Rock salt and other ice melts damage stucco from the bottom up. Salty meltwater soaks into the base of the wall, the stoop and the steps, then grows crystals inside the pores as it dries and pops the surface off. MNM Construction Stucco repairs salt damaged stucco bases across NYC and Long Island: (516) 713-9199.
How Salt Destroys the Bottom of a Stucco Wall
Stucco is porous. That is part of why it works: it takes on a little water and lets it dry back out. The trouble starts when that water is full of salt.
- Splash and wicking. Every shovel of salty slush pushed against the house, and every car that sprays the curb, leaves salt water on the bottom of the wall. The stucco draws it up like a wick.
- Crystals inside the wall. As the water dries, the salt stays behind and crystallizes in the pores just under the surface. Crystals take up more room than the dissolved salt, so they push the finish coat off from behind.
- A wall that stays wet. Salt pulls moisture out of the air, so a salty base dries slowly. A wet base goes through far more freeze and thaw cycles than the rest of the wall.
- Rusting metal. Chlorides corrode the metal lath and the weep screed at the bottom edge. Rusting steel swells, which shows up as rust streaks, cracks and a base that sounds hollow when you tap it.
The Signs, Usually by March
- A white crust or powder along the bottom of the wall or the sides of the stoop. It can look like efflorescence, but it comes back every winter in the same band.
- Finish or paint peeling in a strip from the sidewalk up to roughly a foot or a foot and a half.
- Sandy grit on the sidewalk under the wall.
- Rust colored stains at the base.
- Edges of stuccoed steps and stoop cheeks crumbling or breaking off.
- A dull, hollow sound when you knock on the lower part of the wall.
Why NYC Houses Get It Worse
Three things stack up here. First, the city makes owners clear and treat the sidewalk fast: within 4 hours if the snow stops between 7am and 4:59pm, within 14 hours if it stops between 5pm and 8:59pm, and by 11am if it stops overnight. Fines start around $100 and go up to $350 for repeat violations. So salt goes down quickly and heavily.
Second, a lot of older row houses and two family homes have stucco or parging that runs straight down into the sidewalk or the areaway, with no gap. Current practice puts the bottom edge of new stucco, the weep screed, at least 2 inches above paving and 4 inches above soil, so water can drain out and the wall does not sit in slush. Walls built without that gap drink salt water every storm.
Third, on busy avenues the plows and traffic throw salty slush straight at the first floor of the building.
馃挕 Shovel first, salt second. The less snow left on the ground, the less salt you need to use. A clean shovel pass before salting cuts the salt you need, and the damage along with it.
What to Use Instead, and How
- Calcium magnesium acetate (CMA). Chloride free and far gentler on cement based materials. It costs more, so use it where it matters: the stoop, the steps and the strip of sidewalk against the wall.
- Sand or grit for traction on icy spots. It does not melt anything, but it does not attack the wall either.
- Avoid magnesium chloride on stucco, stoops and concrete. Research on cement based materials puts it among the most destructive deicers.
- Keep salt off the wall. Spread it on the walking path, not against the house, and do not pile salty snow against the building.
- Clean up in spring. Dry brush the white crust off the base once it is dry. Do not pressure wash salt into the wall.
How a Salt Damaged Base Gets Repaired
Patching over salty stucco does not last, because the salt is still in the wall and pushes the new coat off the same way. A proper repair:
- Removes loose and salt contaminated stucco back to sound material.
- Checks the metal lath and weep screed, and replaces anything rusted.
- Sets the new bottom edge above the sidewalk where the building allows it, with a sealant joint at the paving instead of stucco running into the concrete.
- Rebuilds the base coats and finishes with a breathable coat matched to the rest of the wall, using the same approach as a texture and color match.
Small patches usually run a few hundred dollars. A full base band along a row house front is priced by the linear foot after we see how deep the salt went and what the lath looks like.
When to Fix It
Not in January. New stucco needs temperatures above about 40掳F to cure, and there is no point repairing a base that will be salted again next week. Plan it for spring, once salting season is over. The exception is a base that is open enough to let water into the wall; that gets closed up now, as covered in stucco in winter.
Salt Damaged Stucco? Free Base Inspection
We look at the base of the wall, the stoop and the lath, tell you how deep the salt went, and give you an itemized price to fix it in spring. Serving Brooklyn, Queens, Manhattan, the Bronx, Nassau and Suffolk.
馃摓 (516) 713-9199Frequently Asked Questions
Does rock salt damage stucco?
Yes. Salty meltwater soaks into the base of the wall and into stuccoed stoops and steps. As it dries, salt crystals grow inside the pores and push the surface off. The salt also keeps the base wet longer, so freeze and thaw does more damage, and chlorides corrode the metal lath and weep screed at the bottom of the wall.
What ice melt is safe to use near stucco?
Nothing is completely harmless, but calcium magnesium acetate, sold as CMA, is chloride free and far gentler on cement based materials than rock salt. It costs more, so use it on the stoop and the strip of sidewalk against the house. Sand or grit gives traction without melting anything. Avoid magnesium chloride on cement surfaces.
Why is the bottom of my stucco wall flaking?
If the damage is a band from the sidewalk up to about a foot or so, and it gets worse every spring, salt is the usual cause, often combined with stucco that runs straight down into the sidewalk with no gap. Water and salt wick up into the wall, crystallize and break the finish. A white crust or rust stains at the base point the same way.
When should salt damaged stucco be repaired?
In spring, after salting season is over and temperatures stay above 40掳F, so the new stucco can cure properly. The exception is a base that is open enough to let water into the wall. That should be closed up right away and finished properly when the weather allows.
Flaking at the base of the wall? Call (516) 713-9199 or request a free written quote.