Perfect Plaster Starts with Shotcrete
Installing a beautiful and durable plaster or exposed aggregate finish begins with the surface upon which it is installed. Here Jon Temple breaks down the surface preparation process with a concise look at shotcrete and how it sets up a successful plaster installation.
By Jon Temple
When a homeowner admires the shimmering finish of a new pool, they’re usually seeing plaster, pebble, or exposed aggregate. But as every experienced watershaper knows, the beauty and durability of that finish rests on something far less glamorous and completely out of sight: the shotcrete shell beneath it.
If the shell is flawed, unprepared, or poorly managed, no amount of artistry in the finish will save it from problems down the line. Pool builders and plasterers share the ultimate responsibility. The truth is simple: great finishes depend on great concrete.
And while communication is always the first step—builder and plasterer must be in lockstep about expectations—the details of shotcrete placement, curing, and surface preparation make all the difference between a finish that endures and one that becomes a callback nightmare.
The Shotcrete Standard
Shotcrete, whether applied as wet-mix or dry-mix (gunite), is concrete pneumatically applied at 60–80 mph. Properly executed, it creates a watertight structural vessel with tremendous design versatility. Done poorly, it sets the stage for delamination, discoloration, leaks, and costly remediation.
Over the years, we’ve found that improper mix design, water-to-cement ratios and mix time can lead to significant problems with shotcrete quality and durability. Industry best practices are spelled out in American Concrete Institute (ACI) Committee 506 guidelines and American Shotcrete Association (ASA) position papers.
For pools, the benchmark is a minimum 4,000 psi compressive strength. Achieving that standard requires an appropriate water-to-cement ratio, correct aggregate proportions, and shotcrete placement that fully encapsulates steel reinforcement without voids.
Every builder should be mindful of common pitfalls:
- Weak mix design — too much water or sand undermines long-term strength.
- Voids around PVC — pipe penetrations not properly packed allow leaks and structural weakness.
- Steel not encapsulated — exposed rebar creates corrosion pathways.
- Rebound left in place — troweling back “bounced” material compromises the shell.
Beyond these fundamentals, curing cannot be overlooked. ACI defines curing as the maintenance of temperature and moisture to allow concrete hydration to continue. Sprinklers or soaker hoses on a fresh shell keep it cool, limit shrinkage cracking, and improve long-term strength. Neglect curing, and you invite problems before the finish is ever applied.
Prepping for Plaster
From a plasterer’s perspective, the shell is everything. A smooth, over-troweled surface may look neat to a concrete crew, but it creates a bonding challenge for plaster. What plaster needs is a three-dimensional bond plane—a rough, porous surface that allows for mechanical adhesion.
For new pools, best practices include:
- Leaving the shotcrete surface, coarse enough for bonding.
- Thoroughly pressure washing to remove rebound, dirt, and laitance (without acid, if possible).
- Packing fittings, light niches, and tile lines with hydraulic cement to prevent “weepers.”
- Applying a bonding agent in three tacky, layered coats for a strong, consistent adhesion plane.
For remodels, the process begins with investigation: Why did the old finish fail? Delamination? Cracking? Water intrusion? Unless those root causes are identified and corrected—weak bonding agents, bad concrete additives, structural movement—new plaster will inherit the same fate.
Checklist discipline is key. From photographing cracks and weepers, to pressure-testing plumbing, to documenting repairs, every step of surface prep is about setting expectations and eliminating variables.
The Bonding Agent
Bonding agents do more than provide “glue” between shell and finish. Applied correctly, they create a textured three-dimensional surface and regulate substrate absorption, slowing down plaster hydration in hot or dry conditions. This ensures more uniform curing and a longer-lasting finish.
Bonding agents also work to prevent the bleeding of rust from rebar and tie wire, and from concrete additives through the plaster.
Three properly applied coats, with each subsequent coat placed while the previous remains tacky, is the gold standard. Skip steps here, and you risk peeling, delamination, or uneven hydration—the kinds of problems that lead directly to call-backs.
Where Builders Stand
Fact is, plaster failures are often traced back to the substrate. Which means they are ultimately traced back to the builders, with plasterers themselves sharing the blame, and liability.
Our responsibility isn’t just structural. It’s aesthetic. It’s relational. The finish is what clients see, but it’s the unseen work in shotcrete and preparation that determines whether their pool inspires joy for decades or frustration after the first season.
That’s why builders must own the process, communicate clearly with plasterers, and follow best practices in shotcrete placement, curing, and surface prep. Perfect plaster starts with perfect shotcrete. And perfect shotcrete starts with builders who understand that every phase of construction sets the table for the next.
Jon Temple is president and founder of Tempool, a pool-surfacing firm located in Jacksonville, FL. Temple founded the company in 1996, which has plastered more than 30,000 pools. He is a valued Watershape University faculty member.
Jon will be teaching C3611: Essential Plaster Workshop, Dec. 5-6 in Phoenix, at WU’s Education Vacation.