Should you seal, waterproof or paint brick? What the preservation guidance says

Updated November 11, 2026 · KeystoneProGuide editorial team

Should you seal or waterproof brick?

The National Park Service's (NPS) answer, for older masonry, is generally no. It says that waterproofing brick, either with chemicals sold for the purpose or by painting it with a non-permeable paint or coating, "will accelerate the decay" by trapping moisture behind the new coating.

That runs against a common sales pitch. Angi, for example, lists waterproofing at $1 to $4 per square foot as an add-on contractors may suggest after repointing. The price is real; whether the treatment suits your wall is a separate question, and on old brick the federal preservation guidance points the other way.

Why would a coating make things worse?

Because masonry walls get wet whatever you do, and the question is how they dry. The NPS describes water as the greatest and a constant threat to historic structures. It arrives from rain and snow, from sprinklers, from the ground, from roof leaks and even from air conditioning. A traditional wall handles that by letting moisture move out through its soft mortar joints.

A coating that keeps water from getting out holds it in the brick. The NPS explains what follows: salts carried by the water crystallize inside the pores and break the brick apart from within, flaking off its face, and in a climate with winter freezes, trapped water freezes and expands. Its account of an Iowa sandstone house shows the effect of an impervious base coat, or parging: ground moisture wicked up the wall, concentrated just above the parging and broke down the stone, while the damage behind the coating stayed hidden.

Is it ever right to coat brick?

Sometimes. The NPS says that if it is absolutely necessary to coat a brick wall, a water-permeable coating will work best. But it adds a caution: a wall deteriorated enough to need coating has usually lost its hard outer surface to an earlier treatment such as sandblasting. If it has not been abrasively cleaned, the wall needs a closer look at why it is deteriorating before anything is applied.

Its broader rule, in its own words, is that coating with an impervious material such as high-content portland cement "is never recommended".

What should you do instead?

Deal with the water at its source. On the masonry itself, the NPS's remedy is sound, compatible pointing and repair rather than a surface barrier. Around the house, Penn State Extension says downspouts should discharge away from foundations, and the Federal Emergency Management Agency advises sloping soil away from the walls with a binding material such as clay.

Look for the cause before the treatment. Persistent damp at the base of a wall, white salt deposits along a line, or flaking faces above a coating all point to where water is getting in or failing to get out.

How can you tell if a coated wall is trapping moisture?

Look where the coating ends and where water collects. The signs the NPS describes are faces of brick or stone flaking off in slices, white salt deposits that keep returning, and, on a wall parged at its base, damage concentrated in the band just above the coating. In its Iowa example the damage behind the parging could not be seen at all, and the NPS warns that a wall's strength can be compromised without anyone knowing in time. If a coated wall shows these signs, ask a mason experienced with older masonry to assess it before adding another layer.

What about painting brick?

Paint is a coating like any other, and the NPS's warning about non-permeable paint applies. Two more rules come in with paint.

• Lead. If an older painted wall is to be stripped, scraped or repainted, the U.S. Environmental Protection Agency's lead rule applies to homes built before 1978. A paid contractor who disturbs more than 20 square feet of exterior paint must be lead-safe certified, unless the paint has been tested and found lead-free.
• Stripping. Removing paint from masonry means chemicals or abrasion. The NPS says abrasive methods such as sandblasting destroy the hard surface of brick. The General Services Administration's cleaning specification for historic masonry bars raw acids and alkalis and requires surfaces cleaned with chemical products to be fully neutralized and tested afterwards.

Do you need approval to seal or paint in Philadelphia?

If your property is on the Philadelphia Register of Historic Places, yes. The Historical Commission's review covers "painting, coating, staining, or sealing surfaces except wood and metal trim", along with masonry cleaning and painting. Ordinary maintenance such as repainting wood trim does not need review.

What should you ask a contractor who recommends sealing?

• What problem is the sealer meant to solve, and what is causing it?
• Is the product water-repellent only, or does it stop vapor too?
• What will happen to moisture already in the wall?
• Has the mortar been checked, and would repointing address the problem?
• If the house was built before 1978 and is painted, are you lead-safe certified?

For more on the mortar side, see repointing an old brick house. To judge whether a recommendation is an upsell, the scams guide covers the tactics consumer authorities document. Masons are listed on the masonry contractors page.

Sources

1. Common Problems with Brick Masonry, U.S. National Park Service
2. This Masonry is for the Bees!, U.S. National Park Service
3. Mortar, Unsung Hero of History, U.S. National Park Service
4. How Much Does Repointing Brick Cost? [2026 Data], Angi
5. Renovation, Repair and Painting Program: Contractors, U.S. Environmental Protection Agency
6. Get approval for work to a historic property, City of Philadelphia
7. Cleaning historic masonry, U.S. General Services Administration
8. How Can I Control Stormwater on My Property?, Penn State Extension
9. Fact Sheet: Be Flood Smart. Protect Your Property, Federal Emergency Management Agency