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Historic Preservation - Technical Procedures
Applying A Water-Repellent Preservative To Wood
Developed For Hspg (Nps - Sero)
Wood And Plastics
Applying A Water-Repellent Preservative To Wood
APPLYING A WATER-REPELLENT PRESERVATIVE TO WOOD
A. This procedure includes guidance on applying a water-
repellent preservative (WRP) to wood. This coating will
prolong the service life of wood and provide some
protection against agents of deterioration.
NOTE: WATER REPELLENTS AND WATER REPELLENT PRESERVATIVES
ARE ONLY EFFECTIVE ON UNPAINTED WOOD. IF IT IS APPLIED
TO PREVIOUSLY PAINTED WOOD, BRUSH IT THOROUGHLY INTO ANY
JOINTS OR CRACKS AND WIPE ANY EXCESS OFF PAINTED
SURFACES. ALLOW PROPER DRYING TIMES.
B. Natural causes of deterioration include decay,
ultraviolet degradation, insect infestation and excess
C. WRPs are often recommended for humid, southern climates.
Their use can significantly reduce the problems of
peeling, flaking, blistering, etc. of painted wood
D. Some types of problems resulting from the weathering
1. Fungi and/or mildew growth
2. Warped boards
3. Loose fasteners
4. Changes in surface texture resulting in cracks and
E. In addition to opaque paints, various so-called "natural"
finishes and colored stains provide this necessary
protection. And, like paints, proper surface preparation
and application are vital to long lasting protection.
F. 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
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. Water Repellent Preservatives (WRP):
1. Natural, colorless liquids which, when brushed
onto, or soaked into the wood render the wood
impervious to liquid water, inhibit the growth of
mildew and other fungi, and provide protection
against termite and other insect infestation.
2. Their use reduces warping and checking and prevents
water staining at edges of boards and at the end
grain. They do not, however, protect wood from
water vapor or ultraviolet degradation.
3. WRP's will darken wood somewhat though in and of
themselves, they contain no coloring agents.
Though it varies with wood species the ultimate
color is usually a golden tan.
4. WRP's can be used as a natural finish.
1.03 PROJECT/SITE CONDITIONS
A. Environmental Requirements:
1. Unless otherwise recommended by the manufacturer,
the ambient temperature shall be between 50 degrees
F. and 95 degrees F. when applying either a stain
2. Do not apply when the relative humidity exceeds 85%
or the moisture content of the wood exceeds 12% as
measured by an electronic moisture meter.
3. Do not apply a WRP in the direct sun. They shall
be applied only when the surface to be treated is
in the shade and the sun is shining on the opposite
elevation. The west elevation should be treated in
the morning when the sun is shining on the east
elevation; the north elevation should be treated
around noon when the sun is shining on the south
elevation; the east elevation should be treated in
the afternoon when the sun is shining on the west
elevation; and the south elevation should be
treated late in the afternoon when it is in full
4. Do not apply WRP's to damp surfaces, in misty or
rainy weather, in the snow or where there is
visible ice or frost on the surfaces.
A. Water Repellent Preservative Finish (WRP):
1. On smooth wood surfaces, a water repellent
preservative will remain effective for about a
year. If the first application was applied to the
point of refusal, it may remain effective for two
years. On rough or weathered wood, expect a WRP to
remain effective from one to three years.
2. To determine if it is still effective splash some
water on the surface.
a. If the water beads up the WRP is still
providing the necessary protection.
b. If the water soaks into the wood, and/or the
wood has a blotchy appearance (caused by
mildew) it is necessary to retreat.
3. Before applying a new coat of WRP, clean the old
surface with a nonferrous bristle brush.
4. To kill any mildew, wash with a solution of 1/3 cup
of household detergent (NO AMMONIA), 1 quart 5%
bleach, and 3 quarts warm water.
5. Rinse well and let dry thoroughly before reapplying
6. After the treated wood has achieved a uniform tan
color, retreatment will be required every 2 to 4
A. American Building Restoration Chemicals, Inc.
9720 South 60th Street
Franklin, WI 53132
800/346-7532 or 414/421-4125
NOTE: SIMPLE WATER REPELLENTS (WR), BY THEMSELVES, DO NOT
PROVIDE ADEQUATE PROTECTION AGAINST DECAY AND ULTRAVIOLET
DEGRADATION AND ARE NOT TO BE USED AS THE SOLE FINISH.
A. Commercial water-repellent preservative such as "X-100
Natural Seal" (American Building Restoration Chemicals,
Inc.), or approved equal.
A home-made preservative based on the USDA Forest
Products Laboratory formula (see 06310-01-S for guidance
B. Household detergent (NO AMMONIA)
C. Household Bleach:
1. Other chemical or common names include Sodium
Hypochlorite (NaOCl); Bleaching solution*; Laundry
bleach*; Solution of chlorinated soda*.
2. Potential Hazards: CORROSIVE TO FLESH.
3. Available from chemical supply house, grocery store
or supermarket, hardware store or janitorial supply
D. Clean, clear water
1. Use natural bristle paint brushes for oil/alkyd
stains. Precondition by soaking in raw linseed oil
for 24 hours. Use nylon bristle brushes for latex
stains. Do not use the same brush for both types
2. For thin, runny stains, foam pad applicators can be
3. Stiff natural bristle scrub brushes.
A. Surface Preparation: The surface should be free of all
loose fibers, dust and grease before application of a
3.02 ERECTION, INSTALLATION, APPLICATION
A. Prepare the Water-Repellent Preservative (Forest Products
Laboratory formula). See 06310-01-S for guidance.
Use one of the proprietary products listed above.
NOTE: ON A SMOOTH SURFACE 1 GALLON OF WRP WILL COVER
APPROXIMATELY 250 SF. IT WILL COVER APPROXIMATELY
100-150 SF ON A ROUGH SURFACE.
B. Dipping is the most effective means of treatment,
especially for the ends of wood members. Brushing, to
the point of refusal, is the next best method of
1. For treated lumber, dip freshly cut surfaces before
installation, 10 seconds to 3 minutes.
2. For untreated lumber, dip, brush or spray with
preservative. Pay particular attention to end
grain and joints.
3. For wood shingles, dip before installation, with a
second coat brushed onto the surface after
4. On fixed surfaces, use a minimum of two successive
5. For pieces that are removable, soak for 10 seconds
to 3 minutes.
C. Allow adequate time to dry before repainting so that
paint will adhere properly. Follow manufacturer's
1. In general, if the surfaces have been brush
treated, 48 hours at 70oF. is generally sufficient
2. Longer drying times will be required if it gets
colder than 70oF. at any time during this drying
3. Wood that has been dipped for 10 seconds will need
a minimum of one week of similar, ideal drying
4. If work is being done late in the year and it is
too cold in the evenings for a paint film to dry
properly, only apply a WRP and wait until spring to
prime and paint.
D. In addition to adequate drying times, some WR/WRP's must
be allowed to weather before painting. Follow
manufacturer's instructions. Time can vary from six
months to two years.
A. Caulking joints is an important part of surface
preparation. Also caulk after a WR or WRP has been
END OF SECTION