Consult with a local engineering firm that is qualified to develop a coring plan, obtain cores, and perform testing in accordance with ASTM C42/C42M or ASTM C1604/C1604M. Please refer to ASTM C42/C42M for further guidance.
How soon after shooting a pool shell can formwork be removed? How soon can tiling begin?
Vertical formwork can generally be removed the day following the shotcrete installation. If the formwork is supporting a load like a soffit form, the form should not be removed until the shotcrete has attained full strength such that it can support the weight of the member.
Your question regarding the installation of the tile should be directed to a professional who installs tile.
We will be tiling a pool. The pool’s shotcrete walls and floor were placed approximately 10 days ago. What is the earliest we can begin gauging the pool walls and floors?
It is generally good practice to let the shotcrete cure for the full 28 days before attempting to apply coatings or overlays. We would recommend you get a recommendation on the cure time from the manufacturer of the gauging product before doing the work.
I am a pool builder who favors dry-mix shotcrete. I have a project requiring: a) cast-in-place concrete retaining walls, where there will be exposed downhill faces (that are not necessarily meant to be seen). Should my shotcrete contractor be able to finish the exposed face in some sort of reasonable finished appearance? and b) placing a pool house foundation (about 4 ft [1.2 m] high). Would I be able to shoot these? I am thinking not because there is no place for the rebound to go.
a) Shotcrete can be finished in a wide variety of ways. It can be left with anywhere from a very rough to a very smooth finish and a huge variety of other finishes. We suggest you visit ASA’s Web site, click on the tab for Shotcrete magazine, and search the previous articles for finishes and swimming pools. You will find a lot of photos of great-looking walls. Not all shotcrete contractors are proficient in providing these attractive finishes. You need to discuss this with your current shotcrete contractor and/or interview other shotcrete contractors to make sure the chosen contractor can provide what you are looking for. We also suggest you look at work these contractors have previously completed. You can also locate contractors online at ASA’s Buyers Guide, www.Shotcrete.org\BuyersGuide.
b) If the pool house foundation is a footing trenched into the ground 4 ft (1.2 m) deep, dry-mix shotcrete would not be a good solution. If the foundation is 4 ft (1.2 m) above grade, then it could be done with shotcrete against a one-sided form. This would be considered structural shotcrete and not all shotcrete contractors are qualified to place shotcrete for structural walls. Again, we suggest you ensure the chosen contractor is qualified to do the work.
I am reconfiguring the interior of a spa and am wondering if drains and jets can be relocated without compromising the overall structure and getting cold cracks. Can the entire interior be re-shot to maintain the monolithic form and guarantee against failure? Is there an independent professional who could conduct an on-site inspection and recommend a next step?
We are not able to advise you on the structural integrity of a remodel of a spa or any other structure and would suggest you consult with a local engineer who is familiar with pools and spas. Shotcrete is often used to overlay or patch structures and the success of such overlays and patches is highly dependent upon the quality of the surface preparation prior to the application of the shotcrete. With respect to referrals of independent professionals, we would suggest that you use the directory of Corporate Members in the ASA Buyers Guide.
We are having a swimming pool constructed. The pool consultant is concerned about cold joints during construction if walls and the floor are shotcreted on different days. The shotcrete subcontractor states that there is no problem as the next layer of shotcrete will knit itself to the previous placement and form a solid bond. Is the shotcrete subcontractor correct?
Yes, if care is taken to prepare the receiving surface properly. The receiving shotcrete edge must be sound (no loose or unconsolidated material), clean (no traces of laitance or gloss), rough, and dampened to a saturated surface-dry condition. If these steps are followed, there should be no concern about the soundness of the joint.
Can brackish or salt water be used to make shotcrete for a pool and will it have any negative effect on the quality of a shotcrete pool?
As a general rule of thumb, brackish or salt water should not be used as shotcrete mixing water. High chloride ion contents can cause rapid setting of the shotcrete (which can make finishing difficult) and longer-term reinforcing steel corrosion-induced cracking, delamination, and spalling. Other components of brackish water can also be damaging to the fresh and hardened shotcrete. For a detailed statement on what constitutes acceptable contents of various dissolved chemicals for concrete/shotcrete mixing water, refer to the Portland Cement Association publication Design and Control of Concrete Mixtures, Chapter 4, “Mixing Water for Concrete.” One could also consult ASTM C1602/C1602M for limits on the composition of nonpotable water for use in the production of shotcrete.
We have a large pond (12,000 ft2 [1115 m2]) 12 ft (4 m) deep with 2-to-1 sloped sides. It currently has an old PVC liner that is ripped and cannot be repaired. We have no shotcrete experience and wonder if shotcrete would be a better option than installing a new PVC liner?
Shotcrete is used extensively for zooscapes, water parks, museum exhibits, swimming pools, and spas. A shotcrete water feature, although more expensive than PVC liner, would provide a long-term, more aesthetically pleasing alternative to a new PVC pond liner. Shotcrete is very versatile and can be shaped to replicate natural rock ledges or boulders. A properly designed and built water feature would provide a low-maintenance, durable solution.
We are having a swimming pool built with shotcrete. Our question is, what is the required curing time for shotcrete prior to exposure to heavy rain? We are trying to plan the shotcrete installation when the weather looks most favorable.
Shotcrete needs to be protected from rain until it obtains its final set, usually 4 or 5 hours. Following final set, it should be wet cured for at least 4 days, preferably 7 days if possible. The exposure to rain would prove beneficial as the rain would assure the presence of moisture for continued curing.
The Park District Department of our city is in the process of designing a new swimming pool. One of the prospective bidders made a presentation in which they said they would use shotcrete instead of conventional cast in place concrete. Their design is to use 6 in.-thick walls instead of the 12 in.-thick walls as proposed for the cast in place design. They claim that 6 in. of shotcrete is as strong as 12 in. of formed concrete. Is this a true statement?
If this statement was true, there would be a lot more shotcrete projects! The truth is that shotcrete is a method of concrete placement, not a special material. The materials, mix designs, and mix proportions may vary between the shotcrete method and the conventional concrete form and pour method, but the thickness and reinforcing of the structure will be very similar.
There is a subtle difference between the two methods that might affect thickness requirements. Shotcrete is generally placed directly onto the undisturbed soil, joining with the soil to provide the shell for the pool. To use the form and pour method, over-excavation would be required to accommodate two-sided forming. The walls would then have to withstand the forces of backfilling. This may result in a thicker wall requirement. The final decision regarding wall thickness, however, should be made by a structural engineer.
Shotcrete is widely used for swimming pool construction. In some areas it is virtually the only method used. Successful shotcrete swimming pool construction is a result of having an appropriate design, selecting a qualified contractor with certified nozzlemen, selecting appropriate materials and shotcrete mixture design, and following industry recommendations for placing, finishing, and curing.