Sealing Leaky Wood Double-Hung Windows

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.


We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.



A. This procedure includes guidance on sealing leaky windows and includes caulking gaps between the wall and the frame, filling cracks in the wood, repainting and replacing loose window putty.

B. Peeling paint, the absence of putty, and open sash joints are signs of moisture infiltration into the window sash. The wood should be properly sealed against moisture to prevent deterioration in wood.

C. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:

  1. Safety Precautions
  2. Historic Structures Precautions
  3. Submittals
  4. Quality Assurance
  5. Delivery, Storage and Handling
  6. Project/Site Conditions
  7. Sequencing and Scheduling
  8. General Protection (Surface and Surrounding)

These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).



A. Caulking Compound (in order of recommended usage):

  1. Polyurethanes - easily workable; paintable; 15-20 year life span; limited availability.
  2. Polysulfides - slow drying; can be sanded and painted; highly elastic; limited availability.
  3. Butyls - paintable but cannot be sanded; 7-10 year life span.
  4. Silicones - some can be painted but generally not sanded.
  5. Acrylic Latex - for exterior work, their use is best left to tight, narrow joints; short life span especially when compared to polysulfides and polyurethanes.

B. Polyethylene foam backer rod such as "Ethafoam" SB brand backer rod (available at builder's supply houses or concrete materials suppliers), or approved equal.

C. Boiled linseed oil

D. Wood filler (there are four basic types):

  1. Water-mix Wood Putty: Easy to tint and fairly resilient, but has poor moisture resistance.
  2. Solvent-based Wood Filler: Not tintable, but has many color choices. A solvent is needed to clean any excess or spills. It is difficult to sand, but has good adhesion and moisture resistance. It also has a problem with shrinkage.
  3. Acrylic Latex Wood Filler: Better than water-based in adhesion, moisture resistance, and flexibility. Apply the filler in layers to avoid shrinkage.
  4. Two-part Polyester Filler: Similar to auto body filler. It has excellent adherence and moisture resistance with minimal shrinkage. It stains easily, but is time consuming to prepare.

E. Wood water-repellent preservative (see 06310-01-P, Section 2.02 Materials, and 06310-01-S)

F. Paint (see 06300-01-S)

G. Linseed oil putty or other approved product that is complementary to the coating system.

H. Clean, potable water


A. Wire brush

B. Natural bristle brushes for oil-based paints: Precondition by soaking in raw linseed oil for 24 hours. Use nylon bristle brushes for water-based paint. Do not use the same brush for both types of paint.

C. Putty knife

D. Caulking gun



A. Inspect windows periodically, at least yearly. Check for ease of operation, presence and operation of all hardware, and cracked or missing putty and glazing.


A. Recaulk Gaps Between Window Frame and Wall:

  1. Renail any loose boards in the window frame.
  2. Using a wire brush and putty knife, remove any loose dirt and debris that may have collected in the gap.
  3. For gaps 3/8 inch or wider, insert a closed-cell polyurethane backer rod.
  4.  Push the backer rod into the joint to fill up the space behind the caulking.
  5. Fill gap with a flexible caulking or sealant. Apply with a caulking gun until flush with the surface.
  6. If an oil-based caulk is used, allow the caulk to dry for at least 48 hours and then paint. Paint will extend the life of oil-based caulk.

B. Fill holes and cracks with linseed oil and fill with putty (see 06440-04-R for guidance).

C. Examine condition of paint.

  1. If paint has minor cracking or peeling, remove loose paint with a wire brush and putty knife and repaint.
  2.  If paint deterioration is extensive:
    1.  Remove all paint from window (see 06400-07-R and 06400-09-R for guidance).
    2. Liberally apply a wood preservative to the wood (see 06310-01-P for guidance).
    3.  Allow to dry for 24 hours.
    4. Apply a primer that is tinted darker than the final coat, with its choice based on compatibility with the preservative and the desired coating system.
    5. Apply final layers of coating system as per manufacturers specifications and allow to dry before installation (see 06300-01-S, 06300-02-R and 09900-07-S for guidance).

D. Replace Window Putty:

  1. Remove loose or cracked putty using a putty knife.
  2. Using a wire brush, remove loose dirt and debris from within the putty channel.
  3. Brush exposed areas with a preservative (such as a linseed oil mixture) that will not conflict with the chosen coating system. This preservative will be absorbed into the wood and prevent the new putty from drying too quickly and cracking.
  4. Apply fresh window putty and smooth out with a putty knife.