Prerequisites for Decking:
Any kind of add-on structures like BBQ's, Fireplaces, Seating Areas, etc.
that will located on or near the deck should be completed before the decking
is done. Usually, the decking people like to pour their concrete up
against existing structures so that they can plan the drainage strategy
All pipes, conduits, gas lines, and anything else you want under the deck to
be completed before the concrete is poured.
The decking sub is responsible for putting the walkway around
the pool and in other areas that you might want deck surface. The pool
deck has virtually limitless applications. Its bounded only by a person's
standard, most basic surface for pool decking is Kooldeck.
Kooldeck has been around for a long time and is still quite popular with
pools. Kooldeck comes in many different colors and patterns, but the most
common is the Lace pattern. The way that Kooldeck is typically done today
is using a cantilever design which overhangs the inner edge of the bond
beam by 1-1/2". The cantilever
edge design provides nice sharp, defined, straight lines that give pools a very contemporary look, which I
like a lot.
Deck Surface Choices
Today, Kooldeck is just one of a myriad of
decking options to choose from - washed aggregate, acrylic, stamped concrete,
flagstone, saltillo, slate, marble, travertine stone, brick, pavers, and the list goes on -
are just some of the alternative deck surfaces to choose from. I
originally considered doing flagstone for awhile, but after seeing what the cost for
flagstone was, I decided to just go with standard Lace Kooldeck. None of
the other types of stone surfaces really appealed to me. As I talked to
decking subs, I found out that while Kooldeck has very good heat dissipation
qualities, but it also has a very high tendency to chip and crack over
time. Its also very susceptible to staining. That's why
most decking subs will only warranty it for 2 years. Also, the decking sub
told me that Kooldeck usually has to be replaced after 5-6 years. He told
me that he replaces Kooldeck all the time. As I did more
research, I found out that a very good substitute for Kooldeck is Acrylic
Acrylic decking looks very similar to Kooldeck, but it is much more easier to
maintain and is much more resistant to chipping, cracking, and staining.
Its also a bit more expensive and takes longer to construct. While Kooldeck is
formed the same day that the concrete is poured (it needs to bond to the wet
concrete), Acrylic is done a few days
after the concrete has dried. Part of the durability of Acrylic decking is
that it doesn't have to be replaced like Kooldeck does. When I asked a
decking sub about this, he said that since they started installing Acrylic decks
in 1994, they've never had to replace one yet. That was pretty
impressive. I liked the increased durability and
maintainability qualities, and decided to go with
Acrylic Deck Construction Process
The construction of an Acrylic deck for a swimming pool takes place in three phases.
Each of the phases will take close to a full day to complete.
- Setting the forms - this phase involves achieving the
proper grading on the area where the deck will be poured and setting up all
the fiberboard forms around the pool and surrounding area to help form the
concrete so that it keeps its shape when they pour the concrete. Also,
during this time, a expansive soil strategy is implemented. I discuss
this in more detail later. The forms are also set at the proper
elevation to insure that the deck slopes in such a way as to insure that
proper drainage occurs (i.e. standing water drains away from the pool).
- Pouring the concrete - this phase is where the concrete is
poured into the forms, then the surface smoothed down, shaped, and troweled
until the proper grading is achieved. During this phase, plastic
control joints are put in place in the concrete to control where the
sections crack. The Deck-O-Drain is also set during this time.
If Kooldeck were being installed, it would be sprayed on during this phase
while the concrete is still wet and drying.
- Spraying on the Acrylic - this is the phase where the deck
surface is applied to the dried concrete. Kooldeck is formed when the
concrete is still wet, but Acrylic is sprayed onto the dry concrete surface,
then knocked down (i.e. troweled flat). The result is a more resilient
surface that is more resistant to staining, chipping, and cracking.
After the Acrylic is sprayed on, an paint is sprayed onto the drying
The Acrylic can not be applied until the concrete is fully dried and
takes place typically 3-4 days after the concrete is poured and graded.
Decking has a lot of issues associated with it that a lot of people don't
realize. The first one has to do with drainage. The issue here that
was first brought up in the excavation page is that the deck is required by code
to be sloped such that an appreciable amount of standing water does not collect
anywhere on the deck, leading to a potential slipping/safety hazard. To
alleviate that, deck subs will slope decks such that water drains away from the
pool towards the back edge of the deck. For standard Kooldeck, the
requirement is that for each foot of decking run, there needs to be a drop of
1/4". So 4 feet of deck measured out from the edge of the pool would
incur a 4 x 1/4" = 1" drop evenly over that 4 ft run.
For other types of materials, the sloping requirement is slightly different:
- For textured surfaces, which include Kooldeck, Acrylic, and other surfaces
that have a greater ability to hold standing water, the slope requirement is
1/4" for every 1 foot run. The 1/4" requirement is a state
- For smooth concrete, the slope requirement is 1/8" for every 1 foot
run. Smoother surfaces don't retain water as readily as textured
surfaces, so the minimum sloping requirement is not as stringent. In
this case, its only half of what it is for Kooldeck.
- Other materials can take the slope requirement up to 1/2" drop for
every 1 foot run.
Expansive Soil Issues
One of the biggest problems that pool owners here in AZ face is the
problem of expansive soil. Next to the city of Gilbert, Chandler is one of
most notorious cities for having expansive soil problems. In a nutshell, expansive
soil is a soil which expands when moisture gets into it. The subsequent
change in volume can cause structures to move and crack in time if the movement
is great enough.
When I visited my first pool builder (Shasta Pools), they turned out to be the
largest pool builder in the valley. When I walked into the sales person's
office, I immediately noticed that there were enlarged newspaper clippings
pinned up all over the walls. Each one of them was an article about
cracked pools and cracked decks. It didn't take long for the sales guy to
start telling me that cracked decks were one of the biggest issues facing pool
builders in AZ today. He said that was the reason why pool builders
will put into the contract that they are not responsible for damage
caused by expansive soil issues. Its a hard problem to solve. He
went on to say that Shasta Pools, however, has a unique way of handling this
problem. Later as I would visit the other 7 or 8 builders, I did indeed
verify that in their contract (in small print no less), there were very specific
stipulations absolving the builder from responsibility from expansive soil
issues. Pretty convenient. Shasta's approach to the problem was
- Sky bars - Tying the deck to the bond beam by extending rebar from the pool shell and
making it come up/out vertically from the top of the bond beam, bending it
90 degrees so that it points away from the pool water, then securing it right in
the middle of the deck when the concrete is poured.
- Concrete Footer Barrier - Creating an
8" concrete turn down footer along the outer edge of the deck along selected areas
of the deck. As water drains off the pool deck onto the soil substrate,
this barrier prevents moisture from creeping under the
deck, which is the main cause of expansive soil problems. This barrier
is only needed in those sections of decking that are wider than 3
feet. For anything less than that, the decking is really too skinny to
have much of a potential to incur deck cracks.
- Thicker Deck Slab - Adding an extra 1 inch to the slab for the deck (1 inch above
the normal 4 inch decking thickness for a total of 5 inches) so that the slab
itself is stronger/bulkier and more resistant to movement and
cracking. Because this adds an additional expense to the overall cost
of the deck, anything more than an extra inch would be impractical.
approach is not universally accepted by all pool builders. First off, they
say that having the deck tied to the pool shell is not the most desirable thing
when the soil decides to expand. While its true that the tensile strength
of the rebar is able to withstand the expansive force of the soil, the
susceptibility of the deck to cracking is actually increased. This would
be true anywhere along the concrete slab beyond where the rebar is in the deck
because the concrete without rebar has very little tension capacity (this was
also verified by a friend who is a geo-technical engineer for Terracon).
the concrete barrier footer is sufficient when small amounts water drain off the deck,
but it is woefully inadequate when heavy rains or saturation from large amounts
of water get into the soil. While its typically true that expansive soil
generally resists absorbing water, when the saturation is long enough and/or heavy enough, it will go much deeper than the 8
inch barrier. In this case, the soil will start to push up against the barrier actually
acts to retain the moisture under the deck, exasperating the expansion.
while the extra thickness of the the deck slab helps, my friend at Terracon told
me that depending on how bad the expansive soil is in an area, it has the
capability to crack commercial/industrial-type foundations. Also, the
thicker the slab gets, the more expensive the overall job is.
An Alternative Solution
The strategy adopted by most pool builders
that I've spoken to is to leave the deck detached from the pool shell - almost
letting it "float" on top of the bond beam. They believe that
the best way to deal with expansive soil problems is to "work with it
rather than work against it." What they say is
that ultimately, expansive soil is going to cause movement/shifting in your
deck. Its GOING to happen sooner or later. By tying the deck to the
pool shell, you are only asking for trouble. Instead, they say that by letting
the deck float, the deck naturally "breathes" as the soil expands and
contracts over time. When the deck is initially poured, a silicone bead or
a commercial caulking is applied
at the cold joint / air-gap where the top of the bond beam meets the bottom of
the deck to prevent water from getting into the gap and saturating the soil
under the deck.
In time, as the expansive soil starts to work on the deck, it will exert
upward force on the deck, lifting it above the bond beam and breaking the
silicone/caulking seal applied at the cold joint. At this point, all the homeowner
needs to do is to reapply the silicone bead/seal along those areas of the deck
where the expansive soil has broken it. I've heard that typically, its
about 8-9 months before re-sealing is necessary.
Using this method, they say that the
development of deck cracks are minimized and the area where the expansion
affects is hidden under the deck's 1-1/2" cantilever overhang out of
sight. The homeowner needs to be vigilant, however, in checking for broken
seals periodically or else water from the pool could get into the soil
under the deck where the seal is broken and cause even bigger problems.
Decking Sub's View of the World
As I was making my calls for decking bids, I found myself one afternoon talking
to Wayne, the owner of one of the largest decking companies in Arizona. Wayne was a
very pleasant person to talk to and very experienced and knowledgeable. He has been in the pool concrete decking industry
for close to 30 years. His story was fascinating. He actually does
the decking for half of all of Shasta's jobs in a given year. Shasta is
the largest pool builder in Arizona. He says that he does anywhere from
1500 - 1800 pool decks a year for them. He gave me the
whole history behind "Sky bars." He said that originally, it was
never meant to be a solve problems with expansive soil. It was really to
keep the original "cap tile" from the 70's from falling off the area
where the bond beam meets the pool deck. The cap tile had a bull-nose
glass type of look to it and was attached to the area near the deck/bond beam
joint. Every time there was deck movement, the cap tile would fall off, so
they decided to just anchor the deck to the pool shell ("That'll learn
ya!"). Since then, cap tile design
has gone out of style, but the old "Sky bar" design has been refitted
for expansive soil issues. He also mentioned the limited usefulness of the
8" concrete barrier used to prevent water from seeping under the concrete
deck. He said that typically, the soil in AZ has high clay content so
water is very resistant to saturation, so the 8" barrier may be enough. However, there
is still the potential deeper saturation (e.g.
an extended rain/storm, incessant wetting from nearby landscaping plants, leak
in pool plumbing or pool, etc.) that would render the concrete barrier useless.
Wayne mentioned a second method for battling
expansive soil issues. He said that the idea came from a geo-technical
engineer who works for a consulting firm in Tempe, AZ. He said that
another concrete company hired this engineer after seeing a lot of their
customers experience an inordinate amount of deck cracking due to expansive soil. This engineer
was contracted to perform a study on alternative methods of battling expansive
soil issues in problem cities in AZ. During his investigation, he came up with a scheme
called the "Pier System." In this system, a diamond-pattern of 8" wide holes 16"
deep are placed 3 feet apart. Each hole is then covered with a thin sheet
of Masonite to keep the concrete from getting into the hole when its
poured. The cavity remains intact even after the concrete is poured over
it due to the high clay content in the soil. The idea is that when
expansive soils begin to act, the soil expands into these holes, effectively
absorbing the soil's vertical intrusion into the deck and rendering it harmless.
He said that the jury is still out on this method, but that select pool
companies have agreed to pilot this new method for a year with new pool installs
to see what kind of results they get. He said that so far, they have not
reported any kinds of problems.
Note: Jose Raffucci, a regular from poolforum.com,
astutely pointed out that the Masonite material, being made of wood, could be a
potential termite hazzard. I'm sure there are tons of other materials that
could be used to achieve the same purpose as Masonite without having the same
kinds of problems. You can read his posting here.
A Geo-Technical Engineer's View of the World
I have a friend who is a Geo-Technical engineer at Terracon (www.terracon.com).
Geo-technical engineers deal with soil science, earth structures,
slopes/retention systems, pavement/slab/foundation analysis and design. He
works mainly with large state government clients and does work mainly with
industrial/commercial applications. He commented that when expansive soil begins to move, it moves
vertically/upward and has very little lateral / horizontal movement. He said
that this is due to the physical properties of the clay particles that are at
the core of the problem with expansive soils. He said that expansive soils
usually contain a high amount of clay. These clay particles are physically
flat. He said, "Think of a playing card. When you pour soil that has
high clay content into a cup of water, the clay particles do not fall in a
random fashion towards the bottom. They tend to pile on top flat on top of
each other like playing cards. They typically don't fall on their
edge. Since the surface area of the clay particles are greatest in the
vertical direction, when water molecules get between them, it causes the clay
particles to push off from each other in the vertical direction. This is
the reason most of the effects of expansive soil is upward and not horizontally
Because of this property of clay in expansive soil, he questioned the overall
effectiveness of this Pier System method. I asked him then, "What
in your opinion, would be the best way to alleviate expansive soil problems in
AZ?" He replied that its actually pretty simple in concept, but
it just takes a long time to do it, so pool builders and decking subs would
generally be cold to the idea. The solution is simply this:
Saturate the top 12 inches or so of soil that you plan on building
the deck over and allowing the soil to pre-expand so that when you build your
deck, it will be built on expansive soil that has already expanded. Once
the soil has expanded, the surface could be graded to the desired level and
the deck can be poured.
I had a few questions about some of the particulars of this method:
- I asked him how he arrived at the 12 inch number. He said that its a
practical consideration. Because expansive soil has high clay content,
its difficult for the soil to absorb water much deeper than that level
anyways. It would be tough enough to get the entire 12 inch layer of
soil beneath the deck to become completely saturated with water let alone
anything beyond that. He agreed though that the deeper you could go,
the better it would be.
- I asked him how long it would take for the expansion to take place. He mentioned that once the soil becomes completely saturated with water,
the expansion occurs in a relatively rapid rate. He said that it could
take a little as a few hours but generally no more than a day. Of
course, the ground would have to be completely saturated, which is of course
the hard part.
- I asked about how contraction plays a part of all this. What happens the effects of soil
contraction after the soil dries out? Wouldn't that be as bad as the
expansion? He said that typically, contraction is not as much of a
problem as expansion. When soil dries out, it rarely goes back to its
original position before it expanded. Once it expands, it tends to
keep its new position.
The challenges to achieving this were of course getting the water to saturate
the ground through to the 12" depth in a timely fashion - something that
pool builders and decking subs don't have a lot of in the summer when they are
in the full swing of business. I suggested that maybe someone could come
up with a metal probe that could be injected into the ground and break through
to at least the first 12"-18". If this could be hooked up to a
garden hose at a low pressure, theoretically it could get the water directly to
the area where it needs it. Also, a set of these probes could be attached
together so that an entire area could be done all at once. Speaking
of which, Jose Raffuci also mentioned that some neighbors of his drilled 4"
holes all over their yards 5'-6' deep, then filled with a layer of sand,
then put a layer of gravel on top of that. The idea is to get the water away
from the clay before it has a chance to soak in. I thought that was pretty
innovative. The only thing I wonder about is whether or not the hole could
actually exacerbate the problem should water somehow accidentally fill it up and
get in contact with the clay.
An alternative solution suggested by a poolforum member
Because of the same issues facing Southern California as Arizona, Jose mentioned
that after doing some
research, he located some concrete forms from a company called Stegmeier
that seem to be designed for people with this problem. I shamelessly took
some images from their website. From the description, its says: there
is an inside urethane joint seal which prohibits water transfer from pool to
soil. The urethane rubber attaches the form to the tear strip and the tear strip
to the bond beam. When the soil expands and move the decking, the rubber gives
and takes with the movement. Being an inside joint sealant nothing can be seen
from the pool but the clean tear strip.
Jose mentioned that a box of the stuff runs about $190. It
has enough for a 96 foot run and comes with all the necessary accessories to do
the installation. I had a chance to talk to Wayne about this product, but he
didn't seem too overly interested in talking about what it could do. He
seemed to indicate that with the combination of the methods he currently uses,
expansive soil problems are kept under control. I don't know if he's the
type of person who has done something a certain way for so long that he's not
open to new ideas, or if possibly the methods he currently employs are just so
effective, that he doesn't need to be looking for additional solutions.
I'm hoping its the latter, but in either case, he didn't seem to excited about
taking much time to discuss new products. Oh well.
On a related note, another poolforum member, Kevin Masuhara,
posted his experience with these forms. He mentioned that this product
did work for him, but since it does not _prevent_ deck movement, there could be
some issues. When the movement is not severe, the black plastic strip
covers the gap nicely, but when its severe, the black plastic strip tears away
from either the deck or the bond beam, exposing an air gap that could be
potentially an entry way for water to get into the soil. If the gap is big
enough, it needs to be sealed or else water getting to the soil could cause
further soil expansion. He had some issues where putting a silicone bead
along side of the black plastic strip causes some unsightliness, but that its
mainly visible only when he's in the pool. Thats not a bad trade-off, but
you can read about the details of his experiences and his approach to the
problem in his posting.
Yet another solution ...
Kevin mentioned that if he could do it again, he would install a
coping tile that would sit directly on top of the bond beam, then from that
point to the outer edge of the deck, he would install pavers over a foundation
of sand and gravel. The idea is that when the soil begins to expand, he
could just remove the pavers in that problem area, take out just enough sand to
compensate for the vertical rise in the deck, then replace the pavers.
Pretty clever. I drew a little picture that hopefully accurately describes
what he was talking about.
What method to use?
After waiting till the last possible moment, I decided to go ahead and try the
Pier System. After thinking a little more about the Pier System and some
of the comments given to me by my Terra-con friend, I reasoned
that even though expansive soil expands mostly vertically and very little
horizontally, the reason why it would still work is "path of least
resistance." I'm reasoning that when expansive soil starts to exert
pressure vertically and hits the underside of the deck, that the force from
the weight of the deck against the soil will cause the soil to start moving
horizontally toward the holes since the horizontal force exerted against the
moving soil from the hole would be less than the vertical force exerted on the
soil by the weight of the deck slab. Since the holes can "absorb" quite a bit of
soil displacement, the net effect is that the soil ends up "crushing"
the holes, but saving the deck. Depending on how much soil is displaced,
however, the total volume of soil that the holes can "absorb" may or
may not be enough to withstand extreme expansive soil problems. While the
termite potential was a also a cause for concern, those concerns were
somewhat alleviated when I discovered that I misunderstood how the Masonite was
being used. I originally thought that the holes were filled with crushed
Masonite to keep the hole intact. Instead, only a thin sheet of Masonite
is used - its just laid flat on top of the hole to keep the concrete from going
into the hole when the concrete is poured.
The Skybar method was not even an option for me since I would have needed to have the extra long
rebar put in during the steel phase, which I didn't. And besides that,
while it appears the Skybars would certainly keep the deck from lifting from the
bond beam, it doesn't seem that they would do much for deck cracking.
I like the idea of letting the deck
"breathe" and using the caulking to seal the air gap in the cold
joint area. I'm just hoping that it doesn't look too unsightly when
my deck finally does decide to move up.
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