Paints

Paints of all types, such as vinyl-acrylic, modified-acrylic, and oil-based topcoats, are suitable for cedar, but test results show that high-quality 100 percent acrylic latex formulations perform best.

Paint provides the most surface protection against weathering and wetting by water while providing color and concealing some of the wood’s characteristics. Although paint can reduce wood’s absorption of water, paint itself is not a preservative.

Alkyd-oil, stain-blocking primers usually offer the best shield against discoloration by water-soluble extractives. Latex paint, particularly 100 percent acrylic latex formulations, remain more flexible with age and are better able to accommodate dimensional changes by stretching and shrinking with the wood.

Factory finishing is available in many markets and is highly recommended. Factory-finish applications may be available with finish warranties.

Applying Finishes

The application technique, quality and quantity of finish applied, surface condition of the substrate, and weather conditions at the time of application can substantially influence the life expectancy of the finish. The application guidelines suggested here should be followed along with the manufacturer’s directions for the product.

Applying Weathering and Bleaching Products

Weathering and bleaching products refinish the same way as the semitransparent oil-based penetrating stains. Semitransparent latex stains act like very thin paints and may require more extensive surface preparation (scraping, sanding, etc.) before being refinished. Manufacturers’ instructions should be followed carefully.

The application of a finish on WRC is as important for durability and optimal performance as the finish-substrate combination chosen for the job. Finishes can be brushed, rolled, sprayed, or applied by dipping.

When to Refinish

Exterior WRC surfaces only need to be refinished when the old coating has worn thin and no longer affords the wood protection. In refinishing painted or solid-color stained siding and trim, removal of the old coating may be required. This is necessary if, for example, the old finish is severely cracked, peeling, or flaking. These finishes can be removed by a variety of procedures, all of which can be difficult, time-consuming, and expensive processes. Some of these procedures can damage the wood. For example, power washing should never be used for removing coatings from WRC because this process can severely damage the wood surface fibers and make it difficult for the next finish to adhere properly.

Finishing Formulas

When finishing WRC, different formulas of finishing materials are available to be applied to the wood for optimal performances. These formulas vary from market to market based on volatile organic compounds (VOCs), which are organic compounds that easily vaporize at room temperature. Some solvent-borne stains contain high amounts of VOCs. These are well absorbed by cedar and contain mineral spirits. However, due to their volatility, environmental conditions, and local and state laws, these materials are not available everywhere. States like California and Maryland have restricted the use of certain finishing materials and formulas. Before starting a project, make sure to comply with all local and state regulations to ensure safety.

Finishing before Installation

New cedar siding and trim should be protected from the weather before, during, and after construction. Finishing of siding and trim (not decking materials) works best when the product is prefinished on all six sides of the wood prior to installation. Factory finish is preferred.

It is seldom necessary to carry out extensive surface preparation provided the wood has not weathered for more than two weeks and is clean and dry. The moisture content should always be checked as a precaution. The moisture content must below 20 percent. If the wood has been contaminated by dirt, oil, or other foreign substances, it must be cleaned before finishing.

Dirt should be washed from the surface (see section on cleaning and discoloration). For smooth-planed, flat-grained cedar, some surface preparation may be desired. On flat grained wood, the surface should be scuff-sanded with 50–60 grit sandpaper. This procedure will greatly increase the coating’s performance but will not detract from a smooth appearance. Surface preparation is not necessary for clean textured cedar.

When finishing WRC, it is important to follow all manufacturer’s guidelines.

Best Practices for Installing WRC

Installation involves many processes including inspection, storage, fasteners, nailing patterns and placement, and flashing installation.

Inspecting and Storing Materials

As soon a shipment is received, inspect all materials to ensure the proper grade of material for the project. If any of the materials appear damaged in any way, they should not be installed.

Prior to installation, it is important to acclimatize the materials. Since WRC is a natural material, it responds to the environment around it. Cedar siding can swell or shrink as it gains or loses moisture to reach equilibrium with the moisture content of the surrounding air. On the job site, ensure that all WRC siding is protected from direct sunlight, water saturation, snow, ice, dirt, and other elements. Store the siding flat and off the ground on a vapor barrier so that moisture is not absorbed from the lower boards. While it is important to cover the materials, do not completely seal them, as good air circulation is required. Ideal moisture content (MC) for installing WRC is an average of 12 percent MC in most areas in North America.

Determining Hardware

Next, decide which fasteners to use so that the product is properly secured to the building frame and to ensure a durable and long-lasting result. There are various types of appropriate fasteners on the market. Let’s discuss a few options as well as nailing patterns.

Fasteners

Stainless-steel nails are the best choice when installing WRC, especially if the siding is to be finished with transparent stain, semitransparent stain, or bleaching or weathering products. Use No. 304 stainless for general siding applications and No. 316 for seacoast exposures.

Stainless steel, aluminum, and hot-dipped galvanized (as per ASTM A-153) fasteners are all corrosion resistant and can be used to fasten WRC. Other types of fasteners, including electroplated and mechanically galvanized and copper, are not recommended. They can rust, disintegrate, and react adversely to the natural preservative present in cedar, leaving stains and streaks. Hot-dipped galvanized fasteners are only recommended for pre-primed wood that will be topcoated with solid stain or paint.

For best results, use “splitless” ring-shank siding nails. These have thin shanks and blunt points to reduce splitting. Textured heads should be used to reduce the glossy appearance of the nail head.

Proper Nailing Techniques

When installing WRC, hand nailing is preferred. Carefully drive nails into the framing members. To ensure nailing accuracy, run chalk lines to mark framing locations. Heavy nailing distorts the wood and may cause splitting. At mitered corners, near edges, and near ends, nail holes may need to be pre-drilled to avoid splitting. Avoid the use of pneumatic nailers, if possible. If a pneumatic nailer must be used, reduce the air pressure and tap nails flush.

Overdriven nails must be remedied immediately. Fill overdriven nail holes with exterior grade wood putty specifically designed for filling exterior nail holes.

Siding should be fastened to each stud or blocking with nails spaced at a maximum of 24 inches on center. Nail placement depends on the siding pattern and width. The key is to fasten the siding securely without preventing it from moving in response to the moisture content in the air. In general, each piece of siding must be nailed independently. Nailing overlapping pieces together restricts the natural movements of each piece and may cause splitting.

The size of nails to use depends on the type and thickness of siding. Use ring-shank siding nails long enough so that they penetrate solid wood by a minimum of 1¹⁄₄ inches.

Wall Construction

Like all siding materials, WRC performs best when installed properly to a suitable frame. Cedar siding should be securely nailed to framing members, furring members, or blocking between framing members. Standard stud walls generally require no special preparation for horizontal siding installation. Siding should be nailed into wood sheathing and studs or blocking at a maximum of 24 inches on center, and 16 inches on center when siding is installed to furring members or without sheathing. When an airspace between siding and sheathing is desired, nail siding to furring strips, sheathing, and framing. Maximum spacing for furring strips is 16 inches on center. Spacing for furring strips should match the spacing of the studs.

Installing Flashing

Before installing siding, make sure that flashings are properly installed to prevent moisture from entering wall and roof spaces. Flashing is an important line of defense in controlling moisture in wall assemblies. Flashing intercepts and directs the flow of water away from the building to designed drainage paths. Install horizontal flashing extending from the top of all wall penetrations (i.e., all windows and doors) and at any material or material directional change (i.e., bandboards, water tables, or the introduction of any alternative material). The flashing should tilt downward to allow water to drain away from the wall. Siding or trim should be ¼ inch above the flashing ledge. Do not caulk above or below windows and doors. Caulk where siding abuts vertical trim. Note that caulking in lieu of flashing is not acceptable and can allow air and water intrusion to damage the wood.