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Repairing Weather Checks in a Wood Window Sill

By The Old House Web

This procedure includes guidance on repairing a wood window sill that shows weathering of the type described below.

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 tothe sun dries out the inner wood causing the crack to widen. Rainwater and freeze/thaw cycles furtherexacerbate the problem, making the checks wider and deeper.

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 insize from hairline to 1/4" wide and 3/8" deep.

SYSTEM DESCRIPTION

A. A wood window sill in good condition is freefrom decay
and sloped away from the buildingto shed water. The
connection between sill and jamb istight and well
caulked. The sub-sill shouldhave a drip on the bottom
that prevents water from enteringthe building under the
window assembly.

MAINTENANCE

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

B. Provide ventilation between storm windows and sillby
leaving a narrow gap where the twomeet.

C. Remove any impervious coverings (such as sheetmetal)
that may have been installed overthe sill.

D. Clean clogged gutters.

E. Cut back large encroaching plants and shrubbery atleast
2 feet from the sill (10 feet fortrees) to allow
adequate air flow between thebuilding and the plants.

PRODUCTS

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

MATERIALS

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

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

2. The mixture ispoured or brushed on to the surface
whereit penetrates and hardens.

3. Acts as primer forepoxy filler.

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

1. A two-partputty-like filler (a resin paste and a
hardenerpaste) mixed together in equal volumes.

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

3. Applied like aputty; will fill gaps and holes of
anythickness and shape.

C. Oil-base or acrylic latex paint or highperformance
elastomeric coating.

D. Rubber Gloves

E. Disposable vinyl gloves: Available from drugstore or
pharmaceutical supply distributorin 50 count or larger
boxes.

F. Polyethylene sheeting

EQUIPMENT

A. Specially ground scraper

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

C. Applicator bottles: Available from drugstore and sold
for hair dye application usually in8 fl. oz. size; Also
available in bulk from RouxLaboratories. Roux Color
Applicators lend themselves moreeasily to cleaning and
reuse.

D. Rags of different sizes to wipe up spills beforeepoxy
has a chance to harden, small ragsare recommended for
quick one time uses such as wipingoff spouts and caps.

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

F. Goggles and a respirator for protection fromfumes.

G. Putty knives for application of filler

H. Needle nose pliers to pull out hardened epoxy

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

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

K. Stiff, fiber bristle brushes

L. Paint brushes

EXECUTION

EXAMINATION

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

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

PREPARATION

A. Surface Preparation:

1. Remove loose paintand build-up from the surface of
thesill.

2. Clean out all cracksof any dust and debris using a
specialscraper and a stiff, fiber bristle brush.

3. Dry the sill out;cover it loosely with
polyethylenesheeting and allow to sit until a low
moisturelevel is achieved in the wood. This may
takeanywhere from one week to one month.

NOTE: The cracks must be at their widest position
whenthey are filled. Therefore, it is important
thatthe wood be thoroughly dry before proceeding
withthe repair.

ERECTION, INSTALLATION, APPLICATION

A. Prime the edges of the checks with epoxyconsolidant;
inject consolidant into each checkusing a narrow spouted
squeeze bottle; this provides asurface that the filler
can adhere easily to. Avoidgetting consolidant all over
the sill surface.

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

B. After the consolidant has cured, apply epoxy pastefiller
using a putty knife; fill eachcheck completely.

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

1. For very deep ornarrow checks, spread filler with
avery loose consistency into the check using a
puttyknife. Force it deep into the check with the
endof the knife.

2. Then apply a stifferepoxy, again forcing the mix
intothe check with a putty knife.

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

3. The epoxy shouldraise slightly above the surface.

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

Note: If the filler shrinksbelow the surface of the
sill while setting, a secondapplication of epoxy putty
will be necessary.

D. Sand the surface to prepare it for painting.

E. Apply a paintable water-repellent before primingif
desired.

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

NOTE: BE SURE TO PAINT THEUNDERSIDE OF THE SILL.



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