The Seasoning and Preservation of Log Homes BY ALEX BOATWRIGHT, VICE PRESIDENT AAA LOG HOMES, INC.
THERE ARE MANY WAYS TO MAKE A LOG HOME! EVERY LOG HOME COMPANY HAS A DIFFERENT METHOD OF MANUFACTURING LOGS, AND A DIFFERENT DESIGN. THERE IS ONE THING, HOWEVER, THAT ALL THESE COMPANIES HAVE IN COMMON. ALL THESE MANY DIFFERENT LOG HOMES ARE MADE OF WOOD! WOOD IS A WONDERFUL MATERIAL FOR BUILDING. IT'S WARM TO THE TOUCH, IT HAS AN ATTRACTIVE GRAIN PATTERN AND COLOR, IT'S ONE OF THE BEST NATURAL INSULATIONS, IT'S EASY TO WORK WITH, IT'S STRONGER, POUND FOR POUND, THAN STEEL AND IT'S A RENEWABLE RESOURCE. NO OTHER BUILDING MATERIAL HAS SO MANY DESIRABLE CHARACTERISTICS. HOWEVER, AS THE SAYING GOES, 'NOBODY'S PERFECT'. THIS ALSO APPLIES TO OUR MANY SPLENDORED MATERIAL, WOOD. WOOD, IF NOT PROPERLY PROTECTED, FALLS PREY TO SEVERAL DESTRUCTIVE FORCES. AMONG THE MOST IMPORTANT OF THESE ARE ROT AND INSECT ATTACK. BEFORE BECOMING INVOLVED IN THE PREVENTION OF THESE TWO INSIDIOUS ENEMIES OF WOOD, IT'LL BE HELPFUL TO HAVE A BRIEF EXPLANATION OF THE STRUCTURE AND NATURE OF WOOD. SINCE THE VAST MAJORITY OF LOG HOMES ARE MADE OF SOFT WOODS, WE'LL CONFINE OUR DISCUSSION TO THOSE SPECIES. WOOD CELLS WOOD IS MADE UP MOSTLY OF TIGHTLY GROWN-TOGETHER CELLS. CUSTOMARILY CALLED FIBERS OF TRACHEIDS. THESE TRACHEIDS ARE USUALLY LONG AND SKINNY, ABOUT 100 TIMES AS LONG AS THEY ARE IN DIAMETER. SOFT WOOD TRACHEID LENGTHS RANGE FROM ABOUT ONE-EIGHTH TO ONE-THIRD OF AN INCH. THEY TEND TO BE POINTED AT BOTH ENDS. IN THE AVERAGE CONIFEROUS SPECIES, A CUBIC INCH OF WOOD CONTAINS ABOUT FOUR MILLION TRACHEIDS. IN THE "GREEN" STATE, THESE HOLLOW CELLS ARE FILLED WITH WATER, OR SAP. THE WALLS OF THE TRACHEID ARE ALSO SATURATED WITH WATER. THE WATER IN THE CELL IS CALLED FREE WATER. THE WATER IN THE CELL WALLS IS CALLED BOUND WATER. MOST OF ALL PROBLEMS WITH WOOD INVOLVE MOISTURE. MOISTURE CONTENT IS A COMMON TERM OFTEN HEARD IN RELATION TO WOOD. MOISTURE CONTENT MEANS THE RATIO OF THE WEIGHT OF WATER TO THE WEIGHT OF THE WOOD WHEN IT IS COMPLETELY, OR "OVEN" DRY. THAT'S WHY IT'S POSSIBLE FOR WOOD TO HAVE A MOISTURE CONTENT OF 110%, 150% OR EVEN 200%. FEW PROBLEMS OCCUR WHEN THE WOOD HAS A HIGH MOISTURE CONTENT. THE TROUBLES BEGIN WHEN THE MOISTURE STARTS TO LEAVE THE WOOD. DOWN TO ABOUT 28-30% MOISTURE CONTENT, THE WOOD REMAINS RELATIVELY STABLE AND RESISTANT TO DECAY FUNGUS AND INSECT ATTACK. BELOW ABOUT 20% MOISTURE CONTENT, WOOD AGAIN BECOMES RESISTANT TO DECAY FUNGUS. UNTIL THE FREE WATER IN THE CELLS IS GONE, THE BOUND WATER IN THE CELL WALLS REMAIN IN PLACE. UNTIL THE BOUND WATER BEGINS TO MIGRATE TO THE SURFACE AND EVAPORATE, THE CELL WALLS REMAIN SWOLLEN, AND THERE IS LITTLE DIMENSIONAL CHANGE IN THE WOOD. THEREFORE, UNTIL WOOD REACHES APPROXIMATELY 28-30% MOISTURE CONTENT, IT'S ESSENTIALLY STILL "GREEN." THE POINT AT WHICH BOUND WATER STARTS TO ESCAPE (28-30%) IS CALLED THE FIBER SATURATION POINT. WOOD HAS TO DROP BELOW THE FIBER SATURATION POINT BEFORE IT BEGINS TO SHRINK. IN LOG HOME LOGS, THE PROBLEM IS THE SIZE OF THE LOG. BECAUSE OF THE DISTANCE FROM THE CENTER OF THE LOG TO THE OUTSIDE SURFACE OF THE LOG, WATER INSIDE THE LOG MUST MIGRATE. THE SURFACE BEGINS TO GIVE UP MOISTURE TO THE ATMOSPHERE ALMOST IMMEDIATELY AFTER BEING CUT. THE MOISTURE DEEPER WITHIN THE LOG, HOWEVER, MUST MIGRATE TOWARD THE SURFACE BEFORE IT CAN EVAPORATE. THE LARGER THE LOG, THE GREATER DISTANCE THE MOISTURE HAS TO MIGRATE. BECAUSE OF THIS,THE OUT SIDE OF THE LOG BEGINS TO SHRINK BEFORE THE INSIDE. THIS IS A CAUSE OF CHECKS. A CHECK (LENGTHWISE SPLIT OR CRACK) RESULTS WHEN THE SURFACE WOOD SHRINKS, BUT THE INNER WOOD REMAINS THE SAME SIZE. WHEN THIS HAPPENS, THE WOOD ON THE SURFACE SEPARATES ALONG THE GRAIN, CAUSING A CHECK. IT'S LIKE TRYING TO PUT A PAIR OF SIZE 30 JEANS ON A SIZE 42 BODY. CHECKS ARE COMMON TO LARGE TIMBERS, AND AREN'T ESPECIALLY A CAUSE FOR CONCERN IF PROPER PRECAUTIONS ARE TAKEN TO KEEP THE CHECKS FROM HOLDING MOISTURE. FROM A STRENGTH STANDPOINT, A LOG WALL IS USUALLY SO MUCH STRONGER THAN NECESSARY THAT CHECKS HAVE LITTLE OR NO EFFECT ON THE OVERALL STABILITY OF THE WALL. THE MAJOR PROBLEM THAT CAN OCCUR BECAUSE OF CHECKS IS THE TRAPPING OF MOISTURE, SO UPWARD SLANTING CHECKS ARE MUCH MORE CRITICAL THAN DOWN- WARD SLANTING CHECKS. CHECKS INSIDE THE HOME ARE OF ALMOST NO CONCERN, EXCEPT IN A BATHROOM, KITCHEN OR LAUNDRY, WHERE SPLASHES MAY BE TRAPPED IN THEM. FOR THIS REASON, ITS BEST NOT TO LOCATE A BATHTUB NEXT TO A LOG WALL. CHECKS OUTSIDE THE HOME THAT ARE PROTECTED FROM RAIN WATER BY A PORCH OR ROOF OVERHANGS ARE RELATIVELY SAFE FROM MOISTURE ACCUMULATION. LARGE ROOF OVERHANGS ARE RECOMMENDED FOR THIS REASON. THE MINIMUM ROOF OVERHANG SHOULD BE TWO FEET PAST THE LOGS. PORCHES ARE ALWAYS A GOOD IDEA. IF AN OPEN DECK IS DESIRED, GUTTERS SHOULD BE USED TO PREVENT RUNOFF FROM THE ROOF SPLASHING BACK AGAINST THE LOGS. A TWO FOOT MINIMUM LOG HEIGHT ABOVE THE GROUND SHOULD BE MAINTAINED FOR THE SAME REASON. THE IDEA IS TO KEEP THE WOOD AS DRY AS POSSIBLE. REMEMBER, DRIED WOOD THAT BECOMES RE-WETTED PAST THE 20% MOISTURE CONTENT RANGE IS BACK IN THE DANGER ZONE. ANOTHER PLACE THAT WATER CAN BE TRAPPED ON LOGS IS AT THE LOG INTERSECTION. A LOG THAT IS DESIGNED TO SHED WATER INSTEAD OF ALLOWING IT TO REST ON THE SURFACE IS EASIER TO KEEP DRY. SEASONING THERE ARE TWO MAIN METHODS OF SEASONING LOGS FOR LOG HOMES. ONE WAY IS KILN DRYING. THE OTHER IS AIR DRYING. BOTH HAVE THEIR ADVANTAGES AND DISADVANTAGES. KILN DRYING IS THE PROCESS OF ARTIFICIALLY FORCING THE WATER FROM THE CELLS OF THE WOOD BY ENCLOSING THE WOOD IN A LARGE INSULATED BUILDING AND HEATING IT TO A HIGH TEMPERATURE WHILE CIRCULATING AIR WITHIN THE BUILDING. IT'S SIMILAR TO A LARGE OVEN. ONE ADVANTAGE IS THAT ITS FASTER THAN AIR DRYING. KILN DRYING IS ALMOST UNIVERSALLY USED FOR FRAMING LUMBER AND PLANKS. THE DISADVANTAGE WITH LOGS, IS THAT, WHILE IT"S EASY TO DRY THE SURFACE OF A LOG, IT'S VERY DIFFICULT TO GET THE INNER PART OF THE LOG TO THE SAME MOISTURE CONTENT. THE LARGER THE LOG, THE MORE DIFFERENCE BETWEEN THE SURFACE AND THE INSIDE. FOR A LARGE LOG TO BE UNIFORMLY DRIED TO 15% OR BELOW MOISTURE CONTENT (THE REQUIRED FIGURE THAT IS CON- SIDERED KILN DRIED BY ALL THE MAJOR LUMBER ASSOCIATIONS) WOULD REQUIRE A GREAT DEAL OF TIME AND A SPECIAL DRYING SCHEDULE. UNLESS BOUND WATER IS LOWERED TO THE 15% MOISTURE CONTENT LEVEL IN THE CENTER OF THE LOG, AS WELL AS IN THE SURFACE, THE LOG CANNOT PROPERLY BE CONSIDERED KILN DRIED. UNFORTUNATELY, MOISTURE METERS CANNOT PENETRATE DEEPLY ENOUGH INTO A LOG TO MEASURE THE MOISTURE CONTENT IN THE INNERMOST PART SO A LOG WOULD HAVE TO BE CUT TO THE CENTER TO OBTAIN AN ACCURATE MEASUREMENT. MERELY SPENDING SOME TIME IN A KILN IS NOT THE SAME AS BEING KILN DRIED. AIR DRYING USES THE NATURAL FORCES OF SUN AND WIND TO ACCOMPLISH SEASONING. AGAIN, THE THICKNESS OF THE LOG IS THE PROBLEM. TWO-BY-FOURS, FOR EXAMPLE, CAN BE AIR DRIED IN A ONE-TO-SIX MONTH PERIOD. AN EIGHT INCH LOG, HOWEVER, IS ANOTHER STORY. FOR AN EIGHT INCH LOG TO REACH A 15% MOISTURE CONTENT IN THE INNER MOST PART OF THE LOG, IT CAN TAKE ONE, TWO, OR AS MANY AS FOUR YEARS OF AIR DRYING. ONE ADVANTAGE OF AIR DRYING IS THAT THE MOISTURE LEAVES THE WOOD SLOWLY AND NATURALLY, INSTEAD OF BEING FORCED OUT. FORCING THE WATER OUT CAN RUPTURE THE WALLS OF THE CELLS, WHICH CAN CAUSE THE DRIED WOOD TO RE-ABSORB EASIER AND FASTER LATER ON, WHEN THE WOOD IS IN SERVICE. ACCORDING TO THE WOOD HANDBOOK BY THE U.S. FOREST SERVICE. "IDEALLY, SOLID TIMBER (OR LOGS) SHOULD BE SEASONED TO THE AVERAGE MOISTURE CONTENT THEY WILL REACH IN SERVICE. WHILE THIS OPTIMUM IS POSSIBLE WITH LUMBER LESS THAN 3 INCHES THICK, IT IS SELDOM PRACTICAL TO OBTAIN FULLY SEASONED TIMBERS, THICK JOISTS, AND PLANKS. WHEN THICK SOLID MEMBERS ARE USED, SOME SHRINKAGE OF THE ASSEMBLY SHOULD BE EXPECTED." FROM WHAT WE'VE LEARNED ABOUT THE WAY WOOD DRIES, IT'S EASY TO UNDERSTAND WHY MOST LOG HOME MANUFACTURERS ALLOW FOR SETTLEMENT IN THEIR CONSTRUCTION METHODS. ALLOWING FOR SETTLEMENT IS ONE OF THE MOST IMPORTANT WAYS TO ACCOMMODATE THE REMAINING SHRINKAGE INHERENT IN A LOG WALL. KILN DRIED OR AIR DRIED, IT'S NOT VERY LIKELY THAT THE LOGS WILL BE DRY ENOUGH AWAY FROM THE SURFACE TO PREVENT MORE SHRINKAGE. IF SETTLEMENT ISN'T ALLOWED FOR, ITS A PRETTY SAFE BET THAT SOONER OR LATER, SPACES BETWEEN LOGS WILL SHOW UP AND STICKING WINDOWS AND DOORS WILL OCCUR. IF THE SETTLING SYSTEM IS DESIGNED CORRECTLY, A LOG HOUSE CAN COMPLETE IT'S SEASONING PROCESS SLOWLY AND NATURALLY OVER A LONG PERIOD OF TIME. WITH THE LOGS IN PLACE. WOOD PRESERVATION PRESERVING THE WOOD AGAINST ATTACK BY DECAY, FUNGI AND INSECTS IS PROBABLY ONE OF THE MOST IMPORTANT SUBJECTS CONCERNING LOG HOMES. OF COURSE, LOG HOMES ARE NOT THE ONLY ONES TO BE ATTACKED BY THESE PESTS. BUT SOMETIMES PEOPLE SEEM TO THINK THEY ARE. A TERMITE, FOR EXAMPLE, DOESN'T KNOW THE DIFFERENCE BETWEEN A LOG OR A TWO-BY-FOUR. THE BEST PRESERVATIVE IS THE DESIGN OF THE BUILDING ITSELF, AND THE DESIGN OF THE LOGS. IF THE LOGS ARE SELF-DRAINING, THERE'S NOT GOING TO BE MUCH WATER REMAINING ON THE WOOD LONG ENOUGH FOR IT TO SOAK. IF YOU'VE DESIGNED IN A LOT OF ROOF OVERHANG, AND HAVE PORCHES AND GUTTERS TO PREVENT RAIN WATER FROM SOAKING THE LOGS, YOU'VE WON HALF THE BATTLE. ANOTHER THING TO WATCH FOR IS SHRUBBERY NEXT TO THE LOGS. THE LEAVES HOLD WATER, AND THE SHRUBBERY CAN PREVENT THE SUN FROM DRYING WATER ON THE LOG SURFACE. DON'T LET WATER SPLASH BACK ON THE LOGS AFTER SPILLING FROM THE ROOF. ORIENTATION OF THE HOUSE ITSELF CAN MAKE A LOT OF DIFFERENCE. IF YOU KNOW THE DIRECTION FROM WHICH THE PREVAILING WINDS TEND TO BLOW RAIN TOWARD THE HOUSE, HAVE A PORCH FACING THAT WAY. AGAIN, THE MAIN THING IS TO KEEP THE LOGS AS DRY AS POSSIBLE. CHEMICAL PRESERVATIVES ARE USED BY MOST MANUFACTURES. THE MOST PREVALENT CHEMICAL PRESERVATIVES SEEM TO BE CHROMATED COPPER ARSENATE (SALTS, OR CCA), COPPER-8-QUINOLINOLATE, AND ZINC NAPTHANATE. PRESSURE TREATMENT, USUALLY WITH CCA IS CERTAINLY THE MOST PERMANENT OF THE USABLE TREATMENTS, ALTHOUGH THIS DEPENDS ON THE RETENTION OF THE CCA CHEMI- CALS IN THE WOOD. THE EPA HAS RECOMMENDED, THOUGH, THAT ANY WOOD TREATED WITH CCA THAT PEOPLE ARE DIRECTLY EXPOSED TO BE COATED WITH A SEALER. THE ONLY OTHER DRAWBACKS APPEAR TO BE THE COLOR AND THE COST. ZINC NAPTHANATE ADD COPPER-8-QUINOLINOLATE ARE USUALLY DIP OR SPRAY TREATMENTS. THIS MEANS THAT THE FACTORY APPLICATION IS NOT MEANT TO BE PERMANENT AND THE HOUSE WILL NEED PERIODIC APPLICATIONS OF PRESERVATIVES ON THE OUTSIDE. THE ZINC NAPTHANATE HAS AN INTERESTING RECOMMENDATION. THE U.S. ARMY IS NOW USING IT TO PRESERVE THEIR WOODED AMMUNITION BOXES. IT APPARENTLY WON A COMPETITION CONDUCTED BY THE ARMY IN PLACES LIKE PANAMA. IF YOUR HOME NEEDS RETREATING AFTER BUILDING, THE MOST IMPORTANT PLACES ARE THE ENDS OF THE LOGS, AND ANY CHECKS THAT ARE TURNED UP WHERE THEY CAN TRAP RAIN WATER. IT'S WORTHWHILE TO COMPLETELY FILL THESE CHECKS WITH THE PRESERVATIVE, AND LET IT SOAK IN. PROTECTION AGAINST INSECTS IS ANOTHER IMPORTANT SUBJECT FOR THE LOG HOME OWNER. THATS A WHOLE SUBJECT BY ITSELF, AND WE'LL JUST TOUCH ON IT BRIEFLY. THE MAJOR FEAR APPEARS TO BE TERMITES. EARLIER. THE FACT WAS MENTIONED THAT TERMITES DON'T KNOW THE DIFFERENCE BETWEEN A TWO-BY-FOUR AND A LOG. THAT'S TRUE, BUT ANY HOUSE SHOULD HAVE A PROFESSIONAL EXTERMINATOR TREAT THE GROUND BEFORE THE FOOTINGS ARE POURED. IT'S A VERY CHEAP INSURANCE POLICY, AND WORTH IT FOR THE PEACE OF MIND. TO SUM UP WE'VE GONE OVER, VERY BRIEFLY, SOME OF THE MANY ASPECTS OF DRYING AND PRESERVING LOGS IN A LOG HOME. IF YOU HAVE THE URGE TO LEARN MORE ABOUT THE SUBJECT OF WOOD. TWO EXCELLENT BOOKS ARE THE WOOD HANDBOOK, BY THE U.S. DEPARTMENT OF AGRICULTURE, AND UNDERSTANDING WOOD, BY BRUCE HOADLEY. PEOPLE THAT BUY, OR WANT TO BUY, LOG HOMES
TEND TO BE UNIQUE INDIVIDUALS. THEY ARE NOT SATISFIED TO GO TO THE NEAREST SUBDIVISION AND
BUY THE FIRST HOUSE THAT TICKLES THEIR FANCY. THEY WANT TO KNOW TECHNICAL DETAILS, READ
EVERYTHING ABOUT LOG HOMES THAT THEY CAN FIND, AND WATCH OTHER PEOPLE BUILD LOG HOMES. TO
ME,THIS IS AMERICA AT IT'S BEST. PEOPLE THAT ARE WILLING TO GO OUT AND DO SOMETHING
DIFFERENT! PEOPLE THAT, IN MANY INSTANCES, WILL ACTUALLY BUILD THEIR OWN HOME! THIS IS
ALMOST UNHEARD OF IN THIS DAY AND TIME, AND IT MAKES ME VERY PROUD TO BE A PART OF AN
INDUSTRY THAT ENCOURAGES SUCH AN ATTITUDE IN PEOPLE. AS A LAST MINUTE REMINDER, HERE IS A
LIST OF THE THREE MOST IMPORTANT PROCEDURES FOR A LOG HOME ... ALEX BOATWRIGHT, VICE-PRESIDENT OF AAA LOG HOMES, HAS BEEN IN THE LOG HOME INDUSTRY FOR MANY YEARS. BUILDING AND SELLING LOG HOMES. HE IS AN EXPERT ON THE SUBJECT OF WOOD SEASONING AND PRESERVATION. LOG HOME GUIDE FOR BUILDERS & BUYERS |