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Window Sills

Window sill repair, replacement and waterproofing

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Why Choose Allstate?

NYC DOB Licensed & Insured

Free Written Estimates

5-Year Workmanship Warranty

Local Law 11 Expertise

Clean Jobsite Guaranteed

About This Service

Professional Window Sills in NYC

Deteriorated window sills are a direct path for water into your building's walls. Cracked, spalled, or improperly sloped sills allow water to run behind the facade instead of away from it, causing serious interior damage over time. Allstate Construction repairs and replaces window sills in all materials — cast stone, brick, concrete, brownstone, and aluminum.

The Allstate Difference

We use only elastomeric and movement-accommodating sealants — never standard caulk — at all sill-to-masonry and sill-to-window joints. Proper product selection is what makes repairs last.

What's Included

Our Window Sills Services

Cast stone and precast sill replacement
Concrete sill repair and patching
Brownstone sill restoration and consolidation
Aluminum window sill replacement
Sill slope correction for proper drainage
Sill end dam and flashing installation
Caulk joint replacement at sill-to-window junction
Elastomeric waterproof coating on concrete sills
NYC Local Law 11 sill compliance
Entire building sill programs

Our Process

How We Handle Your Window Sills Project

Step by step — from first contact to finished job

Sill Survey

All sills inspected for cracks, spalling, improper slope, and sealant failure.

Repair or Removal

Repairable sills patched and consolidated. Failed sills removed carefully without damaging adjacent masonry.

Replacement

New sill set in full mortar bed with proper slope (1/4" per foot minimum). End dams and flashing installed.

Sealing

All joints caulked with elastomeric sealant. Surface coated with waterproofing if required.

FAQs

Common Questions About Window Sills

Freeze-thaw cycles, improper slope, failed sealant at the window-to-sill joint, and the natural porosity of brownstone and cast stone all contribute to sill deterioration.

Minor cracks and spalls can often be repaired with compatible materials. Sills that are deeply cracked, badly sloped, or structurally compromised should be replaced.

Yes. We use brownstone consolidants, patching mortars, and cast stone units that closely match the original material color and texture.