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Historic Preservation - Technical Procedures

Spectitle:

Repairing Weather Checks In A Wood Window Sill

Procedure code:

0861005R

Source:

Ohj - John Leeke, 3-31-94

Division:

Doors And Windows

Section:

Wood Windows

Last Modified:

02/24/2012

Details:

Repairing Weather Checks In A Wood Window Sill



REPAIRING WEATHER CHECKS IN A WOOD WINDOW SILL


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repairing a wood
         window sill that shows weathering of the type described
         in 1.01 B. and C. below.

    B.   Weather checks are cracks in the wood that develop when
         bare wood is exposed to the weather.  They begin as small
         hairline cracks, but exposure to the sun dries out the
         inner wood causing the crack to widen.  Rainwater and
         freeze/thaw cycles further exacerbate the problem, making
         the checks wider and deeper.

    C.   Weather checks are typically found on the South and West
         sides of a building where the sun has severely dried out
         the wood.  They can range in size from hairline to 1/4"
         wide and 3/8" deep.

    D.   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).

    E.   See also 06300-01-R for additional guidance on epoxy
         repair.

1.02 SYSTEM DESCRIPTION

    A.   A wood window sill in good condition is free from decay
         and sloped away from the building to shed water.  The
         connection between sill and jamb is tight and well
         caulked.  The sub-sill should have a drip on the bottom
         that prevents water from entering the building under the
         window assembly.

1.03 MAINTENANCE

    A.   Inspect the sills every two years for breaks in the
         joints or paint film.  Spot prime, paint and provide
         sealant as needed.

    B.   Provide ventilation between storm windows and sill by
         leaving a narrow gap where the two meet.

    C.   Remove any impervious coverings (such as sheet metal)
         that may have been installed over the sill.

    D.   Clean clogged gutters.

    E.   Cut back large encroaching plants and shrubbery at least
         2 feet from the sill (10 feet for trees) to allow
         adequate air flow between the building and the plants.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Abatron, Inc.
         5501 95th Ave.
         Kenosha, WI 53144
         414/653-2000 or FAX 414/653-2019

    B.   Roux Laboratories
         5344 Overmyer Dr.
         Jacksonville, FL  32205
         904/693-1200

2.02 MATERIALS

    A.   Epoxy consolidant such as "LiquidWood" (Abatron, Inc.),
         or approved equal.

         1.   Consists of two clear liquids (a resin and a
              hardener) mixed together in equal volumes.

         2.   The mixture is poured or brushed on to the surface
              where it penetrates and hardens.

         3.   Acts as primer for epoxy filler.

    B.   Epoxy paste filler such as "WoodEpox" (Abatron, Inc.), or
         approved equal.

         1.   A two-part putty-like filler (a resin paste and a
              hardener paste) mixed together in equal volumes.

         2.   Hardens within 1-2 hours, is lightweight, non-
              shrinking, heat and weather-resistant.

         3.   Applied like a putty; will fill gaps and holes of
              any thickness and shape.

    C.   Oil-base or acrylic latex paint or high performance
         elastomeric coating.

    D.   Rubber Gloves

    E.   Disposable vinyl gloves:  Available from drug store or
         pharmaceutical supply distributor in 50 count or larger
         boxes.

    F.   Polyethylene sheeting

2.03 EQUIPMENT

    A.   Specially ground scraper

    B.   Plastic bottles (narrow spouted), like those used for
         hair dye, to apply the consolidant; having many on hand
         is recommended. Cleaning of the bottles for reuse is
         possible.

    C.   Applicator bottles:  Available from drug store and sold
         for hair dye application usually in 8 fl. oz. size;  Also
         available in bulk from Roux Laboratories.  Roux Color
         Applicators lend themselves more easily to cleaning and
         reuse.

    D.   Rags of different sizes to wipe up spills before epoxy
         has a chance to harden, small rags are recommended for
         quick one time uses such as wiping off spouts and caps.

    E.   Thin wooden sticks, approximately 8" long for scooping
         out paste and mixing consolidant.

    F.   Goggles and a respirator for protection from fumes.

    G.   Putty knives for application of filler

    H.   Needle nose pliers to pull out hardened epoxy

    I.   1/8"x8"x12" Masonite boards for mixing paste filler

    J.   Carbon dioxide fire extinguisher:  Curing epoxy creates
         heat that may cause fire

    K.   Stiff, fiber bristle brushes

    L.   Paint brushes


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Look for breaks in the paint film that may indicate
         checks below the surface.

    B.   DO NOT confuse weather checks with a split sill.  Weather
         checks are deep but do not extend through the entire
         depth of the sill.

3.02 PREPARATION

    A.   Surface Preparation:

         1.   Remove loose paint and build-up from the surface of
              the sill.

         2.   Clean out all cracks of any dust and debris using a
              special scraper and a stiff, fiber bristle brush.

         3.   Dry the sill out; cover it loosely with
              polyethylene sheeting and allow to sit until a low
              moisture level is achieved in the wood.  This may
              take anywhere from one week to one month.

              NOTE:  The cracks must be at their widest position
              when they are filled.  Therefore, it is important
              that the wood be thoroughly dry before proceeding
              with the repair.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   Prime the edges of the checks with epoxy consolidant;
         inject consolidant into each check using a narrow spouted
         squeeze bottle; this provides a surface that the filler
         can adhere easily to.  Avoid getting consolidant all over
         the sill surface.

         NOTE:  MOST OF THE CONSOLIDANT SHOULD SOAK INTO THE WOOD
         IF IT IS DRY.

    B.   After the consolidant has cured, apply epoxy paste filler
         using a putty knife; fill each check completely.  

         NOTE:  DO NOT COVER THE ENTIRE TOP SURFACE OF THE SILL
         WITH EPOXY.  THIS MAY LIMIT THE WOOD'S ABILITY TO DRY OUT
         OR CAUSE IT TO BECOME TOO BRITTLE AND CRACK WITH THERMAL
         MOVEMENT.

         1.   For very deep or narrow checks, spread filler with
              a very loose consistency into the check using a
              putty knife.  Force it deep into the check with the
              end of the knife.

         2.   Then apply a stiffer epoxy, again forcing the mix
              into the check with a putty knife.

              NOTE:  THIS METHOD SHOULD FORCE OUT ANY AIR POCKETS
              OR VOIDS THAT MAY BE PRESENT.

         3.   The epoxy should raise slightly above the surface.

    C.   Allow the filler to set, but before it hardens, trim off
         any excess so that it is flush with the surface using a
         very sharp hook-type paint scraper.

         Note:  If the filler shrinks below the surface of the
         sill while setting, a second application of epoxy putty
         will be necessary.

    D.   Sand the surface to prepare it for painting.

    E.   Apply a paintable water-repellent before priming if
         desired.

    F.   Prime the surface and apply two top coats paint using top
         quality exterior house paint.

         NOTE:  BE SURE TO PAINT THE UNDERSIDE OF THE SILL.

                         END OF SECTION