Drainage and Waterproofing Siesta Key
Foundation Masters provides homeowners, condominium boards and commercial property managers on Siesta Key with engineer designed solutions to stop flooding, water intrusion, hydrostatic pressure and soil erosion.
The sand here is 99 percent quartz, very fine, and almost entirely free of shell, coral, feldspar and mica. That is what makes the beach famous. It is also what makes the ground move.
We are a licensed Florida engineering firm and a repair contractor in the same company, and we were the first engineering firm to pioneer the waterproofing industry in Florida. Qualifying work carries a lifetime transferable warranty.
Contractor Execution With Engineering Behind It
Foundation Masters is a licensed Florida engineering firm, CA# 30969, and a structural repair contractor. We work the length of Siesta Key: the Gulf front houses and estates, the condominium and association buildings from the Village down through Crescent Beach toward Turtle Beach, the canal and bayfront lots on the Sarasota Bay side, and the commercial and hospitality property in the Village.
The work is usually standing water that will not clear, moisture coming up through a slab, hydrostatic pressure against below grade concrete, salt driven spalling on concrete near grade, a seawall with ground dropping behind it, and above all the one this island produces more of than anywhere else we work: material leaving from under things. Pool decks, driveways, walkways, patios and slab edges going hollow.
That last category is not bad luck and it is not bad workmanship. It is what this particular soil does when water moves through it, and once you understand why, the repair strategy changes. We pair contractor work with in house civil engineering, geotechnical engineering in Sarasota and soil borings, so the design and the installation answer to the same firm.
A licensed Florida professional engineer signs and seals the drawings. Inspections are free.
Signs You Need Drainage and Waterproofing on Siesta Key
- Pool deck, patio or walkway that sounds hollow underfoot
- Pavers that have dropped in one panel and nowhere else
- Standing water or soggy yards after storms
- Buckled wood floors or tile popping from slab moisture
- Water stains or efflorescence along baseboards and walls
- Mildew odor or visible mold near slab edges
- A depression appearing near a downspout, a hose bib or a buried line
- Rust staining, cracking or spalling on concrete near grade
- Ground dropping behind a seawall cap on the bay side
The first two and the seventh belong together and they are the Siesta Key signature. All three are the same event: sand has been carried out from underneath by moving water, and the surface only reported it once enough had gone.
The Sand That Made This Island Famous Is the Reason the Ground Moves
Everybody who has been here knows the story. The sand on Siesta Beach is roughly 99 percent quartz, very fine and flour like, with essentially no coral or shell fragments in it. Harvard geologists trace it to the Appalachian Mountains, carried down rivers over millions of years, and describe a material from which the feldspar and the mica have been weathered away, leaving almost pure quartz. It reflects so much light that it stays cool underfoot, and it has been ranked the top beach in the contiguous United States, taking that spot three times since 2015.
Now read that description again as a soils description rather than a tourism one, because every word of it has an engineering meaning.
Almost one mineral. The feldspar and mica are gone. So are the shell and coral fragments that make most Gulf coast sand a mixture. What is left is close to a single mineral in a narrow range of grain sizes, which in soil mechanics is called a uniformly graded soil. Uniformly graded means there are very few small particles to fill the gaps between the larger ones, so the material has a high void ratio and it interlocks poorly.
No fines. Clean sand contains no clay and effectively no silt, which means it has no cohesion at all. Nothing sticks it together. All of its strength is friction between grains, and friction between grains only exists while those grains are confined and pressed against each other. This is why you cannot build a sandcastle with dry Siesta sand and why you can with the shellier stuff further north.
Very high permeability. Water passes through it freely, which is the origin of the most expensive misconception on this island, namely that Siesta Key does not have a drainage problem because everything soaks straight in.
Put those three together and you get the actual condition. A soil that water moves through easily, that has nothing binding it, and whose grains are all much the same size, is the textbook material for internal erosion. Water travelling through it does not simply pass by. It picks the sand up and takes it along. The problem on Siesta Key is not that the ground gets soft. It is that the ground leaves.
Surface Water
Grade, collection and conveyance. The Florida Building Code requires the ground to fall six inches within the first ten feet from the foundation, and two percent on impervious surfaces. Here the point of that fall is as much about controlling where water enters the soil as about where it ends up.
Water Already Under the Slab
Hydrostatic pressure and capillary movement through porous concrete. Free draining sand does not save you from this, because on a barrier island the water only drains as far as a water table that is already close to the surface.
Soil That Travels
The condition specific to this island. In cohesionless, uniformly graded sand, concentrated flow moves material rather than merely passing through it, so a small persistent leak does damage out of all proportion to its size.
A Dripping Downspout Is an Excavation Running at Two Grains a Second
On ordinary ground, a downspout discharging onto the soil beside a patio is a nuisance. It makes a wet patch and it grows moss. On clean, fines free, uniformly graded quartz sand it is something else entirely: a small, continuous, extremely patient excavation.
Every time it rains, that concentrated flow enters the soil at one point and moves through it. The soil has no cohesion, so there is nothing holding the grains in place against the drag of the water. A few grains go with it. Repeat that a few hundred times a year for eight years and the quantity removed is measured in wheelbarrows, all of it from a place nobody can see.
The same thing happens at a separated drain coupling, a cracked hose bib line, an irrigation leak, an unsealed joint where a slab meets a wall, or a pool that has been losing a small amount of water for a long time. None of these look like structural problems. All of them are, on this island, because the material they are running through will not stay put.
And here is the part that catches owners out. A slab spanning a void looks completely normal. Concrete is stiff enough to bridge a surprising amount of nothing. The deck is level, the pavers are flat, the driveway is fine, and then one day a corner drops an inch, or a panel tips, or somebody parks a heavier vehicle in the usual place. The failure is sudden. The cause took most of a decade.
Which is why filling the void is the second half of the job and never the first. Fill it without finding the water and you have bought a season or two. We find where water is entering, interrupt the path, then fill, and we use borings where the question is how far the loss extends rather than whether it happened.
Mostly County, But Check
Siesta Key is one of the places where the permitting answer is genuinely not obvious, and it is worth establishing before anybody starts. The majority of the key is unincorporated Sarasota County, handled as a census designated place, so for most properties the county permits, inspects and administers the floodplain. But a portion of the key lies inside the city boundary of Sarasota, and for those parcels the City is the authority.
That is not a technicality on an island where a great deal of advice travels by conversation. Two owners a few streets apart can be describing two different processes and both be right about their own property. Confirm which applies to your parcel rather than assuming, particularly before anything that turns on a determination.
On the flood side, in a mapped flood hazard area the lowest floor has to be at or above base flood elevation plus one foot, with certification at lowest floor placement and again at final inspection. Whether an older structure gets pulled into that turns on a substantial improvement or substantial damage determination, and the threshold is 50 percent of the market value of the structure alone, not the land. On Siesta Key, where a very large share of value is the location, that denominator is far smaller than owners expect.
One correction while we are here, because it appears on a great many pages about this coast. There is no general Florida rule requiring a finished floor slab to be twelve inches above grade. The code requires the six inch fall in ten feet described above, and a foundation drain only where a foundation both retains earth and encloses habitable or usable space below grade, which a Florida slab on grade house never does.
Check your zone through the FEMA Flood Map Service Center, and take anything that turns on a determination to the authority with jurisdiction over your parcel and to counsel.
Rate Matters More Than Total Here
Pages about this coast routinely quote 50 to 60 inches a year. The nearest well documented long records run below that: the Bradenton normal for 1991 to 2020 is 56.28 inches and the Tampa normal is 49.48 inches. Quoting the top of a range as the average inflates every number that follows from it.
You will also see three inches of rain in an hour described as an ordinary summer storm. It is not. That is close to the peak rate in events the National Weather Service treats as extremely rare.
On Siesta Key the annual total is not the number that matters and neither, oddly, is the peak. What matters is the velocity of water at the point where it enters the soil. Two inches of rain arriving evenly across a lawn does very little. The same two inches arriving through one downspout onto one square foot of unprotected sand does a great deal, because the damage mechanism is drag on individual grains rather than volume.
Which is why on this island the cheapest effective work is frequently not a trench at all. It is taking every concentrated discharge on the property and giving it somewhere controlled to land.
What the Work Actually Is
Foundation Masters developed the first true engineered waterproofing system in Florida to solve these issues. The process is four steps and it does not vary much.
- Excavating a trench to roughly 12 inches below the slab edge to expose the footer and wall
- Applying the Seal Tight Waterproofing System to protect below grade concrete and footings
- Designing engineered drainage piping or sump discharge to safely redirect water away from the structure and the underlying soils
- Installing gutters and grading corrections to control surface runoff
The fourth step is not the afterthought here that it is elsewhere. Gutters, leaders and controlled discharge points are the primary defense against soil loss on this island, because they remove the concentrated flow that does the damage. Alongside that we handle subgrade stabilization and void filling under slabs, decks and pool surrounds, trench drain and catch basin repair, vapor retarder work under new slabs, and seawall repair and permitting on the bay side.
One detail worth naming: we line drainage trenches with geotextile as a matter of course. In a soil with no fines, an unlined gravel trench does not stay a gravel trench. The surrounding sand migrates into the voids between the stones, the trench silts up from the outside in, and the ground around it settles. That is a filtration requirement, not a finishing touch.
The Wall Is Only as Good as What Is Behind It
The canal and bayfront lots on the Sarasota Bay side of the key are where the soil argument on this page becomes most expensive, because a seawall is a structure holding back exactly the kind of material that most wants to travel.
A seawall is not a solid dam. It is a wall with a tide behind it and a tide in front of it, and water moves through and around it. In cohesionless sand, any concentrated path through or behind that wall, a failed joint, a cracked panel, a corroded tieback, a weep hole doing more than weeping, becomes a route for the backfill to leave. The wall stays standing and the ground behind it goes.
That is why the first sign is almost never the wall. It is a dip in the lawn a few feet inland, a paver that has tipped, or a gap opening under a pool deck near the water. By the time the cap is visibly out of line, a great deal of material has already gone.
So on bayside property we look at the drainage crossing the top of the bank, the condition of the wall, what is behind it, and where the discharge elevations sit, as one investigation rather than two. Sheet piling where an edge has to be cut off, and permitting where the fix is structural.
Siesta Key and the Sarasota Keys
The useful question on this island is not which end you are on. It is where water is entering your soil, how concentrated it is when it gets there, and how much has already left.
Siesta Village and the North End
The Village commercial and hospitality property, the condominium buildings, and the residential streets at the north end toward Big Sarasota Pass. Higher density, more paving and more concentrated discharge points per acre than anywhere else on the key.
Crescent Beach and the Gulf Front
The Gulf side houses, estates and resort property. Open exposure, salt reaching structural concrete, and pool decks and terraces sitting on the most mobile material on the island.
The Bayside, the Canals and Turtle Beach
Waterfront lots facing Sarasota Bay and the canals, down through the south end. Seawalls, docks, tidal discharge and backfill that will travel through any path you leave it.
The Neighboring Keys and the Mainland
Conditions differ island by island, so each has its own page: Lido Key, St. Armands Key, Longboat Key and Casey Key, which is the island immediately south. Mainland conditions are on our Sarasota page.
Siesta Key Drainage and Waterproofing
Why does my yard flood even with drains installed?
Barrier islands have shallow groundwater and flat grades. After heavy rain or high tide, soils saturate and drains cannot empty because groundwater is already near the surface. On Siesta Key there is a second reason worth knowing: an unlined gravel trench in fines free sand fills with migrating sand over time, so a system that drained well when it was installed can be substantially blocked from the outside in a few years later.
Why is my slab letting moisture through?
Because water is reaching it and there is nothing between the two. Many houses here were built with slabs at or near grade with vapor barriers to the standards of their day. Concrete is porous, so once the water table contacts the slab, capillary movement carries moisture upward with no crack involved at all. Free draining sand does not prevent this, because the water only drains down to a water table that is already close.
I was told the sand here drains beautifully. Why do I have a water problem?
Because draining fast and draining away are different things. Water moves through this sand easily, then reaches a water table that on a barrier island sits close to the surface, and stops. Meanwhile the same permeability that lets it through so readily is what allows moving water to carry the sand with it. High permeability is genuinely an advantage in some respects. On this island it comes packaged with a soil that has nothing holding it together.
My pool deck sounds hollow. How serious is that?
Serious enough to look at now rather than later. A hollow sound means material has left from underneath, which on Siesta Key is almost always washout rather than compression. Concrete will bridge a void until it will not, and the failure when it comes is sudden even though the cause took years. The important part is not the void, it is finding what is putting water into that spot, because filling it without interrupting the path just restarts the clock.
What is different about the sand on Siesta Key?
It is roughly 99 percent quartz, very fine, and effectively free of shell and coral fragments, with the feldspar and mica weathered out over its journey down from the Appalachians. In soils terms that makes it a clean, uniformly graded, cohesionless sand: high permeability, high void ratio, poor interlock and no binding material at all. It is a lovely thing to walk on and a demanding thing to build on and drain.
Can you waterproof an existing home on Siesta Key?
Yes. Our Seal Tight System is engineered for coastal hydrostatic pressure and is applied to the positive side, the face the groundwater actually touches, which is why it works on a structure that is already built rather than only on new construction.
Do tides and storm surge affect my property on Siesta Key?
Yes. High tides and coastal surges raise nearby groundwater and reduce infiltration, and surge in particular moves large volumes of water through the soil in both directions, which in a cohesionless material means it moves the soil too. That is why substantial voids frequently appear after a surge event on properties that took no visible water inside.
Am I in the City of Sarasota or in Sarasota County?
Most of Siesta Key is unincorporated Sarasota County, but a portion of the key lies inside the city boundary of Sarasota, so it genuinely depends on your parcel. It decides who permits and inspects your work and who makes a substantial improvement determination on your structure, so confirm it rather than relying on what a neighbor was told.
Do you handle commercial parking lot drainage problems?
Yes. We repair and retrofit catch basins, storm pipes and subgrade failures for retail, resorts, condominium associations and HOA property across Siesta Key and Sarasota County. On this island the subgrade is usually the failure rather than the pavement, for the reasons set out above. Details on parking lot drainage systems.
Where can I check my property flood risk?
Use the FEMA Flood Map Service Center. For anything that turns on a determination for your specific structure, go to whichever authority has jurisdiction over your parcel, which on this key means establishing first whether you are city or county, and get the answer in writing.
Do you install French drains on Siesta Key?
Not as a default, and here there are two reasons rather than one. The usual reason applies: a French drain moves water by gravity to a lower point and on a barrier island every lower point is tidal. The reason specific to this island is that an unlined gravel trench in fines free sand becomes a sand trap, filling from the surrounding soil and settling the ground around it. Where a trench is right, it is lined and it discharges somewhere real.
Does drainage and waterproofing work carry the lifetime warranty?
Qualifying drainage and waterproofing work carries a lifetime transferable warranty, which means it passes to the next owner of the property. On an island where a great deal of property changes hands, transferability is the part that matters. The scopes and the exclusions are set out on our warranties page.
Drainage and Waterproofing Services
- Seal Tight Waterproofing System on the positive side of below grade concrete
- Geotextile lined perimeter drainage, because unlined gravel does not survive in this soil
- Gutter, leader and controlled discharge design to remove concentrated flow at source
- Designed sump and pumped discharge where gravity is not available
- Subgrade stabilization and void filling under slabs, pool decks, patios and driveways
- Catch basin, trench drain and storm pipe repair and replacement
- Parking lot drainage systems for commercial and association property
- Grading corrections and paver and deck resetting over stabilized subgrade
- Vapor retarder detailing under new slabs
- Seawall repair, elevation and replacement, and seawall permitting
- Sheet piling where a bayside edge has to be cut off
When the Water Has Already Done Damage
On cohesionless soil the structural side follows the drainage side more often than on almost any other ground, because the failure mode is material leaving rather than material compressing. The drainage work stops the water. The structural work corrects what has already moved.
- Foundation repair on Siesta Key and house leveling on Siesta Key
- Foundation repair in Sarasota
- Foundation settlement repair, which explains uniform settlement, tilt, sagging and hogging
- Helical piers, push piers and pipe pile underpinning through loose coastal sand
- Weathered cracks and how to read what a crack is telling you
- Steel corrosion in coastal concrete
- Geotechnical engineering, Sarasota, flood asset protection and foundation inspection
Statewide context sits on foundation repair in Florida and drainage and waterproofing in Florida.
Where Else We Work
Drainage and Waterproofing Florida · All Locations · Sarasota · Lido Key · St. Armands Key · Longboat Key · Casey Key · Venice · Bradenton · Anna Maria Island · Holmes Beach · Port Charlotte · Punta Gorda · Cape Coral · Madeira Beach · Redington Beach · Tampa · Flood Asset Protection · Efflorescence · Soil Borings · Warranties
Get a Drainage and Waterproofing Inspection on Siesta Key
Because Florida has no statewide waterproofing code, you need people who understand local soils, fluctuating water tables and coastal pressures. What the code does require is narrower than most owners think. The Florida Building Code requires grading that falls six inches within the first ten feet of the foundation, and two percent on impervious surfaces within that distance. It requires a real foundation drain only where a foundation both retains earth and encloses habitable or usable space below grade, which a Florida slab on grade house never does. Outside a mapped flood hazard area there is no minimum finished floor elevation above adjacent grade and no elevation certification.
Put plainly, on a typical Siesta Key house the detail that would keep water out of the slab is not required and is therefore usually not there, and nothing in the code addresses the soil behavior that costs owners the most on this island. We build the detail anyway, because the absence of a requirement is not the same as the absence of a problem.
Under new slabs we detail vapor retarders to ASTM E1745, which caps water vapor permeance at 0.1 perms across all classes and requires 45 pounds per inch tensile and 2,200 grams puncture resistance for Class A. The 2021 IRC raised the residential requirement to a minimum 10 mil Class A sheet with 6 inch lapped joints.
Inspections are free. On Siesta Key the first thing we want to find is every place concentrated water is entering your soil, because on this ground that is where the money goes.
Find Out How Much Has Already Gone
Call for direct help with a hollow pool deck, dropped pavers, standing water, moisture through a slab, hydrostatic pressure, spalling concrete, or ground disappearing behind a seawall. We will tell you what is wrong before we tell you what it costs.