Finishes

Nearly every millwork set carries one general note about finish, and the residential set in hand carries it on all sixteen sheets: FINISHES TO BE REVIEWED AND APPROVED BEFORE FABRICATION. It reads like boilerplate. It is the shop's protection against the most subjective argument in the trade: whether a colour matches.

This chapter explains what that note protects, what a finish specification on a drawing has to contain, and how the published standard handles sheen, samples and defects. The numbers come from the Architectural Woodwork Standards (AWS), 2nd Edition, Section 5, Finishing, and Section 1, Submittals.

Why colour is the hardest thing to agree

The AWS says it plainly: "Color and 'matching' of a sample are often highly subjective. Individual perception, ambient lighting, and reflectivity influence judgement." It adds that the best case achievable with a natural product "in a wide variety of lighting conditions is a good 'blend' of color and tone throughout the project area".

Wood also keeps changing after it leaves the shop. The standard names cherry, fir, American and African mahogany, walnut and teak among species that change colour, and notes that "Filled nail holes will not change with wood." Even a clear topcoat alters the wood's natural colour. Its Submittals section adds: "RANGE OF COLOR shall be expected on finished wood products due to variance in wood color within the same species and even within the same log."

So an approval of "walnut, natural" approves a word, not a colour. Two people will hold different pictures of it. The only thing both can point at is a physical sample, made from the job's material, with the job's finish, signed before the shop sprays a door.

What the general note protects

Read the AWS rules on samples and the note's purpose becomes clear.

• Samples "Be submitted and approved before finishing of product".
• "To establish an acceptable sheen and color range, a minimum of three samples shall be submitted."
• Each sample is at least 12" × 12" (305 mm × 305 mm) on panel product, protected from light, on "material representative of that to be used for the project", and labelled with the job name, the design professional, the contractor and the finish system number.
• The Submittals section asks, for a transparent finish, for "a minimum of three (3) sets, bound together, of three (3) samples each, indicating the range of color and grain to be expected for each finish selection". For an opaque finish, three samples for each colour.

Three samples, not one, because the standard expects a range. An approved set of three says: anything between these is accepted. A single approved chip says: this exact colour, which wood will not deliver twice.

The approved sample then becomes the test. For field finishing, the AWS makes the finisher "responsible for meeting or exceeding the control sample for surface performance characteristics (such as color, texture, and sheen)". The note on your drawing is the hinge between the signature and that test. Without it, the architect can reject finished work against a memory. With it, the argument is about the sample on the table.

Sheen

Sheen names mean different things to different coating makers. The AWS gives measured ranges instead, "developed by measuring the reflectance of a direct light source at a 60 degree angle with a gloss meter":

Name	Gloss units at 60°
Flat	8–14
Satin	15–25
Satin gloss	26–49
Semi gloss	50–70
Gloss	71–90

It also notes: "An untrained eye can see a 10 point or greater difference in sheen." Two cabinets both called "satin" can sit 10 points apart within that one band. Write the number on the drawing, not only the word: SHEEN 20 ±5 @ 60° is a checkable requirement. SATIN is an opinion.

Shop finish or site finish

The AWS permits both, "provided there is no violation of applicable codes or regulations", and describes the difference:

• Factory finishing "is usually specified for high quality work where superior appearance and performance of the finish is desired". Its benefits: consistency, control of film thickness, environmental compliance, and curing in a controlled atmosphere.
• Field finishing "is typically specified when there is not a demand or specific need for a superior appearance and is not necessarily part of the woodwork contract". It normally sits in the painting specification. The painter examines and accepts the woodwork before starting.

The standard's recommendations section says to avoid jobsite finishing "because a factory-controlled finishing environment offers a superior finished product", and to avoid brush-applied finishes, which it does not cover.

The choice changes the drawing. The Woodwork Institute's sample set puts PAINTING/FINISHING BY OTHERS in its general notes. If finish is by others, your set has to say what state the woodwork arrives in: sanded, sealed, primed, or raw. The AWS rule for field-finished work is that exposed woodwork gets "a thorough, final sanding over all surfaces" before finishing, and concealed surfaces that could meet moisture, "such as those adjacent to exterior concrete walls", are primed. When factory finishing is required, priming or sealing is required too.

A split scope is where claims start. If the shop finishes the cabinets and the painter finishes the trim beside them, two finishers are chasing one sample. Show which items each one finishes, on the elevation.

Choosing a finish system

The AWS lists thirteen finishing systems and rates each one from 1 (poor) to 5 (excellent) in general performance, then scores them on chemical and stain tests. The total scores, from its Table 5-003:

System	Total score	The standard's "why not"
1 Lacquer, nitrocellulose	77	Lack of durability and resistance to most solvents and water; yellows over time
2 Lacquer, pre-catalysed	99	Some yellowing; moderate build
3 Lacquer, post-catalysed	124	Some yellowing; moderate build
4 Latex acrylic, water based	94	Low durability; solvent and heat resistance; slow drying
5 Varnish, conversion	129	Occasional lack of finish clarity
6 Oil, synthetic penetrating	57	Labour-intensive to apply and maintain; low resistance
7 Vinyl, catalysed	114	Occasional lack of finish clarity
8 Acrylic cross-linking, water based	109	Possible discoloration over time
9 UV curable, acrylated epoxy, polyester or urethane	134	Difficult to repair with UV finish
10 UV curable, water based	132	Difficult to repair with UV finish
11 Polyurethane, catalysed	133	Slow drying; very difficult to repair
12 Polyurethane, water based	112	Tannins in some species may discolour it
13 Polyester, catalysed	131	Not widely available; slow curing; very difficult to repair; brittle

The standard warns against over-reading the table: "Differences between systems of 10 points or fewer are not generally considered significant enough to justify the typical added expense of a higher-rated system." It also warns against over-specifying: "Unnecessary cost could be added to a project through over specification", and gives polyurethane or polyester topcoats "when they are neither necessary or available from a custom fabricator" as the example.

For the drawing, the Submittals section is exact. The material list includes "Finishing requirements, including AWS System number, sheen and required application steps." A finish line on a sheet should read like this:

F1: WHITE OAK, RIFT. AWS SYSTEM 5, CONVERSION VARNISH. STAIN TO APPROVED SAMPLE F1-A/B/C. SHEEN 20 ±5 @ 60°. NOT FILLED.

Each part answers a question. The system number fixes the chemistry. The sample reference fixes the colour. The sheen number fixes the gloss. "Not filled" matters because the AWS says a filled finish "is only required if so specified", and open-grain species such as oak, ash, walnut and mahogany look different filled and unfilled.

What the standard asks of the finished work

These rules apply to exposed and semi-exposed surfaces visible after installation. Several are drafting decisions in disguise.

• Doors get both faces and both vertical edges finished, with an equal number of coats of the same material on each side. Top and bottom edges and hardware preparations are sealed.
• Casework finishes all exposed and semi-exposed surfaces, and "All six faces of cabinet doors receive the same number of coats to prevent warping and/or twisting."
• Panelling finishes adjacent panels together, and "If possible, entire elevations shall be finished together." Pairs of doors, sidelights and transoms are finished together too. Mark on the elevation which pieces form a finish batch.
• Wood parts on laminate casework, such as pulls, trims, mouldings and edgebands, are in the casework maker's finishing scope.
• Moisture: the finisher reports in writing, before finishing starts, any moisture content of the product or the surrounding drywall or plaster above 12%.
• Temperature: ventilation "with sufficient heat to maintain temperatures above 65° F for 24 hours before, during, and 48 hours after application of finishes."

Defects are judged by grade and viewing distance. Some of the AWS limits:

Defect	Economy	Custom	Premium
Sanding scratches	Inconspicuous beyond 72"	Inconspicuous beyond 36"	Not permitted
Orange peel	Inconspicuous beyond 72"	Inconspicuous beyond 36"	Not permitted
Runs	Inconspicuous beyond 36"	Not permitted
Blushing	Inconspicuous beyond 36"	Not permitted
Filled nail holes	Inconspicuous beyond 108"	Inconspicuous beyond 72"	Inconspicuous beyond 36"
Field repairs and touch-ups	Inconspicuous beyond 108"	Inconspicuous beyond 72"	Inconspicuous beyond 36"

The grade on your cover sheet sets these distances. If the cover sheet says Custom and the client inspects at arm's length, the standard is on the shop's side, but only if the grade is written down.

The hazard the drawing controls

Finish choice is also a health decision. HSE, the UK regulator, says "Spraying isocyanate products is a significant cause of occupational asthma", and warns that continued exposure can cause permanent, severe asthma. The AWS's own table describes catalysed polyurethane as having "some formulations hazardous to spray-personnel without air make-up suits". If the design intent can be met by a lower-hazard system, that is a real choice, and it is made on paper. The product's safety data sheet is the authority on each coating. The safety page covers this in more depth.

Checks before the set leaves

• A finish schedule with a code for every finish, used on every elevation.
• Each code names the species or substrate, the AWS system number (or the standard your spec names), the colour reference, the sheen as a number, and filled or not.
• Samples listed: how many, what size, on what material, and who signs them.
• The general note ties fabrication to sample approval, and appears on every sheet.
• Scope split: which items the shop finishes, which arrive primed or raw, and who finishes those.
• Pieces finished together as a batch are marked.
• Any match between two species or materials has its own sample.
• The grade on the cover sheet matches the spec, because it sets the defect limits.

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Sources

• Architectural Woodwork Standards, 2nd Edition, 1 October 2014, © AWI, AWMAC, WI, full text hosted by the Woodwork Institute. Section 1, printed pp. 27 and 29: range of colour; finishing requirements in the material list; finish sample sets. Section 5, printed pp. 110–113: factory and field finishing, colour, blotching, sheen ranges and the 10-point note, the thirteen systems; printed pp. 113–116: performance tables, usage and "why not", the 10-point significance note, recommendations; printed pp. 117–121: control sample, finisher's report, samples, doors, casework, panelling, defect limits by grade, priming, ventilation. Superseded for jobs bid under later editions. Primary (superseded edition).
• Health and Safety Executive, "Construction isocyanates: Spraying", hse.gov.uk. Isocyanate spraying and occupational asthma. Primary.
• A residential millwork submittal, 16 sheets, revision 0: the general note on every sheet; the maple interior and Baltic birch drawer finish notes on sheet 09. Not reproduced: live job. Document.
• Woodwork Institute, Sample Shop Drawings, specification requirements sheet: "Painting/finishing by others" in the general notes. Document.

The sample finish line (F1 ...) and the sheen tolerance in it are illustrations written for this chapter, not quoted from a standard.