For sprayed kitchen cabinets, vanities and fine millwork, conversion varnish is usually the stronger choice: it is a two-part catalyzed finish that dries fast and holds up to water, heat and household chemicals. Polyurethane earns its place on floors, stairs and other high-impact surfaces, and it can be brushed on site. The right answer depends on the surface, the room and who applies it. Below we explain each finish in plain terms, compare them on the points that matter in a real home, and show where pre-catalyzed lacquer fits.
TL;DR
- Conversion varnish is a catalyzed, spray-applied finish rated for casework, paneling, doors and stair parts. It is the most durable of the catalyzed finishes, and also the most demanding to apply.
- Polyurethane suits floors, stairs and high-impact areas. Oil-based versions can be brushed, which is why they show up in remodel work.
- Both rate Excellent for water, chemical and scratch resistance in the industry comparison table. Conversion varnish is the easier of the two to dry, stack and recoat on a production schedule.
- Pre-catalyzed lacquer is the middle option: easier to handle and repair, with performance close to conversion varnish in some products, but it yellows more and builds less.
- Temperature, sanding grit and the existing finish decide whether either finish bonds and cures properly.
Table of Contents
- What conversion varnish and polyurethane actually are
- Side-by-side: how they compare
- Durability: closer than the internet argues
- Application: where the two really differ
- Drying and cure time
- Repairs and touch-ups
- Where pre-catalyzed lacquer fits
- Which one for which job
- Check these before you finish anything
- Choosing a finish for your project
- Sigma Painting for cabinets, millwork and stairs
- Our perspective
- FAQ
- Sources
What conversion varnish and polyurethane actually are
Conversion varnish is a catalyzed finish. The acid catalyst is packaged separately and mixed in before spraying, which starts a reaction between alkyd and amino resins. The finish cures by that cross-linking rather than by solvent evaporating. Popular Woodworking calls it the most durable of the catalyzed finishes and also the most finicky, partly because it can be hard to get a good bond over stains, glazes, other finishes and even over itself.
Polyurethane is a varnish made with polyurethane resin. According to Canadian Woodworking, the resin adds scratch and heat resistance but makes the film less flexible, and oil-based versions add an amber tone that tends to darken over time. Polyurethane comes in one-part cans you can brush, and in two-part (2K) versions, including waterborne ones, that are mixed with a catalyst like conversion varnish.
So the real contrast is not “catalyzed versus not.” It is a post-catalyzed alkyd-amino coating, built for spraying in controlled conditions, against a family of urethane coatings with a wider range of application methods.
Side-by-side: how they compare
The American Hardwood Information Center rates conversion varnish and catalyzed lacquer Excellent for water, chemical and scratch resistance. Oil-based polyurethane also rates Excellent on those three, but Poor for repairability and ease of application. Its finishing-system guide adds the use cases.
| Conversion varnish | Polyurethane | |
|---|---|---|
| Type | Post-catalyzed, two-part | One-part oil-based, or two-part (2K) |
| Typical application | Spray, in a controlled space | Brush, roller or spray, depending on the product |
| Rated for | Furniture, casework, paneling, ornamental work, stair parts, frames, windows, shutters, doors | Floors, stairs, high-impact areas, some doors |
| Not recommended for | Heavy-traffic floors | Casework, paneling, windows, blinds and shutters (catalyzed polyurethane) |
| Water, chemical, scratch resistance | Excellent | Excellent (oil-based) |
| Repair | Hard to repair invisibly | Hard to repair invisibly |
| Colour over time | Non-yellowing in many clear products | Oil-based types amber and darken |
The same system guide scores conversion varnish 129 (durable, widely available, good build, occasional lack of clarity) and catalyzed polyurethane 133 (durable, good build, slow-drying, very difficult to repair). The scores are close. What separates them is where you use them and how they are applied.
Durability: closer than the internet argues
You will find forum posts claiming one or the other is “the toughest.” The published ratings say both are in the top tier. Popular Woodworking notes that catalyzed finishes have durability similar to oil-based polyurethane, dry quickly and are almost essential to spray.
The differences show up in the details:
- Build. A polyurethane manufacturer’s article reports that conversion varnish is typically limited to 4 to 5 mils of dry film, while polyurethane can be built much thicker. On a kitchen cabinet door, 4 to 5 mils is the target anyway. M.L. Campbell’s product sheet for its Krystal conversion varnish recommends two coats at 4 to 5 mils wet and no more than three coats.
- Chemical and moisture resistance. The same product sheet says Krystal meets or exceeds the chemical resistance requirements of both Architectural Woodwork Standards System 5 (conversion varnish) and System 11 (catalyzed polyurethane). It is designed for kitchen cabinets and surfaces exposed to moisture, heat and household chemicals.
- Clarity. Conversion varnish can be water-clear and non-yellowing. Canlak describes its CanGuard Plus clear conversion varnish as fast drying, non-yellowing and highly mar and chemical resistant. A white or light cabinet is where oil-based polyurethane’s amber drift is most visible.
For a kitchen, where the cabinet around the sink, dishwasher and stove takes steam, splashes and cleaners, conversion varnish matches the demand. For a staircase tread that takes shoes every day, polyurethane’s scratch and heat resistance is the better fit.
Application: where the two really differ
This is the section most homeowners miss, and it often decides the choice.
Conversion varnish is a two-component finish that has to be catalyzed and sprayed. PaintPRO Magazine quotes a finishing pro saying it is typically used in shops rather than on site because it needs a controlled environment, while oil-based polyurethane can be brushed, which suits remodeling work.
Temperature matters more than most people expect. Popular Woodworking advises keeping the temperature above 65°F (70°F is better) during application and for up to six hours afterward, or the finish might not cure properly. In an unheated Ontario garage in November, that is a real constraint. General Finishes’ technical data sheet for its conversion varnish calls for 70°F and 50% humidity, out of direct sunlight, and recommends spray application only.
Sanding also matters. Because of their high solids, catalyzed finishes often bond poorly to wood sanded too fine, especially tight-grained maple and birch. Popular Woodworking’s advice is to sand no finer than 220 grit just before finishing.
Pot life is the last trap. WoodWeb’s catalyzed finishes guide says conversion varnish has an 8 to 12 hour pot life and gels in the can once that is exceeded. Mixed material that sits too long is wasted, so a crew has to plan batches around the day’s work.
Drying and cure time
Speed is conversion varnish’s practical advantage. M.L. Campbell’s Krystal dries to touch in 15 to 25 minutes, sands in 30 to 45 minutes and stacks in 4 to 8 hours at 77°F. General Finishes lists a 30-minute touch-dry, a 2-hour recoat and a 7-day full cure for its version.
Compare a waterborne 2K polyurethane. M.L. Campbell’s Arroyo, according to its product information sheet, is mixed at 100 parts base to 5 parts catalyst, rested for 5 to 10 minutes, and dries to touch in 40 to 45 minutes. It stacks at 10 hours at the earliest. The product sheet also asks for seven to ten days of cure before the surface sees a harsh chemical environment.
Two points follow for a homeowner:
- “Dry to the touch” is not “cured.” Even a fast finish needs days before it should take heavy cleaning or a full load of dishes and appliances against it. Our guide on cabinet paint cure time explains when cabinets are safe to use.
- Fast stacking means doors can be finished and handled sooner, which is why shops running many doors favour conversion varnish.
Repairs and touch-ups
Neither finish is forgiving. Conversion varnish is harder to repair invisibly than lacquer, shellac or water-based finishes, and the industry table rates oil-based polyurethane Poor for repairability. A chip on a finished door is better treated as a refinish of that panel than as a dab of touch-up, much as a scratched panel on any finished surface needs the right procedure, as in this guide to repairing scratched metal panels.
The practical consequence: pick the finish for the surface’s daily life, and expect repairs on cured catalyzed coatings to be done by sanding back and re-spraying a whole door or panel.
Where pre-catalyzed lacquer fits
You will see “precat” next to conversion varnish in almost every cabinet shop’s specification. Pre-catalyzed lacquer arrives with the catalyst already added, so there is no mixing day by day. The trade-off is shelf life: WoodWeb says pre-catalyzed lacquers last from a few months to over a year, while conversion varnish lasts hours once mixed but is more durable. Atlantic Plywood’s expert says a post-catalyzed coating typically outperforms a pre-catalyzed one and recommends it for tables and high-water areas such as bath vanities.
The hardwood information center rates pre-catalyzed lacquer a lower 99 on its scale, with repairability and stain and chemical resistance as strengths, and some yellowing and moderate build as drawbacks. Some modern hybrids close the gap. M.L. Campbell’s Magna-Tek is a self-sealing alkyd-amino hybrid pre-catalyzed lacquer with performance similar to conversion varnish, designed for kitchen cabinets and furniture.
Short version: precat is the easier, more repairable finish, and conversion varnish is the tougher one for wet and heavily cleaned areas.
Which one for which job
| Surface | Better fit | Why |
|---|---|---|
| Kitchen cabinets and island | Conversion varnish | Moisture, heat and cleaner resistance, fast stacking |
| Bathroom vanities | Conversion varnish | High water contact |
| Built-ins, paneling, wood office millwork | Conversion varnish or pre-catalyzed lacquer | Rated for casework and paneling; clear, stable colour |
| Interior doors, trim, shutters | Conversion varnish or precat | Both rated for doors and trim |
| Stair treads, floors | Polyurethane | Rated for floors and stairs; scratch and heat resistance |
| On-site remodel, brush-applied | Oil-based polyurethane | Can be brushed without a spray setup |
For multi-unit work, such as condo suites or rental turnovers, the speed of conversion varnish and the repeatability of spraying matter as much as the finish itself.
Check these before you finish anything
- Existing finish. Conversion varnish works over most stains except oil-heavy ones and can struggle on oily woods such as teak or rosewood. A reference on catalyzed finishes also warns that sealers containing zinc stearate can react with the acid catalyst and cause haze that may not show for weeks or months. WoodWeb adds that two-part polyurethanes tolerate oily stains better, though some need a barrier coat.
- Moisture and conditions. The Red Seal decorative-finishing guide, published for Canadian painters, gives wood at or below 12% moisture, 15 to 30°C and 30 to 60% relative humidity as working conditions.
- Ventilation and protection. Solvent-based conversion varnishes are blends of alkyds, urea formaldehyde and melamine with a strong acid catalyst, with high VOCs and formaldehyde emissions, per PCI Magazine. Spray work calls for the safety data sheet, an organic-vapour respirator rated by NIOSH, nitrile gloves, safety glasses and 6 to 10 air changes per hour. Residents should stay out of the space while it is sprayed and cured.
- Flammability. Axalta’s technical data sheet for a Canadian conversion lacquer lists a closed-cup flash point of 1°F and professional use only. That is the reason these coatings are sprayed by trained crews.
If you are painting over a previously varnished surface, see our guide on painting over varnished wood. If you are still deciding between repainting and replacing doors, read cabinet painting vs refacing.
Choosing a finish for your project
Start with how the surface is used, not the product name. A wet, wiped, handled surface such as a kitchen run wants a catalyzed finish, and a foot-traffic surface wants polyurethane. Then check where it will be applied. A spray finish needs a controlled space and a crew that mixes only what it can spray inside the pot life.
We cover the finish in more depth in our article on conversion varnish on kitchen cabinets, and on how spray finishing works for homeowners.
Sigma Painting for cabinets, millwork and stairs
Sigma Painting offers cabinet painting and refinishing across the GTA, along with fine-finish and millwork spraying, kitchen repainting, stair staining and luxury wood office finishing. Every service comes with premium materials, comprehensive prep and cleanup, and a complimentary colour consultation. Estimates are free, fixed and rapid, and our workmanship is backed by a written warranty.
If you want a straight answer on which finish suits your kitchen, vanity, built-ins or staircase, book a free estimate through our services page.
Our perspective
Most finish arguments are really arguments about the wrong question. Owners ask which coating is toughest, when the useful question is how a surface lives. A cabinet near the sink gets steam, wet cloths and cleaner every day. A stair tread gets shoes. Those are different jobs, and a good finisher matches the coating to each.
We also think the finish is only as good as the prep underneath it. Sanding to the right grit, dealing with the old coating, and keeping the space clean while the finish cures are where a premium result is made. That is why we put so much weight on comprehensive prep and a spotless worksite, and why we back the work with a written workmanship warranty.
For homeowners, builders and property managers, the best outcome is a finish chosen for the room and applied by a crew that does this every week. Tell us the surface and how it is used, and we will recommend the right approach.
Enrico
FAQ
Is conversion varnish better than polyurethane for kitchen cabinets?
For sprayed cabinets, usually yes. It is rated for casework and doors, resists moisture, heat and household chemicals, and dries and stacks quickly. Oil-based polyurethane is also very durable, but it is rated better for floors and stairs, and it ambers over time.
What is the difference between conversion varnish and precatalyzed lacquer?
The catalyst. Conversion varnish has it packaged separately and mixed before use, with a pot life of hours. Pre-catalyzed lacquer has it already added, with a shelf life of months. Post-catalyzed coatings typically outperform pre-catalyzed ones on durability, while precat is easier to handle and repair.
Can you brush conversion varnish?
It is made for spraying. Manufacturers such as General Finishes recommend spray application only, and pros typically apply it in a controlled shop environment. Brush-on finishes for on-site work are generally oil-based polyurethane.
How long does conversion varnish take to cure?
Touch-dry takes minutes and stacking takes hours, but full cure takes longer. One manufacturer lists 7 days at 70°F and 50% humidity. Keep the room warm, above 65°F, while it cures, and go easy on cleaning and heavy use until then.
Sources
- Catalyzed Finishes, Popular Woodworking
- Finishing Touch: Film finishes, Canadian Woodworking
- Comparison of Finish Products, American Hardwood Information Center
- Selecting a Finishing System, American Hardwood Information Center
- M.L. Campbell Krystal product information sheet
- Clear Sealers & Topcoats, Canlak
- Cabinets, Wood Finishes for Cabinetry, PaintPRO Magazine
- General Finishes Enduro Conversion Varnish data sheet
- Catalyzed Finishes, WoodWeb
- Ask the Expert: Lacquer, Atlantic Plywood
- M.L. Campbell Magna-Tek sell sheet
- Decorative Finishes and Faux Techniques, Red Seal study guide
- Waterborne UV-Curable Resins for Industrial Wood, PCI Magazine
- Conversion Lacquer technical data sheet, Axalta
