EXTERIOR FINISHES FOR LOG HOMES

The unique characteristics of wood make it suitabledo not trap moisture in the wood, and they do not
for a variety of applications in the building industry: logpeel or blister.
or timber homes, decks, rough-sawn siding, fences,Natural oils (linseed and tung, for example) are initially
and shingles. Without protection from sun andvery effective in stopping the absorption of water
moisture, wood "weathers" and deteriorates. Finishesinto wood, but tend to darken over time because
are used to enhance appearance and dimensionalthey are a food for fungi. Buildings treated with
stability, and to prevent deterioration.natural oils and resins generally need extensive
Weathering of wood is a combination of chemical,cleaning before reapplying the finish.
mechanical, biological, and sunlight-induced processesSome of the newer water-based systems have
that change the appearance and structure of wood.synthetic oils and resins and they provide excellent
After two months of exposure, all woods will turnwater repellency and color retention. One of the main
yellowish or brownish, and then gray. Dark woods willadvantages of synthetic resins is that unlike natural
become lighter, while light woods eventually darken.oils, they do not serve as a food for most biological
Surface checks, raised grain, cupping, and warpinggrowth, making future coats easier to apply.
develop as wood continues to weather.APPLYING THE FINISH
Recent research conducted by the Forest ProductCorrect application is critical to performance. Follow
Laboratory indicates that failure to properly treatthe manufacturers' instructions, particularly with the
new lumber can reduce the average life of wood bynewer water-based formulations. All finishes should be
20 percent.applied to a clean surface, but penetrating finishes
Understanding the differences between finishesmust be applied to surfaces that are porous and free
makes it easier to select the right product. In thefrom previous coatings.
past, finishes were made from alkyd or natural oilAlthough chlorine beach will effectively remove many
resins such as linseed, tung, soya and paraffin. Thestains like mold and mildew, it can damage wood and
resins were often blended with waxes to provideis toxic to people and plant life. Newer, chlorine-free
additional water repellency, and then diluted with acleaners are environmentally safe and can actually
mineral spirits solvent.increase product penetration up to 25%. Wood that
Technological advances and environmental regulationsis pre-treated with a cleaner or pressure washer will
on emission level of volatile organic compoundsprobably have some raised grain, but will also have a
(VOC's) have spurred the development of newbetter finish penetration.
products. Water-based products, particularly thoseWater-based finishes tend to dry faster than
formulated with certain water-reducible synthetic oilsoil-based products. To avoid lap marks, particularly on
and resins, have excellent penetration and perform ashot sunny days, apply these only in the shade: the
well as, or better than, oil-based (alkyd) finishes.cooler surface will absorb better and allow for easier
The performance of commercially available woodapplication of a second coat.
finishes is often listed on a product label or inLog structures can pose special application problems.
literature supplied by the manufacturer. The AmericanMoisture contents higher than 20% can cause a finish
Society for Testing and Materials (ASTM) hasto creak and peel as the log dries. Test logs with a
standardized test methods to measure the watermoisture meter before applying or re-applying,
repellency and color retention of wood finishes.especially when using film-forming or water-based
In ASTM test D5401-93, a finish is applied to a 2" byproducts.
4" section of wood, allowed to cure for seven daysAnother problem is that the up-facing curves of logs
under controlled conditions, and then tested forare subjected to intense UV rays and moisture when
water absorbency. Standard ASTM G53-88 evaluateswhen and snow accumulate in cracks and crevices
the water repellency of coatings exposed tocausing the finish to crack and peel. Log homes at
ultraviolet light and condensation in a weatherhigher elevations are especially subject to
exposure chamber for 1000 hours. Manufacturers alsotemperature extremes that cause wood to
use outdoor tests to measure weathering in variouscontinually expand and contract. This affects
climates, and they might provide test results if youadhesion, water repellency and color retention of
request them.finishes.
Finishes are generally classified into two basicExposed end grain at corners can encourage water
categories: those that form a film or coating onpenetration. Make sure that end grain is adequately
wood and those that penetrate.treated and that large checks are sealed properly.
FILM FORMERSApply finish liberally to the courses of logs near the
These products form a coating, or film, that is afoundation where moisture and dirt are likely to be a
barrier between wood and the elements. Film-formersproblem.
include many alkyds, latex/acrylics, and varnish resinsProtecting logs from rain prolongs a finish and greatly
in solvent or water-based finishes. Products withoutreduces maintenance. Wide roof overhangs, gutters
pigments are considered to be a clear or transparentand down spouts, and good drainage around a
finish, and have little or not protection from ultravioletfoundation can help you avoid many problems. The
(UV) radiation. Pigments are added to paints, solidcombination of a high performance finish and good
color stains, and semi-transparent finishes to changedesign and construction will help ensure that moisture
the appearance of the wood and to providedoes not deteriorate logs.
protection from UV rays.MAINTENANCE
Some of the newer water-based coatings areRoutine maintenance is necessary, but the life-span
semi-transparent acrylic blends that have excellentof a finish depends on a variety of factors.
flexibility. Unfortunately, due to their higher molecularConstruction details, exposure to the elements,
weight, acrylics still form a film on the surface ofproduct choice, surface preparation and application
wood, and are subject to the cracking that istechniques are all essential to success. Some finishes
characteristic of all film-forming finishes. A film finishmay even require chemical stripping or sandblasting to
cracks as wood expands and contracts during normalrestore wood to the proper condition before
moisture cycling and water gets underneath the finishre-treatment. Finishes that weather unevenly and are
and deteriorates the wood. Removing film-formingre-coated without removing the old finish will have an
wood finishes can be difficult, but is often necessaryunsightly, patchy appearance.
before re-application. If the failing coat is notAlthough the wood finish is only a small percent of
removed, then the new coat may blister and peel.the cost of a log home, it is one of the more critical
PENETRATING FINISHESelements in construction. To most consumers,
Penetrating wood finishes are oil or water-basedaesthetic appeal is just as important as performance
products that saturate wood pores to prevent waterwhen selecting a wood finish. Understanding the
penetration. They typically contain a drying oil or resinproperties and expected performance of various
in a transparent or semi-transparent stain.products makes the decision process much easier for
Advantages of penetrating finishes over films areyou.
that they provide long-term water repellency, they