The ICC (International Code Council) Building Code requires a 7-day wet cure, which is good practice for concrete or shotcrete. The Aquron Technical Data Sheet mentions prewetting the surface prior to application, but we do not see the direction on the timing. You may want to question the product representative regarding how to accomplish the ICC curing requirements and also get the best results from their product.
We are in the process of renovating a commercial pool with a gutter system. The plaster surface has been removed along with some of the concrete. The wall of the gutter on the water side is tiled and is crumbling away. Our plan is to shotcrete the walls and gutter. When we shoot the walls back we will be adding 1 to 2 in. (25 to 51 mm) of shotcrete at a maximum. Is this too thin for shotcrete? Also, the gutter edge will be 2 in. (51 mm) thick and 4 in. (102 mm) in height without any reinforcing bar—will this have much strength?
Shotcrete can be placed as thin as 1 to 2 in. (25 to 51 mm), but will do little more than to provide a new surface to apply the plaster. To do a proper job you need to remove all loose and deteriorated existing shotcrete and should likely add in a layer of reinforcement or use structural fibers (either steel or synthetic) in the shotcrete mixture. The surface preparation should be done to the standards outlined by the International Concrete Repair Institute (ICRI).
We will be shotcreting a pool and the designer has put an expansion joint in the pool going from the top of one wall through the floor to the top of the other wall. It also shows a 9 in. (229 mm) polyvinyl chloride (PVC) waterstop in this joint. I have seen this used with cast-in-place concrete, but not with shotcrete. I was wondering if there are any guidelines on shooting around a PVC waterstop.
This detail is normally only used on very large competition pools on the order of 164 ft (50 m) in length. It takes a lot of skill, technique, and care to properly encapsulate the waterstop and it should only be attempted by a shotcrete contractor with experience in this application. The successful encapsulation of the waterstop is more challenging with the dry-mix process than when using wet-mix shotcrete. The techniques for the proper encapsulation are generally developed by the individual shotcrete contractor and there is no specific “guideline” available for encasing waterstops.
We are designing a 41 x 60 ft (12 x 18 m), 2.5 to 4.5 ft (0.8 to 1.4 m) deep swimming pool. The walls and floor are 8 in. (203 mm) thick with No. 4 (No. 13) bars. We are specifying shotcrete to build the pool. What should be the minimum spacing for the expansion joint?
You need to address this question to a professional engineer who is knowledgeable in the characteristics of shotcrete and concrete. Shotcrete is a method of placing concrete and the same parameters used in concrete design apply to shotcrete placements. Many pools of this size are designed and built without expansion joints, but it is beyond the scope of our association to provide further guidance.
I have a newly constructed in-ground pool in which shotcrete was used. The pool has been holding dirty water since just after the shotcrete cured. Does the shotcrete have to be cleaned and/or treated before an overlay is applied?
To ensure a good bond between the shotcrete shell and the overlay, the surface should be cleaned and allowed to dry before application of the overlay material.
I am doing an owner/builder pool. The shotcrete company I hired left an approximately 4 x 4 in. (102 x 102 mm) hole in the deep end of the pool on the side wall. What is the proper way to patch this hole prior to plastering? (The shotcrete was applied a month ago.)
The normal repair is to pressure wash with at least 3000 psi (21 MPa) of water pressure to remove any dirt and laitance on the surface of the concrete. Given the rather small size of the hole, it can be hand-patched with a nonshrink hydraulic cement with at least 4000 psi (28 MPa) 28-day compressive strength to plug the hole. After the patch is completed, roughen the surface that will receive the plaster.
I am looking for some technical assistance concerning temperature guidelines for shooting gunite pools. Is there a suggested range of air temperature and humidity that is recommended? Thanks for your help!
Shotcrete is a method of placing concrete. The basic guidelines for placing concrete or shotcrete can be found in documents ACI 305R-10, “Guide to Hot Weather Concreting,” and ACI 306R-10, “Guide to Cold Weather Concreting.” There are some basic “rules of thumb,” such as 40°F (4°C) and rising for starting concrete/shotcrete operations and 40°F (4°C) and falling for stopping concrete/shotcrete operations. With proper planning and procedures, concrete or shotcrete can be placed at below-freezing temperatures and at very hot temperatures, but only with proper planning, procedures, and likely at some cost.
We are in the process of building a shotcrete pool and are required to wet-test the pool before set, waterproofing, and tile. What is the expected water-loss percentage? We are required to achieve 1%.
We are not aware of a specific standard for pools. However, ACI 350.1-10, “Specification for Tightness Testing of Environmental Engineering Concrete Containment Structures,” specifies a volume loss of 0.05% of volume per day conducted over a 72-hour test period for “hydrostatic tightness testing of open liquid containment structures. Specifics of conducting the test can be found in the ACI 350.1-10 document.
It should be noted that the pool should be filled and allowed to saturate for 3 days before beginning the measurements.
We just shot a wet-mix swimming pool for a customer. The shallow end depth starts at 39 in. (991 mm) to the top of the beam and over 10 ft (3 m) linear slopes down to 54 in. (1372 mm). From there we maintain our 1 to 3 ft (0.3 to 0.9 m) slope down to 8 ft (2 m) for the diving end of the pool. The customer would like to raise the entire shallow end pool floor up to the 39 in. (991 mm) depth. We prefer to use wet-mix shotcrete. The overlay would be tapered from the 39 in. (991 mm) start to 15 in. (381 mm) thick at the 54 in. (1372 mm) depth. What would you recommend for this overlay to bond and not “pop loose” or cause crack transfer to pool plaster?
The proposed overlay will be similar to any repair where shotcrete is placed over existing concrete. Proper surface preparation is essential for allowing good bond. Guidance on surface preparation can be found in ACI 506R-05, “Guide to Shotcrete”. It also appears you are suggesting tapering the thickness from 15 to 0 in. (381 to 0 mm). Feathering thickness down to 0 in. (0 mm) is not encouraged, and a minimum thickness should be established. Because the overlay section will be quite thick and experience differential shrinkage from the previously shot material, the overlay will require additional reinforcement to accommodate temperature and shrinkage stresses. You should consult with an engineer experienced in shotcrete design to establish the proper amount of reinforcement. The required reinforcement and cover over the reinforcement will control your minimum overlay thickness.
We have a two-story shotcrete wall enclosing an indoor community pool. We are specifying a board-form finish for the interior and the exterior will have a parge finish coat. Are there any issues with the consistent moisture from the pool that should be addressed in the concrete mixture or topical sealant? How should we deal with the exterior versus interior finishes in regards to water intrusion protection and allowing the green concrete to “dry out” over time?
Shotcrete is a method of placing concrete and the characteristics of shotcrete are those of cast concrete. Although the enclosed swimming pool will increase the interior humidity, the high humidity should have no detrimental effects on the exposed shotcrete, and may even be beneficial in reducing long-term drying shrinkage of the wall.
Both cast-in-place and shotcreted concrete are commonly used for construction of water tanks with constant exposure to water under significant hydraulic pressure. Using good construction techniques with good-quality concrete to build the tank’s walls produces walls with no moisture evident on the exterior face of the tanks. Simply having a high-humidity atmosphere is a much less severe exposure and should not result in interior air moisture being transmitted into and through the shotcrete wall. Any coatings considered for aesthetics should follow the manufacturer’s recommendations for drying time of concrete before application. If there is a concern about the permeability of the shotcrete wall, a premium shotcrete mixture including silica fume might prevent some issues on this application.