Marine Varnish: Spar Varnish vs Cetol vs Satin, and How Many Coats

Boat Suppliers

07 October 2026

Marine varnish comes down to three choices: a classic spar varnish for exterior brightwork, a translucent wood finish like Cetol when you want fewer coats and easier upkeep, and a satin urethane varnish for interior wood that never sees sun. The number that settles most arguments is coat count. Exterior spar varnish on bare wood is 6 to 8 coats, sanded with 220 to 320 between, one coat a day at 70°F (21°C). Cetol is 3 coats plus 2 of gloss with no sanding between. Interior satin is 2 to 3. Here is how to pick the finish, build it, and keep it alive in the sun.

Marine varnish types: spar varnish vs Cetol vs interior satin

	Spar varnish	Cetol Marine	Interior satin varnish
What it is	Tung oil and phenolic resin with UV filters	Translucent alkyd wood finish with UV absorbers	Modified urethane, low luster
Look	Deep gloss, shows the grain	Amber tint, softer sheen; Light version is less orange	Flat satin, no glare
Coats on bare wood	6 to 8, or 5 to 6 with Schooner Gold	3, plus 2 of Cetol Gloss	2 to 3
Sanding between coats	220 first two coats, then 320	None inside the recoat window	220
Recoat at 70°F (21°C)	Overnight	24 hours	Overnight
Maintenance	1 to 2 fresh coats every 6 to 12 months	1 coat of gloss a year	As needed, no sun to fight
Where	Exterior and interior	Exterior above the waterline, interior	Interior only

Spar varnish looks best and costs the most hours; Cetol looks like Cetol and costs a third of the hours; satin urethane is for the cabin table nobody will sand on a dock in August. Whichever you pick, you cannot switch mid-life: varnish will not bond over Cetol, so a Cetol boat stays Cetol until you strip to bare wood.

Spar varnish: Schooner and Schooner Gold

A spar varnish is a long-oil varnish, tung oil cooked with a phenolic resin so the film stays flexible when the wood moves, plus enough UV filter to stand up to sun for a season. Interlux Schooner is the classic version of that recipe. Schooner Gold is the same class at a higher viscosity and higher build per coat, for people who would rather lay fewer, heavier coats, or who have 40 ft (12 m) of cap rail to do. Epifanes Clear Gloss sits in the same class and builds at about the same rate, and the schedule below works for it too.

Step	Spec
Bare wood prep	120 grit, then 180, with the grain; solvent wipe, tack
Coat 1	Thinned 25 to 50% with the brushing thinner the can names, so it soaks into the grain
Coat 2	Thinned about 10%
Coats 3 to 8	Full strength, one coat a day
Sanding	220 after coats 1 and 2, 320 after every coat from 3 on, 400 wet before the last
Recoat at 70°F (21°C)	Overnight; the can lists the window by temperature
Coverage	Roughly 100 to 125 sq ft per quart per coat
Conditions	55 to 85°F (13 to 29°C), out of direct sun, after the dew, before the evening damp

Six coats is the floor for exterior brightwork and eight is where it stops improving. The first two thinned coats are not optional; a full-strength first coat sits on top of the grain and the whole stack lets go from underneath in two summers. Brush it with a badger or ox-hair brush, never shake the can, and pour a working amount into a clean container so the bristles never go back into the can. A fitted P100 with organic vapor cartridges, nitrile gloves and eye protection for the sanding and the varnishing.

Schooner Gold changes one number: its higher build gets you to a finished film in fewer coats. We plan on 5 to 6 where Schooner takes 7 or 8, and the coat count on the can is the one to follow. It is thicker in the can, so it wants a heavier brush and a warmer day, and it is less forgiving of over-thinning. If you are learning to varnish, learn on Schooner. If you have varnished a whole boat before and have another one to do, Schooner Gold gives the afternoons back.

Filling the grain: Interstain

On open-grained wood like mahogany, half of your first four coats of varnish disappear into the pores. Interlux Interstain is a filler stain that packs the grain and colors it in one step, in three mahogany shades, so the varnish starts on a level surface and you cut 2 to 3 coats off the schedule. Brush it on, let it flash until it dulls, wipe across the grain with burlap to pack the pores and pull the excess, and let it dry as long as the can says before the first thinned varnish coat. It goes under varnish only; do not put Cetol over it. On teak, skip it; the oil in teak wants the varnish, not a filler.

Cetol Marine Light and Cetol Marine Gloss

Cetol is not varnish and does not pretend to be. It is a translucent wood finish that soaks in, flexes with the wood and does not need sanding between coats inside the recoat window. The original Cetol Marine reads orange; Cetol Marine Light is the same finish with less pigment and shows the wood's own color. The schedule is 3 coats of Cetol Marine Light, 24 hours apart at 70°F (21°C), on wood sanded to 120 grit, and then 2 coats of Cetol Marine Gloss over it for a harder, brighter surface that the sun takes longer to dull. Maintenance is one coat of gloss a year, lightly scuffed with a maroon pad, no stripping. The price is the look: a soft sheen over an amber tint rather than the glass of a varnished transom.

Interior: Goldspar Satin

Interior wood has no sun to fight and a lot of glare to avoid. Interlux Goldspar Satin is a modified urethane varnish with a low-luster finish made for exactly that: cabin soles, bulkheads, tables and companionway trim, where gloss shows every fingerprint. It sands with 220 between coats, and 2 to 3 coats over sealed wood is the finished job. It is interior only; the satin flattener has nothing in it to hold off UV, and a satin finish outdoors clouds in a season.

Which one to buy

For exterior brightwork you are proud of, Interlux Schooner Marine Varnish at 6 to 8 coats, or Interlux Schooner Gold Marine Varnish QT at 5 to 6 if you have done this before. Under either, on mahogany, Interlux Interstain Wood Filler Stain in the mahogany shade closest to the boat's existing trim. For a cap rail you want to maintain in an afternoon a year, Interlux Sikkens Cetol Marine Light Wood Finish at 3 coats and Interlux Sikkens Cetol Marine Gloss Finish at 2. For everything below deck, Interlux Goldspar Satin Marine Varnish- Quart. A quart of any of them does roughly 100 sq ft per coat, so a 30 ft (9 m) boat's cap rails, handrails and hatch trim at 8 coats is about two quarts of Schooner.

Keeping it alive

Exterior varnish fails from the top down: gloss first, then clouding, then cracks and gray wood, and at that point you are stripping. The maintenance rule is to recoat while it still looks fine: in Florida sun, 1 to 2 fresh coats every 6 months on horizontal surfaces and every 12 on vertical ones, after a 320 grit scuff and a wipe. Up north, once a year in the spring covers it. Cetol is the same rule with one coat of gloss a year. If you see any gray wood under the film, no number of coats on top will fix it; sand or strip to bare, and start the schedule at coat one.

Frequently asked questions

How many coats of marine varnish on bare wood?

Six to eight coats of spar varnish for exterior brightwork, with the first thinned 25 to 50% and the second about 10% so they soak into the grain, then full-strength coats one a day at 70°F (21°C), sanded with 320 between. Schooner Gold's higher build gets there in 5 to 6. Interior satin needs 2 to 3. Fewer than 6 outdoors fails in the second summer.

What is the difference between spar varnish and regular varnish?

Spar varnish is a long-oil varnish, tung oil with a phenolic resin, so the film stays flexible as the wood swells and shrinks, and it carries UV filters for sun. A furniture or floor varnish is harder, more brittle and has little or no UV protection, and it cracks on a cap rail in one season. Use a marine spar varnish like Schooner outside; a hard urethane like Goldspar Satin belongs inside.

Is Cetol better than varnish?

It is easier, not better looking. Cetol Marine Light goes on in 3 coats 24 hours apart with no sanding between, takes 2 coats of Cetol Gloss on top, and is maintained with 1 coat a year. Varnish is 6 to 8 coats and 1 to 2 fresh coats every 6 to 12 months, and it looks like glass. Pick Cetol for a cruising boat's cap rail, varnish for a transom you want to show.

Can I put varnish over Cetol?

No. Varnish does not bond to a Cetol film and will peel, so a Cetol boat stays on Cetol Marine and Cetol Gloss until you strip to bare wood, which means a heat gun or stripper and 80 grit before you start a varnish schedule at coat one. The reverse, Cetol over varnish, is also a strip job. Decide once, on bare wood, and stay with it.

How often do you have to revarnish a boat?

Before it looks like it needs it. In Florida sun, 1 to 2 fresh coats every 6 months on horizontal brightwork and every 12 months on vertical, after a 320 grit scuff. In a northern season, once a year in spring. If the gloss has gone cloudy or you can see gray wood under the film, maintenance is over; sand or strip to bare and rebuild all 6 to 8 coats.