BE SURE TO CURE A CONCRETE POOL!
For best results, cure promptly and protect the pool during hot and cold weather.
As a consultant, and former concrete pool builder, I believe there is not a better method of building a swimming pool that will last several lifetimes than pneumatically placed concrete. The method offers the designer and builder more flexibility and design creativity than any other means of pool construction.
There is little argument that the process of shotcrete pool construction is laborious and demanding, and that it requires crucial effort and timing. With all the phass of construction involved, there are a couple of critical processes that I feel too many builders overlook.
The pool contractor/s, the expert who has been hired by the owner, and is totally responsible for the installation of a quality product. As such, the builder is responsible for properly fulfilling each and every step of the construction process. That includes placing and properly curing the concrete shell.
Expecting the owner to periodically dampen the shell in an attempt to cure it is no longer appropriate, nor should it have ever been. When highways and bridge decks are being built, DOT people are not on site soaking the concrete. That task is the responsibility of the contractor, not the owner. Pool builders have that obligation in their performance of construction.
In the field, moisture curing is the best method for this application during the hot and dry periods of the year. Obviously, there are local climatic conditions that will have an influence on the application, such as temperature, humidity, winds, etc.
The simplest method for moisture curing is to set-up oscillating sprinkler/s on a tripod, and broadcast water over the entire pool surface.
Another method is to place a drip/weep hose on the bond beam, and allow the water to run down the walls. To conserve water, use a submersible pump with either method, once you have a reserve water supply in the bowl of the shell.
It is imperative that the entire surface receives water for
a minimum of three days, and preferably seven days. This will achieve complete hydration and reduce/control drying shrinkage.
If you’ve forgotten what drying shrinkage looks like, refer
to the larger masses of concrete in shells, particularly around steps and benches.
The ideal time to start moisture curing is as soon possible after the placement and finishing. Time is important, but not too soon, were the stream of water will dilute the surface.
It is vital to slow the hydration/drying process so that the concrete will achieve its greatest strength.
The Portland Cement Association’s ‘Design and Control of Concrete Mixtures’ states, “Since all the desirable properties of concrete are improved by curing, the curing period should be
as long as practical” (pg 128).
Proper protection of freshly placed concrete must occur during cold-weather shotcreting as well as hot-weather shotcreting;
and is paramount to providing quality control and assurance. The American Concrete Institute’s ‘Specification for Shotcrete
(ACI 506.2-95)’ states the following: “CURING Immediately after finishing, cure shotcrete continuously by maintaining in a moist condition for seven days or until specified strength is attained or until succeeding shotcrete layers are placed.
Cure by one of the following methods:
• Ponding or continuous sprinkling
• Covering with impervious sheet material
• Curing compounds
Natural curing shall be permitted if ambient relative humidity is maintained above 95 percent. HOT WEATHER SHOTCRETING Do not place shotcrete when material temperature is above 90 ° F for wet mix; 100 ° F for dry mix. Lower temperature of reinforcement and receiving surfaces below 100 ° F prior to shooting.
COLD WEATHER SHOTCRETING
Shooting may proceed when ambient temperature is 40 ° F and rising. 50 ° F for latex-modified shotcrete. Shooting shall discontinue when ambient temperature is 40 ° F and falling unless protective measures are taken to protect shotcrete. Shotcrete material temperature, when shot, shall not be less than 50 ° F or more
than 90 ° F. Shotcrete shall not be placed against frozen surfaces. Applicable procedures used for cold weather concreting may be used for cold weather shotcreting.”
There are many methods of protecting the shell after it has been placed during cold weather. One of the simplest and most effective is achieved by placing a heater in the deep end, and covering the pool with a vinyl air structure. Sheet vinyl and lumber also work very well in fabricating an enclosure.
Curing temperatures should be maintained in the 50 ° F to 70° F range. Expect to loose moisture during this process, and anticipate dampening the surface, even though the humidity may gain. The enclosure must also be properly ventilated, depending on the type of fuel heater. Exposing freshly placed shotcrete to exhaust gases may cause dusting as a result of rapid carbonation. It may be beneficial to pressure wash the surface prior to applying the finish coat.
Most concrete pools that I evaluate will probably outlive us all. However, I have also seen the use and misuse of concrete. It amazes me that such a tremendous effort is put forward in building a shotcrete pool, only to expose it to conditions that will harm the shell; and expose the builder to potential litigation.
With all the effort involved by the builder in designing, selling, and constructing the pool, and the money invested by the owner; it seems sacrilege not to properly protect freshly placed concrete.
Consider that it probably takes more time to obtain a building permit than it does to set-up a moisture curing system. And
the fact that perhaps fifty percent of the strength of the mix design may not be achieved because of poor quality concrete practices.
It is imperative to properly protect pool shells, no matter what the weather conditions. The builder is responsible for the structure during the entire course of construction, and into the warranty periods.
In this litigious society that we live, contractors should expect to defend themselves in a courtroom if they are not complying with industry standards. The pool industry does not have its own set of standards, but rather is accountable to industry standards for reinforced concrete.
Please put forth the effort for the owner, yourself, and everyone involved. It’s not worth the time going to court.
