Clear Exterior Finishes Finding

Document Sample
Clear Exterior Finishes Finding Powered By Docstoc
Finding the Balance
Between Aesthetics
and Durability

Tom    Daniel
Samuel Cabot, Inc.
                               C      onsumers can easily be confused by the abundance of choices to make when
                              selecting a clear wood finish. There are many types of clear finishes with different
                              characteristics and product claims. This article is designed to help consumers sort
Marc S. Hirsch                out the different finishes and effectively choose which product would be best for
Dow Chemical Co.              their purpose. First, we cover the causes and mechanism of wood degradation. It is
                              important to know what we are protecting wood from rand why. Then we describe in
Ken    McClelland             detail the different kinds of clear wood finishes and how they are designed to work.
Luxor Industrial Corp.        We also cover the attributes of wood as a building material, which explains why
                             people are so interested in using it in the first place.
Alan S. Ross
                              INTRODUCTION                                          owner wants the natural beauty of
R. Sam Williams*                                                                    the wood to show through the fin-
                                 Wood has long been admired for
USDA Forest Service                                                                 ish. This natural wood appearance,
                              its natural beauty, durability, and
Forest Products Laboratory                                                          although desirable, is difficult to
                              strength. Because of the increasing
                                                                                    maintain. The harmful effects of na-
                              value of wood used for exterior ap-
                                                                                    ture (primarily sun and rain) de-
                              plications, such as siding decks,
                                                                                    grade the wood surface, both aes-
                              walkways, fences, gazebos, etc.,
                                                                                    thetically and functionally. In recent
                              homeowners want to protect their
                                                                                    years, a number of clear wood fin-
                              investment by applying a protective
                                                                                    ishes have been developed that pro-
                              finish to the wood. Homeowners
                                                                                    tect wood while accentuating its
                              and professional painters have tra-
                                                                                    natural beauty (Figure 1). Although
                              ditionally used protective finishes,
                                                                                    the consumer can choose from a
                              such as paint, but these finishes
                                                                                    vast array of finishes that have a
                              hide the natural beauty of the
                                                                                    wide range of pigments and hiding
                              wood. In many cases, the home-

                                *Author to whom correspondence should be addressed: One Gifford Pinchot Drive, Madison, WI
                                    The use of trade or firm names in this publication is for reader information and does not imply
                                endorsement by the U.S. Department of Agriculture of any product or service.
                                    The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin.
                                This article was written and prepared by U.S. Government employees on official time, and it is
                                therefore in the public domain and not subject to copyright.

42      September 2004                                                                                        JCT Coatings Tech
                                                                                           Consumer Corner

                                          is important to consider the             wood fibers at the surface. Rain
                                          amount and type of pigment that          washes the degraded wood fibers
                                          might be included in the finish.         from the surface causing the surface
                                             When choosing a finish for            to erode Erosion is more rapid in
                                          wood, there are two elements to          the less dense earlywood than in
                                          consider: aesthetics and protection.     the more dense, harder latewood,
                                          These two elements can sometimes         causing an uneven surface. Mildew
                                          be at odds with each other.              growth may also occur as the sur-
                                          Aesthetically, there is a growing        face weathers, which darkens the
                                          trend among homeowners to main-          wood’s surface. However, in some
                                          tain the dear natural look of the        climates, such as along the seashore,
                                          wood’s original color. However, the      wood tends to weather to a silvery
                                          best protection from the sun’s ultra-    gray. Mildew seems to be less of a
                                          violet radiation is obtained from        problem in these areas. The sun‘s
                                          pigmented products, which tend to        UV radiation also degrades dear
                                          cover the wood´s natural grain and       natural finishes.
                                          texture. Thus, the problem arises:
                                          how to balance the aesthetic desires                   Moisture
                                          of the homeowner for a natural
power, the focus of this paper is on      look with the protective require-           Water also degrades wood.
those finishes that have little visible   ments of the wood surface                Whether in the form of liquid or va-
pigment. In some cases, the pig-                                                   por, absorption and desorption of
ments are included but are finely                                                  water causes dimensional changes
ground so that the coating is trans-                                               of the wood, which can lead to pre-
parent to visible light.
                                          WHY PROTECT WOOD?                        mature degradation of the finish.
   Most natural clear wood finishes          Although wood is naturally            Water causes cracking checking,
are designed to protect and beautify      durable and strong the effects of        and warping of the finish and can
wood. Although this may sound             outdoor exposure on wood can de-         also lead to decay (rot) in wood. In
simple, manufacturers’ claims that        grade not only these physical prop-      general, it accelerates the weather-
products protect, preserve, seal, last    erties but its natural beauty as well.   ing of wood exposed outdoors.
longer, work better, and spread far-      Wood exposed outdoors is sub-               SHRINKING AND SWELLING: Wood
ther than competitors’ products are       jected to both rain (moisture) and
                                                                                   shrinks as it loses moisture and
often conflicting and can confuse         sun (ultraviolet radiation), two ma-     swells as it gains moisture. More pre-
both the homeowner and profes-            jor factors that can ultimately cause    cisely, wood only changes dimension
sional painter. In fact, many of the      wood to lose both its natural beauty     between an absolutely dry state
terms used to describe exterior           and strength.                            (completely free of moisture) and its
wood finishes are used incorrectly,                                                fiber saturation point (the point at
thus adding to the confusion. So let              Ultraviolet Radiation            which the cell walls of the wood
us take a look at the problems fac-                                                fibers are completely saturated with
ing the homeowner and profes-                Unprotected wood ages when ex-
                                                                                   moisture). This fiber saturation point
sional contractor as they try to          posed outdoors. The sun’s ultravio-
                                                                                   typically occurs at about 30% mois-
maintain the natural appearance of        let (UV) radiation degrades the sur-
                                                                                   ture for most species of wood. At
wood. In recent articles that com-        face of unprotected wood within
                                                                                   this point. all the wood’s water is
pared the performance of various          weeks of outdoor exposure (Figures
                                                                                   bound within the cell wall. As mois-
coatings for wood, the performance        2 and 3). The early phase of UV
                                                                                   ture content changes above fiber sat-
of clear coatings was often com-          degradation is manifest as a change
                                                                                   uration, the cell cavities take on or
pared with pigmented finishes. To         in color. Dark wood, such as red-
                                                                                   lose unbound water but the wood
be fair, the pigmented and nonpig-        wood and the cedars, tends to get
                                                                                   cell walls do not change dimension-
mented finishes should not be             lighter after initial installation as
                                                                                   ally. Below the fiber saturation point,
compared. For example, two years          the colored extractives degrade.
                                                                                   however, the wood will change di-
of performance of a penetrating           Light wood, such as pine and fir,
                                                                                   mension with changing moisture
clear finish on a deck would be           tends to get darker. As the degrada-
considered excellent. Two years un-       tion continues, the lignin at the sur-
der the same exposure for a pig-          face [top 75 to 100 µm                      WATER AND WATER VAPOR EFFECTS:
mented finish would be considered         (0.003-0.004 in.)] begins to de-         Shrinking and swelling of wood oc-
poor. In comparing clear finishes, it     grade, which in turn loosens the         curs whether the water is in the                                                                            September 2004         43
Figure 1—Examples of natural finishes on siding and logs.         and condensation of           tive bleeding, iron stain, and
                                                                  water vapor as it             mildew. These discolorations, al-
                                                                  moves in or out of a          though not harmful to the wood,
                                                                  building. The dimen-          give an objectionable appearance to
                                                                  sional changes                the wood surface.
                                                                  caused by daily and
                                                                                                   EXTRACTIVE BLEEDING: Certain
                                                                  seasonal changes in
                                                                                                types of lumber such as cedar, red-
                                                                  RH have little effect
                                                                                                wood, mahogany, and Douglas-fir
                                                                  on the performance
                                                                                                contain water-soluble extractives
                                                                  of wood finishes.
                                                                                                that can be leached to the surface of
                                                                      Poor performance
                                                                                                the wood (Figure 4). As water moves
                                                                  of wood finishes
                                                                                                through wood or as the surface of
                                                                  may occur when the
                                                                                                the wood gets wet, water-soluble ex-
                                                                  moisture content of
                                                                                                tractives are dissolved. As the water
                                                                  wood reaches or
                                                                                                evaporates, these extractives are de-
                                                                  goes beyond fiber
                                                                                                posited on the exterior surface and
                                                                  saturation. A large
                                                                                                appear as a reddish brown stain. If
                                                                  percentage of wood
                                                                                                the wood finish is not formulated
                                                                  finish degradation
                                                                                                to block the diffusion of these ex-
                                                                   (e.g., paint ox stain
                                                                                                tractives, they can cause an un-
                                                                  defects, peeling,
                                                                                                sightly residue on the finish, partic-
                                                                  cracking) results
                                                                                                ularly with light-colored finishes.
                                                                  from moisture
                                                                                                Extractive-related discolorations can
                                                                  changes in the wood
                                                                                                be difficult to remove if they are al-
                                                                  and subsequent di-
                                                                                                lowed to remain on a surface for a
                                                                  mensional instabil-
                                                                                                long period of time. Although ex-
                                                                  ity. Water also de-
                                                                                                tractives in wood give the wood its
                                                                  creases paint bond
                                                                                                natural color and resistance to de-
                                                                  strength, thus in-
                                                                                                cay (for some wood species), they
                                                                  creasing the chance
                                                                                                must be sealed in the wood with a
                                                                  for peeling. The wet-
                                                                                                stain-blocking primer when using
                                                                  ting-drying cycles of
                                                                                                light-colored finishes. Extractive-
form of vapor or liquid. For exam-               wood exposed outdoors can raise
                                                                                                related discolorations are usually
ple, wood swells during periods of               the grain of the wood. If the raised
                                                                                                not a serious problem when using
high humidity and shrinks during                 grain is severe, it can cause cracks in
                                                                                                dark stain or dear finishes.
periods of low humidity. If wood is              paint, particularly in oil-based paints.
exposed to 100% relative humidity                   For wood finished with clear                    IRON STAIN: Iron stain occurs in
(RH) for an extended period, the                 penetrating finishes, dimensional              two ways on wood. Rust from iron
moisture content will eventually                 changes caused by wetting-drying               or steel fasteners, railings, supports
reach the fiber saturation point but             cycles may lead to raised grain,               for window air conditioners, etc.,
it will not go beyond this point                 checking, and cracking of
without the presence of liquid wa-               the wood. This roughened
ter. Wood exposed outdoors goes                  surface increases water up- Figure 2—Surface changes on typical softwood during the
through a daily and seasonal                     take, thus accelerating the        naturalweathering process.
change in moisture content as de-                degradation process. On
termined by the RH. It is almost                 flat-grained lumber, the
never exposed to extended periods                raised grain may appear as
of 100% RH. Even in the hot humid                thin knife-like feathers
areas of the south, the moisture                 along the earlywood-late-
content of wood stays well below                 wood interface.
20% as long as the wood does not
get wet. Water, however, can cause                          Discolorations
wood to quickly reach, and even go
beyond, fiber saturation. The source                 Moisture contributes to
of this water can be rain, dew, melt-             many common wood dis-
ing ice or snow, plumbing leaks,                  colorations, such as extrac-

44        September 2004                                                                                           JCT Coatings Tech
                                                                                                  Consumer Corner

can be washed down a structure by         the require-          Figure 3—The weathering process (degradation worsens A through D).
rain and absorbed by the wood or          ments needed
finished wood to cause brown dis-         for mildew
coloration. Iron can also react with      growth, mois-
the extractives in wood to give a         ture is the only
blue-black stain. Although these          one that can
stains can sometimes be removed           be controlled.
by treatment with oxalic add or           It is impossi-
sodium biflouride, it is best to          ble to control
mid the problem by using corro-           colonization,
sion resistant materials.                 food source,
    MILDEW: Airborne mildew spores        or oxygen, and
are ubiquitous and microscopic and         it is difficult to
therefore are difficult to detect until    control mois-
they colonize a surface. They are          ture; therefore,
transported easily by air currents,        paint and stain
insects, and animals. These spores         companies in-
can cause mildew fungus growth on          corporate
any surface that provides a food           mildewcides in
source. Food sources for mildew in-        their products
clude wood extractives, plant and          to retard
tree pollens, natural oils such as lin-    mildew growth.
seed and tung oils, bacteria, dirt,
and other natural organic materials.          In the absence of a mildewcide,            solids, water-based, oil emulsion,
Because mildew uses organic mate-         wood that gets wet or damp (even               and traditional solvent-based for-
rials for food, it has a greater ten-     for a short period of time) may                mulations are just a few examples
dency to grow on organic surfaces         develop mildew. As the mildew                  of the different types of dear fin-
such as wood, leather, and paper          fungi grow, they become visible                ishes sold within each of the cate-
rather than inorganic surfaces such       because they often develop highly              gories of dear natural finishes. Air
as aluminum, vinyl, and glass.            colored pigmentation. Gray or                  quality regulations have limited the
Mildew can also grow on these sub-        black coloration is the most typi-             amount of volatile organic com-
strates, but it must then depend on       cal, but various other colors com-             pounds (VOCs) permissible in
airborne food sources. Although ex-       monly occur. The mildewcides                   paints, which has motivated paint
tractives and natural oils give some      found in paints and stains are not             manufacturers to formulate an
species of wood their deep rich           very effective in destroying pre-ex-           abundance of new water-based dear
color, these organic compounds            isting mildew. Therefore, it is im-            finishes. Another reason for the
 also make wood an ideal substrate        portant that mildew be com-                    abundance of new finishes is con-
 for mildew growth, if there is           pletely destroyed prior to staining            sumer demand. Some of these new
enough moisture available (Figure         or painting.                                   clear natural finishes may be film-
5). Therefore, because wood has                                                          forming and therefore, they may
 readily available food for mildew                                                       not penetrate the wood´s surface
growth, mildew grows more readily         CLEAR NATURAL FINISHES                         very well. Clear finishes also de-
 on bare wood surfaces than on                                                           grade from UV radiation and mois-
                                             Stain and paint manufacturers               ture. For penetrating finishes, this
 painted wood, particularly wood
                                          have produced a number of clear                degradation is not serious because
 painted with synthetic organic poly-     products to meet the aesthetic de-
 mers such as acrylics.                                                                  the wood can be refinished without
                                          sires of the homeowner while meet-             extensive surface preparation; film-
    Following colonization, mildew        ing the requirements of wood pro-              forming finishes often require ex-
 needs food, moisture, air (oxygen),      tection. Clear natural finishes                tensive surface preparation, even to
 and moderate temperatures [usually       generally fit into four categories:            the extent of complete removal of
 between 4.4°C and 32.2°C (40°F           waterproofing, water-repellent seal-           the old finish, prior to refinishing.
 and 90°F)]. Because of the extreme       ers, wood preservatives, and UV-re-            Thus, when choosing a clear prod-
 of conditions in which it can flour-     sistant clears (blocking or absorb-            uct, it is important to match the
 ish and the wide variety of species,     ing). Some dear natural finishes on             aesthetic desires and the exposure
 mildew is very hard to control and       the market today may be combina-                to the weather with the protective
 impossible to totally eliminate. Of      tions of these categories. High                 requirements of the wood and, at                                                                                   September 2004               45
Figure 4—Examples of extractives bleed on   creases the amount of water ab-           placed into use ensures end-grain
finished wood.                              sorbed into the wood, thus decreas-       penetration of the sealer.
                                            ing dimensional changes, warping
                                            and splitting. They also contain an            Wood-Preserving finishes
                                            oil or resin that helps seal the sur-
                                                                                          Clear wood-preserving finishes
                                            face and a solvent to facilitate ab-
                                                                                      differ from Water-repellent finishes
                                            sorption of the other ingredients.
                                                                                      in that they also contain an appro-
                                                Water repellents were tradition-      priate amount of a U.S.
                                            ally formulated with organic sol-         Environmental Protection Agency
                                            vents; however, contemporary for-         (EPA) approved and registered fun-
                                            mulations may be water-based or           gicide. These clear finishes are very
                                            solvent-based, or in some cases,          similar in appearance to water-
                                            may use paraffin oil with no other        repellent sealers. If the fungicide is
                                            solvent. The type and amount of           incorporated to preserve the wood
                                            material used to impart water repel-      itself, the product must be EPA reg-
                                            lence may affect future paintability      istered. If the fungicide is present
                                            of the treated surface. Water-repel-      only to protect the clear finish, the
                                            lent sealers designed for use prior to    product does not have to be regis-
                                            painting have about 1% wax or sim-        tered. The commonly used fungi-
                                            ilar water repellent in a curable         cides are also effective in control-
                                            resin. Because moisture is repelled,      ling mildew (mildewcides).
                                            mildew growth may be slowed but
                                                                                          Fungicides are important to all
                                            is not prevented. These products of-
the same time, to understand the                                                      dear natural finish formulations,
                                            ten provide spectacular beading of
performance limitations of the fin-                                                   and most manufacturers incorpo-
                                            water upon initial application.
ish.                                                                                  rate some level of them into their
                                            However, they offer wood little pro-
                                                                                      products. The addition of these spe-
                                            tection from the sun's UV radiation
                                                                                      cific EPA-approved fungicides to the
       Waterproofing Products               or mildew growth; they weather to
                                                                                      product, in specific quantities, and
                                            gray and then black from the
   Waterproofing clear products are                                                   the subsequent EPA registration, al-
                                            growth of mildew, unless a mildew-
often confused with water-repellent                                                   lows manufacturers to make specific
                                            cide is added to the product (see
products. Waterproofing products                                                      claims about controlling decay and
                                            the Wood-Preserving Finishes sec-
form a membrane designed to                                                           mildew when describing their prod-
                                            tion). When water-repellent sealers
withstand hydrostatic pressure (like                                                  ucts. Some common fungicides
                                            are subjected to degradation by the
wind-driven rain) and keep water                                                      used in these products that can pro-
                                            sun's W radiation, the result is a
out of a home throughout long pe-                                                     vide decay and mildew resistance to
                                            gradual loss of the water beading ef-
riods of wetting. Waterproofing                                                       wood include 3-iodo-2-propynyl
                                            fect. The life expectancy of these
coatings are often elastomeric and                                                    butyl carbamate, zinc naphthenate,
                                            products typically ranges from six
are designed for brick, stucco, and                                                   copper naphthenate, bis (tributyl-
                                             months to one year on horizontal
other masonry surfaces, not wood.                                                     tin) oxide (TBTO), N-trichlorometh-
                                             surfaces (for example, decks) and
They are products used around                                                         ylthio phthalimide, and copper-8-
                                             one to two years on vertical sur-
flashing to completely stop water                                                     hydroxyquinolate.
                                             faces, The exposed surfaces of lum-
absorption.                                  ber are typically lateral grain. These       Penetrating wood-preserving fin-
                                             sealer treatments do not absorb very      ishes may also be used as a treat-
        Water-Repellent Sealers              well into lateral gain; however, they     ment for bare wood before priming
                                             absorb readily into the end-grain of      and painting or in areas where old
   Water repellents shed water for           lumber and thus give many years of       paint has peeled, exposing bare
short periods, like rain or water            efficacy preventing end-grain ab-        wood. This treatment gives a sec-
from a sprinkler. They are not com-          sorption of water. Since the end-         ond "wall" of protection against
pletely impervious to water absorp-          grain of wood absorbs water much         water that has penetrated the paint
tion. Clear products that fall into          more readily than the lateral grain,      film. This is especially effective to
the water-repellent category are the                                                   prevent absorption of water at
                                             protecting end-grain is more critical
penetrating finishes. They typically         to long-term durability than pro-         joints and at end-grain, thus de-
contain a small amount of wax                                                          creasing the swelling of the wood.
                                             tecting the lateral grain. Treating
(1–3%), usually paraffin, or other                                                     As a result, less stress is placed on
                                             each piece of wood before it is
water-repellent material that de-

 46       September 2004                                                                                   JCT Coatings Tech
                                                                                           Consumer Corner
the paint film and its service life is   dioxide that reflects UV radiation.     WHY WOOD ANYWAY?
extended. For treating bare wood,        The organic chemical additives are
make certain that the manufac-           of two types–UV absorbers (UVA)             Wood is the material of choice
turer's label indicates that the clear   and hindered amine light stabilizers    for a wide range of building proj-
wood preservative is paintable.          (HALs).                                 ects. It offers the builder a long list
Some products have too much wax              Ultraviolet absorbers are de-       of features that work together to
or other water repellent and the         signed to absorb selective portions     meet the end user's expectations for
paint will not adhere adequately or      of sunlight, especially UV radiation,   service, cost, and appearance.
dry properly.                            and dissipate that energy as heat.          Perhaps the greatest attribute of
    Water-repellent sealers and clear    During this process, some absorbers     wood is its versatility. Wood can be
wood-preserving finishes give some       are destroyed, limiting the effective   used indoors and outdoors in both
protection to the wood surface from      life of the product. The HALs act as    structural and appearance applica-
weathering by minimizing the ef-         scavengers for the components of        tions. Whether the needs are clear
fects of water. The wax in the prod-     the finish (binder and pigments)        or knotty appearance, rough or
uct ultimately breaks down on the        during degradation and then block       smooth texture, wood can meet the
exposed lateral surfaces, and the wa-    further degradation of the dear fin-    changes in design and fashion. It
ter beading properties decrease. The     ish and the wood. Generally, UVAs,      can be specified from the hundreds
life expectancy of the water repel-      HALs, and pigments are used to-         of standard sizes and patterns or
lency of these products typically        gether and offer the best protection    custom ordered to meet particular
ranges from six months to one year       to the wood surface.                    needs. Wood products are widely
on exposed surfaces. However, the             Many people feel UV-resistant      distributed and readily available
water repellent absorbed in the end-     dear finishes are the solution to the   throughout the United States and
grain will be effective for many         delicate balancing act of the aes-      Canada.
years. Also, after the wood has grad-    thetic desires of the homeowner             Another factor favoring the use
ually weathered, additional treat-       and the protective requirements for     of wood is its ease of handling and
ments may last longer because the        the wood. The UV-resistant clears       fabrication. Wood can be shaped,
weathered boards absorb more fin-        are not as dear as water; they im-      drilled, cut, and fastened with com-
 ish. The UV radiation can still de-     part a slight color or tone to the fin- mon tools that can be operated by
grade the surface causing the release    ish because they contain translucent    homeowners and professional con-
 of wood fibers and thus the erosion     transoxide pigments or titanium         tractors alike.
 of the surface. Including a UV ab-      dioxide. Thus, with UV-resistant            Buildings constructed from wood
 sorber or some other type of UV         clears, various shades of color are     have a history of excellent service.
 stabilizer in the formulation can       available. Transoxide pigments are       Interior beams, ceilings, paneling.
 slow this degradation for a short       translucent and thus highlight the       and trim will last the lifetime of the
 time.                                   natural grain, texture, and beauty of   building. Wood products are widely
                                         the wood. Transoxide pigments are       used for exterior siding. trim, decks,
                                          also versatile; they are used not only  and landscape projects. Species such
ULTRAVIOLET-RESISTANT                    in traditional solvent- and oil-based    as redwood and cedar contain natu-
CLEAR FINISHES                           product formulas but also in the         ral preservatives that make them
   The only way to slow the UV           latest formulas that meet tighter air    particularly well suited to exterior
degradation of the surface is to in-      quality (VOC) regulations, such as      environments.
corporate a pigment or a UV stabi-        oil emulsion, high solid
lizer into the formulation. Thus, the     oils, and water-based for-
UV-resistant clear water-repellent        mulations. The penetrating Figure 5—Mildew on wood siding.
preservative represents the broadest      and film-forming character-
category of clear natural finishes on     istics can vary considerably
the market. Pigments and organic          among these types of prod-
chemical additives are used as light      ucts. The life expectancy of
absorbers (ox screeners) to protect       a UV-resistant clear finish is
the products' binders and the wood        typically twice that of other
from degradation by the sun's UV          dear finishes and can range
radiation. The pigments that are          from one to two years on
used most frequently are either a         horizontal surfaces (for ex-
transparent form of iron oxide            ample, decks) and two to
(transoxide) or ultrafine titanium        four years on vertical sur-
                                          faces.                                                                            September 2004       47
    Using wood rather than other       practices (for example, the planting   enhanced and preserved through
materials is environmentally           of more than two billion trees each    the proper selection, application,
friendly. The production of wood       year in North America) assures a       and maintenance of a finish.
products generally requires much       continued supply of wood for gen-
less energy than producing alterna-    erations into the future.              SUMMARY
tive products, which lowers both          The beauty of wood has long
fuel consumption and air emis-         been admired. The warm colors and          Matching the aesthetic desires of
sions. And, wood is the only mew-      rich grain patterns have decorated     homeowners with the protective
able building material. The nation's   homes and their landscapes for cen-    requirements of wood using tech-
move toward sustainable forestry       turies. This natural beauty can be     nologies available today is a deli-
                                                                              cate balancing act. By having an
                                                                              understanding of the benefits and
                                                                              limitations of the various natural
                                                                              clear finishes, the homeowner's ex-
                                                                              pectations for performance and
                                                                              maintenance can 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 blend-
                                                                              ing and balancing of the various
                                                                              raw materials used in the coatings
                                                                              formula. High quality, dear wood
                                                                              finishes should be easy to use, con-
                                                                              tain mildew-preventing ingredi-
                                                                              ents, provide some degree of water
                                                                              repellency, and contain UV radia-
                                                                              tion absorbers. Generally, clear fin-
                                                                              ishes fully exposed to the weather
                                                                              last one to two years; however,
                                                                              some last less than a year. Research
                                                                              is needed to achieve a quantum
                                                                              leap in the technology of clear fin-
                                                                              ishes for wood.


48      September 2004                                                                           JCT Coatings Tech