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The Preservation and Repair
of Historic Log Buildings
Bruce D. Bomberger
The intent of this Brief is to present a concise history and description
of the diversity of American log buildings and to provide basic guidance
regarding their preservation and maintenance. A log building is defined
as a building whose structural walls are composed of horizontally laid
or vertically positioned logs. While this Brief will focus upon horizontally-laid,
corner-notched log construction, and, in particular, houses as a building
type, the basic approach to preservation presented here, as well as
many of the physical treatments, can be applied to virtually any kind
of log structure.
Log buildings, because of their distinct material, physical structure,
and sometimes their architectural design, can develop their own unique
deterioration problems. The information presented here is intended to
convey the range of appropriate preservation techniques available. It
does not, however, detail how to perform these treatments; this work
should be left to professionals experienced in the preservation of historic
log buildings.
Despite the publication since the 1930s of a number of books and articles
on the history of log construction in America, some misconceptions persist
about log buildings. Log cabins were not the first type of shelter built
by all American colonists. The term "log cabin" today is often loosely
applied to any type of log house, regardless of its form and the historic
context of its setting. "Log cabin" or "log house" often conjures up
associations with colonial American history and rough frontier life
(Fig. 1). While unaltered colonial era buildings in general are rare,
historic log buildings as a group are neither as old nor as rare as
generally believed. One and two-story log houses were built in towns
and settlements across the country until about the middle of the 19th
century, and in many areas, particularly in the West, as well as the
Midwest and southern mountain regions, log continued to be a basic building
material despite the introduction of wooden balloon frame construction
(Fig. 2). By the early 20th century, the popularity of "rustic" architecture
had revived log construction throughout the country, and in many areas
where it had not been used for decades.
A distinction should be drawn between the traditional meanings of
"log cabin" and "log house." "Log cabin" generally denotes a simple
one, or one-and-one-half story structure, somewhat impermanent, and
less finished or less architecturally sophisticated. A "log cabin" was
usually constructed with round rather than hewn, or hand-worked, logs,
and it was the first generation homestead erected quickly for frontier
shelter. "Log house" historically denotes a more permanent, hewn-log
dwelling, either one or two stories, of more complex design, often built
as a second generation replacement. Many of the earliest 18th and early
19th century log houses were traditionally clad, sooner or later, with
wood siding or stucco.
Historical
Background
No other architectural form has so captured the imagination of the
American people than the log cabin. Political supporters of 1840 presidential
candidate William Henry Harrison appropriated the log cabin as a campaign
symbol. The log cabin was birthplace and home for young Abe Lincoln,
as well as other national figures, and assumed by many 19th century
historians to be the very first type of house constructed by English
colonists. In 1893 Frederick Jackson Turner in his influential paper,
"The Significance of the Frontier in American History" suggested that
European colonists had adopted this means of shelter from the Indians.
More recent 20th century scholarship has demonstrated that horizontal
log buildings were not the first form of shelter erected by all colonists
in America. Nor was log construction technology invented here, but brought
by Northern and Central European colonists. Finnish and Swedish settlers
are credited with first introducing horizontal log building in the colony
of New Sweden (now Pennsylvania) on the upper shores of Delaware Bay
in 1638, who later passed on their tradition of log construction to
the Welsh settlers in Pennsylvania.
During the 17th and 18th centuries, new waves of Eastern and Central
Europeans, including Swiss and Germans, came to America bringing their
knowledge of log construction. Even the Scotch-Irish, who did not possess
a log building tradition of their own, adapted the form of the stone
houses of their native country to log construction, and contributed
to spreading it across the frontier. In the Mississippi Valley, Colonial
French fur traders and settlers had introduced vertical log construction
in the 17th century.
Through the late 18th and early 19th centuries, frontier settlers
erected log cabins as they cleared land, winding their way south in
and along the Appalachian valleys through the back country areas of
Maryland, Virginia, the Carolinas and Georgia. They moved westward across
the Appalachian Mountain barrier into the Ohio and Mississippi River
valleys transporting their indispensable logcraft with them, into Kentucky
and Tennessee, and as far to the southwest as eastern Texas. Log buildings
are known to have been constructed as temporary shelters by soldiers
during the Revolutionary War, and across the country, Americans used
logs not only to build houses, but also commercial structures, schools,
churches, gristmills, barns, corncribs and a variety of outbuildings
(Fig. 3).
Around the mid-19th century, successive generations of fur traders,
metal prospectors, and settlers that included farmers and ranchers began
to construct log buildings in the Rocky Mountains, the Northwest, California,
and Alaska (Fig. 4). In California and Alaska, Americans encountered
log buildings that had been erected by Russian traders and colonists
in the late 18th and early 19th centuries. Scandinavian and Finnish
immigrants who settled in the Upper Midwest later in the 19th century
also brought their own log building techniques with them. And, many
log structures in the Southwest, particularly in New Mexico, show Hispanic
influences of its early settlers.
While many parts of the country never stopped building with logs,
wooden balloon frame construction had made it obsolete in some of the
more populous parts of the country by about the mid-19th century. However,
later in the century, log construction was employed in new ways. In
the 1870s, wealthy Americans initiated the Great Camp Movement for rustic
vacation retreats in the Adirondack Mountains of upstate New York. Developers
such as William Durant, who used natural materials, including wood shingles,
stone, and log -- often with its bark retained to emphasize the Rustic
style -- designed comfortable summer houses and lodges that blended
with the natural setting (Fig. 5). Durant and other creators of the
Rustic style drew upon Swiss chalets, traditional Japanese design, and
other sources for simple compositions harmonious with nature.
The Adirondack or Rustic style was balanced in the West with construction
of the Old Faithful Inn at Yellowstone National Park in Wyoming, designed
by Robert C. Reamer, and begun in 1903 (Fig. 6). This popular resort
was tremendously influential in its use of locally-available natural
materials, especially log, and gave impetus to Rustic as a true national
style. From the turn of the century through the 1920s, Gustav Stickley
and other leaders of the Craftsman Movement promoted exposed log construction.
During the 1930s and 40s, the Civilian Conservation Corps (CCC) used
log construction extensively in many of the country's Federal and State
parks to build cabins, lean-tos, visitor centers, and maintenance and
support buildings that are still in service (Fig. 7).
Traditional
Log Construction Plan and Form
When settlers took the craft of log construction with them onto the
frontier, they successfully adapted it to regional materials, climates
and terrains. One of the most notable characteristics of the earliest
18th and 19th century log houses is the plan and form. The plan can
sometimes provide clues to the ethnic origin or route of migration of
the original inhabitant or builder. But in the absence of corroborating
documentary evidence, it is important not to infer too much about the
ethnic craft traditions of a particular log house.
Historians have identified a number of traditional house plans and
forms as prototypes (Fig. 8). They were often repeated with simple variations.
The basic unit of each of these types is the one room enclosure formed
by four log walls joined at their corners, called a single "pen" or
"crib." The single pen was improved upon by installing interior partitions
or by adding another log pen. Some variations of historic log house
plans include: the typically mid-Atlantic "continental" plan, consisting
of a single-pen of three rooms organized around a central hearth; the
"saddlebag" or double-pen plan, composed of two contiguous log pens;
and the "dogtrot" plan, formed by two pens separated by an open passage
space (sometimes enclosed later), all covered by a continuous roof.
The continental plan originated in central and eastern Europe and is
attributed to 18th century German immigrants to Pennsylvania. Non-log
interior partition walls form the multi-room plan within the exterior
log walls. The saddlebag plan consists of two adjoining log pens that
share a central chimney. A saddlebag is often the evolution of a single
pen with an end chimney, expanded by adding a second pen onto the chimney
endwall. The saddlebag was built in a number of different regions across
the country. The dogtrot plan may be seen with variation in many parts
of the country, although it is sometimes, perhaps erroneously, considered
the most typically southern, because its covered passageway provided
both air circulation and shelter from the heat. All these plan types
were typically built in the form of one or one-and-one-half story settlement
cabins.
A somewhat different form evolved in the West around the middle of
the 19th century which became especially distinctive of the Rocky Mountain
cabin. While the entrance doorway to most earlier log houses was generally
placed beneath the eaves, as a means of adapting to the greater snowfall
in the Rockies, here the entrance was placed in the gable end, and sometimes
protected from roof slides by a porch supported by two corner posts
created by an extension of the roof beyond the gable wall (Fig. 9).
From the late 18th through the mid-19th centuries, Americans also
built many substantial two-story log houses in towns throughout the
eastern half of the country. In rural areas two-story log houses were
sometimes built to replace earlier, first-generation settlement cabins,
but just as often the early hewn-log house was retained and enlarged.
A second story was added by removing the roof and gables, constructing
a second floor, laying additional courses of logs, and building a new
roof, or reassembling the old one. Each generation of owners might expand
an early log core building by adding on new log pens, or masonry or
wood frame extensions. The addition of a rear ell, or infill construction
to link a formerly freestanding outbuilding, such as a kitchen to the
log main house was particularly common. Such a layering of alterations
is part of the evolution of many log buildings.
Corner Notching and Other Fastening Techniques
Corner notching is another of the characteristic features of log construction.
Most notching methods provide structural integrity, by locking the log
ends in place, and give the pen rigidity and stability. Like the floor
plan, the type of corner notching can sometimes be a clue to the ethnic
craft origin of a log building, but it is important not to draw conclusions
based only on notching details. Numerous corner notching techniques
have been identified throughout the country (Fig. 10). They range from
the simple "saddle" notching, which demands minimal time and hewing
skill, to the very common "V" notching or "steeple" notching, to "full
dovetail" notching, one of the tightest but most time-consuming to accomplish,
"half-dovetail" notching which is probably one of the most common, and
"square" notching secured with pegs or spikes.
The notching method on some of the earliest eastern cabins and most
19th century western cabins, particularly saddle notching, left an extended
log end or "crown." Crowns are especially pronounced or exaggerated
in Rustic style structures, and sometimes they are cut shorter as the
wall rises, creating a buttress effect at the corners of the building.
Another method of securing log ends consists of fastening logs that
are laid without notching ("false notching") with tenons into vertical
corner posts, or using spikes or pegs to attach them to vertical corner
planks. Vertically positioned logs were secured at their top and bottom
ends, usually into roof and sill plate timbers.
Selecting Logs and Assembling the Building
Although wood selection was most likely to be determined by availability,
chestnut, white oak, cedar, and fir were preferred because these trees
could provide long, straight, rot-resistant logs. Pine, which also provided
long straight logs, was also used in areas where it was plentiful. Woods
were often mixed, utilizing harder, heavier rot-resistant wood such
as white oak for the foundation,"sill log", and lighter, more easily
hewn wood such as yellow poplar for the
upper log courses.
One of the principal advantages of log construction was the economy
of tools required to complete a structure (Fig. 11). A felling axe was
the traditional tool for bringing down the tree and cutting the logs
to length. For many frontier and western structures the round logs were
debarked or used in their original form with the bark left on, or one
or more sides of the logs were hewn flat with a broadaxe, or more finely
finished with an adze as smooth thick planks. Notching was done with
an axe, hatchet or saw; openings for doors and windows were usually
cut after the logs were set into place, and door and window frames,
particularly jambs, were put in place during construction to help hold
the logs in place. Roof framing members and floor joists were either
hewn from logs or of milled lumber. A log cabin could be raised and
largely completed with as few as two to four different tools, including
a felling axe, a broad axe, and a hand saw or crosscut saw.
The upper gable walls were completed with logs if the roof was constructed
with purlins, which is more typical of Scandinavian or Finnish construction,
and western and 20th century Rustic styles. However, vertical or horizontal
weatherboard sheathing was commonly used throughout the country to cover
wood-framed gables.
Chinking and Daubing
The horizontal spaces or joints between logs are usually filled with
a combination of materials that together is known as "chinking" and
"daubing." Chinking and daubing completed the exterior walls of the
log pen by sealing them against driving wind and snow, helping them
to shed rain, and blocking the entry of vermin. In addition, chinking
and daubing could compensate for a minimal amount of hewing and save
time if immediate shelter was needed. Not all types of log buildings
were chinked. Corncribs, and sometimes portions of barns where ventilation
was needed were not chinked. While more typical of Swedish or Finnish
techniques, and not as common in American log construction, tight-fitting
plank-hewn or scribed-fit round logs have little or no need for chinking
and daubing.
A variety of materials were used for chinking and daubing, including
whatever was most conveniently at hand. Generally though, it is a three-part
system applied in several steps. The chinking consists of two parts:
first, a dry, bulky, rigid blocking, such as wood slabs or stones is
inserted into the joint, followed by a soft packing filler such as oakum,
moss, clay, or dried animal dung (Fig. 12). Daubing, which completes
the system, is the outer wet-troweled finish layer of varying composition,
but often consisting of a mixture of clay and lime or other locally
available materials. Instead of daubing, carefully fitted quarter poles
or narrow wood strips were sometimes nailed lengthwise across the log
joints.
Chinking, especially the daubing, is the least durable part of a log
building. It is susceptible to cracking as a result of freeze-thaw action,
structural settlement, drying of the logs, and a thermal expansion-contraction
rate that differs from that of the logs. Seasonal deterioration of chinking
necessitates continual inspection and regular patching or replacement.
Exterior Wall Treatments
Although the exterior logs of cabins in the West, and 20th century
Rustic buildings are generally not covered, many 18th and 19th century
log houses east of the Mississippi, with the exception of some of the
simpler cabins and houses in remote or poorer areas, were covered with
exterior cladding. The exterior of the log walls was covered for both
aesthetic and practical reasons either as soon as the building was completed
or sometime later.
In some instances, the exterior (and interior) of the logs was whitewashed.
This served to discourage insects, and sealed hairline cracks in the
daubing and fissures between the daubing and logs. Although the solubility
of whitewash allows it to heal some of its own hairline cracks with
the wash of rain, like daubing it has to be periodically reapplied.
Usually, a more permanent covering such as wood siding or stucco was
applied to the walls, which provided better insulation and protection,
and reduced the maintenance of the log walls.
Sometimes log houses were sided or stuccoed later in an attempt to
express a newly-achieved financial or social status. Many log houses
were immediately sided and trimmed upon completion to disguise their
simple construction beneath Georgian, Federal and later architectural
styles. Frequently a log house was covered, or recovered, when a new
addition was erected in order to harmonize the whole, especially if
the original core and its addition were constructed of different materials
such as log and wood frame (Fig. 13).
Vertical wood furring strips were generally nailed to the logs prior
to applying weatherboarding or stucco (Fig. 14). This ensured that the
walls would be plumb, and provided a base on which to attach the clapboards,
or on which to nail the wood lath for stucco.
Foundations
Log building foundations varied considerably in quality, material,
and configuration. In many cases, the foundation consisted of a continuous
course of flat stones (with or without mortar),
several piers consisting of rubblestone, single stones, brick, short
vertical log pilings, or horizontal log "sleepers" set on grade. The
two "sill logs," were laid directly upon one of these types of foundations.
Climate and intended permanence of the structure were the primary
factors affecting foundation construction. The earliest log cabins,
and temporary log dwellings in general, were the most likely to be constructed
on log pilings or log sleepers set directly on grade. Where a more permanent
log dwelling was intended, or where a warm, humid climate accelerated
wood decay, such as in the South, it was sometimes more common to use
stone piers which allowed air to circulate beneath the sill logs. Full
cellars were not generally included in the original construction of
most of the earliest log houses, but root cellars were often dug later.
Roofs
Log buildings were roofed with a variety of different framing systems
and covering materials. Like log house plans and corner notching styles,
the types of roof framing systems used were often variations on particular
ethnic and regional carpentry traditions. In most cases wood shingles
were the first roof covering used on the earliest 18th and 19th century
log houses. As wood shingle roofs deteriorated, many were replaced with
standing seam metal roofs, many of which continue to provide good service
today. Later pioneer log buildings west of the Mississippi were likely
to be roofed with metal or roll roofing, or even with sod. Other log
buildings have been re-roofed in the 20th century with asphalt shingles.
For some rustic log buildings in the West and Great Camps in the Adirondacks,
asphalt shingles are the original historic roofing material.
Chimneys
Ethnic tradition and regional adaptation also influenced chimney construction
and placement. Chimneys in log houses were usually built of stone or
brick, a combination of the two, or even clay-lined, notched logs or
smaller sticks (Fig. 15). Later log buildings were frequently constructed
with only metal stacks to accommodate wood stoves. The chimneys of log
buildings erected in cold climates tended to be located entirely inside
the house to maximize heat retention. In the South, where winters were
less severe the chimney stack was more typically constructed outside
the log walls. With the advent of more efficient heating systems, interior
chimneys were frequently demolished or relocated and rebuilt to maximize
interior space.
Interior Finishes
Logs on the interiors of many of the simpler cabins and Rustic style
structures were often given a flattened surface or left exposed. But,
in the more finished log houses of the 18th and 19th century, they were
more commonly covered for most of the same reasons that the exterior
of the logs was covered--improved insulation, ease of maintenance, aesthetics,
and keeping out vermin. Covering the interior log walls with planks,
lath and plaster, boards pasted with newspaper, fabric such as muslin,
or wallpaper increased their resistance to air infiltration and their
insulation value. Finished walls could be cleaned and painted more easily,
and plastered walls and ceilings obscured the rough log construction
and prepared interior surfaces for decorative wood trim in the current
styles (Fig. 16).
Historical Evaluation and Damage Assessment
Before undertaking preservation work on a historic log building, its
history and design should be investigated, and physical condition evaluated.
It is always advisable to hire a historical architect or qualified professional
experienced in preservation work to supervise the project. In addition,
State Historic Preservation Offices, regional offices of the National
Park Service, and local historical commissions may also provide technical
and procedural advice.
The historical investigation should be carried out in conjunction
with a visual inspection of the log building. Physical assessment needs
to be systematic and thorough. It should include taking notes, photographs
or video recording, and making drawings of existing conditions, including
overall and detail views. This will serve as a record of the appearance
and condition which can be referred to once work is under way. A physical
assessment should also identify causes of deterioration, not just symptoms
or manifestations and, in some instances, may need to include a structural
investigation.
Foundation Inspection
The foundation of a log building should always be inspected before
beginning work because, as in any building, foundation-related problems
can transfer structural defects to other components of the building.
Settling of the foundation is a typical condition of log buildings.
If settlement is not severe and is no longer active, it is not necessarily
a problem. If, however, settlement is active or uneven, if it is shifting
structural weight to unintended bearing points away from the intended
main bearing points of the corner notches and sill log, serious wall
deflections may have resulted. Causes of settlement may include foundation
or chimney stones or sill logs that have sunk into the ground, decay
of log pilings, log sleepers, or of the sill logs themselves.
Log Inspection
Foundation problems usually result in damage to the sill logs and
spandrels, which are often the most susceptible to deterioration. Sill
logs, along with the corner notching, tend to bear most of the weight
of the building, and are closest to vegetation and the ground, which
harbors wood-destroying moisture and insects. If the sill log has come
into contact with the ground, deterioration is probably underway or
likely to begin (Fig. 17). It is also important to check the drainage
around the building. The building assessment should note the condition
of each log and attempt to identify the sources of problems that appear
to exist.
Sill log inspection should not necessitate destruction of historic
exterior cladding if it exists. Inspection can usually be made in areas
where cladding is missing, loose, or deteriorated. Sill log, as well
as upper log, deterioration may also be revealed by loose or peeling
areas of the cladding. If pieces of cladding must be removed for log
inspection, they should be labeled and saved for reinstallation, or
as samples for replacement work. Historic cladding generally need not
be disturbed unless there are obvious signs of settling or other indications
of deterioration.
Other areas of the log walls which are particularly susceptible to
deterioration include window and door sills, corner notches, and crowns,
and any other areas regularly saturated by rain runoff or backsplash.
The characteristic design feature of Adirondack or Rustic style log
buildings of leaving log ends or crowns to extend beyond the notched
corners of the building positions the crowns beyond the drip-line of
the roof edge. This makes them vulnerable to saturation from roof runoff,
and a likely spot for deterioration. Saddle notching in which the cut
was made out of the top surface of the log and which cups upward, and
flat notching, may also be especially susceptible to collecting runoff
moisture.
Detection of decay requires thorough inspection. Probing for rot should
be done carefully since repair techniques can sometimes save even badly
deteriorated logs. Soft areas should be probed with a small knife blade
or icepick to determine the depth of decay. Logs should be gently tapped
at regular intervals up and down their lengths with the tool handle
to detect hollow-sounding areas of possible interior decay. Long cracks
which run with the wood grain, called "checks," are not signs of rot,
but are characteristic features of the seasoning of the logs. However,
a check can admit moisture and fungal decay into a log, especially if
it is located on the log's upper surface. Checks should also be probed
with a tool blade to determine whether decay is underway inside the
log.
Sill log ground contact and relative moisture content also provide
ideal conditions for certain types of insect infestation. Wood building
members, such as sill logs or weatherboarding, less than eight inches
from th~ ground, should be noted as a potential problem for monitoring
or correction. Sighting of insects, or their damage, or telltale signs
of their activity, such as mud tunnels, exit holes, or "frass," a sawdust-like
powder, should be recorded. Insect infestation is best treated by a
professionally licensed exterminator, as the chemicals used to kill
wood-destroying insects and deter reinfestation are generally toxic.
Roof Inspection
Along with the foundation, the roof is the other most vital component
of any building. The roof system consists of, from top to bottom, the
covering, usually some form of shingles or metal sheeting and flashing;
board sheathing or roof lath strips; the framing structure, such as
rafters or purlins; the top log, sometimes referred to as the "roof
plate" or "rafter plate;" and, sometimes, but not always, gutters and
downspouts.
The roof and gutters should be inspected and checked for leaks both
from the exterior, as well as inside if possible. Inspection may reveal
evidence of an earlier roof type, or covering, and sometimes remnants
of more than one historic covering material. The roof may be the result
of a later alteration, or raised when a second story was added, or repaired
as the result of storm or fire damage. Often, roof framing may be composed
of reused material recycled from earlier buildings. Inspection of the
roof framing should note its configuration and condition. Typical problems
to look for are framing members that have been dislodged from their
sockets in the roof plate, or that are cracked, ridge damage, sagging
rafters, broken ties and braces, and decay of exterior exposed rafter
or purlin ends, especially common on Rustic style buildings (Fig. 18).
Other Features
The rest of the building should also be inspected as part of the overall
assessment, including siding, window sash and frames, door frames and
leafs, chimneys, porches, and interior walls, trim, and finishes. Any
of these features may exhibit deterioration problems, inherent to the
material or to a construction detail, or may show the effects of problems
transmitted from elsewhere, such as a deformed or misshapen window frame
resulting from a failed sill log. The inspection should note alterations
and repairs made over time, and identify those modifications which have
acquired significance and should be preserved. Nothing should be removed
or altered before it has been examined and its historical significance
noted.
Preservation
Treatments
Since excessive moisture promotes and hastens both fungal and insect
attack, it should be dealt with immediately. Not only must the roof
and gutters be repaired --if none exist, gutters should probably be
added--but the foundation grade should be sloped to ensure drainage
away from the building. If the distance from the ground to the sill
log or exterior sheathing is less than eight inches, the ground should
be graded to achieve this minimum distance. Excess vegetation and debris
such as firewood, dead leaves, or rubbish should be cleared from the
foundation perimeter, and climbing vines whose leaves retain moisture
and tendrils erode daubing, should be killed and removed. Moisture problems
due to faulty interior plumbing should also be remedied. Solving or
reducing moisture problems may in itself end or halt the progress of
rot and wood-destroying insects.
Log Repair
Stabilizing and repairing a log that has been only partially damaged
by decay or insects is always preferable to replacing it. Retaining
the log, rather than substituting a new one, preserves more of the building's
integrity, including historic tool marks and the wood species which
may no longer be obtainable in original dimensions. Log repair can generally
be done with the log in place at less cost, in less time, and with less
damage to building fabric, than by removing, and installing a new hewn
and notched replacement log. Log repair is accomplished by two basic
methods: traditional methods of splicing in new or old wood, or through
the use of epoxies. These treatments are sometimes combined, and may
also be used in conjunction with reinforcing members. Historic log repair,
whether it involves patching techniques or the use of epoxies, should
always be performed only by an experienced craftsperson or architectural
conservator.
Wood Splicing
Wood splicing can involve several types of techniques. Also referred
to as "piecing-in" or "Dutchman" repair, it involves treating a localized
area of deterioration by cutting out the decayed area of the log, and
carefully carving and installing a matching, seasoned wood replacement
plug or splice. The wood species, if available, and the direction and
pattern of the grain should match that of adjacent original wood. The
location and depth of decay should determine the splicing technique
to be used. In a case where decay runs deep within a log, a full-depth
segment containing the affected area can be cut out, severing the log
completely, and a new segment of log spliced in, using angled "scarf"
joints or square-cut "half-lap" joints (Fig. 19). The splice is secured
to the severed log by angling lag screws or bolts through the upper
and lower surfaces that will be concealed by daubing.
Splicing can also be performed using epoxy as an adhesive. A log with
shallow decay on its outer face can be cut back to sound depth, and
a half-log face spliced on, adhered with epoxy, screws or bolts. A technique
for the repair of badly deteriorated log crowns involves cutting them
back to sound wood, and into the notching joint if necessary, and installing
new crowns cut to match. Fiberglass or aluminum reinforcement rods are
inserted into holes drilled into the new crowns, and into corresponding
holes drilled in the ends of the original cutoff logs. Epoxy is used
as an adhesive to attach and hold the new crowns in place. Long lag
screws can be angled up through the underside of the crown into the
log above to provide additional support for the repair.
Epoxy Consolidation and Repair
In some instances, epoxies may be used by themselves to consolidate
and fill the voids left by deteriorated wood. Epoxies are versatile
in performance, relatively easy to use by experts, and, after curing,
may be shaped with woodworking tools. Their use requires that sufficient
sound wood survives for the epoxy to adhere. But they can be used to
stabilize rotted wood, return full or greater than original strength
to decayed structure-bearing members, and to reconstitute the shape
of decayed log ends. Epoxies resist decay and insects, and while epoxy
itself is resistant to moisture, epoxy tends to cause adjacent wood
to retain moisture rather than dry out, and if not used in the right
location, can actually further a continuing cycle of wood decay. Hence,
epoxy repairs are most successful in areas where they are protected
from moisture. Epoxies, of which there are a variety of commercially-available
products on the market, are prepared in essentially two forms: a liquid
consolidant and a flexible putty filler.
Each consists of a resin and a hardener which must be mixed prior to
use.
The technique of treating, for an example, a decayed log crown with
epoxies is begun by removing loose decayed wood, and drying the area
if necessary (Fig. 20). The rot-affected cavity and surface of the log
end is then saturated with liquid epoxy by repeated brushing, or by
soaking it in a plastic bag filled with epoxy that is attached to the
log. The porous condition of the rot-damaged wood will draw up the epoxy
like a lamp wick. Once the liquid epoxy has saturated the log end and
cured, the log end has been consolidated, and is ready for the application
of an epoxy putty filler. The filler resin and hardener must also be
mixed, pigments must be mixed with the filler epoxy to color the patch,
and more importantly to protect it from ultraviolet sunlight. The filler
can be applied with a putty knife, pressing it into the irregularities
of the cavity. The cured patch can be worked like wood and painted with
an opaque stain or a dull finish paint to help it blend with surrounding
wood, although epoxy repairs can be difficult to disguise on natural,
unpainted wood.
Epoxies can be used to consolidate and repair other areas of a log,
including rotted internal areas which have not yet progressed to damage
the log's outer surface. Saturation of small internal areas can be accomplished
by drilling several random holes into the log through an area that will
be concealed by daubing, and then pouring in liquid epoxy. If a pure
resin is used, it should be a casting resin to minimize shrinkage, and
it is best to fill voids with a resin that contains aggregates such
as sand, or micro-balloons. Epoxy is frequently used by architectural
conservators to strengthen deteriorated structural members. The damaged
log can be strengthened by removing the deteriorated wood, and filling
the void by imbedding a reinforcing bar in epoxy filler, making sure
the void is properly sealed to contain the epoxy before using it (Fig.
21). Sometimes larger decayed internal areas of a log can be more easily
accessed and repaired from the interior of a structure. This may be
a useful technique if it can be accomplished without causing undue damage
to the interior finishes in the log building. However, despite its many
advantages, epoxy may not be an appropriate treatment for all log repairs,
and it should not be used in an attempt to conceal checking, or extensive
log surface patching that is exposed to view, or logs that are substantially
decayed or collapsed.
Log Replacement
Repairing or replacing only a segment of a log is not always possible.
Replacement of an entire log may be the only solution if it has been
substantially lost to decay and collapsed under the weight of logs above
it. Log replacement, which should be carried out only by experienced
craftspersons, is begun by temporarily supporting the logs above, and
then jacking them up just enough to insert the new log. Potential danger
to the structure may include creating inadequate temporary bearing points,
and crushing chinking and interior finishes which may have settled slowly
into non-original positions that cannot withstand jacking.
To begin the process of log replacement, the entire length of the
log must be inspected from the exterior and the interior of the structure
to determine whether it supports any structural members or features,
and how their load can be taken up by bracing during jacking and removal.
On the exterior, sheathing such as weatherboard, and adjacent chinking,
must be removed along the length of the log to perform this inspection.
Likewise, on the interior, abutting partition walls and plaster may
also need to be removed around the log to determine what, if any, features
are supported by or tied into the log to be removed.
A replacement log should be obtained to match the wood species of
the original being removed. If it is a hewn log, then the replacement
must be hewn to replicate the dimensions and tool marks of the original
(Fig. 22). If the same wood species cannot be obtained in the original
dimensions, a substitute species may have to be used, and may even be
preferable in some instances if a more durable wood can be found than
the original wood species. It should, however, be chosen to match the
visual characteristics of the original species as closely as possible.
Wood Preservatives
In most instances, the use of chemical wood preservatives is not generally
recommended on historic log buildings. Preservatives tend to change
the color or appearance of the logs. In addition, many are toxic, they
tend to leach out of the wood over time, and like paint, must be periodically
reapplied. Many of the late 19th and early 20th century Rustic structures
were constructed of logs with the bark left on which may provide protection,
while others have been painted. However, some log buildings, and especially
log houses that have been inappropriately stripped of historic cladding
in an earlier restoration, and now show signs of weathering, such as
deep checking, may be exceptions to this guidance. A preservative treatment
may be worth considering in these cases. Boiled linseed oil may sometimes
be appropriate to use on selected exposures of a building that are particularly
vulnerable to weathering, although linseed oil does tend to darken over
time. Borate solutions, which do not alter the color or appearance of
wood, may be another of the few effective, nonhazardous preservatives
available. However, borate solutions do not penetrate dry wood well,
and thus the wood must be green or wet. Because borate solutions are
water-soluble, after treating, the wood must be coated with a water-repellent
coating. In some instances, it may be appropriate to reapply varnish
where it was used as the original finish treatment. Pressure-treating,
while effective for new wood, is not applicable to in-place log treatment,
and is generally not effective for large timbers and logs because it
does not penetrate deeply enough.
Foundation Repair
The foundation should have good drainage, be stable, adequately support
the building as well as any future floorloads, and keep the sill log
sufficiently clear of the ground and moisture to deter decay and insect
infestation. Log buildings with cellars are less likely to suffer problems
than those built upon the ground or with crawl spaces, as long as the
cellar is kept dry and ventilated. Because the foundations of many log
buildings were neither dug nor laid below the frost-like, they generally
tend to be susceptible to freeze-thaw ground heaving and settlement.
Also, as previously noted, some foundations consisted of wooden sleepers
or pilings in direct contact with the ground. If a foundation problem
is minor, such as the need for repointing or resetting a few stones,
work should address only those areas. Loose stones should be reset in
their original locations if possible. A clearly inadequate foundation
that has virtually disappeared into the ground, or where large areas
of masonry have buckled or sunk, resulting in excessively uneven or
active settlement, will need to be rebuilt using modern construction
methods but to match the historic appearance.
Chinking Repair
Repair of chinking, whether it is finished on the exterior with wooden
strips or with daubing, should not be done until all log repair or replacement,
structural jacking and shoring is completed, and all replacement logs
have seasoned. Historically, patching and replacing daubing on a routine
basis was a seasonal chore. This was because environmental factors--building
settlement, seasonal expansion and contraction of logs, and moisture
infiltration followed by freeze-thaw action--cracks and loosens daubing.
If the exterior log walls are exposed, and the chinking or daubing requires
repair, as much of the remaining inner blocking filler and daubing should
be retained as possible. A daubing formula and tooled finish that matches
the historic daubing, if known, should be used, or based on one of the
mixes listed here. For the most part, modern commercially-available
chinking products are not suitable for use on historic log buildings,
although an exception might be on the interior of a log building where
it will be covered by plaster or wood, and will not be visible. These
products tend to have a sandy appearance that may be compatible with
some historic daubing, but the color, and other visual and physical
characteristics are generally incompatible with historic log surfaces.
Sections of wood chinking which are gone or cannot be made weathertight
should be replaced with same-sized species saplings or quarter poles
cut to fit. Generally, unless bark was used originally, it should be
removed before nailing the new wood chinking replacements tightly into
place.
Analysis of daubing can be done in much the same way as mortar analysis.
If that is not feasible, by crushing a loose piece of daubing its constituent
parts can be exposed, which may typically include lime, sand, clay,
and, as binders, straw or animal hair. The color imparted by the sand
or pigmented constituents should be noted, and any areas of original
daubing should be recorded with color film for later reference. Daubing
that is loose or is not adhered to the logs must first be cleaned out
by hand. Blocking filler should be left intact, refitting only loose
pieces. (Sometimes it may be difficult to obtain a good bond in which
case it may be necessary to clean out the joint entirely.) If needed,
soft filler should be added, such as jute or bits of fiberglass batt,
pressed firmly into voids with a stick or blunt tool. Concealed reinforcement
may sometimes be used, depending upon the authenticity of the restoration.
This can include galvanized nails partially inserted only on the upper
side of the log to allow for the daubing to move with the upper log
and keep the top joint sealed, or galvanized wire mesh secured with
galvanized nails (Fig. 23). Like repointing masonry, daubing should
not be done in full sun, excessive heat or when freezing temperatures
are expected. The daubing materials should be dry-mixed, the chinking
rechecked as being tight and secure, and the mix wetted and stirred
to a stiff, paste-like consistency. The mix dries quickly, so no more
daubing should be prepared at a time than can be applied in about 30
minutes. A test patch of new daubing, either on the building, or in
a mockup elsewhere, will help test the suitability of the formula's
color and texture match.
Before applying the daubing, the chinking area, including filler and
log surfaces to be covered, should be sprayed with water to prevent
the dry filler from too rapidly drawing off the daubing moisture which
will result in hairline cracking. A trowel, ground to the width of the
daubing, is used to press the daubing into the chinking space, and to
smooth the filled areas. Wide or deep chinking spaces or joints may
have to be daubed in layers, to prevent sagging and separation from
the logs, by applying one or two scratch coats before finishing the
surface.
Portland cement was a part of the original daubing used in many late
19th and early 20th century log buildings, and is therefore appropriate
to include in repairing buildings of this period. Although a small amount
of portland cement may be added to a lime, clay and sand mix for workability,
there should not be more than 1 part portland cement to 2 parts of lime
in daubing mixes intended for most historic log buildings. Portland
cement tends to shrink and develop hairline cracks, and retain moisture,
all of which can be potentially damaging to the logs.
----------------------------------------------------------------
Daubing Mixes
parts (volume) material
MIX A
1/4 cement
1 lime
4 sand
1/8 dry color
hog bristles or excelsior
MIX B
6 sand
4 lime
1 cement
MIX C
1 portland cement
4-8 lime
7-10 sand
Mix A (Donald A. Hutsler, "Log Cabin Restoration: Guidelines for the
Historical Society," American Association for State and Local History,
Technical Leaflet No. 74, "History News," Vol. 29, No. 5 (May 1974.)
Mix B and C are reprinted from "Log Structures: Preservation and Problem-Solving,"
by Harrison Goodall and Renee Friedman, Nashville, TN: American Association
for State and Local History, 1980.
----------------------------------------------------------------
Interior Treatments
There is no single appropriate way to finish or restore the interior
of a historic log house. Each building and its history is unique. The
temptation should be resisted to impart an unfinished frontier character
by removing plaster to expose interior log walls or joists in the ceiling.
Instead, interior treatments should be based on existing evidence, and
guided by old photographs, written documentation, and interviews with
previous owners. Interior features and finishes that might exist in
some 18th and 19th century log houses include wood paneled walls, wood
moldings, stairs, and fireplace mantels; where they have survived, these
features should be retained. Many of the more rustic log buildings built
later in the 19th or early 20th century intentionally featured exposed
interior log walls, sometimes with the logs peeled and varnished. If
interior plaster is severely damaged or has previously been removed,
and evidence such as lath ghosting on the logs exists, walls should
be replastered or recovered with gypsum board or dry wall to match the
historic appearance.
Preserving
Log Buildings in Their Historic Settings
Log buildings are too often viewed as portable resources. Like other
historic buildings, moved or relocated log structures can suffer a loss
of integrity of materials and of setting (Fig. 24). Historic buildings
listed in the National Register of Historic Places may be subject to
loss of that status if moved. Despite the popularity of dismantling
and relocating log buildings, they should be moved only as a last resort,
if that is the only way to save them from demolition. If they must be
moved, it is preferable that they be moved intact-- that is, in one
piece rather than disassembled. Disassembling and moving a log building
can result in considerable loss of the historic building materials.
While the logs and roof framing members can be numbered for reassembly,
dismantling a log building can result in loss of such features as foundation
and chimney, chinking and daubing, exterior cladding, and interior finishes.
Furthermore, log buildings can rarely be put back together as easily
as they were taken apart.
Summary
Historic log buildings regardless of whether they are of horizontal
or vertical construction, or whether they are 18th century log houses
or early 20th century Rustic style cabins, are unique. Their conservation
essentially centers on the preservation and repair of the logs, and
appropriate repairs to chinking and daubing, which like repointing of
masonry, is necessary to ensure that most log buildings are weathertight.
Log building preservation may be accomplished with a variety of techniques
including splicing and piecing-in, the use of epoxy, or a combination
of patching and epoxy, and often, selected replacement. But, like any
historic building, a log structure is a system that functions through
the maintenance of the totality of its parts.
The exterior of many of the earliest late 18th and 19th century log
buildings, and particularly those east of the Mississippi, were commonly
covered with some type of cladding, either horizontal or vertical wood
siding, stucco, or sometimes a combination. If extant, this historic
cladding, which may be hidden under a later, non-historic artificial
siding such as aluminum, vinyl, or asbestos, should be preserved and
repaired, or replaced if evidence indicates that it existed, as a significant
character-defining feature of the building (Fig. 25).
Selected Reading
Briscoe, Frank. "Wood-Destroying Insects." The Old-House Journal.
Vol. XIX, No. 2 (March/April 1991), pp. 3439.
Caron, Peter. "Jacking Techniques for Log Buildings." Association
for Preservation Technology Bulletin. Special Issue: Alberta Culture.
Vol. XX, No. 4 (1988), pp. 4254.
Cotton, J. Randall. "Log Houses in America." The Old-House Journal.
Vol. XVIII, No. 1 (January/February 1990), pp. 37-44.
Elbert, Duane E., and Keith A. Sculle. Log Buildings in Illinois:
Their Interpretation and Preservation. Illinois Preservation Series:
Number 3. Springfield, IL: Illinois Department of Conservation, Division
of Historic Sites, 1982.
Goodall, Harrison. "Log Crown Repair and Selective Replacement Using
Epoxy and Fiberglass Reinforcing Rebars: Lamar Barn, Yellowstone National
Park, Wyoming." Preservation Tech Notes, Exterior Woodwork Number 3.
Washington, D.C.: Preservation Assistance Division, National Park Service,
U.S. Department of the Interior, 1989.
----------, and Renee Friedman. Log Structures: Preservation and Problem-Solving.
Nashville, TN: American Association for State and Local History, 1980.
Hutslar, Donald A. The Architecture of Migration: Log Construction
in the Ohio Country, 17501850. Athens, OH: Ohio University Press, 1986.
----------. Log Cabin Restoration: Guidelines for the Historical Society.
American Association for State and Local History Technical Leaflet 74.
History News. Vol. 29, No. 5, May 1974.
Jordan, Terry G. American Log Buildings: An Old World Heritage. Chapel
Hill, NC: The University of North Carolina Press, 1985.
Kaiser, Harvey H. Great Camps of the Adirondacks. Boston: David R.
Godine Publisher, Inc., 1986.
Merrill, William. "Wood Deterioration: Causes, Detection and Prevention."
American Association for State and Local History Technical Leaflet 77.
History News. Vol. 29, No. 8, August, 1974.
Rowell, R.M., J.M. Black, L.R. Gjovik, and W.C. Feist. Protecting
Log Cabins from Decay. U.S.D.A. Forest Service Products Laboratory,
General Technical Report, FPL11. Madison, WI: Forest Products Laboratory,
Forest Service, U.S. Department of Agriculture, 1977.
St. George, R.A. Protecting Log Cabins, Rustic Work and Unseasoned
Wood from Injurious Insects in the Eastern United States. Farmer's Bulletin
No. 2104, United States Department of Agriculture. Washington, D.C.:
Government Printing Office, 1962 (Rev. 1970).
Tweed, William C., Laura E. Soulliere, and Henry G. Law. National
Park Service Rustic Architecture: 19161942. San Francisco, CA: Division
of Cultural Resource Management, Western Regional Office, National Park
Service, February 1977.
Wilson, Mary. Log Cabin Studies. Cultural Resources Report No. 9.
Ogden, UT: United States Department of Agriculture, Forest Service,
1984.
Acknowledgements
The author, a Preservation Specialist at the Pennsylvania Historical
and Museum Commission, wishes to thank those experts who reviewed and
commented upon the draft manuscript: James Caufield; J. Randall Cotton;
Harrison Goodall; Donald A. Hutslar; Terry G. Jordan; Bernard Weisgerber;
Rodd Wheaton; and National Park Service professional staff. Anne E.
Grimmer is credited with directing this cooperative publication project
and general editorship.
Washington, D.C. September, 1991
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