Of first importance in protecting a log cabin from decay or insect damage is the foun- dation (Figure 1).
Drainage.–Good drainage will help keep the foundation dry. Storm water should not be allowed to accumulate around the foundation or under the building. The cabin site should be graded or ditched so that water drains away from the building. Eave troughs, downspouts, and wide eaves will direct the water away from the cabin and, therefore, help greatly in keep- ing the foundation dry.
Piers and posts.–All too often, log cabin builders take the course of least resistance and lay the bottom logs directly on or close to the ground. Placing untreated wood in direct con- tact with the ground is one of the surest ways of hastening its decay. When wood is placed in contact with the ground, the soil moisture has direct access to the wood and keeps it con- stantly damp. This dampness sets up condi- tions that are most favorable for growth of the fungi that cause decay.
Unless the logs are treated in accordance with preservatives III or IV (appendix), good building practice dictates that bottom logs or sills be placed 12 to 18 inches above the ground on foundations that will keep the wood dry. Stone or concrete foundations or piers are excellent.
Ventilation.–Good ventilation beneath the floor is important because it keeps the soil and the wood dry. Foundation posts or piers allow good ventilation unless the spaces between them are filled solid. Screen or latticework between the piers will improve the appearance, keep animals out, and still allow good ventilation. Wood lattice, unless it is made of decay- resistant or treated wood, should not touch the ground.
If solid foundation walls are preferred to piers, generous openings should be provided at frequent intervals to allow good air circula- tion. When solid foundation walls are used on damp sites, a soil cover of heavy grade roll roofing or polyethylene sheeting will help to prevent moisture evaporation from the soil and thereby reduce the decay hazard.
If the building is used throughout the year in the colder parts of the United States, good ventilation will cause cold floors in the winter. This may be prevented by insulating the floor under the cabin and boarding up the openings in cold weather. Openings should be un- covered during the rest of the year.
In some parts of the country, termites cause considerable trouble to log cabins. The ground-inhabiting termites are the most plentiful and most important type in the United States. These termites leave an outside shell of wood intact when working above ground, and may do a great deal of damage before being discovered. A common method of protection is the application of a soil poison around the foundation with an EPA-registered pesticide. Wood properly treated with preservatives is protected against termites, so thorough treatment of the foundation timbers, at least, is desirable. Masonry or similar foundations, 18 to 24 inches high and free from cracks, will offer only limited protection from termite attack. In using bricks, the joints should be filled with a cement mortar dense enough that termites cannot tunnel through it. Hollow block foundations should be capped with a layer of reinforced concrete at least 4 inches thick. If termites are very active, they may build mud tunnels over the treated wood or masonry foundation, until they can enter the untreated wood above.
In putting up the walls of a log cabin and in framing the window and door openings, care should be taken to avoid forming crevices where water can accumulate and soak into the wood. Fittings should be made as tight as prac- ticable, and they should be supplemented by calking at places most likely to take up water. Storm water does little harm to the cabin if it can run off quickly. However, if the water is caught in joints, crevices, or checks, it will soak into the wood and dry out very slowly. Decay may easily start in these damp areas. In con- structing the cabin, major cracks or checks in the logs should be placed down so they will not entrap water.
The joints between logs are of special con- cern as possible water-trapping zones. It is important, therefore, that they be suitably chinked.
One of the most practical methods of chinking is to staple 2-inch strips of metal lath on the outside of the cracks and to chink with standard chimney mortar. The mortar consists of two parts of cement, one part of dry hydra- ted lime, and six parts of clean, sharp, screened sand. This mortar must be mixed in small batches to keep it from hardening before it can be applied.
The Oklahoma State University of Agricul- ture and Applied Science, Stillwater, Okla., has reported a successful method of chinking with spar varnish, linseed oil, and mineral wool of the kind sold in batts for insulation. Exterior varnish is brushed on the joints between the logs. Before it dries, rock wool is tamped into place with the end of a board about 3/8 inch thick and 6 inches wide. Varnish or linseed oil is applied to the exposed surface of the rock wool by sweeping the brush over the surface quickly to avoid deep penetration of the liquid. Brown rock wool can be used on the outside and white on the inside of the building. This chinking adheres tenaciously to the logs. It has enough elasticity to compensate for log shrinkage except where the logs have twisted badly. Where the chinking has broken loose because of such twisting, it can easily be tamped back into place. Insects and rodents are not inclined to attack chinking of this kind.
Other methods of chinking include the use of oakum or moss driven tightly between the logs, and the use of commercial calking or filling compounds.
Tight joints may also be obtained by cut- ting deep grooves accurately in the top and bottom surfaces of each log and inserting a spline, or by hollowing out the underside of each log carefully to fit the log beneath (Figure 2).
A wide roof overhang is one of the most effective features to be built into a log cabin. It helps combat decay in walls and foundations and around doors and windows. Good pro- jection of eaves and slope of the roof will divert much rainwater that would otherwise flow over the walls. The greater the pitch of the roof, the faster the rainwater moves down, projecting the water farther away from the house. Recom- mended projection is not less than 18 inches (preferably 24 in.) for a one-story house, and not less than 24 inches (preferably 36 in.) for a two-story house. The wider overhangs are par- ticularly desirable in areas of high rainfall.
Roof-supporting members of logs or of sawn lumber should not project beyond the eaves. If they do, they will become easily wet- ted and susceptible to decay.
For the cabin builder or the cabin buyer, the price for a sound, enduring cabin is good care. A finish on the inside and outside sur- faces of a brand new cabin completes the decay-resistant construction. An older cabin, too, profits from an occasional coat of preserv- ative. Also, throughout the service life of the trating oils, or lacquers, however, can also be used. When staining of the wood is desired, it is advisable to seal the wood first, then apply the stain and follow with another coat of clear sealer or varnish. Stain may be combined with the sealer in the second application.
The preferred finishes for log cabins are those that are generally referred to as the natural type of finish. These are either the penetrating water-repellent preservatives or the penetrating pigmented stains. Penetrating finishes have the very distinct advantage of not failing by blistering or peeling like varnish or paint and are, therefore, very easily maintained or refinished.
Preservative-type finishes contain a fungi- cide and inhibit the growth of fungus (mildew), which is the primary cause of graying of wood. These finishes allow the wood to weather to a very natural light brown or tan color. An effec- tive practical treatment includes thoroughly brushing the exterior of the cabin with a water- repellent preservative solution after erection (preservative V in the appendix).
Because the joints between logs, exposed end grain, and any drying cracks that develop are common water-trapping zones, particular attention should be given to these areas and heavy application of the water-repellent solu- tion is advised every other year as a mainte- nance procedure. This finish usually lasts about 2 years before small gray spots of fungal growth start to appear on surfaces, indicating a need for refinishing.
Penetrating pigmented stains (preserva- tive VI) are also very effective natural finishes for log cabins. These finishes change the color of wood, obscure part of the grain, and are less natural in appearance than the preservative finishes. These stains, when applied as de- scribed in the appendix, can last 10 years or longer.
Film-forming exterior varnishes, even marine or spar varnish grades, are not recom- mended because of their short life when fully exposed to the direct sun and because of the difficulty in refinishing.
Except for sills and the lower rail in win- dows, there is no need for interior application of preservative solutions. Because the inside is exposed to relatively constant low moisture conditions, the inside surfaces are not sus- ceptible to mold growth.
A good finish for the interior of log cabins should prevent soiling or staining, provide for good cleanability, and enhance the natural color and grain of wood. A non-yellowing alkyd varnish based on safflower or soybean oil would serve exceptionally well.