Why Waterproofing Masonry in NYC Requires Diagnosis First

The most common waterproofing mistake in NYC is treating the symptom rather than the cause. Interior water stains can originate from failed pointing, a cracked lintel, a missing coping stone, failed flashing at the chimney, or many other entry points. Applying a waterproofing coating to the exterior wall surface without fixing the actual entry point is wasted money — water always finds another way in.

We perform a water test on every project before specifying any waterproofing solution. This involves controlled water application at suspected entry points while someone monitors the interior — isolating the actual source before any work begins.

Where Water Enters NYC Masonry Buildings

Failed mortar joints — the most common entry point in pre-war brick buildings
Cracked or missing coping stones on parapet walls
Failed flashing at chimney-to-roof, parapet-to-roof, or window-to-wall joints
Cracked lintels above windows — allows water to enter behind the lintel
Spalled or cracked brick face
Below-grade basement walls — hydrostatic pressure from saturated soil

Waterproofing Solutions We Apply

Exterior Wall Waterproofing

After all masonry defects are repaired, we apply a breathable penetrating sealer or elastomeric coating to the wall face. Breathable sealers allow vapor to escape from the wall while blocking liquid water — critical for older NYC brick buildings that need to breathe. Non-breathable coatings trap moisture inside the wall and cause accelerated deterioration.

Parapet Wall Waterproofing

After pointing and coping work, we apply waterproofing membrane from the base of the parapet up — including the coping bed joints and the full interior face where the parapet meets the roof membrane.

Basement Wall Waterproofing

Below-grade water intrusion is addressed with crystalline waterproofing compounds that penetrate the concrete or block and fill the capillary structure, or interior drainage systems where exterior excavation isn't feasible. We assess which approach is appropriate for each condition.

Frequently Asked Questions

Why is my brick wall wet inside even though the exterior looks dry?

Brick is porous and absorbs water through failed mortar joints — which may be invisible from a distance — and through micro-cracks in the brick face. Water then migrates through the wall cavity and appears on interior surfaces, sometimes several feet from the actual entry point.

What's the difference between a waterproofing sealer and a coating?

Penetrating sealers (silane/siloxane-based) enter the pore structure and repel water without changing appearance. Elastomeric coatings form a film over the surface. For historic brick buildings, penetrating sealers are preferred — coatings can trap moisture and cause accelerated spalling.

Can waterproofing fix active water infiltration in my basement?

The right approach depends on the source. If water is coming through wall cracks or mortar joints, crack injection and crystalline waterproofing are effective. If water enters under the footing due to hydrostatic pressure, an interior drainage system may be needed. We assess before recommending.

Do you perform a water test before waterproofing?

Yes — we perform a water test on every project before specifying any waterproofing solution. This is included at no extra charge. Applying waterproofing without first identifying the exact entry point is one of the most common and expensive masonry mistakes in NYC.

Masonry Waterproofing NYC