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IT MAY NOT BE THE MOST GLAMOROUS TOPIC, but your pool needs to be reinforced properly so that it can last for generations, and that takes reinforcing bar – otherwise known as rebar.
Without rebar, your pool wouldn’t survive the first filling. The reason for this is that gunite, which is essentially concrete, is extremely strong under compression, and extremely weak under tension. As the pool fills, and the water splashes about, the corners and walls come under strong tension as they try to hold the water inside. Sure, the earth outside keeps the water in, but it wouldn’t be enough to stop the gunite from cracking, resulting in, at the very least, a chronically leaky pool.
Enter rebar. Reinforcing bar is nothing more than steel bar built with ribs so that it grips the surface, namely concrete, and resists pulling out of the mixture. Since rebar has nearly the same expansion coefficient as concrete, they expand and contract with each other meaning that your pool will have one really great quality – no cracks, and therefore, no leaks.
Reinforcement is necessary with concrete, especially pools, namely because of the extreme loads imposed by housing tons of water, especially in areas with seismic concerns. The gunite in the pool is subject to not only pressure from the water inside the pool, but also pressure from the earth squeezing the pool, not to mention any seismic events. Building with rebar is a simple process, and happens right after the pool excavation.
Once the pool is excavated and the ground is leveled, the rebar is laid down in a grid pattern on the bottom and sides of the pool. The object here is to create a metal basket that is like the skeleton of the pool. Care must be taken to bind each piece of rebar to the next adjoining piece, usually with baling wire. The rebar is also woven and set in a pre-determined pattern dictated by the engineer, and the finished result is a mechanically strong basket that forms the basis for applying the gunite.
The gunite itself is sprayed over top the rebar, and during construction, the rebar gives the gunite the bite it needs to initially stick to something, since it is essentially a dense liquid at this point. Much like paper mache is a liquid that is draped over a form of some sort, so is gunite draped over a framework of rebar.
When the gunite cures, the remaining structure is an unbelievably strong composite unibody that can withstand tremendous loads, far more than anything the pool can deliver. The plaster can then be comfortably applied knowing that the swimming pool will never leak due to cracked gunite. Additionally, rebar can be bent and formed into a multitude of shapes, meaning that your pool can be anything you want it to be, and always super strong. Rebar is inexpensive and plentiful and can be worked by just about anyone, although the placement of the bars and the spacing should be dictated by a qualified engineer.
Placing of the rebar is critical, of course, and should be placed by an experienced crew. Foam or concrete blocks will be used to keep the rebar cage above the dirt on the bottom so the shotcrete or gunite can fill the void, and there must be a minimum distance maintained from the rebar to the water, because concrete is porous and water could leach into the rebar, causing the rebar to corrode, become ineffective, and burst or crack the concrete.
When your pool is complete and you enjoy the fruits of your labor the very first time, taking a long deserved splash off the diving board, you’ll be glad you decided to reinforce your pool with rebar.