I have started construction of a concrete accessory to my pool. The pool is surrounded by a paver deck but I had a concrete slab pad poured for future construction of a water fall. Now is the time. I have worked with concrete on a few projects (slabs, steps, etc.) but have never erected a vertical structure.
The pad is eye-shaped and approx. 17' x 9' x 4" (5.25m x 2.75m x 10cm) thick and was reinforced with 3/8 (9mm) rebar. It sits on top of about 6" (15cm) of compacted limestone and has not moved or subsided in the two years since it was poured. In any event, though the pool edge part of my design will involve some construction on top of the natural rock pool coping, I intend to divide the part on top of the coping from the part on the pad and seal the thin gap. This is to prevent any pad subsidence from pulling/cracking the coping portion.
I am using an old, sturdy fiberglass, octagonal-shaped hot tub as the base. The steps that used to go down into the tub will now be the steps that go up to the top. The top will be a seating area inside a shallow grotto large enough for two adults. from th epool edge and around the left side of the steps/grotto, I intend to fabricate setps that curve up and around the back of the grotto top and lead to a slide that will curve around and eject into the pool on the right. Between the lower half of the slide and the grotto, in the back corner, I want to add a seat for two with a shallow basin in front. The basin will hold about 4" (10cm) of water and be just large enough for a couple of adults to lay down in. The back wall will also be eye-shaped with its highest point behind the landing for the slide. At that point, the wall will be about 8' (2.5m) high.
I will route the water and install valves so that I can control the flow of water a. down the slide, b. forming the water curtain in front of the grotto, c. down in to the basin, and d. down the steps. These valves will be accessible from the back an inside a smallish storage area beneath the slide, slide landing and steps and under the hot tub base. I designed the storage area for storage of pool chemicals and maintenance products and to reduce the total weight of the structure.
I mocked up the design with pvc piping and have determined how I'll tie it all together with rebar and concrete to support the loads (the rear wall, the steps, the slide, and the grotto). I plan to pour another 2" (5cm) of high-strength concrete on top of the existing pad and stack another 4" h x 6" w (10cm x 15cm) around the perimeter for a beam and the bottom course of concrete for the wall. I have already strung a double course of 3/8" (9mm) rebar in the beam and a single course grid at about 16" spacing across the pad. The first pour will encapsulated this rebar and secure the submerged lip of the hot tub. The additional pour to finish the beam will involve another double course of rebar tied to vertical rebar posts on 16" (38cm) spacing. Thus, the finished beam will be 6" x 6" (13cm x 13 cm), have 4 courses of rebar, and sit on top of the 4" (10cm) pad. I didn't see the pad poured and want to make sure that the completed project is structurally sound. I figure, if the pad subsides, as long as the structure on top remains sound, I can have it raised via the foam injection method. To prepare for that possibility, I am using short sections of 1/2" pvc pipe tied vertically to the rebar in 6 places, so that only the pad will have to be drilled through to install the foam injection ports.
I will form the walls and load bearing portions using 4" x 16" x 8" (10cm x 39cm x 20cm) semi-hollow concrete block, 6" (15cm) grid wire fencing mesh, and concrete liberally reinforced with rebar. As the structure rises, I have some ideas for reducing weight by sandwiching solid foam inside the concrete and between load bearing areas. The hot tub base will be covered with a rebar-reinforced layer of concrete 1" to 2" (2.5cm to 5cm) thick. I have some 3" I.D. cardboard tubes that I will use to pour rebar-reinforced support columns for the middle and lower height portions of the steps and slide.
The grotto will be formed using rebar-reinforced concrete and wire mesh walls, domed on the interior with a shallow basin on top. The water that forms the grotto waterfall curtain will pool in the basin and flow out of a slit across the front. The front lip will be wide enough to serve as a platform for jumping/diving into the deep end of the pool.
I plan to finish off all of the portions intended to hold water with water resistant concrete. The water that flows down the several routes should flow in the basin and over a lip (the part of the structure on top of the coping) and back into the pool. The water will come from the main return line, shared with 2 or 3 (the 3rd is the Polaris and can be open or closed) and pushed by the 2 h.p. main pump, but may be supplemented by the 3/4 h.p. Polaris pump. Because the structure needs to return all of the water back to the pool, except for the gap I'll seal along the joint with the pool coping, I plan to construct as a single piece without relief joints.
Ideally, I'll end up with a structure that will not seriously crack, that won't leak water outside of the pool, that is strong enough to allow adults to climb up on top of the grotto and jump into the pool, and safe enough to allow adults and children to climb the steps and slide down without too much risk.
I am in Houston, Texas, USA, where summer temps may go a bit above 100 degrees F and winter temps are usually no lower than the upper 20s, and only rarely occasionally dip below the 20s.
I plan to buy a 3 cubic foot powered cement mixer and mix my own portland cement, sand, and gravel aggregate. I'll hand-form the surfaces and plan to go for a smooth natural boulder effect. I will probably paint some of the surfaces and stain others. I may use some decorative tile on the steps, the seat, the basin, and maybe the slide. Regarding the slide, I'm not yet sure how I'll make it slippery and non abrasive.
Just writing this has helped me put my ideas in a more concrete (pun intended). Any advice on any aspect of the structural construction would be greatly appreciated.
Pool waterfall, slide, grotto construction of concrete
Re: Pool waterfall, slide, grotto construction of concrete
