Floating vs. Locking vs. Key-Locking Pool Decks: What Arizona Pool Buyers Should Know Before They Build

Let’s be honest: when you picture your dream pool, you’re probably imagining sparkling blue water, floating in the water with a drink…but not the concrete deck surrounding it. Here’s the catch — the way your pool deck is constructed can make or “break” your pool investment in Arizona.

Pool builders don’t often bring this up because most homeowners never ask and, candidly, pool companies have decided how they want to build it already. Deck construction is usually treated as a behind-the-scenes detail. But choosing (or at least understanding) how your pool deck is built can mean the difference between:

• A backyard you love for decades
• Or hairline cracks, broken tile, a gap under the pool deck and costly repairs just a few years in

So, let’s dive into the three main deck construction methods you’ll run across: floating, locking, and key-locking decks. By the end, you’ll know the right questions to ask, how each option performs in Arizona’s tricky soils, and which one fits your priorities best. Remember, it’s YOUR pool, not the pool builder’s pool; the investment has to make sense to you.

What Is Expansive Soil—and How Does It Affect Your Pool in Arizona?

Before we get to the deck options, let’s talk about the ground beneath them. If you’ve ever wondered why sidewalks or driveways in Phoenix crack, the answer is often expansive soils.

Expansive soil is a clay-rich soil type that swells when wet and shrinks when dry (USDA NRCS). These soils are well-documented across Arizona. The City of Phoenix even publishes guidance on expansive soil conditions for construction projects (City of Phoenix Technical Bulletin).

Outside of pools, expansive soil is responsible for cracks in:

• Home foundations: Post-tensioning is often required in Arizona home slabs to manage soil movement (Post-Tensioning Institute).
• Sidewalks and driveways: Uneven heaving and gaps appear as the ground shifts.

Now imagine pouring a rigid concrete deck right next to your pool shell, with no separation. Every time the ground expands or contracts, your pool and deck fight each other. That’s where construction method becomes critical. It’s a large permanent investment that you should feel a peace of mind about…surprises are not welcome with an investment of this size.

What Are the Differences Between Floating, Locking, and Key-Locking Pool Decks?

1) What Is a Floating Pool Deck and Is It Good for Arizona Homes?

Why is it so common in the pool industry?

How it’s built: A floating deck is poured as a slab with a flexible isolation joint separating it from the pool shell. Think of it like giving the pool and the deck their own “breathing space.” The break or mastic joint is absolutely imperative in floating deck construction. The purpose of the joint is to separate the poured deck from bonding with the top of the pool shell, called “bond beam”. The mastic joint must be applied for the entire width of the bond beam so it prevents the concrete deck from bonding with the pool shell.

It allows movement, yes we said “movement”, between the pool deck and pool shell. On a floating deck if there is no movement can cause unsightly cracks because of the pressure the deck and the pool shell exert onto each other. If the pool deck bonds to the pool shell, it actually significantly increases the risk of cracking and/or causing tile to pop off. If a floating deck is for you, then a break and mastic joint should be demanded. Most pool company warranties should cover coming out one time, in the first two years, to "re-caulk" the joint between the deck and the pool.  After that, you're on your own to do it yourself so take notes.

Why it’s popular: It’s the cheapest upfront cost in Arizona and the fastest way for a builder to finish your deck. 

Pros:

• Affordable and widely available.
• The isolation joint lets the deck move independently of the pool shell.
• A proven method recognized by pool engineers (Pool Engineering Inc.).

Cons:

• Your plumbing connected to your pool shell and your pool deck is not elastic. Its important to have the expectation that even though your floating deck is designed to move, your plumbing isn’t. Expansive soil is common “voider” of the plumbing attached to your decking (i.e. - auto water leveler, skimmer housing, aerator, certain types of water features, etc.)
• That joint needs maintenance. Over time, mastic or sealant wears out, letting the deck bond back to the pool and causing stress (Trouble Free Pool). DON’T LET THE DECK BOND TO THE POOL.
• Still higher long-term risk of cracking in Arizona soils compared to more advanced methods.

Bottom line: Floating decks are attractive because of their low initial price, but homeowners need to understand the potential maintenance commitment and potential of the deck separating from the pool.

2) What Is a Locking Pool Deck and Why Is It No Longer Common in Arizona?

How it’s built: The concrete deck is poured tight against the pool shell (sometimes with rebar dowels tying them together).

Why it was popular: Builders liked it because it was a medium-cost option that avoided using flexible joints. It gave the pool and deck a “one-piece” look that partially bonded the pool deck and pool shell via the steel rebar of the pool (the rebar is the steel, “skeletal” structure of the pool shell). The goal was a more cost effective construction technique, that didn’t require significant technical labor, that reduced the deck movement and save the life of the plumbing…the RESULT? …cracking on the top of the deck where the rebar ended.  With the cracking being visible from the surface of the deck, this construction technique has gone the way of the dinosaur. 

Pros:

• Moderate upfront price.
• Simple, straightforward construction with an attempt tie in the pool deck to prevent the potential of unsightly gaps between the pool deck, shell and movement with the plumbing causing leaks.

Cons:

• In Arizona’s expansive soils, locking decks caused major problems. As the ground moved, decks transferred that stress right into the pool’s bond beam and tile line, leading to cracks on top of the pool deck and lifted coping.
• This reputation is why locking decks have largely disappeared in Arizona — they just didn’t hold up.

Bottom line: While it might sound like a compromise between cost and durability, in Arizona soils it’s more like the worst of both worlds. When built, the cracks were so visible…you noticed the moment you stepped out of the patio door onto the pool deck. 

3) Is a Key-Locking Pool Deck Worth the Extra Cost in Arizona?

How it’s built: Key-locking decks use a special cantilever forming system (such as Key-Lock™) that creates a durable, monolithic bond between the pool deck and pool shell. Importantly, this construction technique still isolates the deck from the pool shell while “keying” into a track for strength and prevents movement that can cause the plumbing to stress and crack. Simply put, the skeletal structure of the pool, is running into the pool deck and bent down into the ground with periodic concrete footers to prevent deck lifting and moisture from getting underneath the deck to enhance the expansive soil problem. This technique has been confirmed by engineers as a legitimate way to reduce movement and cracking. Some in the industry have called it a "sales tactic" to impress potential customers but that would be a business 101 stupid decision because it is so much more involved and costly for the company to construct decking this way.

Why it’s chosen: For homeowners who want a premium look and the lowest long-term risk of soil-related issues, this method is unmatched.

Pros:

• Longest-lasting performance against Arizona soil movement.
• Premium, customizable edge profiles for a high-end finish.
• Reduced chance of cracks or damage at the tile line.

Cons:

• Highest upfront cost of the three methods.
• Requires skilled installation. more labor and more material.

Bottom line: If you plan to stay in your home long-term and want fewer repair potential, the higher upfront investment can save money down the road.

Which Pool Deck Type Is Best for Arizona? Here’s a Side-by-Side Comparison

*Floating Deck photo in expansive soil area in Arizona– No Bond Breaker/Mastic Joint Installed (deck within 4 years pictured left and pool over 20 years old pictured right)

What Questions Should You Ask About Pool Deck Construction Before You Build?

Most builders won’t volunteer this information, so here are the questions that put you back in control:

• “Which deck method are you planning to use on my pool?”
  • If they just say “standard deck” — that’s not enough detail. Push for clarity…it's your permanent investment.
• “If my deck is a floating deck, will my deck be isolated from the pool shell so it doesn’t bond to the deck in any way? Are you installing a break or mastic joint?”
  • Isolation is crucial in Arizona. If there is no break or mastic joint, demand it and request proof.
• "Is the deck construction type you use have a warranty covering expansive soil damage?"
  • If a company claims that the deck construction technique they use is "superior", then the warranty should be proof of that confidence.
• “What maintenance will I need to do on the joints? Is there any risk of deck lifting from the shell? If there is a risk of lifting, is it a part of the warranty that you will come out to re-caulk any gaps between the deck and the pool?"
  • Deck ownership doesn’t end when the concrete cures. You are owed all of the facts up front so there are no surprises later...it's too big of an investment.
    
    
• Red flag: If you hear “we pour the deck right up against the pool,” or “floating deck is the highest level of deck quality”, proceed with caution because your builder may be saying that because it’s cheaper for them to build it that way. It isn’t the end of the world but clear and proper expectations on an investment this size should be a given.
• Green flag: A builder who explains floating and key-locking methods, in detail, and why they recommend them is giving you transparency. It should feel like demonstrable proof before you make a permanent investment in YOUR backyard.

What’s the Best Pool Deck for Long-Term Value in Arizona? Final Takeaway – Cheapest Now or Cheapest Later?

Here’s the reality:

• Floating decks are the most common because they’re the cheapest for builders to install.
• Locking decks were once common but failed against Arizona soils, and the problems they caused are why you rarely see them today. Good intent, long term failed execution.
• Key-locking decks cost the most upfront but offer the best long-term quality and peace of mind.

When shopping for a pool, you don’t always get a menu of deck construction options and, without the knowledge, you wouldn’t even know to ask. But if you don’t ask, you could end up with something that costs you more in the long run or severely missed expectation.

So, next time you sit down with a pool company, bring this knowledge with you. The more you know, the better your pool will serve you — not just this summer, but for decades.

Want to learn more or get more clarity on floating, locking, and key-locking decks in Arizona? Reach out to Shasta Pools and we’ll show you photos and explain how each one performs in the Valley’s unique soil conditions…we will even pull up an expansive soil map, type in your address and see what type of soil you are in.