Application of exterior finishes

How a finish is applied to cedar is as important for durability and good performance as is the finish-substrate combination chosen for the job. Finishes can be brushed, rolled, sprayed or applied by dipping. The application technique, the quality and quantity of finish applied, the surface condition of the substrate, and the weather conditions at the time of application can substantially influence the life expectancy of the finish. The application guidelines suggested here should be followed in concert with the manufacturer's directions for the product.

Paints of all types such as vinyl-acrylic, modified-acrylic, and oil-based top coats are all suitable for cedar but test results show that good-quality 100%-acrylic formulations perform best. To achieve maximum paint life, follow these steps:

1. On bare new or restored cedar, apply one coat only of water-repellent preservative (1% or less of wax by volume and content). Allow it to dry for the period of time recommended by the manufacturer. If the wood has been dip treated, a longer drying time may be needed. Do not paint before the solvent from the water-repellent preservative has evaporated because the paint may then be slow to dry, may discolor, or dry with a rough surface.

2. Apply a good quality stain-blocking primer as soon as possible after the water-repellent has dried. The primer coat is very important because it forms a base for all succeeding paint coats and should be used whether the top coat is oil-based or latex-based. Application rates recommended by the manufacturer should be followed.

3. Apply the top coat over the primer. If two top coats are to be applied, allow the first to cure for the period recommended by the manufacturer before applying the second. In cold or damp weather, allow extra time between coats.

Water-repellent preservatives should be used only on newly manufactured bare cedar, on restored bare cedar, or on cedar previously treated with the same type of product. Application of preservative by brush, pad, or roller followed by thorough back-brushing is equally effective. When cedar is treated after the structure has been completed, liberal amounts of the solution should be applied to all lap and butt joints, edges and ends of boards. Other areas vulnerable to moisture penetration, such as below doors and window frames, also need to be treated.

When used as a natural finish, the service life of a water-repellent is only one to two years depending upon the wood and the exposure. Treatments on textured surfaces generally last longer than those on smooth surfaces. Dip treatment prior to installation or repeated brush treatment to the point of refusal will enhance the finish durability. The more finish absorbed by the wood, the longer the service life. If a water-repellent preservative is used as a pre-treatment before painting, apply only a single coat, and use caution to avoid excessive build-up.