

Aggressive Chemical Attack

Cementitious surface coatings are susceptible to chemically aggressive swimming pool water or to any chemical that is capable of deteriorating the cementitious materials of a surface coating. Swimming pool water that is not in Ideal Range of acceptable tolerance (or “balanced”) as in accordance with the ANSI/APSP Standards is considered to be detrimental to cementitious surface coatings. Depending on the direction of the imbalance a coating can either be stained or etched. Often, both staining and etching are exhibited on the surface of a coating as the pool water fluctuates from one extreme to the other. Visible signs of salt crystallization, surface efflorescence, or cracks that are emitting efflorescence or salt deposits are common to a coating in contact with a positive saturation index (+ LSI), or “scaling” condition. If the water is capable of leaching cement compounds from within the surface coating, then that water is in a negative saturation index (LSI), or "aggressive" condition.

If care is not taken to ensure that the water of a swimming pool is kept in an Ideal Range that is considered by ANSI/APSP to be balanced, and further that a sufficient amount of carbonate alkalinity buffer is constantly present, then the cementitious surface coating should be considered susceptible to damage from that water and deterioration may result. Water-soluble salts, acids, or ions such as sulfates, chlorides, and carbonates, can be transported into a cementitious surface coating and react with the cementitious compounds. The resulting chemical reaction between the cementitious compounds and these salts, acids, or ions, in the presence of water, can cause deterioration to the coating. 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.

The National Plasterers Council's technical experts have covered this issue in great detail on YouTube, which you can watch by clicking here. The NPC encourages you to watch these videos and take the time to educate yourself in order to better maintain your pool's plaster.

The NPC Technical Manual includes industry guidelines and recommendations that are based on the current-accepted trade practice for swimming pool plastering in the United States. The NPC Technical Manual is recognized and referred to by several organizations, such as ACI, APSP, PCA, ASA, ICC, and ANSI, as well as many regional Health Departments, and Local, State, and Federal Agencies. The document is periodically canvased, reviewed, and revised to update and incorporate the latest information on common trade practice. The Technical Manual includes a comprehensive overview of materials and application for swimming pool plastering, to include:

• Aesthetics and Tolerances
• Materials Guidelines
• Surface Preparations for Pool Substrates
• Common Trade Practices – Mixing and Finishing Techniques
• and General Performance Guidelines

This great resource of expert-driven information can be found on the NPC's website here.

A more detailed listing of the topics covered includes:

Aesthetics and Tolerances: general application, water-tightness, smoothness, texture, levelness, thickness, thickness exceptions, maintainability and service life, and arbitration.

Materials Guidelines: batching and mixing, mix design ratios, field water-to-cement ratio, cementitious materials, sand/aggregate, water, admixtures, calcium chloride, polymeric admixtures, pozzolanic admixtures, and pigments.

Surface Preparations for Pool Substrates: surface conditions for new pool substrates, surface conditions for renovation pool substrates, surface-applied bonding agents, integrally-mixed bonding agents.

Common Trade Practices – Mixing and Finishing Techniques: proper usage of mix water (Temper water) and supplemental mix water (Retemper water), proper usage of lubricating water.

General Performance Guidelines for Exposed-Aggregate Finishes: exposed finish types, exposed-aggregate finish, exposed-quartz finish, polished finish, general characteristics, water-tightness, over-exposed finishes, under-exposed finishes, determining exposure tolerances.

Calcium carbonate formations on the surface of a finish coat are generally the result of the percolation of water that is capable of dissolving or leaching cement compounds or calcium from voids, bond failures and cracks, which is then precipitated onto the surface. These are known throughout the industry by the slang terms “nodules” or “calcium nodules.” The actual mechanism and source of the precipitated calcium formations can be from:

1. a failure to achieve an adequate bond between the interior finish coating and the substrate surface, or
2. a prolonged 'aggressive' pool water that attacks the cement compounds just below the finish surface (the sub-boundary zone). These YouTube videos help to explain the cause of these formations and what can be done to remedy the issue.

Debonding is an “adhesive” bond failure, or the failure of the interior finish coating to bond to the cementitious substrate.

Delamination is a “cohesive” bond failure, or the failure of the interior finish coat to hold together, or to split apart.

Debonding failures generally occur during the original placement of the interior finish coating, from a failure to achieve an adequate bond with the substrate surface

Further information can be found within the NPC Technical Manual (a portion of which is given below):

A coating that has achieved a proper mechanical bond will generally maintain that bond throughout the service life of the coating. A physical bond, or a mechanical bond, is created when the plasterer forces the wet coating material into the open, porous, scratched, etched, or otherwise roughened substrate or undercoat, thereby keying into, or interlocking the two surfaces. The failure of a cementitious surface coating to properly bond with the solid substrate or cementitious surface undercoat is generally due to one of more of the following:

• Surface carbonation of the undercoat or solid substrate increases the surface density, or decreases the porosity of that surface, which can reduce or prevent the ability of a surface coating to achieve proper bond.
• Surface efflorescence or surface laitance on the substrate or undercoat can reduce or prevent the ability of a surface coating to achieve proper bond.
• An overly smooth or overly dense substrate surface or undercoat surface can inhibit a surface coating from keying into, or bonding with, the substrate or undercoat.
• An overly dry substrate or undercoat, or a substrate or undercoat having a high rate of absorption. A rapid moisture loss from the coating at the interface of the coating and the substrate can cause the coating at this interface to stiffen quickly. Rapid drying at this interface, as opposed to a slow stiffening or setting can cause debonding. This scenario leaves the plasterer with little or no time to force the wet coating material into the pores of the substrate before rapid drying occurs.
• A solid substrate or undercoat that is overly wetted, or overly water­ saturated, prior to receiving the surface coating. Water or moisture that is visible on or within a substrate that occupies the open pore spaces, restricts the ability of the coating to key into the substrate, as well as, reduces the absorption capability of the substrate. This can prevent or reduce the proper bond of the surface coating to the substrate.
• A coat that is applied too thinly over the substrate can dry before it sets. Thin coats can have excessive and/or tensile cracking within the coating caused by the normal stresses of shrinkage far exceeding the low tensile strength of the thin coat. The result is a weak cementitious surface that may not maintain bond.
• A surface coat that is applied overly thick. The coating can exhibit abnormally high shrinkage resulting in the structural cracking of the coating and possible debonding.
• Contaminated substrate surfaces can reduce or prevent bond. Examples of contaminants would be dirt, oil, acid, form-release agents, or loose debris.
• A scratch-coat, brown-coat, or other surface undercoat that is not properly scratched, scored, notched, or otherwise properly prepared to receive the surface coating.
• Delamination within the upper nominal 1/8" (3.2mm) of the surface coating can be caused by over­ troweling the finish surface of a coating, or by troweling the finish surface of the coating beyond the time the coating is fully hardened. Failure to immerse the surface coating placement underwater after coating underwater after placement.
• Failure to maintain immersion of the surface coating underwater throughout the service life.
• Failure to maintain constant moisture to the surface coating in the rare event that a swimming pool is drained.

Buckles, Blisters and Spalls

Buckles are bulges of the surface coating due to a separation from the substrate, or from the undercoat (debonding), or from a delamination within the coating that have not yet lifted off or broken away. Buckles are generally caused by a failure of one coat to bond to another coat, or the failure of the surface coating to bond to the substrate. (see Section 7.4.1) Buckles are caused by the same issues as delamination or debonding.

Blisters are small round bumps on the finish of a surface coating. Blisters are separations occurring within the top coat or finish coat that have not yet lifted off or broken away. Generally, blisters are caused by trapped air during the finishing process, over-troweling, or troweling beyond final set.

Spalls are upper-layer delaminations or separations occurring within the top coat or finish coat that have lifted off or broken away. Spalls can be caused by abrasion or hard blows to the plaster surface, aggressive water chemistry, or from the plaster not being submerged in water, and/or being dry for too long.

Blisters and spalls are generally delaminations of the thin upper-finish layer of the surface coating.

Blistering and spalling can be caused from the following:

• Over-troweling of the finish.
• Troweling past final set.
• Failure to immerse the surface coating underwater after placement.
• Failure to maintain immersion of the surface coating underwater throughout the surface life.
• Failure to maintain constant moisture within the surface coating in the rare event that a swimming pool is drained.
• Repetitive impact or abrasion to the surface coating during service life.
• Overly-aggressive swimming pool water chemistry. Over time, aggressive water will attack and deteriorate cementitious products. The upper-finish layer of the surface coating (approximately 1/8" [3.2 mm] in depth) is especially affected. Calcium hydroxide, the weakest hydration product of the cementitious surface coating that can be leached from this layer causing this upper layer to weaken and/or detach from the remainder of the top coat.2,7,9,11,16,17,22,23,24
• Freezing temperatures that occur after final set but prior to submersion.

Remedy

Isolated debonded areas should be removed. The surface that is to be patched should be clean and made free of all loose materials or contaminants. A bonding agent should be used prior to, or in conjunction with, the application of the repair coatings. The new coats should be applied in a similar manner, and in the same number of coats, as the existing cementitious surface. It is considered common practice to remove completely, the portion in need of repair down to the substrate, thereby ensuring that the new coating is properly keyed into the substrate and the remaining coating. The repair coating should be properly cured. The entire coating can be removed and replaced, re-coated or multi-coated, stained, painted, or otherwise treated if the repairs are too numerous or overly noticeable to the point of being unacceptable.

Small blisters and spalls, lifted areas, broken or chipped areas, and minor blemishes can sometimes be repaired underwater. Buckles, blisters, and spalls that have not yet lifted off or broken away can be left alone without fear of damage to the structural integrity of the swimming pool; however, any visible cracks should be filled underwater to prevent water from freely entering into the void space and leaching cementitious compounds or other coating materials.

Note: The NPC's recommendations for ideal water chemistry are similar to those of the APSP. Some high-performance finish coatings may recommend slightly different parameters. While the NPC recommends water chemistry ranges based on trade and industry consensus, it is recommended to verify with the Builder, Plasterer, or Product Manufacturer as to the specific ranges they require. Contractual agreements supersede NPC recommendations.

Water chemistry for your pool varies depending on whether or not the plaster is within the first 28 days of its life. After the 28 Day Start-Up Procedure has been performed, daily water chemistry should be maintained within the 'ideal range.' This range is as follows:

• Free Chlorine = 1 to 3 ppm
• Total Chlorine = 1 to 3 ppm
• Sequestering Agent as per Manufacturer's directions
• pH = 7.2 to 7.6
• Carbonate Alkalinity = 80 to 120 ppm
• Calcium Hardness = 200 to 400 ppm
• Cyanuric Acid = 30 to 50 ppm
• TDS = 300 to 1800 ppm (non-salt pools)
• Salt Level = according to the manufacturer recommendations (salt chlorination ONLY)

Using the LSI Calculator (Langelier Saturation Index) you can determine if your water chemistry is balanced within the spectrum of |Scaling --- Corrosive|. The LSI of your pool's water should be 0.0 to +0.3. You can find the LSI Calculator on the NPC Start-Up Procedures Card here.

In many regions of the country, freezing and thawing (freeze/thaw) damage of a swimming pool surface coating is rare, as the coating remains underwater during its lifetime. However, any portion of the interior finish coating that is not constantly underwater is susceptible to freeze/thaw deterioration and damage.

Cementitious finish coatings are most susceptible to freeze/thaw deterioration when a portion of the coating is partly submersed in water and a portion is partly open to the air. Pool finish coatings are not capable of withstanding the internal expansion forces created under these conditions. In the presence of moisture and intermittent cycles of freezing temperatures, the portion of the surface coating that is within 3” above of the water level, as well as the portion that is within 1” – 2” below the water level, are very susceptible to severe deterioration and damage. The deterioration will initially present itself as a horizontal line or area of discoloration near the water level, and often a heavy calcium salt deposit is present in the same area, as the cement binder is compromised. The deterioration will progress with future freeze/thaw cycles, and as the internal expansion and contraction destroys the cement binder system, causing a weak upper-surface. This is followed by peeling, delaminating, and eventually the complete failure of the coating. Most warranties do not cover freeze/thaw damage.

It is recommended, for the durability and long-term service life of the pool interior finish coating, that it remain underwater. Therefore, winterizing methods that do not include the draining of a portion of the pool's water are preferred. Other methods of winterization, which prefer the protection of the plumbing, equipment, and tile at the expense of the interior finish coating, often result in unsightly damage and a dramatic reduction on the finish coating's lifespan.

At no time should any person or pets be allowed in the pool during the fill. Do not allow any external sources of water to enter the pool to help prevent streaking. It is recommended that you do not swim in the pool until the water is properly balanced, sanitized and the there is no more loose plaster dust from brushing; however, entering the pool once it is filled with water will not harm the finish.

Plaster and all cementitious interior pool finishes are a hand crafted product. In section 3.1 of the National Plasterer Council Manual 8th edition it states - General Tolerance Determinations: "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." As it says some fluctuations and waviness in the pool surfaces are normal. If you cannot observe them in normal daylight viewing conditions it is probably normal.

Yes- surfaces such as quartz, mini pebble, and pebble and polished surfaces are now available throughout the United States. Many of these products also have special modifiers in them such as pozzolans or polymers which enhance the long term durability of these surfaces. You should ask your remodeler about these types of surfaces.

Carbonate alkalinity is also known as corrected or adjusted alkalinity. The three most important water chemistry parameters necessary to have “balanced” water are A) pH, B) Carbonate Alkalinity and C) Calcium Hardness in their correct ranges. Most test kits test total alkalinity, but carbonate alkalinity is calculated by taking approximately one third of your stabilizer or cyanuric acid content and subtracting it from your tested alkalinity. Remember, only carbonate alkalinity can be used to calculate the Saturation Index and determine whether your water is in balance.

You are probably experiencing some type of metal stains. The most common metal stains are copper and iron. Take a piece of #80 wet/dry sand paper or a diamond hand pad, and see if the stains will sand off. The four most likely sources of copper metal are 1) fill water, especially well water or trucked in water. 2) Improperly maintained pool water that becomes corrosive and attacks heat exchangers and other metal components. 3) Certain ionization systems that are not maintained properly and contain copper. 4) Copper based algaecides that are improperly dosed, most often to kill algae. The most common sources for iron include 1) metal pipes 2) fill water, especially well water or trucked in water 3) iron-based fertilizer accidently broadcast into the water, or by entering the water through wind and rain from surrounding landscaping

Based on your description these brown spots may be a) small metal particles from nearby work, such as the installation of wrought iron fencing or other metal work b) fertilizer stains from an iron or ammonium sulfate type granular fertilizer. c) some impurity within the finish. Usually these small spots will sand off with a piece of wet/dry sand paper or a diamond hand pad. If the spots do not sand off, there may be some impurity within the material, which will need to be treated chemically or picked out and patched by the builder or installer.

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.

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.

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.

Brushing the surface of a new pool finish is vital to the proper outcome of a start-up procedure, and just as important in the ongoing weekly maintenance of a finish. When new, the finish is especially susceptible to staining that can occur from "plaster dust", dirt, and debris that is allowed to settle and stick to the new surface. The brushing action will help to maintain both the appearance and smooth texture of the new finish. Most start-up procedures require twice-a-day brushing during the start-up, and eventually tapering off towards the end of the start-up. Older, established finishes also need to be brushed on a regular basis. The surface of any finish will have some microscopic depressions. These are normal with any hand troweled product. These depressions allow for the accumulation of tiny particles of dirt and various types of debris. Eventually this accumulation becomes visible as a discoloration of the finish. At this point, the discoloration may require more than just brushing as a remedy. Exposed aggregate finishes need the same care when it comes to brushing. These finishes tend to hide dirt accumulation better than other types of finishes because of the textured surface. Once-a-week brushing of established finishes is a practice that will help extend the longevity of your finish while maintaining the aesthetics.

Most cracks that appear in pool finishes can be classified in three different categories. Closed shrinkage cracks, open shrinkage cracks, and structural movement cracks. Closed shrinkage cracks, or "normal" shrinkage cracks occur from the normal volume loss that occurs when the finish sets and dries. This loss of water, or volume loss, creates stress in the finish as it sets. This stress is relieved by cracking. This is considered normal as the finish sets. The shrinkage cracks will normally seal themselves shut underwater, as the pool fills. The cracks are filled with new calcium compounds that are generated in the hydration process. Many times, these cracks are not visible until the pool is drained. Closed shrinkage cracks do not affect the performance of the finish and are considered a cosmetic issue. Open shrinkage-related cracks are also formed by the loss of water during the drying and setting of the finish. These cracks do not re-seal themselves. For that reason, these cracks will require remedial work. Structural movement cracks extend completely through the finish. These cracks are usually related to structural movement occurring under the pool finish. Structural movement cracks require remedial work to stop the movement that is causing the cracks.

There is no one single answer to this question, as there are many factors that need careful consideration prior to draining the pool. Pool finishes are designed to stay wet, and simply exposing a finish to the air will start to dry out a finish. Regardless of the type of finish in your pool, extended exposure to the elements can dry out and cause possible damage to the finish. Draining a pool or spa during hot, dry, or windy conditions should be given careful consideration, as these factors will accelerate the drying out of the finish. Adverse weather conditions are the number one factor when considering when and how long a pool can remain empty. When extreme weather conditions are expected during the time of draining, re-scheduling is always the best option, especially when an extended period of downtime is anticipated. Newer finishes that are still actively hydrating are more susceptible to drain-related issues, as the hydration process is interrupted by the lack of water. Areas where a high water table is present will also present a unique set of problems when draining a pool. Unless the elevated hydrostatic pressure is relieved, the possibility of the pool "popping" out of the ground is real. Verify that a hydrostatic valve is in place to ensure proper management of this pressure prior to draining of the pool.

With so many different variables affecting each pool and spa, it is not possible to develop one timeframe that covers all pools and spas. When draining a pool or spa for any reason, best practices should start with careful planning, scheduling, and proper staffing of crews to ensure timely completion of all phases of work. All of this is followed by a quick fill time. Remember, these finishes are not designed to be dry, especially for extended periods of time. Everything that you can do to minimize exposure of the finish to the elements will be beneficial to your project, your customer, and your company.

The swimming pool industry has a wide variety of chlorine types available for sanitation and oxidation purposes. All of these chlorines are effective and each of them has specific characteristics that should be thoroughly understood prior to usage. Certain types of chlorine will raise the pH and calcium hardness, while others will lower the pH and alkalinity. All types of chlorine require care in their transportation, storage, and usage. Liquid chlorine, calcium hypochlorite, Trichlor tablets, and granular Dichlor are some of the different types of chlorine on the market. Saltwater chlorine generators are also utilized as a method of sanitation. To determine which chlorine is right for you, talk with an experienced pool professional about the specific needs and conditions of your pool to determine which chlorine type will work best for your pool.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

Example:
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.

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.

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.

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.