Diagnosis

Signs of Moisture Behind Your Stucco, and What to Do

Trapped water leaves evidence long before the wall fails. Here is what to look for outside and inside a Port St. Lucie home, how water actually gets in, and what to do first.

What moisture behind stucco actually means

Stucco is not a raincoat. It is a cement skin that sheds most water and absorbs some, and every wall behind it assumes a little water will get in and needs a route back out. On a concrete block home in Port St. Lucie, the block manages that water and the stucco is bonded straight to it. On an older frame home, and Fort Pierce and Stuart have plenty, there is lath, a weather resistant barrier, and a drainage plane behind the plaster.

Problems begin when water enters faster than it can leave, or enters somewhere the wall was never designed to drain. On block that shows as saturation, salt deposits, and eventually loss of bond. On frame it shows as rotted sheathing and rusted lath. Keep it in mind while you walk your house. The newer block stock in Tradition, St. Lucie West, and Palm City telegraphs moisture on the surface. Older frame walls in Fort Pierce and Stuart hide it for years.

What you can see from the driveway

Start on a dry day, two or three days after the last real rain, and walk the perimeter slowly. Waiting matters, because everything looks dark right after a storm. What counts is what stays dark once the rest of the wall has dried.

Look with the light across the wall rather than straight at it. Standing at a corner and sighting down the face shows bulges and blisters that are invisible head on. Do this on every elevation, and look hardest at the walls that catch driving rain in a summer storm.

• Patches that stay dark long after the surrounding wall has dried
• Vertical staining below a window sill, a light fixture, or a hose bib
• White powdery or crusty deposits, usually low on the wall or near a crack
• Bulges or blisters visible when you sight along the wall face
• Paint lifting in sheets rather than chalking evenly
• A cluster of fine cracks in one area while the rest of the wall is clean
• Growth in a single patch rather than across a whole shaded side

What you find by touching and tapping the wall

Sounding a wall is the most useful thing a homeowner can do without a single tool. Use a knuckle or the plastic handle of a screwdriver and tap in a grid, roughly every foot. Bonded stucco on block rings hard and bright. Delaminated stucco thuds, or gives back a dull drum note. Nobody needs training for this. The difference is obvious the moment you hear both within a few seconds of each other.

When you find a dull spot, work outward until the sound goes solid again, and mark that boundary with chalk or painter tape. The hollow area is nearly always larger than the damage you can see, and mapping it honestly is what tells a contractor how big the real repair is.

Then use a flat palm. Stucco that flexes under hand pressure has lost its grip. On frame walls a hollow note between studs is normal, so listen for a change in tone rather than for hollowness itself. Anything soft or punky, or that lets a screwdriver tip sink in, means the substrate is gone, not just the finish.

The signs that show up inside the house

Inside evidence arrives late on a block home and early on a frame one, which is worth knowing before you treat a clean interior as proof that everything is fine. Block holds a lot of water before it passes any through.

Walk the inside of every exterior wall, especially under windows and in closets, which are the two places nobody looks. If your home has tile on slab, check the grout lines along the outside walls.

• Baseboard staining, swelling, or paint lifting along an exterior wall
• Grout lines darkening in a band that follows one outside wall
• A musty smell in a closet or corner that never quite clears
• Bubbling paint on the inside face of a block wall
• White salt deposits on an interior block wall or in the garage

Where the water is actually getting in

The stucco field is rarely the culprit. Water almost always enters at a transition, a penetration, or a skipped detail, then travels sideways or down before it shows up somewhere else. That is why chasing a stain instead of the entry point wastes so much money.

Work down this list before anyone talks about removing stucco. Several cost nothing to check and very little to fix, and they account for a real share of the calls we take across St. Lucie, Martin, and Indian River counties.

• Window and door perimeters where the sealant has split, shrunk, or was never tooled properly
• Missing kick-out flashing where a roof edge dies into a wall, which dumps a whole roof plane behind the stucco
• Roof to wall transitions on barrel tile, where valley discharge concentrates water in one spot
• Sprinkler heads hitting the wall and soaking the same band several times a week, year round
• Negative grade, mulch, or new sod stacked up so the stucco runs below finished ground
• A weep screed at the base of the wall that is buried, painted shut, or packed with debris
• Penetrations with no sealant behind the flange: hose bibs, light fixtures, dryer vents, cable mounts
• Wind driven rain in hurricane season pushing water uphill through joints that shed a normal shower fine

What a moisture meter can and cannot tell you

There are two kinds worth knowing. A pinless meter reads moisture near the surface and leaves no mark. A probe meter puts two small pins through a drilled hole to read at depth. Both are useful and both get badly oversold on sales calls.

What a meter does well is compare. Take twenty readings across one elevation, mark them on a photo, and the wet zone draws itself. Follow that zone up and sideways, then repeat the same grid in a month to see whether the wall is drying. What a meter cannot do is tell you where the water came from, or separate a wall wet from this morning's rain from one wet for two years. It reads unreliably through elastomeric coatings and metal lath, and absolute numbers on cement mean little because most meter scales are calibrated for wood. Anyone quoting a demolition scope off a single reading is guessing.

What to do, in the order we would do it

Start with the water you can stop today. Turning a sprinkler head and pulling mulch off a blocked weep screed cost nothing and resolve a surprising number of dark wall complaints. Give it a few good storms and look again. Rain here means you will not wait long for a test.

Next, fix the details. Replace failed sealant at windows and doors, seal behind fixture flanges, and get a roofer to add kick-out flashing where a roof edge meets a wall without one. These are ordinary maintenance items, not emergencies. Only then, if the signs persist after real rain, does opening the wall make sense. A test cut is small, usually a foot or two, placed at the worst part of your sounding map so it shows the real condition of the lath, the barrier, or the block.

• Redirect sprinklers and clear anything stacked against the base of the wall
• Correct grade so water runs away from the house
• Replace failed sealant at window and door perimeters
• Add kick-out flashing where a roof edge terminates into a wall
• Re-check after several real rains before committing to anything larger