Selecting a Finishing System

Here is an overview of the Architectural Woodwork Institute’s Standard Finishing Systems:

Notes: Due to changing environmental regulations and finish technologies, design professionals need to discuss finish option with a manufacturer located in the area of the project. Specification of a system requires listing both the system number and the name, along with any desired enhancements.

Comparison Table of Usages and Performance Scores

Note: T = Transparent and O = Opaque. Scores are out of a possible 135; evaluations included Chemical Resistance Testing – ASTM D1308, Wear Index-Abrasion Testing – ASTM D4060, Cold Check Resistance – ASTM D1211, Cross Hatch Adhesion – ASTM D3359.

General Performance Characteristics

Note: 5 = Excellent; 1 = Poor. The numerical ratings are subjective judgments based on the general performance of generic products. Special formulations and facilities will influence some of the performance characteristics.

Cost
Top coat costs vary greatly, yet a low-cost finish may have only 18 percent solids and 82 percent solvent. A more expensive finish might have 70 percent solids, 10 percent catalyst and 20 percent solvent. The environmental cost should be computed because the least expensive finish (containing 82 percent solvent) may cost the most when environmental considerations for waste disposal are taken into account.

Many woodworkers and owners fool themselves by using thin coats of finish. Yet these thin coatings do not protect or moisture-proof the wooden surface. Also, a thin, light coat of finish will often leave the surface dry with completely open pores.

The least expensive oil finish requires eight coats to equal two coats of a catalyzed urethane, yet the oil will not protect the surface against water or chemicals.

Wear Resistance
Wear resistance usually depends on the coating’s strength, which is based on its molecular makeup, solid content and the thickness with which it can be applied. Most wood finishes are made of complex mixes of resins, ranging from simple long grain oils to lacquers, varnishes, vinyls, urethanes and polyesters.

Chemical Resistance
Most household cleaners contain strong chemicals and many will harm finishes. The relative resistance to these chemicals is an important issue when specifying.

Reparability
Scratches in the top clear layers of the finish are fairly easily repaired with any of the finishing systems.

Scratches which penetrate the stain will require the addition of colorant and a clear coat.

Scratches which go deeply into the wood will have to have filler or binder added to build up the damaged area before application of a new top layer of finish.

Repairs made with soft-colored putty will look fine the first day, but given a few weeks and viewed from the side they may show small smudges of oily residue and will attract dirt or dust.

Adhesion
Adhesion is the finish’s ability to stick to the wood’s surface – the molecular attraction of the finish to the wood. It works in much the same way as a glue or adhesive. Adhesion is very important because a nick or dent can break the bond between the wood and finish. At that point the finish will become translucent and flake off. In some cases stains or solvents can interfere with the process of adhesion.

Almost all touch-up color should be a similar coating to the finish surrounding it. A competent touch-up or repair requires a good eye for color, color surface effect, gloss and grain character. Almost all finish is repairable, but high gloss finishes are the hardest to repair.

Clarity
Some finishes are clearer than others. Conversion varnishes and water-borne applications may appear milky when small bubbles are entrapped in the finish. This “microfoam” also will show up as a consistently milky area when applied over a dark stain. Many finishes have an amber color, and thus appear to be less clear. The typical term used in the profession when looking for a clear finish is “water white.” However, on wood such as red oak, or white oak, a yellowish finish may enhance the character of the wood and be aesthetically pleasing. When trying to attain a clear dark color, the best results come from a finish which has a high clarity.

Elasticity and Hardness
Wood is an elastic natural material which moves constantly with changes in humidity and temperature. Finishes which are too brittle or inelastic, or become so over time, are not recommended for wood.

All information provided by the Architectural Woodwork Institute, Potomac Falls, Va. www.awinet.org, 571.323.3636.