John Leeke's Historic HomeWorks™
207 773-2306 26 Higgins St. Portland, ME 04103
|
John Leeke's Historic HomeWorks™ |
|
207 773-2306 26 Higgins St. Portland, ME 04103 |
|
| [Home][Library][Restoration Reports][Seminars][Forum][Internships][Office][Workshop][Front Porch][Search] info.© 1994-2009 JohnC.Leeke |
(Return to the List of Articles)
"Clear Exteriors
Finishes"
Joint Coatings/Forest Products Committee
Chairman: Tom Daniels, Cabot, Newburyport, MA (1-978-465-1900)
Marc Hirsch, Dow Chemical Co., Midland, MI Ken McClelland,
Western Red Cedar Lumber Association, Vancouver, BC Dr. Alan
Ross, Kop-Coat Inc., Pittsburgh, PA Sam Williams, USDA Forest
Products Laboratory, Madison, WI
Wood has long been admired for it's natural beauty, durability,
and strength. With the increasing value of wood used for exterior
applications--siding, decks, walkways, fences, gazebo's,
etc.--homeowners want to protect their investment by applying a
protective finish to the wood. Homeowners and professional
painters have traditionally used protective finishes, such as
paint, but these finishes hide the natural beauty of the wood. In
many cases the homeowner wants the natural beauty of the wood to
show through the finish. This natural wood appearance, although
desirable, is difficult to maintain. The harmful effects of
nature (primarily sun and rain), degrade the wood surface, both
aesthetically and functionally. In recent years, a number of
clear wood finishes have been developed that protect wood while
accentuating its natural beauty (Figure 1). Although the consumer
can choose from a vast array of finishes having a wide range of
pigments and hiding power, the focus of this publication is on
those finishes having little visible pigment. In some cases, the
pigments are included, but are finely ground to give a coating
that is transparent to visible light.
Most natural clear wood finishes are designed to protect and
beautify wood. Although this may sound simple, manufacturer's
claims that products protect, preserve, seal, last longer, work
better, and spread farther than competitors products can often
confuse both the homeowner and professional painter alike. In
fact, many of the terms used to describe exterior wood finishes
are used interchangeably and often incorrectly, thus adding to
the confusion. So let's take a look at the problems facing the
homeowner or professional contractor as they try to maintain the
natural appearance of wood. In recent articles that compared the
performance of various coatings for wood, the performance of
clear coatings was often compared with pigmented finishes. In
order to make a fair comparison, the pigmented and non-pigmented
finishes should not be compared. For example, two years
performance of a penetrating clear finish on a deck would be
considered excellent. Two years under the same exposure for a
pigmented finish, would be considered poor. In comparing clear
finishes, it is important to consider the amount and type of
pigment that may be included in the finish.
When choosing a finish for wood, there are two elements to
consider: aesthetics and protection. These two qualities can
sometimes be at odds with each other. Aesthetically, there is a
growing trend among homeowners to maintain the clear natural look
of the wood's original color. However, the best protection from
the sun's ultraviolet radiation is obtained from pigmented
products, which tend to cover the wood's natural grain and
texture. Thus the problem: balancing the aesthetic desires of the
homeowner for a natural look with the protective requirements of
the wood surface.
Why Protect Wood..........(Return to
Table of Contents)
Although wood is naturally durable and strong, the effects of
outdoor exposure on wood can degrade not only these physical
properties, but its natural beauty as well. Wood exposed outdoors
is subjected both to rain (moisture) and sun (ultraviolet
radiation), two major factors that can ultimately cause wood to
lose both its natural beauty and strength.
Ultraviolet (UV) Radiation..........(Return to
Table of Contents)
Unprotected wood ages when exposed outdoors. The sun's
ultraviolet (UV) radiation degrades the surface of unprotected
wood within weeks of outdoor exposure (Figure 2). The early phase
of UV degradation is manifest as a change in color. Dark wood,
such as redwood and the cedars will tend to get lighter after
initial installation as the colored extractives degrade. Light
wood, such as pine and fir, tend to get darker. As the
degradation continues, the lignin at the surface (top 75-100
microns (0.003-0.004 in.)) begins to degrade, which in turn
loosens the wood fibers at the surface. Rain washes the degraded
wood fibers from the surface causing the surface to erode.
Erosion is more rapid in the less dense earlywood than in the
harder, more dense latewood; this causes an uneven surface.
Mildew growth may also occur as the surface weathers, which
darkens the wood's surface. However in some climates, such as
along the seashore, wood tends to weather to a silvery gray. The
sun's UV radiation also degrades clear natural finishes.
Moisture..........(Return to
Table of Contents)
Water also degrades wood. Whether in the form of liquid or vapor,
absorption and evaporation of water causes dimensional changes of
the wood, which can lead to premature degradation of the finish.
Water causes cracking, checking, and warping and can also lead to
decay (rot) in wood. In general, it accelerates the weathering of
wood exposed outdoors.
Shrinking and Swelling..........(Return to
Table of Contents)
Wood shrinks as it loses moisture and swells as it gains
moisture. More precisely, wood only changes dimension between an
absolutely dry state (completely free of moisture) and its fiber
saturation point (the point at which the cell walls of the wood
fibers are completely saturated with moisture). This fiber
saturation point typically occurs at about 30% moisture for most
species of wood. At this point, all the wood's water is bound
within the cell wall. As moisture content changes above fiber
saturation, the cell cavities take on or lose unbound water, but
the wood cell walls do not change dimensionally. Below the fiber
saturation point, however, the wood will change dimension with
changing moisture content.
Water/Water Vapor Effects..........(Return to
Table of Contents)
Shrinking and swelling of wood occurs whether the water is in the
form of vapor or liquid. For example, wood swells during periods
of high humidity and shrinks during periods of low humidity. If
wood is exposed to 100% relative humidity (RH) for an extended
period, the moisture content will eventually reach the fiber
saturation point, but it will not go beyond this point without
the presence of liquid water. Wood exposed outdoors goes through
a daily and seasonal change in moisture content as determined by
the RH. It is almost never exposed to extended periods of 100%
RH. Even in the hot humid areas of the south, the moisture
content of wood stays well below 20% as long as the wood doesn't
get wet. Water, however can cause wood to quickly reach, or even
go beyond, fiber saturation. The source of this water can be
rain, dew, melting ice or snow, plumbing leaks, and condensation
of water vapor as it moves in or out of a building. The
dimensional changes caused by daily and seasonal changes in RH
have little effect on the performance of wood finishes.
Poor performance of wood finishes may occur when the moisture
content of wood reaches or goes beyond fiber saturation. A large
percentage of wood finish degradation (e.g., paint/stain defects,
peeling, cracking) results from moisture changes in the wood and
subsequent dimensional instability. Water also decreases paint
bond strength, thus increasing the chance for peeling. The
wetting/drying cycles of wood exposed outdoors can raise the
grain of the wood. If this raised grain is severe, it can cause
cracks in paint, particularly oil-based paints.
For wood finished with clear penetrating finishes, dimensional
changes caused by wetting/drying cycles may lead to raised grain,
checking, and cracking of the wood. This roughened surface
increases water uptake, thus accelerating the degradation
process. On flat-grained lumber, the raised grain may appear as
thin, knife-like feathers along the earlywood-latewood interface.
Discolorations..........(Return to
Table of Contents)
Moisture contributes to many common wood
discolorations--extractive bleeding , iron stain, and mildew.
These discolorations, although not harmful to the wood, give an
objectionable appearance to the wood surface.
Extractive Bleeding..........(Return to
Table of Contents)
Certain types of lumber such as cedar, redwood, mahogany, Douglas
fir, etc., contain water soluble extractives that can be leached
to the surface of the wood (Figure 3). As water moves through
wood or as the surface of the wood gets wet, water soluble
extractives are dissolved; these extractives are deposited on the
exterior surface, as the water evaporates, and appears as a
reddish brown stain. If the wood finish is not formulated to
block the diffusion of these extractives, they can cause an
unsightly residue on the finish, particularly with light colored
finishes. Extractive-related discolorations can be difficult to
remove if they are allowed to remain on a surface for a long
period of time. Although extractives in wood give the wood its
natural color and resistance to decay (for some wood species),
they must be sealed in the wood with a stain-blocking primer,
when using light colored finishes. This is usually not a serious
problem for dark stains or with natural finishes.
Iron Stain..........(Return to
Table of Contents)
Iron stain occurs in two ways on wood. Rust from iron/steel
fasteners, railings, supports for window air conditioners, etc.
can be washed down a structure by rain and absorbed by the wood
or finished wood to cause brown discoloration. Iron can also
react with the extractives in wood to give a blue-black stain.
Although these stains can sometimes be removed by treatment with
oxalic acid or sodium biflouride, it is best to avoid the problem
by using corrosion resistant materials.
Mildew..........(Return to
Table of Contents)
Airborne mildew spores are ubiquitous and microscopic, and
therefore are difficult to detect until they colonize a surface.
They are transported easily by air currents, insects, and
animals. These spores can cause mildew fungus growth on any
surface that provides a food source. Food sources for mildew
include wood extractives, plant and tree pollens, natural oils
such as linseed and tung oils, bacteria, dirt, and other natural
organic materials. Because mildew uses organic materials for
food, it has a greater tendency to grow on organic surfaces such
as wood, leather, and paper versus inorganic surfaces such as
aluminum, vinyl, and glass. Mildew can also grow on these
substrates, but it must then depend on airborne food sources.
Much of the deep rich color of some wood species is determined by
their extractives content and natural oils; these organic
compounds also make wood an ideal substrate for mildew growth, if
there is enough moisture available (Figure 4). Therefore, because
wood has readily available food for mildew growth, it grows more
readily on wood surfaces than on painted wood, particularly wood
painted with synthetic organic polymers such as acrylics.
Following colonization, mildew needs food, moisture, air (oxygen)
and moderate temperatures (usually between 40 and 90 degrees F).
Because of the extremes of conditions in which it can flourish
and the wide variety of species, mildew is very hard to control
and impossible to totally eliminate. Of the requirements needed
for mildew growth, moisture is the only one that can be
controlled. It is impossible to control colonization, food
source, temperature, or oxygen and it is difficult to control
moisture, therefore, paint and stain companies incorporate
mildewcides in their products to retard mildew growth.
In the absence of a mildewcide, wood that gets wet or damp (even
for a short period of time), may develop mildew. As the mildew
fungi grow, they become visible because they often develop highly
colored pigmentation. Gray or black coloration is the most
typical, but various other colors commonly occur. The mildewcides
found in paints and stains are not very effective in destroying
pre-existing mildew. Therefore, it is important that mildew be
completely destroyed prior to staining or painting.
Clear Natural Finishes..........(Return to
Table of Contents)
Stain and paint manufacturers have produced a number of clear
products to meet the aesthetic desires of the homeowner, while
meeting the requirements to protect the wood. Clear natural
finishes generally fit into four categories: Waterproofing, Water
Repellent Sealers, Wood Preservatives, and UV-Resistant Clears
(blocking or absorbing). Some clear natural finishes on the
market today may be combinations of these categories. High
solids, water-based, oil emulsion, and traditional solvent based
formulations are just a few examples of the different types of
clear finishes sold within each of the categories of clear
natural finishes. Air quality regulations along with changing
technology have made available, to the consumer, an abundance of
new water-based clear formulations. Some of these new clear
natural finishes may be film-forming, and therefore they may not
penetrate the wood's surface very well. Clear finishes also
degrade from UV radiations and moisture. For penetrating
finishes, this degradation is not serious because the wood can be
refinished without extensive surface preparation; film-forming
finishes often require extensive surface preparation, even to the
extent of complete removal of the old finish prior to
refinishing. Thus, when choosing a clear product, it is important
to match the aesthetic desires and the exposure to the weather,
with the protective requirements of the wood and, at the same
time to understand the performance limitations of the finish.
Water Proofing Water-proofing clear products are often confused
with water-repellent products. Water-proofing products form a
membrane designed to withstand hydrostatic pressure (like
wind-driven rain) and keep water out of a home throughout long
periods of wetting. Water-proofing coatings are often elastomeric
and are designed for brick, stucco and other masonry surfaces,
not wood. They are products used around flashing to completely
stop water absorption.
Water Repellent Sealers..........(Return to
Table of Contents)
Water repellents shed water for short periods, like rain or water
from a sprinkler. They are not completely impervious to water
absorption. Clear products that fall into the water repellent
category are penetrating finishes. They typically contain a small
amount of wax (1 to 3%) , usually paraffin or other water
repellent material that decreases the amount of water absorbed
into the wood, thus decreasing dimensional changes, warping, and
splitting. They also contain an oil or resin that helps seal the
surface and a solvent to facilitate absorption of the other
ingredients. Water repellents were traditionally formulated with
organic solvents, however contemporary formulations may be
water-borne, solvent-borne, or in some cases may use paraffin oil
with no other solvent. The type and amount of material used to
impart water repellence may affect future paintability of the
treated surface. Water repellent sealers designed for use prior
to painting have about 1% wax or similar water repellent in a
curable resin. Because moisture is repelled, mildew growth may be
slowed, but is not prevented. These products often provide
spectacular beading of water upon initial application. However,
they offer wood little protection from the sun's UV radiation or
mildew growth; they weather to gray, and then black from the
growth of mildew, unless a mildewcide is added to the product
(see Wood Preserving Finishes). When water repellent sealers are
subjected to degradation by the sun's UV radiation, the result is
a gradual loss of the water beading effect. The life expectancy
of these products typically ranges from six months to one year on
horizontal surfaces (e.g. decks), and one to two years on
vertical surfaces. It should be noted, however that the
treatments absorb readily into the end-grain of lumber and thus
give many years of efficacy preventing end-grain absorption of
water. End-grain absorption of water is much greater than
lateral-grain absorption, therefore the products last many years
in this critical zone (the most important place to prevent water
absorption).
Wood Preserving Finishes..........(Return to
Table of Contents)
Wood-Preserving Clear Finishes differ from water repellent
finishes in that they also contain an appropriate amount of an
United States Environmental Protection Agency (EPA) approved and
registered fungicide. These clear finishes are very similar in
appearance to water-repellent sealers. If the fungicide is
incorporated to preserve the wood itself, the product must be EPA
registered. If the fungicide is present only to protect the clear
finish, the product does not have to be registered. The commonly
used fungicides are also effective in controlling mildew
(mildewcides). Fungicides are important to all clear natural
finish formulations and most manufacturers incorporate some level
of them into their products. The addition of these specific EPA
approved fungicides to the product, in specific quantities, and
the subsequent EPA registration, allows manufacturers to make
specific claims about controlling decay and mildew when
describing their products. Some common fungicides used in these
products which can provide decay and mildew resistance to wood
include: 3-iodo-2-propynyl butyl carbamate, zinc naphthenate,
copper naphthenate, bis (tributyltin) oxide (TBTO),
N-trichloromethylthio phthalimide and copper-8-hydroxyquinolate.
Penetrating wood preserving finishes may also be used as a
treatment for bare wood before priming and painting or in areas
where old paint has peeled, exposing bare wood. This treatment
gives a second "wall" of protection against water that
has penetrated the paint film; they are especially effective to
prevent absorption of water at joints and at end-grain, thus
decreasing the swelling of the wood. As a result, less stress is
placed on the paint film, and its service life is extended. For
treating bare wood, make certain that the manufacturer's label
indicates that the Clear Wood Preservative is paintable. Some
products have too much wax or other water repellent and the paint
will not adhere adequately and/or dry properly.
Water repellent sealers and Clear Wood Preserving finishes give
some protection to the wood surface from weathering by minimizing
the effects of water. The wax in the product ultimately breaks
down on the exposed lateral surfaces and the water beading
properties decrease. The water repellent life expectancy of these
products typically ranges from six months to one year on exposed
surfaces. However, the water repellent absorbed in the end grain
will be effective for many years. Also, after the wood has
gradually weathered, additional treatments may last longer
because the weathered boards absorb more finish. The UV radiation
can still degrade the surface causing the release of wood fibers
and thus the erosion of the surface; the inclusion of a UV
absorber or some other type of UV stabilizer in the formulation
can slow this degradation for a short time.
UV Resistant Clears..........(Return to
Table of Contents)
The only way to slow the UV degradation of the surface is to
incorporate a pigment or a UV stabilizer into the formulation.
Thus the UV resistant clear water-repellent preservative
represents the broadest category of clear natural finishes on the
market. Pigments and organic chemical additives are used as light
absorbers (or screeners) to protect the products' binders and the
wood from degradation by the sun's UV radiation. The pigments
that are used most frequently are either a transparent form of
iron oxide (transoxide) or ultrafine titanium dioxide that
reflects UV radiation. The organic chemical additives are of two
types--UV absorbers (U-VA) and hindered amine light stabilizers
(HALS).
UV absorbers are designed to work by absorbing selective portions
of sunlight, especially UV radiation and dissipating the energy
as heat. During this process, some are destroyed, limiting the
effective life of the product. Hindered amine light stabilizers
(HALS), act as scavengers for the components of the coating
(binder and pigments) during degradation, and through this
process, block further degradation of the clear finish and the
wood. Generally, U-VA's, HALS, and pigments are used together and
offer the best protection to the wood surface.
Many people feel UV Resistant Clears are the solution to the
delicate balancing act of the aesthetic desires of the homeowner
and the protective requirements for the wood. UV-resistant Clears
are not "water" clear, but impart a slight color or
tone to the finish from the use of translucent transoxide
pigments or titanium dioxide. Thus, with UV Resistant Clears,
various "colors" are available. Transoxide pigments are
translucent and thus highlight the natural grain, texture, and
beauty of the wood. Transoxide pigments are also versatile,
finding success not only in traditional solvent and oil based
product formulas, but also in the latest formulas to meet tighter
air quality (VOC) regulations, such as oil emulsion, high solid
oils, and water-based formulations. The penetrating/film-forming
characteristic can vary considerably among these types of
products. The life expectancy of a UV-Resistant Clear finish is
typically twice that of other clear finishes and can range from
one to two years on horizontal surfaces (e.g. decks), to two to
four years on vertical surfaces.
Why Wood Anyway?..........(Return to
Table of Contents)
Wood is the material of choice for a wide range of building
projects. It offers the builder a long list of features which
work together to meet the end user's expectations for service,
cost and appearance.
Perhaps the greatest attribute of wood is its versatility. Wood
can be used indoors and outdoors in both structural and
appearance applications. Whether the needs are clear or knotty
appearance, rough or smooth textured, wood can meet the changes
in design and fashion. It can be specified from the hundreds of
standard sizes and patterns or custom ordered to meet particular
end-use needs. Wood products are widely distributed and readily
available throughout the United States and Canada.
Another factor favoring the use of wood is its ease of handling
and fabrication. Wood can be shaped, drilled, cut and fastened
with common tools which can be operated by homeowners and
professional contractors alike.
Buildings constructed from wood have a history of excellent
service. Interior beams, ceiling, paneling and trim will last the
lifetime of the building. Wood products are widely used for
exterior sidings, trim, decks and landscape projects. Species
such as Redwood and Cedar contain natural preservatives, which
make them particularly well suited to the exterior environment.
The choice of wood is an environmentally friendly one. The
production of wood products generally requires much less energy
than alternative products, which lower both fuel consumption and
air emissions. Wood is the only renewable building material. The
nation's move toward sustainable forestry practices (e.g. the
planting of more than two billion trees each year in North
America) assures a continued supply of wood for generations into
the future.
The beauty of wood has long been admired. The warm colors and
rich grain patterns have decorated homes and their landscapes for
centuries. This natural beauty can be enhanced and preserved
through the proper selection, application and maintenance of a
finish.
Summary..........(Return to
Table of Contents)
Matching the aesthetic desires of the homeowner with the
protective requirements of wood using technologies available
today is a delicate balancing act. By having an understanding of
the benefits and limitations of the various natural clear
finishes, the homeowner's expectations for performance and
maintenance will be satisfied. Determining which product to use
can be difficult. Product quality is often defined by the
reputation of the manufacturer, the ingredients used (in
sufficient quantities to be effective), and the delicate blending
and balancing of the various raw materials used in the coatings
formula. High quality, clear wood finishes should be easy to use,
contain mildew-preventing ingredients, provide some degree of
water repellency, and contain UV radiation absorbers. Generally,
clear finishes fully exposed to the weather last one to two
years; however, some last less than a year. Research is needed to
foster a quantum leap in the technology of clear finishes for
wood.
Figures..........(Return to
Table of Contents)
1. Examples of natural finishes on siding and logs.
2. Schematic of color and surface changes on a typical softwood
during the natural weathering process (a). Artists depiction of
the weathering process (b).
3. Examples of extractives bleed on finished wood.
4. Mildew on wood siding.
Note to editor. The inclusion of this glossary is probably not
necessary for publication of this article in the Journal of
Coatings Technology. But please keep it on file in case the
article is not suitable for this outlet. The article was
originally prepared for a trade journal outlet. Since the
Federation of Societies for Coatings Technology sponsors the
preparation of these articles, we submit all of our manuscripts
to them for consideration.
Glossary of Terms..........(Return to
Table of Contents)
Acrylic - A synthetic resin used in high-performance water-based
coatings. Also used for a coating in which the binder contains
acrylic resins.
Adhesion - The ability of stain or paint to attach to and remain
fixed on the surface without blistering, flaking, cracking, or
peeling. Adhesion is probably the single most important property
of paint or stain. Wet adhesion, the ability of dry stain or
paint to adhere to the surface in spite of wet conditions, is
particularly important for exterior coatings.
Alkyd - Synthetic resin modified with oil, or a coating that
contains alkyd resins in the binder.
Binder - Solid ingredients in a coating that hold the pigment
particles in suspension and attach them to the substrate.
Consists of resins (e.g., oils, alkyd, latex).
Blistering - The formation of bubbles or pimples on the painted
surface caused by moisture in the wood, by painting before the
previous coat has dried thoroughly, by excessive heat, or grease
under the paint.
Chalking - The oxidation of paint, usually due to weathering,
which causes a powder on the film surface.
Coating - A stain, paint, varnish, lacquer, or other finish used
to create a protective and/or decorative layer.
Coverage - The area over which a given amount of paint will
spread and hide the underlying surface. Also called Spread Rate.
Usually expressed in square feet per gallon.
Cracking - Splitting of a coating usually due to aging paint. It
can also be caused by subsurface expansion under a brittle
topcoat.
Dimensional Stability (of Wood) - The measurement of the
percentage change in the wood substrate as it absorbs and
releases moisture.
Extractive Bleeding (Tannin Bleeding) - Paint discoloration
caused by the leaching of water-soluble chemicals such as tannins
found in the heartwood of most wood species, e.g. western red
cedar, redwood and Douglas fir.
Fading - The loss of color due to exposure to light, heat, or
weathering.
Fungicide - An agent that can prevent decay in wood by inhibiting
the growth of decay fungi; they often act as mildewcides to
prevent mildew fungi growth on wood and painted wood. Not all
fungicides are effective mildewcides, but mildewcides are a type
of fungicide.
Grain - The natural look or pattern of wood. Texture due to
alignment of the wood fibers.
HALS (Hindered Amine Light Stabilizer) - A chemical additive
which functions by capturing alkoxy and hydroxy radicals from
photodegradation.
Hide or Hiding Power - The ability of the paint or coating to
mask or cover the surface.
Latex - General term used for water-based emulsion stain or paint
made with synthetic binders such as 100% acrylic, vinyl acrylic,
terpolymer, or styrene acrylic. A stable emulsion of polymers and
pigment in water.
Linseed Oil - Drying oil extracted from the flax seed. Used as a
binder in stains, inks, and many oil-based paints.
Mildew - A type of fungus that thrives in the presence of
moisture, nutrients, and warmth. It usually causes a black
discoloration to the surface of wood.
Mildewcide - Chemical agent added to a coating that retards the
growth or may destroy mildew.
Oil Stain - There are two types of oil stains, penetrating and
non-penetrating. Penetrating oil stains contain dyes and/or
pigments and resins that penetrate the surface; non-penetrating
oil stains contain larger amounts of pigments and are usually
opaque or translucent.
Opacity - Ability of a coating to hide or conceal the underlying
surface. Light cannot penetrate an opaque coating. A stain with a
high opacity value will cover well.
Oxidation - Chemical reaction upon exposure to oxygen. Some
coatings cure by oxidation, when oxygen enters the liquid coating
and cross-links the resin molecules. This film-forming method is
also called Air Cure and Air Dry. Oxidation also causes rust on
metals and chalking paint.
Pesticide - A chemical additive for killing pests, such as
insects and fungi. Most are registered with the United States
Environmental Protection Agency (EPA).
Paint - A coating including resin, a solvent, additives,
pigments, and in some products, a diluent. In general, paints are
opaque.
Penetrating Finish - A finish that sinks into the surface, as
opposed to settling on the surface.
Pigment - Insoluble, finely ground materials that give the paint
its properties of color and hide.
Resin - Synthetic or natural material used as the binder in
coatings. Example: Acrylic, alkyd, epoxy, polyurethane.
Stain - Usually used to change the natural color of wood. Coating
that is absorbed into the substrate, rather than resting on the
surface.
Substrate - Any surface to which a coating is applied.
Tinting - Act of changing the intensity of a color that is not
saturated by adding white.
Topcoat - The last or final coating of a stain or paint,
sometimes referred to as "overcoat."
Transparent or Semi-Transparent - A coating which light can
penetrate; one which we look through and see the surface
underneath.
UV-A (Ultraviolet absorber) - A chemical additive which functions
by absorbing the ultraviolet energy from the sun and dissipating
the energy as heat.
Ultraviolet Radiation - The sun radiates energy to the earth in
electromagnetic waves over a range of wavelengths known as the
solar spectrum, which is known to cause the breakdown of exterior
coatings. The solar spectrum is divided into three bands:
ultraviolet (UV), visible light and infrared radiation. Both UV
and infrared light are invisible to the human eye.
Volatile Organic Chemical (VOC) - A liquid or solvent used in
stains or paints that evaporates quickly when exposed to air.
Most VOC's are registered by the United States Environmental
Protection Agency (EPA).
Water Repellent - A chemical agent that, when applied to a wood
substrate, prohibits or decreases the absorption of water into
the wood.
Water Spotting - Smallish spots that can form on the surface of a
coating. Several types exist; water soluble soaps can exude to
the surface, while it can also be caused by the reaction of
acidic rain with certain pigments that may be in the paint.
Wood Preservative Finish - A protective coatings containing one
or more Environmental Protection Agency (EPA) registered
fungicides.
References/Resources..........(Return to
Table of Contents)
1. Sam Williams, William C. Feist, "Water Repellents and
Water-Repellent Preservative Finishes for Wood."
FPL-GTR-109, January, 1999.
2. Cabot Stains Technical Bulletin No. 6, Fall 1993.
3. Cabot Stains Technical Bulletin No. 8, Summer 1994.
4. John Rogers, "Clear Protective Finishes." Paint
& Wallcovering Contractor, July-August, 1991, pages 37-44.
5. Gale Murphy, Richard Glass, "Wood Preservative
Finishes." Paint & Coatings Industry, September, 1994,
pages 43-46.
6. Dave Messmer, "Natural Wood Finishes. Fact vs.
Fiction." The Paint Dealer, July, 1995, pages 30-35.
7. Tamela Adamson-McMullen, "Beauty Well-Preserved."
Decorating Retailer, September, 1992, pages 34-36.
8. R. Sam Williams, Mark T. Knaebe, and, William C. Feist,
"Finishing Wood Exteriors-Selection, Application and
Maintenance." Forest Products Society, Madison WI. 1996.
127p.
Webpage creation by Dan Mitchell, working in
the Historic Home Works Assistantship Program. Dan is a
preservation enthusiast on Cobbosseeconte Lake in Maine.
(Return to the List of Articles)
|
John Leeke's Historic HomeWorks™ |
|
207 773-2306 26 Higgins St. Portland, ME 04103 |
|
| [Home][Library][Restoration Reports][Seminars][Forum][Internships][Office][Workshop][Front Porch][Search] info.© 1994-2009 JohnC.Leeke |