Pool Info: Pool Plaster Information
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. Then the drains, skimmers, return lines, and in-floor cleaning system are set into place. After that, the pool is shot with gunite. Then, the tile and coping stones are set in place. Finally, the pool is shot and troweled with plaster. Once the plaster is finished, the company usually starts 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.
Also called whitecoat or marcite, 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.
Types of Swimming Pool Plaster
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.
Plaster has Shading Variations?
Known as mottling, and distinct from surface stains and deposits, mottling may appear as grayish hued areas. Rarely do I see a plaster job that is white like milk. They're usually 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.
Plaster is Stained?
Different from mottling, stains are usually localized and distinct in color from the plaster. Most stains are caused by heavy metal minerals coming out of solutions and depositing themselves on the nearest structure they find. They may also remain suspended in water, providing dramatic new color schemes. Below is a chart listing common metals found in pools, where they came from, and their identifying colors.
|Calcium||Plaster, grout, mortar, cal-hypo chlorine shock||white crystals or precipitate|
|Cobalt||Fiberglass shells||red, blue, gray or black|
|Copper||Copper algaecides, ionizers, corrosion of copper and brass pipes, fittings and heaters||blue, green & blue/green black, dark red or teal|
|Iron||Well water, corrosion of iron pipe and fittings||dark red, brown, black, gray or green|
|Manganese||Well water||pink, red, black or red|
If any of the above causes apply to you, your pool should be using a sequestering agent which aids your water balance in preventing the metal from dropping out of solution and staining underwater surfaces. Most stains left by precipitated metals can be removed by one form or another. An acid wash every few years will keep a pool looking nice.
Plaster has Crystalline Deposits?
Your pool water has precipitated metallic salts out of solution. 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 sanding of the pool surfaces. It’s best avoided to begin with, and is especially common in hard water areas.
Want to increase the life of your plaster?
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, or at least don’t make it an annual custom.
Maintain your pH levels at between 7.4 - 7.6.
Heavy Metals cause Plaster Stains.
Metallic salts cause scale. These salts are primarily forms of calcium and magnesium which can deposit on your plaster, pipes and equipment. They may arise from the use of calcium based sanitizers or the fill water may have high calcium hardness levels. Keep metals and minerals in solution by using a sequestrant or chelator chemical.
Keep your calcium hardness levels between 200 - 400 ppm.
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.
Pool plaster is Pitted or Etched?
If your plaster has surface irregularities, which may take on a beige hue, you have what's commonly called etching. This etching can be caused by low pH or alkalinity; an acidic condition. It may begin within the plaster, from the original mix on application, or etching may start from the gunite side of the plaster and work itself from the outside in. Plaster etching can also be the result of aggressive or improper acid washing.
Pool plaster has large, Dark Areas?
You may be seeing the gunite or shotcrete beneath the plaster beginning to show through. You better start budgeting for that re-plaster.
Pool plaster has Small Cracks?
Known as crazing or checking, the tiny, barely visible cracks are usually caused by extreme temperature variations, especially during initial curing. These are not actually 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 sealant can be used where further movement is suspected.
Plaster has Delaminated?
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 hole is to begin with. Chip & chisel to break up and rough up the surface, clean and brush on a bonding additive.
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 supplies. Use a bonding additive (like Acryl 60) to mix the plaster with, and prep 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 moist towels or burlap.
The delaminated area is chipped outwards until good bond is found. The surface is roughened and plastered is troweled in place by hand. Cost depends on the size and location of the patch. Pool plaster supplies can be purchased at most pool stores. Plaster mix is a mixture of white Portland cement and marble dust. A bonding additive such as Acryl 60 should be used when mixing, and for wetting the area just before patching.
Re-Plastering or New Whitecoat:
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. A scratch coat is applied first, followed by a finish coat. The pool is filled immediately; 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.
Black or gray plaster is popular, and other colored additives can produce varied color effects. Any colored plaster will show more mottling than white pools, however. If you plaster in any color other than white, expect streaking and uneven hues. Don't expect a flat black color, for example. Using a combination of colorants and large aggregate will produce more consistent color.
What about Pool Painting?
Before plastering became popular, pool shells were painted. These were low grade paints that barely lasted one season. The annual drain & paint was gladly given up when plaster became popular. The underwater epoxies used today offer a 7 year life span for about half 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 class choice to re-plastering. It may be half the cost, but will last only half as long (at best). If you start painting, you keep painting, unless you sandblast it off to allow re-plastering. We tend to discourage our customers from painting a pool. A few dollars saved in the short run will cost more in the long run.
The pool is drained and degreased. It is then acid etched and degreased again. After drying, a primer coat is applied, followed by two coats of the chosen color(s). Again with the drying, and the pool is filled. Price will vary according to size and prep factors. Expect $2,500 for a pool painter, additional cost for pool artwork.
Want to Re-plaster the pool yourself?
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. Small plaster patches? OK, but re-plastering the entire pool? I would leave that to plasterers. If YOU prep the pool for plaster, however, you could possibly negotiate a discount on the job.
How to Prep the Pool for a new Whitecoat?
Preparation 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 etch material, often called a scratch coat. Other plasterers may scarify the pool surface, or use other methods or treatments to improve the plaster bond.
What is the procedure for starting up a freshly plastered pool?
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. Use the pool brush and leaf rake to keep the pool as clean as possible; fresh plaster can stain easily from leaves and debris.
New Plaster Acid Start Procedure
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.
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 daily 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 level (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.
Do not shock the pool for 3-4 weeks.
No pool cleaner for 3-4 weeks.
Maintain chlorine level at 1-2 ppm
Add pH decreaser regularly to maintain pH at 7.4-7.6
New Plaster Chlorine Start Procedure
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 the filter as needed, when the pressure gauge rises 5+ psi, or the flow is noticeably diminishes.
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 level (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.
Brush the pool 2-3 times per day. Cover the entire interior surfaces, walls, steps, floor. Brush the plaster dust toward the drains and skimmers. Most important step helps to 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 (don’t overdose).
Do not shock the pool for 3-4 weeks.
No pool cleaner for 3-4 weeks.
Maintain chlorine level at 1-2 ppm
Add pH decreaser regularly to maintain pH at 7.4-7.6