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Concrete pools are the oldest form of building pools. The process starts with digging a hole in the ground and lining the hole with rebar. The main drains, skimmers, return lines, pool lights etc., are set into place. After that, the pool is shot with gunite (or shotcrete), which is concrete that is shot out of a gun or large spray nozzle, and troweled to the finished shape. The tile and coping stones are set in place. As the final step in the pool construction process, the pool interior is sprayed with a wet plaster mix, and troweled smooth. Once the plasterers apply the finishing touches, they start filling the pool with water immediately, as plaster cures under water.
Once the pool is full, the system is started up and balanced with chemicals. This is the time that takes the most work, usually a lot of brushing and backwashing due to dusting from the new plaster. pH will rise the first season with new plaster, so get a large bucket of pH Decreaser, to keep the pH in the 7.6 range, and a bucket of Alkalinity Increaser, which will drop with the frequent pH Down adjustments.
Also called whitecoat or marcite, pool plaster is an age old process of finishing many structures. Used underwater, it provides the watertight seal that the more porous gunite or shotcrete beneath it cannot. Plaster finishes provide twenty years of service under ideal conditions, however, ours is rarely an ideal world. The plaster surface is meant to degrade slowly, eventually requiring a fresh coat, or at least some pool plaster repair.
It’s been a long time since they could say “You can plaster your pool in any color you want, as long as that color is white”. Pool plaster is traditionally a mix of white Portland cement and marble dust, but there are dozens of additives for strength, ease of application and color. Plasterers can add color additives to produce any shade of plaster, or use quartz, glass or ceramic aggregate to add flecks of specific hues. Pebble surfaces are also popular, using pea gravel sized, or slightly larger pebbles, pressed into the plaster surface.
Known as mottling, and distinct from surface stains and deposits, mottling may appear as grayish hued areas. Plaster is not white like milk, it’s white like clouds. Being a natural product, mottling is inherent in any plaster job and should not be considered a defect. There has been much research on the subject in recent years; however no consensus has been reached on the causes and cure of mottling.
Different from mottling, stains are usually localized and distinct in color from the plaster. Most stains that are not from organic sources are caused by heavy metals and minerals coming out of solution and depositing themselves. They may also remain suspended in water, providing dramatic new color schemes.
If any of this will apply to you, your pool should be using a sequestering agent such as Metal Free or our Stain Away. These chemicals are added weekly, to keep metals and minerals in solution, and prevent staining of underwater surfaces. Most stains left by precipitated metals can be removed with Stain Free or our EZ Stain Remover. A light acid wash every few3-5 years years will keep a plaster pool looking nice.
Small crystals can form in the right conditions with high calcium hardness and pH levels. This will create areas of the pool which are extremely rough and scaly. There are several ways to remove these deposits, including acid washing, or using a pumice cleaning stone on the pool surfaces. It’s best avoided to begin with, and is especially common in hard water areas.
Barring problems in the mixing, application and curing processes, the pool owner, or service company controls its condition and life span. Keeping your water chemistry in balance and most importantly, preventing corrosive water environments of low pH and low alkalinity will reduce wear and tear. Avoid acid washing the surface too often, don’t make it an annual custom, or plaster will wear thin.
Brushing your pool is an often-ignored pool task that is excellent for pool plaster surfaces. Regular brushing removes films and deposits before they harden into stains. Brushing kicks up small silty dirt and tiny aggregate that can provide food for algae and bacteria, and it helps keep your plaster surface smooth and soft. Be sure that your pool brush is in good shape, they wear out after a few years of use.
Low pH levels in a pool creates spot etching or corrosion of soft areas in the plaster, areas of delamination, or in areas where the plaster is ‘bent’, such as on steps and in corners. These etched areas become stained easily, making them more visible, and most are too shallow to patch effectively. Pitted, etched plaster provides a safe harbor for dirt and algae to grow; and is rough or uncomfortable for swimmers. The absolute lowest pH level for your pool should be 7.2, used for greater potency during shock treatments, however for normal operation, keep your pH between 7.4-7.6 with pH Increasers.
Alkalinity should be kept between 90- 120 ppm. Lower levels may contribute to corrosion of the plaster, as it seeks to pull carbonates from the plaster. Low Alkalinity also allows your pH to fluctuate rapidly, which can also cause similar surface problems (see above). To raise Total Alkalinity in pools, add Alkalinity Increaser, and to lower TA, use pH Decreaser, aka Dry Acid. Keep Alkalinity from rising above 120 ppm, which can make pH adjustment difficult and then it becomes hard to lower the Alkalinity without pummeling the pH, since the same chemical (dry acid) is used to lower both pH/Alkalinity.
Metals such as iron, copper and even gold are in your water right now. When they rise to high levels, they can be knocked out of solution, and deposit as stains. Likewise, minerals cause scale. These salts are primarily forms of calcium and magnesium which can mix with dirt and other gunk, and deposit on your plaster, pipes and equipment. Keep metals and minerals in solution by using a sequestrant or chelator chemical such as Metal Free or our Stain Away
A level that is above this may find it easy to precipitate out of solution. This is known as a scaling condition. Conversely, water with low levels of hardness will produce an aggressive condition. In aggressive conditions (soft water), the water will take the calcium it wants directly out of your plaster, resulting in plaster breakdown and bond failure in extreme cases. Add Calcium Increaser to your pool if your level is lower than 200 ppm, to keep your pool water from stealing it from your plaster surfaces. When calcium is too high, certain conditions can cause cloudy water, or scale and film to form on surfaces. To lower high calcium hardness levels, above 400 ppm, drain and refill a portion of the pool water; the solution is dilution.
If your plaster has surface irregularities, which may take on a beige hue, you have what's commonly called etching. This etching or pitting can be caused by low pH or alkalinity; an acidic condition. Etching can also be the result of plaster problems, from the many plaster mix, application or curing variables. Plaster etching can also be the result of aggressive or improper acid washing.
You may be seeing the gunite or shotcrete beneath the plaster beginning to show through. You better start budgeting for that re-plaster. Relax, it’s probably a stain, especially if it is around the main drains and you just opened the pool (worms). But, when plaster does wear very thin, you will begin to see the gray or tan colored substrate showing through. This would be a good time to re-plaster, or you can mix-up some of our pool plaster mix, and make a plaster patch, dry or underwater.
Known as crazing or checking, the tiny, barely visible cracks are usually caused by extreme temperature variations, especially during initial curing. These are only shrinkage cracks, and pose no structural hazard or danger of leaking. Light acid washing could remove the crazed layer. Larger cracks should be cut out in a butterfly or dovetail fashion with a 4" or 7" grinder, and filled with a pool plaster repair mix or a Flexible Sealer can be used where further movement is suspected.
Known as bond failure, this will occur as areas where the plaster has popped off. This is a common pool plaster repair, usually seen on re-plaster jobs, where the plaster to plaster bond may never be as strong as the original plaster to concrete bond. This is repaired with a pool plaster repair mix. Plaster normally does not delaminate from the gunite; this bond failure can more easily occur, plaster to plaster.
Chip away any loose material around the edge of the delaminated area. This will sometimes make the patch much bigger than the original pop-off, but you want to get all of the loose plaster replaced, so you don’t have to do it again next year. Chip & chisel to break up and rough up the surface, clean and brush on a bonding additive, like Acryl 60.
For your pool plaster supplies, pour in premixed white Portland cement and marble dust; 2:1. Or use a pool plaster repair kit, like our EZ Patch pool plaster with bonding additive. Use the bonding additive (to mix the plaster with, and wet the area to be patched. Trowel smooth with a round ended trowel. Keep the patch from drying too quickly by doing this repair in the evening and covering with a thin, moist towel or burlap, until the water level begins to cover the patched area.
The delaminated or rough area is chipped outwards until good bond is found. The surface is cleaned with a degreaser and roughened with an acid wash. Mix up the pool plaster mix, and trowel in place by hand. A bonding additive such as Acryl 60 should be used when mixing (included in our plaster mix kits) and wet the area just before patching, so it won’t suck the moisture out of your patch. Keep your patch protected from direct sunlight, and try to fill the pool back up, over the patched area as soon as possible. Patches are best performed in cool and moist weather, avoid very hot dry air if possible.
Pool plaster can also be patched underwater, for small areas, without draining the pool. The delaminated or rough area is chipped outwards until good bond is found. The surface is cleaned with a scrub brush or wire brush to remove any films and oils. Mix up EZ Patch 1-FS (Fast Set) into an amount to cover the area to the depth you want. Mix the plaster mix on the dry side, then roll into a single ball. Wearing a mask, dive underwater and push the plaster mix ball into the area with a trowel, gently smoothing it while firmly pushing it, into the area. Do not over-trowel, but try to complete the patch within 1 minute, or 4 breaths, whichever comes first.
Matching the Color of your Plaster
“Guaranteed not to match…” is what I used to tell customers of plaster patching. Our plaster mix is a bright white finish (at first, it will tone down over time), and older finishes are not usually as white, so some purchasers are surprised to see how visible the patch is, if the rest of the pool is less than bright white. Acid washing the pool before patching can reduce the color difference, but what if it doesn’t, or what if your pool plaster isn’t white?
You can mix small amounts of brown sand into the plaster mix, pool filter sand, or any clean and washed sand works nicely, to tone down the bright white color, and better match a slightly stained plaster coat. I find it best to mix in a small amount, and then press in more sand on top if needed for a darker hue. For colored plaster pools, you can add tempera paint to the plaster mix, powdered or liquid, to obtain light or dark shades of gray, blue, black or tan, to more closely match nearly any pool plaster color.
The pool is drained and acid etched several times. Chipping and cutting around all fittings and under the tile allows the new coat to be feathered up to the edges. A scratch coat is applied first, followed by a finish coat. The pool is filled immediately, as the plaster cures underwater. The surface must then be brushed twice daily, with vacuuming and continuous filtering to remove the plaster dust. Cost for a re-plaster is based on surface square footage. Expect prices around $5,000 for an average residential pool to be re-plastered.
Colored Plaster? Black or gray plaster is popular, and blue and tan pools are gaining in popularity. Any colored plaster will show more mottling than white pools, however. If you plaster in any color other than white, expect to see some uneven hues, as films of calcium deposit themselves on the pool surface (which aren’t visible on white pools so much). Don't expect a flat black color, for example. Using a combination of plaster dye and large colored aggregate can create a less-consistent color, which blends to an even tone.
Before plastering became popular, pool shells were painted every spring. These were low grade paints that barely lasted one season. The annual drain & paint was gladly given up when plaster became popular. The underwater pool paints today offer a 7 year life span for a fraction of the cost of re-plastering. Paint adheres very well to properly prepped plaster, and offers a wide variety of colors and graphic capabilities. Pool painting is a second choice to re-plastering however. It is much cheaper, but it does not last even half as long. And once you start painting, you keep painting, unless you sandblast it off to allow re-plastering.
To paint a pool, the pool is drained and degreased with TSP. It is then acid etched and degreased again. After drying, a primer coat is applied, followed by two coats of the Epoxy pool paint. Again with the drying, for several days, and then the pool is filled. Price will vary according to size and prep factors. Expect $3,000 for a pool painter, additional cost for pool artwork. DIY costs are usually around $1000.
I would discourage this. Plastering is nothing short of an art and science. Experienced plasterers know how to get the mix right, with numerous variables that can affect the finished product. They also work in a team of 4 - 6 workers, to get it up before it sets (and cracks), and have custom rigs and equipment to do the best possible job. A small plaster patch sure, but re-plastering the entire pool? I would leave that to plasterers. If you drain and prep the pool to their specifications however, you could earn a discount on the job price perhaps.
Pool Plaster Prep, or preparation of the surfaces for a new coat of plaster, aka whitecoat, involves draining and acid etching the surface with an aggressive acid wash. Loose or hollow areas should be chipped up, and any cracks opened up and cleaned. Handheld pneumatic or electric hammers are used to chip away the plaster underneath the perimeter tile line. The pool returns, pool lights, main drains, trim tile, and other fittings or decorative accents in the plaster must also have the plaster chipped out around them. This allows the plasterer to feather up to the edge of any wall or floor insert. Some plasterers will also add a rough coating of bonding material to the pool after the acid etching, often called a scratch coat. Other plasterers may scarify the pool surface, or use other methods or treatments to improve the plaster bond.
There are basically two methods, chlorine start, or acid start. Avoid swimming during the break-in period, and no pool cleaner use, and only light vacuuming. Buy a new pool brush and a good leaf rake to keep the pool as clean as possible; fresh plaster can stain easily from leaves and debris.
The acid start for new plaster eliminates the brushing and filtering of plaster dust. The idea is to drop the Total Alkalinity level to zero, and then rebuild it with the carbonates that are contained in the plaster dust.
Here's how I do it. As the pool is filling, immediately after plastering, add 1 gallon of muriatic acid directly to the water (don't splash it on the bare plaster) for each 5,000 gallons of fill water. With a watch, time the amount of time it takes to fill up a 1 gallon or 5 gallon bucket with the hose(s) used to fill up the pool. Do the math to determine how many gallons are added every hour. Divide 5,000 by the number of gallons coming out of your hose(s) per hour, and you will know how long it takes to fill 5,000 gallons from the hoses. As each 5000 gal increment of water is added, add another gallon of acid.
When the pool is full, test the Total Alkalinity. It should be zero. Then test the pH, and do a base demand test to determine how much pH increaser to add. Add up to 6 lbs of pH increaser at a time, brushing the pool to distribute fully. Wait a few hours in between 6 lb additions. When all of the pH increaser is added, recheck pH and Total Alkalinity. Add additional pH and alkalinity increasers if needed, until your pH is 7.4 and your Alkalinity is at least 80 ppm. You’ll need a good test kit for this, test strips won’t do the demand testing needed; I recommend the Taylor K2006, K2005 or K2105 test kits.
Leave the pool filter (and heater, and pool cleaner) off until the pH and alkalinity are restored, then start up the filter and run it 24 hrs for several days. Brush frequently to distribute chemicals and circulate the water. Add a stain & scale chemical to help prevent mineral and metal stains on the fresh plaster.
Check Calcium Hardness levels. If below 180 ppm, add Calcium Chloride in dissolved form to bring the levels up. Brush pool after any addition of chemicals.
After pH, Alkalinity and Calcium levels are balanced, add cyanuric acid (stabilizer or conditioner). At a rate of 2lbs per 10000 gallons, and then begin to chlorinate the pool using chlorine tablets; 1-2 tabs per 10000 gallons, in a floater or feeder.
The chlorine start is done differently – and is most often the traditional recommended way to start up a newly plastered pool. But it’s a lot of work in brushing the pool 2-3 times daily for at least a week, while the filter traps the plaster dust.
Start the filter immediately and run it 24 hours per day until the water clears. Backwash or clean the filter as needed, when the pressure gauge rises 5+ psi, or when flow is noticeably diminished.
Balance the chemistry for proper pH, Alkalinity and Calcium Hardness. Add a sequestrant chemical to help control metals and minerals. Circulate for several hours and add a clarifier to the pool to help coagulate the plaster dust.
Begin to chlorinate the water using chlorine sticks or tablets. Add cyanuric acid (stabilizer or conditioner), at a rate of 2lbs per 10000 gallons, and then begin to chlorinate the pool using chlorine tablets; 1-2 tabs per 10000 gallons, in a floater or feeder.
Get a nice, big 24” or 36” brush, and brush the pool 2-3 times per day. Cover the entire interior surfaces, walls, steps, and floor. Brush the plaster dust toward the drains and skimmers. Brushing is key to help smooth the plaster and prevent stains, in addition to getting the plaster dust into the filter, and off the pool surfaces.
Check and adjust the pool pH, Alkalinity and Chlorine levels daily. Add repeat dose of clarifier 5-7 days after the initial dose, following bottle dosage instructions.
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