Practicing the Craft - (continued)
Where chain saws are allowed, native logs are available, and distance or other factors preclude hauling in treated timbers, consider using an Alaskan sawmill (figure 97). This is about the only way to effectively channel the power of the saw to create uniform, square planks. Several sizes of mills are available. A basic mill costs less than $200. You also need a powerful chain saw, one equipped with ripper teeth.
Figure 97-An Alaskan sawmill works great for creating planks from
native logs. The mill requires a powerful chain saw (at least 3.8 cubic inches of
displacement, more is better) and a special ripping chain.
Rough-sawn timbers are splintery, and some species of wood are more prone to splinter than others. To avoid a handful of splinters, wear good-quality, heavy work gloves.
Timbers to be used in a horizontal plane, (ledgers, stringers, and culvert inverts) should be checked for camber, a slight bend in the length of a piece of wood. Although camber usually is slight-less than ½ inch per 10-foot length-it should be used to your advantage.
Camber can usually be determined by sighting along all the surfaces of the timber from one end. Sometimes a stringline held to each end of the timber helps to identify camber. Many timbers will not have any camber.
If camber is present, the convex face should be placed up and the concave face placed down, even if this contradicts the "green-side up" general rule of placing growth rings down to reduce cupping. Weight on a timber will cause the timber to deflect or sag. With the convex surface up, deflection will act to straighten the timber. If camber is ignored and the timber is installed with the concave surface up, it is already sagging. Additional weight will cause the timber to sag even more.
At a preservative treatment plant, freshly treated wood is stacked on areas of concrete where excess preservative drips from the stack and is collected and recycled. The treated wood is air dried, which works well in a dry climate. However, the wood is sometimes dry at the surface but wet below the surface when it is shipped. This wood will weigh more because of the moisture. You need to consider this factor when transporting the wood to remote locations. The high moisture content of newly treated wood will also cause tools to bind and tear the wood. This is not intended to deter you from using treated wood, but it is something you need to be aware of.
Treated wood may be kiln dried if that process is specified. Kiln drying to 19- percent humidity can be required. However, the minimum order for large plants may be a truckload. Most small local plants probably cannot do this at all. Kiln drying does cost more.
Driftpins (usually ½-inch-diameter steel reinforcing bars) are used to pin logs and timbers. Some trail crews prefer to use driftpins cut from ½-inch -inside-diameter galvanized steel pipe. The length of the driftpins will vary. When driftpins are used to anchor a log or timber to the ground, about 12 to 18 inches of the driftpin should be in the ground. If rock or boulders are encountered before the driftpin is driven its full length, it will have to be cut off with a hacksaw. When pinning one log or timber to another, the driftpins should be long enough to go through the upper piece and all the way through the lower piece, or at least 12 inches into it.
First, drill holes in the wood. Before driving the pins, dip the lower end of the driftpin in heavy automobile grease. The lubricant will make it easier to drive the driftpins, will protect the driftpin from the weather, and will provide a thin, protective film between the steel and the copper in treated wood. Driving the driftpins is much easier if you make a striking plate out of a short piece of pipe with a 2- to 3-inch round plate welded to one end.
The top of the driftpin should be countersunk (figure 98). Countersinking can be done neatly by placing a 4- to 6-inch piece of steel pipe around the driftpin and a 12-inch piece of a smaller diameter steel bar inside it. With the pipe resting on the log or timber and the smaller diameter steel bar resting on the driftpin, hit the steel bar with a sledge hammer until the top of the driftpin is below the surface of the wood. This depression can be filled with grease to protect the steel from rusting. Wipe any surplus lubricant off of the wood.
- Slippery Wooden Treads
- Trail Grade
- Cross Slope
- Soil Conditions
- Surface Treatments
- Latex Paint
- Walnut Chips
- Mineral Products
- Nonslip Gratings and Grit-Treated Mats
We are frequently asked how to correct a slippery wooden tread. Often, the surface is not the source of the problem. The slippery surface usually is the result of overlooking factors such as trail grade, cross slope, or soil conditions.
If the grade of the trail surface is too steep, there is little that can be put on the tread to eliminate slipperiness. A wooden surface that has been installed at an 8-percent grade will be slippery with only a heavy dew. Pedestrians will find a wooden surface built at 5- percent grade slippery with frost or light rain. Shaded and north-facing sites aggravate the problem. The maximum grade for a trail with a wooden surface should be 2 percent (¼ inch per foot).
Another cause of a slippery tread is a cross slope that is too steep. To prevent excessive cross slope use, use a simple carpenters, masons, or torpedo level to identify any difference in elevation between parallel stringers, the notch in sleepers, and ledgers attached to the piles. To eliminate or reduce cross slope, shim up the stringers or ledgers, excavate the high end of the sleepers, redrill the bolt holes, or replace the ledgers (figure 99).
It is much cheaper to build the foundation correctly than to try to correct problems later through maintenance.
Another factor that can create a slippery tread is settlement, a problem that occurs when soil settles after a trail has been constructed. The trail may have been built properly, but all or part of the trail may have settled over time. Perhaps sleepers or a bent on end-bearing piles were used instead of a bent on friction piles. That part of the foundation settled over time, causing the trail to sag. The result is that one or both sections of trail on each side of the sag are steeper than intended.
One part of a trail support may settle. For example, one end of a sleeper may settle and the other end may not, or one pile in a bent may settle and the other may not. Both piles may settle, but one may settle more than the other. This type of settling will affect cross slope.
Cross slope of ¼ inch per foot (2 percent) is common for concrete and asphalt surfaces, but is excessive for wood. The cross slope should be level or one-eighth of an inch or less per foot (0 to 1 percent). Settlement can be corrected by shimming the low side, notching the high side, or a little of each. This is extremely difficult to do after construction and can be avoided to a degree by taking ample rod soundings and digging a number of test holes during the design phase. During construction, the crew should be alert for changes in soil conditions and should take remedial actions when necessary.
If the hazard of a slippery tread cannot be corrected by shimming, notching, or adding steps, a few surface treatments can be applied. These treatments will require maintenance.
A nonskid latex paint is made for boat decks. This paint is opaque, unlike a clear wood stain, but it can be tinted. As with all painted surfaces, peeling, scraping, and periodic repainting must be expected.
Walnut chips are a hard, angular material produced in various sizes. The number 4 size is suitable for nonslip surfaces. Walnut chips can be applied to a wooden surface by sand painting (using chips and paint mixed at the factory), using chips mixed into the paint at the site, or by painting the wood and sprinkling on chips while the paint is wet.
Nonslip products are also made from pumice and aluminum oxide. Some are premixed. Others are sold as a gritty powder that is mixed with paint.
Another method for correcting a slippery trail tread is to replace a wooden plank tread with nonslip gratings or to apply grit-treated fiberglass mats to the planks.
The construction industry recognizes differences between rock, stone, and gravel. It helps to understand the differences in the materials so you will know what to specify or order.
Rock is the parent material in and under the ground. Sometimes it is called bedrock or ledgerock. Moving rock usually requires drilling and the use of explosives.
When rock is broken or crushed, the pieces are referred to as stone. Stone, when used in construction, describes usable pieces of what once had been rock. Stone may be large enough to use for walls, or it may be small pieces that have been through a rock crusher for use as aggregate in concrete or as a base course in a road. Stone is angular on all sides.
Among the byproducts of rock-crushing operations are "crusher fines," screened material smaller than ¼ inch that is not suitable for most crushed stone contracts. This material is often sold at a discount at crusher operations and makes a fine trail surface when it is wetted and compacted.
Small pieces of rock that have broken naturally and have been subject to glacial action or tumbled in a river or creek are called gravel. The glacial action or the effect of water has rounded and removed all the corners of the original piece of rock.
Rock is rarely found in a wetland. Stone can be brought to the site for use as riprap. Crushed stone can be used for walking surfaces. Because crushed stone is angular, when it is compacted it will knit together to form a solid mass. Gravel cannot be compacted to produce a solid mass. Gravel's rounded shape is useful because water can move through the spaces between the gravel particles. Crushed stone should not be used for drainage (around perforated pipe or to carry water from one point to another). Use gravel for drainage (figure 100).
Figure 100-Crushed stone has angular edges and compacts well. It is good for
tread surfacing. Gravel does not make good surfacing because it has rounded edges. Gravel is
good for subsurface drainage because water flows freely through it.