The Basics on Concrete Swimming Pools

So you have finally made the decision into having a pool installed at your home. As you begin to look at the different options that are available, you are unsure of the type of pool that you would want to use. The addition of a pool is a huge investment and the planning behind it should not be taken lightly. So after deciding where you would like to have it installed, the next question is what kind of pool shell will work best. There are three primary types of pools-vinyl liner, concrete, and fiberglass. Depending on the type of pool you have installed, costs of installation and maintenance will vary as well as plenty of pros and cons for each type.
They say that knowledge is power, and that is true for making the right sound decision for the style of pool you own. For some people, concrete or gunite swimming pools seems to be the more popular choice. Regardless of where you are at in planning your pool project, whether you just started looking or if you are revisiting the idea: here is what you need to know about concrete or gunite swimming pools:
  • Components
  • Price
  • Pros and Cons
  • Making it a reality

The Facts Behind Concrete

Most people think that concrete and cement are one and the same. That is not actually true. Concrete is actually a mixture of cement, sand, water and a coarse stone or gravel. The concrete shell of a pool is created by spraying either shotcrete, which is a wet mix, or gunite which is dry. There is no difference in results between the two if used correctly.
Once sprayed on, the concrete will need time to reach maximum potential. The concrete will harden and strengthen in a process known as curing. A pool shell will take up to 28 days to fully cure.
The strength of concrete is measured in PSI. The average strength of concrete will measure between 3500-4000 psi. The amount of cement that is added will determine the strength of the concrete. Adding stone or gravel will make the concrete that much stronger since it has a very high compressive strength as well.
Unfortunately concrete lacks in tensile strength, which means that it lacks strength when it is stretched or pulled. That is why concrete will crack when you try to bend it or stretch it. This is what causes surface cracks or structural cracks on a concrete pool. Pool builders combat this problem by using a web of steel to frame the pool shell. The combination of concrete and steel make for a solid structure that can withstand the forces of water and gravity.

What is the Cost

Depending on where you live a concrete pool can cost anywhere from $70,000-$150,000. The cost can significantly increase with the addition of landscaping and other accessories. Maintenance over the life of the pool will include having to clean it by acid wash every 3-5 years and regularly seasonal cleaning. Replaster or tiling the pool interior is something that also needs to be done every 10-15 years. These jobs will easily add about $20,000 on top of the initial installation costs.

Pros and Cons

One thing is for sure, a concrete pool has significant advantages in regards to its appearance, but maintaining that appearance will take a lot of money, time, and personal effort.

Advantages of Concrete

  • Ability to Customize
  • Tough
  • Appealing

Ability to Customize

Working with concrete gives a builder the opportunity to customize the shape, size and any additional features that you are looking for.

Tough

Just like fibreglass, concrete is durable. Unlike a vinyl liner, there is no fear of any rips or tears to the shell from sharp objects. You can even let your dog take a dip, and have no fear from nails scratching and tearing up the walls. The plaster that is laid on the interior of the pool is not as durable as the concrete itself. The interior will require refinishing every 10 -15 years, which is all part of the maintenance costs.

Appealing

Concrete just looks good. Concrete gives a pool a classic look, and if you stay on top of the cleaning, you can avoid staining and algae that will diminish its appearance.
Disadvantages of Concrete

Disadvantages of Using Concrete

  • Length of time for Completion
  • Rough Texture
  • Maintenance Costs
  • Time and Money
  • The Need to Refinish

Length of Time for Completion

Remember that it takes at least a month for the concrete to cure. Now include the other processes that go into the construction of your pool, you are looking at anywhere from 3-6 months to complete. That is in comparison to just a couple of weeks for a vinyl or fibreglass pool.

Rough Texture

As durable and tough as the interior of a pool may be, it is also rough and capable of scraping your skin, for kids especially. Unfortunately, even refinishing the plaster on a regular basis will not improve the rough texture.

Maintenance Costs

Concrete pools require a lot of maintenance. Follow-up costs and required regular maintenance is much higher than those of a vinyl or fibreglass pool. Due to its porous texture, the interior of a concrete pool is perfect for algae growth. Once on the surface, the alga is extremely difficult to remove. Most builders recommend you brush the surface of your concrete pool at least once a week with a steel brush. Most of this routine maintenance will not cost a lot of money but will take time and your own personal effort. Or you can hire a professional pool cleaner, then you will save on time but will add an expense.

Time and Money

Another issue with concrete pools is maintaining the water chemistry. Water from a concrete pool needs to be tested regularly. This is due to having to add more chemicals to the water to kill and destroy the algae. Another reason is to control the ph levels of the pool water. Since concrete is alkaline-based, this causes the ph of the pool water to increase. Adding acid regularly to the pool water will help keep it in balance.

The Need to Refinish
Since concrete and salt do not mix, the dissolved salt in the water will shorten the lifespan of the interior finish of a concrete pool. The need to hire professionals to refinish and plaster every 8-13 years is an additional expense that comes with owning a concrete pool.

How Concrete Gunite Pools Are Made

1.Excavation
The builders will start by digging up the dirt and either hauling it away or re-use it on the property.
Depending on the size of the pool, this could take several hours to several days.

2. Steel is Added to Shape the Pool
Rebar, which is a cage of steel bars is used and then covered in a concrete shell. By creating this web of strength, the steel helps prevent the structure from failing. Adding the steel to a concrete structure increases its ability to move and flex with its environment.

Timespan 2-4 days

3. Plumbing
The majority of the plumbing needed to navigate the pool water is installed during the steel phase before the concrete shell is laid. However, there is some plumbing that is supported by the steel therefore installed after. A cap and pressure test of the plumbing should be completed at this time before the placement of the concrete. Usually, a steel and plumbing inspection is necessary before concrete is sprayed to create the pool shell interior.
Timespan 1-2 days

4. Concrete Gunite is Shot
Concrete (either shotcrete or gunite) is shot into place using a nozzle and then shaped using Flat and straight edged trowels.
Timespan 1-2 days

5. Cure Time
When the molecules within the cement become more hydrated, the cement will increase in strength. This process is known as curing.  The longer the concrete is able to cure, the stronger it gets.

Timespan: Roughly 28 days for the cement to fully cure

6. Waterproofing
Any rough areas of the shell are smoothed out, and the surface is then cleaned. Waterproofing material is then either sprayed or rolled on the surface of the concrete.
Timespan- 1-3 days

7. Coping and Tiling 
Since concrete is porous, it is necessary to install tile along the top 6 inches of the pool. This is to prevent staining at the waterline.
The stone or concrete border that runs along the perimeter is called coping. Coping is added to provide a smooth conversion from the pool to the patio.
Timespan- 3 days to 2 weeks

Image Source: Leo Marblelite

8. The Patio & Landscaping is completed
The foundation of the patio is prepared by placing and compacting stone. The Natural Stone or Pavers  are then installed.
Timespan- 1-2 weeks

9. Plaster or Marblelite Colour Epoxy Finish
The surface of the pool is applied to the concrete. Plaster, which is a mixture of cement, marble dust, sand, water, and a pigment is typically used. The plaster is pumped through a hose, blasted onto the shell, and troweled to a flat finish.
Timespan 1-2 days

10. After Completion
You will need to check the chemistry of the water on a daily basis. For the first 10 days after the pool is filled, the pool will need to be brushed twice a day. This is to remove any dust from the plaster from the surface. Pool heaters should not be turned on until the plaster dust is removed from the pool. No chlorine should be added to the pool for the first 48 hours.

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