Cracked pool deck: repair, resurface or call an engineer

Run a fingernail across it. If the nail glides over the crack without catching, the two sides are level and the crack is almost certainly cosmetic — the concrete trade's own literature says most random cracks that appear early, however unsightly, rarely affect the slab's integrity. If the nail catches on an edge, one side has moved relative to the other, and that is a different conversation. That is the whole first test, and it takes ten seconds.

The rest of this page is how to read what you found, why Florida decks crack the way they do, and which of four honest answers your crack points to: seal it and live with it, lift the slab, resurface it, or take it out. We pour a shell topping, so one of those four is ours; the other three are not, and we will say when they are the right call. Nobody in Florida is writing this down — the pages that rank are either written for a freeze-thaw climate or written by companies that lift slabs — so here it is for the Gulf Coast.

Reading the crack

Six things, in the order that matters. ACI's guide to cracks in concrete names width, pattern and depth as the indicators, and whether the crack is still moving; this is that list in a homeowner's hands.

• Width. Hairline — under about an eighth of an inch, thinner than a credit card — is usually cosmetic. A crack a card slips into deserves a look. Past about a quarter inch, or anything that is opening, a topping stops being an answer.
• Lift. Is one side higher than the other? Any vertical offset — even the quarter inch that the accessibility code treats as a trip — means the slab has moved, not just shrunk. A surface cannot fix a slab.
• Pattern. A crack that follows a straight line at a joint, or runs from a corner of the pool, is the slab relieving itself where it was told to, or where it wanted to. A web of fine cracks across a patch — crazing — is a finishing or curing story on the surface only. A long wandering crack that crosses joints is a slab story.
• Sound. Tap around it with a coin or a screwdriver handle. Solid concrete rings; a hollow, drummy sound over an area means something under the surface has let go — a coating from the slab, or the slab from its base.
• Movement. Mark the ends with a pencil and a date. Look again after the wet season and after the dry one. A crack the same length in March and October is dormant; one that has grown is active, and an active crack will come back through anything laid over it.
• Water. Does water sit in the crack, or drain toward it? A crack that holds water is being widened by it, and a deck that puddles anywhere is a drainage problem before it is a concrete one.

If you poured a deck recently and are worried about hairlines at the joints, the first month after your deck is poured is the normal-and-not-normal list for a new pour; this page is the same test applied to an old one.

Why Florida decks crack

Shrinkage, and the joints that were not there

Every concrete slab shrinks as it cures and cracks somewhere; the only question is whether it cracks where somebody decided. Control joints — cut early, sized to the pour — give it a line. A deck poured without them, or with them cut too late or too far apart, chooses its own line, usually from an inside corner or the corner of the pool. In Bradenton, where most of what we pour is driveways, this is the argument we make before every job, and it applies to a deck exactly.

The ground, and the water in it

Gulf Coast soils are not one thing. Sand drains and stays put; the organic and expansive layers under parts of Manatee and Sarasota counties compress, swell and shrink with the water table, and a slab on them moves with them. Water does the rest: a downspout emptying beside the deck, an irrigation head aimed at it, a pool or a supply line leaking, all wash the fine material out from under a slab until a corner has nothing to sit on. That is the sinking deck — settlement — and it is a ground problem wearing a concrete costume. The Florida Geological Survey is careful to say that subsidence from soils like these can mimic sinkhole activity, and that a depression is a subsidence incident until a licensed professional geologist or engineer says otherwise. We are neither, and this page will not tell you which yours is.

Roots

A sabal palm or a live oak within a few yards of a deck will lift a section of it over a decade, and it lifts pavers and poured slabs alike — the pavers comparison has the same example. A root under a crack is usually a vertical offset, which means it is on the wrong side of the fingernail test.

A failed coating over a slab that did not fail

This is the one that sends the most people to a search box. An acrylic "cool deck" coating that has chalked and is coming off in sheets looks like a deck disintegrating. It is not; it is a paint film that has reached the end of its bond, over a slab that may be perfectly sound. The test is the tap: a coating letting go sounds hollow in patches and the slab underneath rings. If your deck was coated and the coating is what is failing, you are in the best possible position on this list, and sealing a shell deck explains why the replacement should not be another film.

The pool itself

A pool that is losing water is undermining its own deck, and a deck pulling away from the coping — a widening gap where the deck meets the pool shell — is a symptom of the pool or the ground, not of the deck. Call the pool company first. A deck resurfaced over a leaking shell will crack again, and the money spent on the surface will have bought nothing.

The four honest outcomes

Seal it and live with it

Right when: a dormant hairline, level on both sides, on a slab that rings solid, that you can accept seeing. A flexible sealant routed into the crack keeps water out and moves with the slab. It will show; a rigid patch will show more and crack beside the old line. Wrong when: the crack is active, or offset, or one of many across an area — sealing a symptom on a moving slab buys a season.

Lift the slab

Right when: the slab is sound but has settled — a corner has dropped, a panel tilts toward the house, the deck has separated from the coping — and the ground under it can be filled and packed. Polyurethane and mudjacking crews do this; it is a real trade and it is not ours. Wrong when: the slab is cracked through and moving in pieces, in which case lifting one piece moves the crack.

Resurface it

Right when: the slab is structurally intact and dry — cracks are hairline or crazing, the coating (if any) can be removed, nothing is offset and nothing has grown between seasons. Then a topping bonded to the slab gives you a new surface without demolition, and this is where Shellcrete by SRQ Modern comes in. Wrong when: any item in the next section is true. A topping follows whatever is beneath it.

Take it out and repour

Right when: the slab is cracked through and moving, too thin to bond to, sitting on a base that has washed out, or a terrace over occupied space whose waterproofing has failed — that last conversation starts with the waterproofing, not the finish. It is the expensive answer and it is sometimes the only honest one. In Sarasota, where most of what we look at was poured between 1965 and 1990, roughly one job in six ends with this answer after we have looked, and we would rather say so at the quote than after the pour.

What a topping can bridge, and what it cannot

A bonded shell topping is an inch and a half to two inches of new concrete, ground back to expose the shell, bonded to the slab it is poured on. Because it is bonded, it has the slab's strengths and the slab's problems.

It can bridge: hairline and craze cracking, after the cracks are routed and filled; surface scaling and spalling, once the loose material is ground off; a chalked or sheet-failing coating, once it is removed to sound concrete; the wrong colour; a slippery gloss sealer; a surface that has simply worn out.

It cannot bridge: an active crack, which will reappear in the new surface within a season; a displaced crack, which it will follow; a sinking slab, which it will sink with; an area that sounds hollow, which has nothing to bond to; a slab too thin or too weak to bond to at all; a terrace over occupied space with failed waterproofing.

And the rule under all of it: the joints in the old slab are cut through the new surface in the same places, because a topping poured across a joint is a crack waiting for the first hot afternoon. Bond is checked rather than assumed — the concrete repair trade has a pull-off test for exactly this — and the surface is prepared to a profile the topping can grip. The finish is decided afterwards; exposed shell is the one most old decks end up wearing, because it grips wet and reads as stone.

When to call a structural engineer

Call a Florida-licensed engineer, before any contractor, when: the two sides of a crack are offset by more than about a quarter inch; a crack has grown across a season; the deck is pulling away from the pool shell; the deck is a terrace over a room, a garage or a lanai; the ground has visibly dropped; or you suspect subsidence of any kind. An engineer's letter is a few hundred words that decide whether the next call is to a lifting crew, a demolition crew or to us, and it is the cheapest thing on this page. The Florida Board of Professional Engineers keeps the licence register.

Call the pool company first when the pool is losing water or the coping is separating; a deck is not the patient in that case.

What happens when you send photos

Photographs before a site visit — years of wasted drive time taught us that. Send four: the whole deck from a step-ladder or a balcony, the worst crack with a coin beside it for scale, the same crack with a straight edge laid across it to show any offset, and wherever water sits after rain. From those we can usually say which of the four outcomes you are looking at, and whether we are the right people to come and tap it. If we are, the pool decks page is where the form lives; if we are not, we will say who is.

What a resurfacing quote depends on — the state of the slab being the first thing — is on the cost guide, which is also the one place on this site a figure appears. We look at cracked decks across Manatee and Sarasota counties, and the two city pages say what the slabs in each usually turn out to be hiding.