Mastering Fibreglass Pool Installations

by jason_cramp | June 17, 2015 8:30 am

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By Ted Baudendistel and Dave Throckmorton

Fibreglass inground pools are becoming a popular choice for homeowners and pool builders in Canada. One particular advantage is their one-piece construction eliminates a lot of the time-consuming labour that is required to install other types of inground pools. In essence, a pre-constructed composite shell is placed into a prepared hole in the ground, as opposed to assembling a truck full of components or pouring and curing large amounts of concrete.

This does not mean every fibreglass pool installation is cut and dried, however. In fact, every installation is different and there is potential for any one of a number of problems to arise—from the type of terrain, to the site grade, and especially water and soil conditions. To master these challenges, it is important to be mindful of several core principles and take steps to always ensure they are addressed. This article will discuss several of the most common challenges and provide guidelines to overcome them successfully. It should also be emphasized beforehand that the manufacturer’s supplied dig sheet should always be followed. They know their products best, and following their instructions is important to ensuring a successful job.

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Watch the water table

Every pool installed in an excavated hole faces the same challenge: the changing nature of the water table, which comprises the upper level of underground soil or rocks that are saturated with water. A hole dug today may appear perfectly dry, but a few months from now, or next season, the water table may rise due to changes in precipitation, variations in climate, or the amount of water being drawn from wells in the area. Therefore, do not assume a high altitude will exempt the job site from water problems—groundwater complications can even be experienced on top of mountains.

The water table needs to be taken into account as excess hydrostatic pressure, from outside the pool wall, can cause structural damage. One of the key principles to fibreglass pool installation is to consistently maintain equal pressure inside and outside the pool—no matter the water table level.

Dewater the excavation

When excavating for fibreglass pools, look to dig  a fairly tight hole. This will not present a problem during construction because not much work needs to be performed between the one-piece fibreglass shell and the sides of the hole, so extra room is not required. Therefore, the excavation should be prepared very close to the actual pool size, taking into account the size of the coping being installed (typically 152 to 305 mm [6 to 12 in.].

Should the excavation be too big, additional labour and materials will be required. That said, an over-dig of 76 to 100 mm (3 to 4 in.) for the floor and 152 mm (6 in.) for the walls is recommended. Should the over-dig exceed these measurements, never use excavated material to backfill, as it will settle. Should backfill be required, follow the manufacturer’s guidelines with regards to the proper materials.

If water is found during the excavation process, the hole will need to be dewatered. In this case, there are a number of techniques to consider. One best practice is to install multiple well points (i.e. pipes in the ground) that will draw water out from several locations. A gravity-fed daylight drain is also an acceptable choice.

For fibreglass pools, the installation of a permanent sump pipe is strongly recommended (see Figure 1). This provides a means of checking for groundwater around the pool and evacuating it in the event the water table rises at some point in the future. Further, should the pool need any work later on which requires the water level to be lowered, the sump pipe can be used to minimize hydrostatic pressure outside the pool. This can be considered the cheapest form of insurance that the installation will not face any problems later on.

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To install the sump pipe, dig a 0.45- x 2.4- x 0.45-m (1.5- x 8- x 1.5-ft) trench across the deep end of the excavation. Place 152 mm (6 in.) of clean 13-mm (0.5-in.) gravel in the bottom of the trench. Then, place a section of 76-mm (3-in.) perforated polyvinyl chloride (PVC) pipe on the gravel base and connect it to a 203-mm (8-in.) vertical stand of PVC pipe running to the surface of the excavation.

Cover the new sump pipe with landscaping fabric (a.k.a. geotextile). This textile is manufactured from chemical-resistant synthetic fibres, which do not biodegrade. The fabric allows water to flow through while preventing the soil and backfill materials from entering and clogging the PVC pipe. After making the connection to the vertical stand, cover the perforated pipe, to the bottom of the excavation, with an additional 13 to 25 mm (0.5 to 1 in.) of clean gravel. Finally, trim the 203-mm (8-in.) PVC riser and install a skimmer ring and lid for esthetics and safety.

Base preparation for challenging soil conditions

In addition to the presence of water, the soil condition can present potential challenges. In Canada, the soil quality can vary—from being sandy in lake areas to spongy, loamy conditions often referred to as ‘gumbo.’ Proper soil compaction is critical to have a stable and well-fitting fibreglass pool installation. It should be kept in mind how heavy a pool filled with water is. For instance, a typical 4.8- x 12-m (16- x 40-ft) pool will contain 56,781 L (15,000 gal) of water, which is equal to 54,431 kg (120,000 lbs). This does not take into account the fibreglass shell which weighs approximately 1134 kg (2500 lbs). Considering this, thorough preparation of the base of the excavation will prevent the pool from settling and the creation of stress cracks.

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If the soil condition is predominantly compact sand, base preparation is fairly straightforward. The goal is proper compaction free of undulations (i.e. an uneven base). First, install screed rails using stakes. Adjust the screed rails to the proper height using a transit. Then, spread a layer of recommended compaction material evenly over the bottom of the excavation. Compact the material and screed the floor flat, filling any low spots during this process. Repeat several times as necessary. On projects where sand or engineered fill is used, the completed area will resemble a slab of finished concrete.

Additional work will be required when dealing with muddy, clay-laden soil. In this case, the hole should be excavated deeper and the base firmed up using 13- to 19-mm (0.5- to 0.75-in.) stone (typically limestone) to create a solid foundation. On installations that have breached the water table, and the soil is extremely muddy and unstable, the hole should be excavated an additional 152 to 305 mm (6 to 12 in.). Then, larger stones (i.e. road base) should be used to build the base before covering it with smaller 13-mm (0.5-in.) rocks or gravel. Geotextile fabric should be placed on top of this base to serve as a filter. Finally, place a layer of backfill on top of the fabric which will allow water, but not the fill, to filter through.

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The same technique should be used if there are any voids in the excavated base; for example, if a tree stump had to be removed or solid granite had to be blasted out. Fill the void with road base, then smaller gravel, then fabric, and build the base on top.

In some cases, where soil conditions are severe (e.g. comprising a soupy tar mix), the only answer is to pour a cement base. In these instances, a foundation must be created similar to what is used to build slab houses, using 254 mm (10 in.) of cement with 25-mm (1-in.) rebar.

Extreme freeze/thaw conditions

In Canada, climate is always an issue for pool builders. During the winter, multiple freeze-thaw cycles have the potential to cause damage to any type of inground pool as water expands when it turns to ice. That said, fibreglass pools are no more susceptible to freeze-thaw damage than any other type of pool. One particular advantage they have in this regard is the flexural strength of the fibreglass shell, which allows it to bend without breaking.

By far the most important step to help maintain equal pressure inside and outside of the pool during freeze-thaw cycles is to never drain the pool during the off-season (or ever). This cannot be over-emphasized and should be communicated to the homeowner. Even in extreme conditions, a full pool will ensure hydrostatic pressure remains equalized.

By following these recommendations and installing a sump pipe or daylight drain, it will help keep melting snow and ice away from the pool. Another important factor to an incident-free winter is the proper construction of a standard cantilevered concrete deck. A typical 0.9-m (3-ft) (minimum) deck will be designed to slope 6 mm (0.25 in.) per 305 mm (12 in.) away from the pool. This angle will allow melting snow and ice to naturally flow away from the sides of the pool. Needless to say, the manufacturer’s instructions pertaining to deck construction should always be followed.

Fibreglass pool installation tips

• Always build in a way to evacuate groundwater from outside the pool, in the event future work on the pool is required. • Always ensure proper compaction of the base around the radius of the pool. • Always follow the manufacturer’s dig sheet and installation instructions—do not take shortcuts. • Always contact the manufacturer should any situation occur where construction procedures are unknown. • Most importantly, always be sure to instruct the homeowner to never drain their pool.

In addition to keeping the pool filled, there are other steps for proper winterization that should be communicated to the homeowner. These include:

• Never drain the pool below the skimmer opening;
• Never let the pool overflow;
• Remove pool water from all equipment and plumbing lines that are above the frost line;
• Do not remove water from a pool cover without simultaneously adding the same amount of water to the pool; and
• Never allow exterior water to overflow into the pool.

Popping out

One concern heard from time to time about fibreglass pools is they can ‘pop out’ of the ground. In response to this, like everything else on earth, fibreglass pools follow the laws of physics. Therefore, yes, fibreglass pools can float. If the pool is not filled and there is more water pressure outside than inside the vessel, it will act like a boat. (After all, a fibreglass pool is essentially an inside-out boat. They are designed to hold water in, while boats hold water out.) In fact, a steel, polymer, or concrete pool will float, too if there is more water around it than inside it.

That said, should the builder and homeowner follow the guidelines described in this article, the chance of this happening is unlikely. Both authors have more than 40 years of experience in the manufacture and installation of fibreglass pools. During this period, both authors have never seen or heard of any documented cases where a fibreglass pool spontaneously ‘popped’ out of the ground that was not the result of homeowner error or negligence.

Common errors that lead to problems

1. The homeowner takes the cover off his/her pool in the spring and sees dirty, algae-filled water. As a result, he/she makes the disastrous decision to drain the pool in attempt to clean it. By the time he/she realizes outside groundwater exists, it is too late as hydrostatic pressure has created problems.
2. A more seemingly benign type of neglect is ignoring evaporation. Homeowners should be educated that as water evaporates from the pool they must continually add water to maintain the proper level and to ensure pressure on the pool shell’s side walls remains constant. Doing so will also help prevent hydrostatic pressure problems that can be caused by high groundwater conditions.

Case in point

In terms of hydrostatic pressure and proper pool installation, both authors witnessed a case in which a homeowner with a fibreglass pool experienced flooding throughout their entire backyard. In fact, the water level spilled over the entire pool and onto the deck and the pool did not budge. Why? Because the ground was completely saturated and there was no hydrostatic pressure due to differences in water level.

As the flood waters receded, the pool remained full and the homeowner removed groundwater from around the pool with the builder-installed sump system. Further, because the earth around the pool shell was not disturbed, the pool stayed in place. The only maintenance that was required was several back-to-back routine cleanings to remove the flood debris.

As mentioned previously, every installation is different and no one can control future conditions at the installation site. However, following these best practices can go a long way to ensuring a successful installation, while also preventing problems down the road.

[6]Ted Baudendistel is the general manager of Trilogy Pools, Latham Pool Products’ fibreglass division, and has more than 15 years’ experience in the pool business. He can be reached via e-mail ted@trilogypools.com[7].

 

 

 

[8]Dave Throckmorton is the business development manager for the Latham Pool Products’ fibreglass division. He has more than 25 years’ experience in the pool business. He can be reached via e-mail at dthrockmorton@vikingpools.net[9].

Source URL: https://www.poolspamarketing.com/trade/mastering-fibreglass-pool-installations/

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