The first sealer I ever brushed onto my own house was a mistake, and I paid for it about three winters later when a whole section of my chimney’s south face started shedding little chips of brick like fish scales. I’d trapped moisture behind a film that looked great on day one. My name’s Dave Marchetti, and I’ve spent the last 26 years repointing, tuckpointing, and patching up the brick and stone rowhomes and Victorians scattered across Staten Island, from St. George down through Tottenville.
So when a reader from Tottenville, out on the south tip of the island, wrote to ask whether he should seal the coastal brick on his 1920s house against the salt spray coming off Raritan Bay, I knew exactly what was driving the question. My honest answer was: sometimes, but be careful, because the wrong sealer on old masonry does more damage than the salt ever will.
What a sealer does to brick that’s built to breathe
Masonry is designed to breathe. Brick, natural stone, and the lime or portland mortar between them all absorb a little water and let it evaporate back out. That cycle is normal and healthy — it’s how these walls have survived a century of Staten Island winters. A sealer changes it. Depending on the product, you’re either coating the surface with a film or soaking a repellent down into the pores. The goal is to slow water from getting in, which in a place like Tottenville means slowing the salt-laden spray that wicks into soft old brick, crystallizes, and pops the face off from the inside.
The mistake I keep seeing near St. George
A lot of homeowners reach for a glossy acrylic thinking more coating equals more protection. On a dense new paver or a poured concrete stoop, fine. On soft, 100-year-old brick, it’s a trap. Water always finds a way in — through a hairline crack, or the back of the wall — and once it’s behind a non-breathable film it can’t dry outward. Come January it freezes, expands, and blows the brick face clean off. I’ve seen sealed row-home fronts near St. George look worse after five years than their untouched neighbors did after fifty.
Where I’d actually recommend sealing
There are real cases where I tell homeowners to go ahead:
- Below-grade foundation walls that stay damp year-round.
- Concrete or bluestone stoops taking road salt and de-icer every winter — you genuinely want to slow chloride absorption here.
- Coastal stone sills and caps sitting in salt spray, like the Tottenville reader’s.
In every one of those, the product matters as much as the decision to seal. I look for a breathable penetrating sealer — a silane or siloxane — that soaks in and repels water without forming a surface skin. Done right, it leaves the masonry looking natural, no shine, no plastic look.
Mortar repair comes before any sealer
The other time sealing makes sense is right after a proper cleaning, once you’ve dealt with whatever’s actually causing the damage. If your brick is spalling because water is getting in through failed mortar joints, a sealer won’t save it — you fix the mortar first. Repointing and mortar repair are the real work; sealing is the last five percent, not the fix. I’d sort out surface staining before ever touching a repellent, too, which I’ve written about separately in cleaning brick without damaging the mortar.
When to leave the brick alone
Skip the sealer entirely if your brick is soft, historic, or already spalling. Skip it if you can’t confirm the product is vapor-permeable. And never seal a wall with an active water problem you haven’t traced yet, because you’ll just lock that water inside. The EPA’s guidance on moisture makes the same core point about buildings generally: control the source of water first, since trapping it behind a barrier creates worse problems than the water alone. Their moisture and health guidance lays out the reasoning if you want the fuller version.
What it costs and how long it lasts
| Item | Detail | Typical value |
|---|---|---|
| Penetrating sealer, material only | Cost per gallon | $30–$60 |
| Penetrating sealer, coverage | Square feet per gallon on porous brick | 100–200 sq ft |
| Professional application | Cost per square foot, including prep and cleaning | $1.50–$4 |
| Breathable penetrating sealer | Years before reapplication | 7–10 years |
| Cheap film-forming sealer | Years before it peels | 3–5 years |
| Average Staten Island row-home front | Total job cost | $600–$2,000 |
Where you land in that range on a rowhome front comes down to height, access, and how much prep the brick needs before anything gets applied.
Questions I get asked about sealing old brick
Does sealing brick stop it from spalling? Not by itself. Spalling comes from water freezing inside the brick, so if water’s already getting in through failed joints or a bad cap, a surface sealer can trap it and speed up the damage. Fix the water source first — that usually means mortar repair or chimney repointing — then a breathable penetrating repellent can help.
Is it better to repair old brick or replace it? Repair almost always comes first. Spalled or cracked brick on a historic or heritage masonry wall can usually be cut out and replaced brick by brick, with the surrounding mortar repointed to match, rather than tearing out a whole section. Full replacement only makes sense once the damage has spread wide enough that spot repairs would cost close to the same as a re-do.
What kind of sealer is safe for old brick? A penetrating silane or siloxane repellent that soaks in and lets vapor escape. Avoid glossy acrylic or silicone film-formers on soft historic brick — they create a non-breathable skin that leads straight to freeze-thaw damage. Coatings behave differently on a slab than on a wall — an epoxy flooring installer in Las Vegas is picking for hot-tire pickup and UV, not vapor permeability.
How much does it cost to seal a house on Staten Island? Materials run $30 to $60 per gallon covering 100 to 200 square feet, and professional application runs $1.50 to $4 per square foot. A typical row-home front comes to roughly $600 to $2,000 depending on access and prep.
