Gunite Curing: How Fast Is Too Fast?
Ask ten pool builders how long gunite takes to cure, and you'll get a number. Usually twenty-eight days.
It isn't the wrong answer. It's just an answer to the wrong question.
The question that actually matters is: when does my gunite shell approach 4,000 PSI?
That's the number your shell is engineered around, and the honest answer is that it depends on three things: the strength of your mix, the quality of your shoot, and how hydrated the shell is kept. Two pools guniteed on the same morning by different companies can be in meaningfully different conditions a week later.
Here's how each of the three works, and what you can reasonably ask your builder about them.
What gunite actually is
Gunite is a dry mix. The dry material is pushed through a hose under pressure and combines with water at the very last moment, right at the nozzle, at the point of application. It's then troweled into the floor and walls by hand.
That last-second combination is the entire reason gunite works for pools. Because the material arrives dry and gets shaped in place, it can form any curve, depth, or radius a designer draws — a freeform lagoon, a negative edge, a raised spa wall. A pre-formed shell can't do that.
The trade-off is that gunite depends more on skill than a factory-moulded product does. The mix has to be right, the person on the nozzle has to know what they're doing, and the shell has to be looked after in the days that follow. Concrete pools last considerably longer than fiberglass or vinyl and need less maintenance, but they ask more of whoever builds them.
Factor one: the strength of the mix
Not all gunite is the same material, and your builder's supplier choice is a decision you inherit for the life of the pool.
Mix quality determines the ceiling on your shell's strength. A weaker mix can be shot perfectly and hydrated diligently and still take longer to approach 4,000 PSI — or not get there at all.
The thing to ask about is verification. A supplier worth using shoots test panels and pulls cores routinely to confirm PSI rather than asserting it. That's the difference between a specification and a marketing claim, and it's the standard we hold our own supplier to.
This is also the least visible quality decision in the entire build. You will never see your gunite mix. Nobody inspects it after the fact without drilling into your pool. It comes down entirely to who your builder buys from and whether they check.
Factor two: the quality of the shoot
How the gunite goes on determines whether the mix's potential actually reaches your shell.
Two things matter here. The first is thickness. We build to a minimum of nine inches of gunite through both the walls and the floor. That's a deliberate specification, and in Texas, where expansive clay soil swells and shrinks with every wet and dry cycle, shell thickness is doing real structural work against soil that never stops moving.
The second is application quality: whether the gunite is packed properly behind, over, and around the steel rebar rather than bridging over it and leaving voids. A void behind rebar is a weak point you cannot see and will not find until it matters.
Once the concrete sets, we apply a Concrete Pool Shell Protector (CPSP) seal. This shields the shell from the elements and keeps the bond from breaking down.
If you want to know where your money goes on a gunite pool, it's here in the phase of the build that buries everything before it and gets buried by everything after.
Factor three: hydration — and this one is partly your job
Gunite gains strength through hydration, not by drying out.
This is the single most misunderstood thing about a new pool shell, and it's the factor most likely to be neglected, because it requires someone to actually do something for several days running.
After your shell is shot, we will ask you to water your pool. Do not fill it with water, keeping the fresh gunite wet through the early stage of the curing process. It feels strange. It is not optional.
A shell that's left to bake through a run of North Texas hundred-degree days without being kept wet can shrink, craze, and crack. Worse, the strength it fails to develop in those first days cannot be added back later. There's no remedial step. Our summers are hard on a curing shell in a way that builders in milder climates don't have to plan around.
So, where does twenty-eight days come from?
Twenty-eight days became an industry best practice because it's the most conservative estimate of when a wide range of different-quality gunite mixes will be near 4,000 PSI.
Read that again, because the important word is conservative. Twenty-eight days isn't a physical property of gunite. It's a safety margin wide enough to cover a bad mix, an indifferent shoot, and a shell nobody watered.
With a high-quality mix, a good shoot, and proper hydration, our gunite reaches between 70 and 85 percent of its needed 4,000 PSI by the end of the seventh day.
And we still plaster after day twenty-eight.
That may look like a contradiction. It isn't. We wait the full period because there is no advantage in not waiting — the schedule doesn't need those days, and the shell benefits from every one of them. Gunite, like ordinary concrete, keeps curing for years after it's shot. Twenty-eight days isn't the finish line. It's a sensible point at which to move on.
What this means for your build schedule
Here's how the two numbers reconcile against a real calendar:
| Phase | When | What's happening |
|---|---|---|
| Gunite shot | Target: day 7 of construction | Shell formed, CPSP applied once set |
| Hydration period | Days 1–7 after shooting | You water the shell. Strength climbs to roughly 70–85% of target |
| Continued cure | Days 8–28 | Tile, coping, decking, electrical and masonry proceed |
| Plaster | After day 28 | Shell has had the full conservative window |
Shooting gunite early and plastering late is the combination worth looking for. It means the shell gets maximum cure time without the overall build stretching out a schedule that doesn't require a slow build to be a careful one.
Be a little cautious of the reverse: a builder who is late to gunite and quick to plaster is compressing the one window that shouldn't be compressed.
Frequently asked questions
How many days does gunite take to cure? Functionally, a good shell reaches 70 to 85 percent of its 4,000 PSI target by the end of day seven when it's kept properly hydrated. The twenty-eight-day industry standard is a conservative window that accommodates lower-quality mixes, and it's still worth observing before plaster. Technically, gunite continues to cure for years.
What is gunite supposed to test at? Around 4,000 PSI is the figure a residential pool shell is generally built toward. The way to have confidence in it is a supplier who shoots test panels and pulls cores to verify, rather than one who simply states a number.
Why do I have to water my own pool shell? Because hydration is how gunite gains strength. Keeping the fresh shell wet during its early curing days is the difference between reaching design strength and falling short of it permanently. It's the one construction task a homeowner genuinely contributes to.
What happens if gunite dries out too fast? It can shrink, craze, and crack, and it may never reach its intended strength. The consequences are structural, and they aren't reversible by anything done later, which is why the watering instruction isn't a formality.
Is gunite the same as shotcrete? They're closely related but not identical. Gunite is a dry mix that meets water at the nozzle; shotcrete is typically delivered wet-mixed. Both are pneumatically applied concrete. In North Texas residential pool construction, gunite is the common approach, and its ability to be shaped in place is why.
How thick should a gunite shell be? Thicker than the minimum a builder can get away with. We specify at least nine inches through the walls and floor. In expansive clay soil, that thickness is structural, not decorative and it's not something you can add later.
Does gunite crack? Concrete moves, and hairline surface crazing in plaster is a different thing from a structural crack in a shell. A properly mixed, properly shot, properly hydrated shell at adequate thickness is built to handle North Texas soil movement. One that failed any of those four conditions is where real cracking tends to originate.
The honest summary
Providing a shell that genuinely stands the test of time is a priority of Larry's, and after thirty years of building pools, he has fairly firm views about which corners get cut in this industry and what it costs the homeowner later.
Three things determine your shell: the mix, the shoot, and the water. You can't inspect the first two after the fact. You can ask about all three before you sign.
Who You Build With Matters®, and on a gunite shell, it matters most in the week nobody's watching.
Why wait to swim if you don't need to? It's hot out there, y'all. If you want to see how gunite fits into the rest of the build, or you'd rather just talk it through with someone who'll answer the technical questions properly, give us a shout.
