Concrete Construction Techniques

Wet or Dry Guniting?

As if the process of deciding on a pool builder were not daunting enough, there comes the argument between “wet” or “dry” guniting. Perhaps a little bit of information can help clarify the differences and help you make a more informed decision.

In the past, concrete pools were constructed in one of two ways. Either they were formed and poured (much like your basement foundation) or they were “dry packed” where the concrete was basically dumped in the bottom of the pool and shovelled up the walls by hand. Both of these methods have serious structural deficiencies.

Formed and poured structures have cold joints and are susceptible to cracking as well having severe design limitations due to the limited number of form shapes. The dry packed pools suffer from inconsistencies in the placement of the concrete resulting in voids etc. You can imagine the problems inherent in such a low tech process.

With the exception of a few remaining stragglers, those types of concrete pool construction were eclipsed by the invention and implementation of shotcreting beginning in the 1970′s. Shotcreting involves the pumping of concrete through pipes or hoses and then applying the concrete pneumatically (under great pressure) to the interior of the pool.

DRY GUN PROCESS: Originally, the material pumped through the hoses contained only the dry components of the concrete (sand, cement, gravel) and then the water was added at the nozzle tip to create the final mix. This is actually called “guniting” and the equipment required to do this is essentially a glorified sandblasting unit with a garden hose attached to the end. This summarizes the dry gun process.

WET GUN PROCESS: As technology improved, it became possible to pump ready mixed concrete through pipes and hoses and add only compressed air at the nozzle tip. This method involved much more sophisticated pumping equipment as it is much more difficult to pump heavy wet concrete than it is to pump dry mixes. In this process, the concrete is batched at the plant and delivered to the site where it is placed into the pump. This is essentially how the wet gun process works.

Having been in business for nearly 60 years, Oasis Pools has been heavily involved in the implementation of technological improvements in concrete placement. We have extensive experience in all of the above methods and have come to the conclusion that the wet gun process is clearly superior for the following reasons:

  1.  Advanced Concrete  Concrete is much more than sand, cement and water. The chemistry behind today’s concrete is constantly improving. The additions of plasticizers, water reducing agents, polymers, accelerators, retarders etc. mean that today’s concrete is much more workable and more durable than ever before. The pace of innovation in concrete chemistry is only increasing. Only through the use of ready mixed pre-batched concrete are we able to take advantage of these product innovations.
  2.  No “Rebound”  Studies have shown that up to 50% of dry gunite actually bounces off the structure and ends up on the floor of the pool. This is improperly mixed concrete and needs to be shoveled out of the pool lest the structure is compromised. This, of course, is physically impossible and just never happens, resulting in a poor structure.
  3. Design flexibility  Because wet gunite is more workable, we are able to create much more complex one piece structures. Using our innovative finishing techniques, we are able to complete nearly all of our pool shells in one day resulting in zero cold joints. Dry guniting often necessitates multi stage construction due to its poor workability.
  4. Environmental control  The use of advanced admixtures in ready mixed concrete allows product consistency in a wide variety of environments resulting in a longer build season and better customer service. Simple sand and cement dry gun mixtures are completely dependent upon a narrow range of weather conditions for proper placement and curing.

It is for these reasons that Oasis Pools utilizes wet gunning in all of its shells. This is in spite of the higher costs associated with the pumping systems and admixtures required. We encourage you to research this further as this is a substantial investment that deserves careful consideration.