How do I know if I need waterproofing or just better drainage outside?

If water appears only during heavy rain and grading slopes toward the house, exterior drainage fixes may be enough. Water seeping up through floor cracks or weeping through walls in dry weather points to groundwater pressure — that needs a real waterproofing system. We'll diagnose it on site.

How long does waterproofing last?

A properly installed interior drainage system lasts decades — the sump pump itself typically needs replacement every 7 to 10 years. Exterior membranes are generally warranted for the life of the foundation when installed correctly.

Can you waterproof a finished basement?

Yes. We can install interior drainage with minimal disruption to finished walls, and we rebuild whatever we open. If you're finishing a basement, waterproof first — it's far cheaper than repairing a finished space after a flood.

Basement Waterproofing in Brooklyn, Manhattan, Queens & Staten Island

Water in the basement is one of the most common — and most misdiagnosed — problems in New York City homes. High water tables near the East River and the harbor, aging foundations in pre-war houses, failed exterior coatings, and hydrostatic pressure pushing up through floor slabs all show up as the same puddle on the floor. M&M GC Contractor Inc has been waterproofing basements and foundations across Brooklyn, Manhattan, Queens, and Staten Island since 2001.

We don't sell one system for every house. We find the water's entry point first, then recommend the fix that actually addresses it — interior drainage, exterior excavation and membrane, or both.

Where NYC water problems actually come from

In Brooklyn's older housing stock, water usually enters through deteriorated foundation walls, failed parging, or the cove joint where the wall meets the floor slab. In Staten Island, high water tables and poor grading push water up through slabs and in around penetrations. Every diagnosis starts with a thorough inspection of the foundation, grading, gutters, and interior signs — efflorescence, staining patterns, and seasonal behavior all tell a story.

Getting the diagnosis right matters because the wrong system wastes your money. An interior drain won't fix water pouring through a cracked foundation wall from the outside, and exterior excavation is overkill for condensation issues. We tell you which one you actually have.

Interior and exterior waterproofing systems

Our interior systems include perimeter French drains tied to sump pumps with battery backup, wall vapor barriers, and sealed, dehumidified spaces that turn damp cellars into usable rooms. For exterior problems, we excavate to the footing, repair and parge the foundation wall, apply waterproof membranes, install exterior drainage board and footing drains, and backfill properly.

We also correct the contributors: regrading soil away from the foundation, extending downspouts, and repairing areaway and bulkhead leaks. Waterproofing works best as a system, not a single product.

Why homeowners and businesses choose M&M

Licensed & insured general contractor operating in New York City since 2001 — over two decades of finished jobs, not promises.
Big jobs only. We do full renovations, kitchens, bathrooms, brownstones, waterproofing, roofing, commercial and exterior work. We don't do handyman calls, which means your project gets a real crew and real project management.
In-house crews for demolition, framing, drywall, flooring, electrical and plumbing — fewer subcontractors, fewer delays, one accountable team.
NYC building know-how: DOB permits, co-op and condo board packages, Landmarks Preservation Commission approvals, occupied-building logistics — we've done it hundreds of times.
Direct line to the owner. Call (917) 251-9318 and you talk to the people actually running your job.

How your project runs, start to finish

Consultation & site visit. We walk the space, listen to what you want, and flag anything structural, code-related, or permit-related up front.
Detailed scope & estimate. You get a clear written scope and a firm price — no allowances hiding the real number, no surprise change orders later.
Construction. Our in-house crews handle demolition through final finishes. The site stays clean, protected, and on schedule, with one point of contact throughout.
Final walkthrough. We go through every detail together before sign-off. If something isn't right, we fix it. That's the "built on trust since 2001" part.

Proudly serving Brooklyn, Manhattan, Queens & Staten Island

We're a local contractor, not a lead broker. Our crews work every day across the three boroughs we serve:

Brooklyn — Park Slope, Bay Ridge, Williamsburg, Bushwick, Flatbush, Brooklyn Heights, Bed-Stuy
Manhattan — Upper East Side, Upper West Side, Harlem, Chelsea, Lower East Side, Washington Heights
Staten Island — St. George, Stapleton, New Dorp, Tottenville, Great Kills, Annadale

If your project is in one of these boroughs, we'll come out, walk the space, and give you a straight answer on scope and price.

Common questions

How do I know if I need waterproofing or just better drainage outside?: If water appears only during heavy rain and grading slopes toward the house, exterior drainage fixes may be enough. Water seeping up through floor cracks or weeping through walls in dry weather points to groundwater pressure — that needs a real waterproofing system. We'll diagnose it on site.
How long does waterproofing last?: A properly installed interior drainage system lasts decades — the sump pump itself typically needs replacement every 7 to 10 years. Exterior membranes are generally warranted for the life of the foundation when installed correctly.
Can you waterproof a finished basement?: Yes. We can install interior drainage with minimal disruption to finished walls, and we rebuild whatever we open. If you're finishing a basement, waterproof first — it's far cheaper than repairing a finished space after a flood.

Related guide: Basement Flooded in NYC? What to Do in the First 24 Hours — a step-by-step emergency guide from our team.