# The Film Hewn Shop Notes · https://hewn.build/shop-notes/the-film AI-drafted, not yet checked: Drafted by Chip, the writing system Hewn runs on Claude, from Hewn's craft corpus. Jonathan Salomons has not read this note yet, and no outside reader has checked it. Read it as a shop note: check a number before you cut to it. Cite as: "The Film." Hewn Shop Notes, hewn.build/shop-notes/the-film. Drafted 2026-05-01; AI-drafted, not yet checked. --- Oil finishes fail quietly. They go dull, dry out, scratch through without drama. You wipe on another coat and you're back. Film finishes fail differently. They peel. They craze. They flake off in plates. Repair means stripping and starting over, which is a bigger operation than anything in the oil world. That's the tradeoff you're taking on when you build a layer on top of the wood instead of sinking into it. Know what the film is actually doing, and you pick the right tool. Misunderstand it, and you're scheduling a refinishing job five years from now. --- **Shellac** Every finisher should have shellac in the shop even if they never use it as a primary finish. Here's why: shellac is the only film finish that's compatible with everything else. Oil, wax, lacquer, paint — shellac goes over any of them, under any of them, and nothing rejects it. It's also the only film finish you can strip and re-coat without solvents that damage surrounding surfaces. The carrier is denatured alcohol. Heat it back up with more alcohol and it re-dissolves. That reversibility is the feature. Shellac comes in flakes you dissolve yourself, or pre-mixed in a can. Flakes are better quality. The cut rating is simple: a 2-pound cut is 2 lbs of flake per gallon of alcohol. Medium body, appropriate for most furniture. Thinner cuts for sealing, thicker for topcoats. Amber adds warmth; dewaxed blonde is as close to neutral as film finishes get. Two limitations, and they're real: shellac is not water-resistant and not heat-resistant. A wet glass will leave a white ring. A casserole dish will soften it. Keep it off surfaces that see regular moisture or heat. Everything else is a candidate. A sequence worth using constantly: two coats of dewaxed blonde shellac, scuff with 400, apply whatever topcoat you want. It gives you a clean, uniform base and eliminates the compatibility question entirely. Dewaxed specifically — waxed shellac doesn't accept topcoats. --- **Lacquer** Nitrocellulose lacquer is what most factory furniture is finished with. Fast-drying, sprayable, sandable between coats. Hard, durable, reversible with lacquer thinner. If you have a spray rig and a proper booth and you're running production volume, lacquer is the answer. If you don't have that infrastructure, lacquer is harder to justify. Brushable versions exist but they're inferior. The VOCs are significant — flammable, strong fumes, not something to run casually in an attached garage. Catalyzed lacquer (two-part conversion varnish, pre-cat) produces the hardest film available for furniture. What professional cabinet shops use. The catch: pot life. Catalyzed finishes have a working window before they gel. And they can't be re-coated after full cure without scuffing. Plan the sequence before you start. --- **Polyurethane** Poly has a bad reputation in craft woodworking circles. Most of it is undeserved. Oil-based polyurethane is genuinely durable. It's the right call for tabletops, floors, and anything that needs long-term protection. Slow to dry — 4 to 6 hours between coats — and it yellows. Significantly on light-colored woods. The application window can bite you: too much buildup between coats causes adhesion failure. Water-based poly dries in 1 to 2 hours and stays clear. Softer than oil-based. For clear protection on maple, ash, or birch, it's usually the better choice despite the durability trade. Wipe-on polyurethane deserves its own mention because it closes the application skill gap. Standard poly requires real brush technique to avoid runs and lap marks. Wipe-on is thinned enough to apply with a rag, the same flood-and-wipe motion as an oil finish. Thinner coats, not as durable as brushed, but actually achievable without spray infrastructure. For commission pieces where the client needs film protection and you don't have a spray room, this is the realistic answer. --- **How film finishes fail** Three causes, almost always. Contamination. Oil, wax, silicone, or any prior finish residue that wasn't fully removed. Film finishes need clean wood or a scuffed, clean existing film. Anything in between and the new coat doesn't bond. Temperature. Film finishes are more sensitive to this than penetrating finishes. Lacquer below 10°C or above 85% humidity can blush — the finish clouds as moisture gets trapped. Water-based poly at 5°C doesn't coalesce properly. At 35°F, don't apply. In a BC Interior shop that cycles through cold nights, double the listed dry times or bring the piece inside. Incompatible layers. Shellac is compatible with everything. Most other film finishes are not compatible with each other unless the system is designed that way. Lacquer over oil-based poly can lift. Water-based finish over oil-based primer can fisheye. Know what's in the system before you add a layer. --- **The recommendation** Default to oil finishes for most work. Add shellac as a sealer before oil on end grain and figured wood, and as a standalone finish on shop fixtures, tool handles, and boxes. Use wipe-on poly when the piece needs more protection than oil provides and you don't have spray infrastructure. Reserve lacquer for when you have the setup and the volume. The goal is a system you can execute consistently, in your conditions, with your tools. Not the most sophisticated system. The one that works.