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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

System Typical Usage Score Why and Why Not
1. Lacquer,
Nitrocellulose
Interior use for trims, furniture, paneling,
and ornamental work
77-T
75-O
Why: Repairable; widely available; quickdrying
Why Not: Lack of durability and resistance to most solvents and water; yellows over time
2. Lacquer, Precatalyzed Interior use for furniture, casework,
paneling, ornamental work, stair parts
(except treads), frames, windows, blinds,
shutters, and doors
99-T
97-O
Why: Repairable; stain-, abrasion-, chemical-resistance
Why Not: Some yellowing; moderate build
3. Lacquer,
Postcatalyzed
Interior use for furniture, casework,
paneling, ornamental work, stair parts
(except treads), frames, windows, blinds,
shutters, and doors
124-T
123-O
Why: Repairable; finish clarity; stain-, heat-, abrasion-, chemical-resistance
Why Not: Some yellowing; moderate build
4. Latex Acrylic, Water-
Based
Interior use for furniture, casework,
paneling, ornamental work, stair parts
(except treads), frames, windows, blinds,
shutters, and doors
94-T
94-O
Why: Low VOCs; finish clarity (some formulations); stain- and yellowing resistance
Why Not: Low durability; solvent- and heat-resistance; slow drying time
5. Varnish, Conversion Interior use for furniture, casework,
paneling, ornamental work, stair parts,
frames, windows, blinds, shutters, and
doors
129-T
129-O
Why: Durable; widely available; good build
Why Not: Occasional lack of finish clarity
6. Oil, Synthetic
Penetrating (available
in transparent only)
Interior use on furniture or trims
requiring a close-to-the-wood look or
very low sheen
57-T Why: Close-to-wood, antique look; low sheen
Why Not: Labor intensive to apply and maintain, refreshing finish required from time to time; low resistance properties to most substances
7. Vinyl, Catalyzed Interior use, often on kitchen, bath, office
furniture, and laboratory casework
114-T
114-O
Why: Durable; widely available; fastdrying
Why Not: Occasional lack of finish clarity
8. Acrylic Cross Linking,
Water-Based
Interior use for furniture, case work,
paneling, ornamental work, stair parts,
frames, windows, blinds, shutters, and
doors
99-T
99-O
Why: Fine durability; excellent abrasion-, solvent-, stain-, and chemical-resistance; moderately fast-drying; resists moisture
Why Not: Possibility of discoloration over time
9. UV Curable, Acrylated
Epoxy, Polyester or
Urethane
Interior use, doors, paneling, flooring,
stair parts, and casework where
applicable; consult your finisher before
specifying
134-T
133-O
Why: Low VOCs; durable; near 100% solids usage; quick-drying (cure), may qualify as Green Guard
Why Not: Difficult to repair with UV finish, as this requires a handheld UV lamp; availability varies; easy repair with lacquers or conversion varnish
10. UV Curable, Water-
Based
Interior use, doors, paneling, flooring,
stair parts, and casework where
applicable; consult your finisher before
specifying
132-T
132-O
Why: Low VOCs; quick-drying; (cure), may qualify for Green Guard
Why Not: Difficult to repair with UV finish, as this requires handheld UV lamp; availability varies; easy repair with lacquers or conversion varnish
11. Polyurethane,
Catalyzed
Interior use; some formulas available for
exterior; floors, stairs, high-impact
areas; some doors; generally not good
for casework, paneling, windows, blinds,
and shutters
133-T
132-O
Why: Durable; good build
Why Not: Slow-drying; very difficult to repair; some formulations hazardous to spray-personnel without air make-up suits
12. Polyurethane, Water-
Based
Interior use for furniture, casework,
paneling, ornamental work, stair parts,
frames, windows, blinds, shutters, and
doors
112-T
112-O
Why: Improved durability; excellent abrasion-, solvent-, stain-, and chemicalresistance; moderately fast-drying; resists moisture
Why Not: Tannins in some wood species may cause discoloration over time
13. Polyester, Catalyzed Interior use for furniture, casework,
paneling, ornamental work, windows,
blinds, shutters, and some doors
131-T
131-O
Why: Durable; good build; can be polished
Why Not: Not widely available; slowcuring; requires special facilities and skills; very difficult to repair; brittle finish flexibility

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

System Number
1 2 3 4 5 6 7 8 9 10 11 12 13
General Durability 2 2 3 2 4 1 4 2 5 5 5 3 5
Reparability 5 4 4 3 3 5 4 4 5 3 2 4 1
Abrasion Resistance 2 4 4 3 4 1 4 4 5 4 5 4 5
Finish Clarity 5 4 5 2 3 5 3 4 5 5 3 4 4
Yellowing in Time 1 2 3 1 5 2 3 4 5 5 4 4 4
Finish Flexibility 1 2 3 3 4 5 4 3 2 3 4 4 1
Moisture Resistance 3 3 4 1 4 1 5 3 5 4 5 4 5
Solvent Resistance 1 2 4 1 5 1 5 3 5 5 5 4 5
Stain Resistance 4 4 5 3 5 1 5 4 5 5 5 4 5
Heat Resistance 1 2 5 1 5 1 5 3 5 5 5 4 5
Household Chemical Resistance 3 4 5 3 5 2 5 4 5 5 5 4 5
Build/Solids 2 3 3 3 4 1 4 3 5 4 4 3 4
Drying Time 5 5 5 2 4 2 5 4 5 5 3 5 2
Affects Wood Flame Spread Yes Yes Yes No No No No No No No No No Yes

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.

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