Exterior projects
Deck stain coverage: new wood, weathered wood and product type
Deck stain coverage is set by the wood, not the can. A new, smooth deck might take a gallon; the same deck weathered and grey takes two. Here is how to tell which you have.
Why stain coverage varies so much
Paint forms a film on top of a surface, so its coverage depends mainly on how thick the film is. Penetrating deck stain works differently: it soaks into the wood, and the wood decides how much it takes. New, smooth, dense boards accept a thin coat and shed the rest. Weathered boards, grey and fibrous after a few years of sun and rain, soak up stain like a sponge. Rough-sawn or very dry wood takes more still. That is why deck stain cans quote wide ranges, and why the most useful thing you can know before buying is the condition of your wood.
Coverage by wood condition
| Wood | Typical coverage | Signs |
|---|---|---|
| New or smooth, sealed | 300 sq ft/gal | Smooth to the touch, water beads on it |
| Weathered or previously stained | 175 sq ft/gal | Grey, slightly fuzzy, water darkens it and soaks in |
| Rough, dry or very porous | 150 sq ft/gal | Rough-sawn, splintery, water disappears at once |
These are typical figures from deck stain data sheets (Behr, Cabot, Olympic, Thompson’s), and they are the defaults in the deck stain calculator. A simple test tells you where your deck sits: sprinkle water on a board. If it beads, the wood is sealed or new and will take little stain; if it soaks in within a minute, the wood is thirsty.
Note that very new pressure-treated lumber is often too wet to take stain well for its first weeks or months; the same water test tells you when it is ready.
Measuring a deck
A deck has three parts to measure, each handled differently:
The railing allowance is the one people forget. Balusters, posts and rails have far more surface than their outline suggests, because each baluster has four faces. Two square feet per linear foot of railing is a site estimate for a typical baluster railing, both sides.
A worked deck
A 16 × 12 ft deck with a railing and steps
40 ft of railing, 3 steps, weathered wood, one coat of penetrating stain, 5% allowance.
- Boards: 16 × 12 = 192 sq ft
- Railings: 40 × 2 = 80 sq ft
- Steps: 3 × 5 = 15 sq ft
- Total: 287 sq ft
- Stain at 175 sq ft per gallon: 287 ÷ 175 × 1.05 = 1.72 gallons, buy 1 gallon + 3 quarts
The same deck when new and smooth, at 300 sq ft per gallon, takes 1 gallon; when rough or very dry, at 150, it takes 2.01 gallons. With two coats on the weathered deck, 3.44 gallons. All from the deck stain calculator.
The railings are over a quarter of the area on this deck. On a deck with a long railing and few boards, they can be most of it.
Which stain
| Product | Looks | Coats | Lasts | Coverage |
|---|---|---|---|---|
| Clear or toner | Shows the wood, little colour | 1 | Shortest | Highest |
| Semi-transparent | Colour with grain showing | 1, sometimes 2 | Medium | High |
| Solid-colour stain | Opaque, like a flat paint | 2 | Longer | Lower |
| Deck and porch paint | Opaque film | 2, over primer | Longest between coats, but can peel | Lowest per coat on rough wood |
The trade-off is between looks, maintenance and failure mode. Penetrating stains wear away gradually and are recoated easily, without stripping. Solid stains and paints last longer between coats but, being films, eventually peel on horizontal boards where water sits and feet scuff, and peeling film has to be scraped or stripped before recoating. For porch floors that are painted rather than stained, the porch and floor paint calculator covers floor enamels.
One coat or two
Penetrating oil stains are usually one coat, because the wood can only absorb so much; a second coat sits on the surface, stays tacky and wears off unevenly. Some products specify a second coat “wet on wet”, applied before the first dries, on very absorbent wood. Solid-colour stains need two coats to hide. The can’s own instructions decide; the calculator defaults to one coat and lets you change it.
Prep for a deck
- Clean. A deck cleaner and a stiff brush remove dirt, mildew and grey fibres. Rinse well.
- Strip or brighten if needed. Old film-forming stain that is peeling needs a stripper; a brightener restores the wood’s colour after cleaning and neutralises cleaners.
- Sand rough spots and set any raised nails or screws.
- Let it dry. Wood should be dry to the touch and pass the water test, usually after a day or two of dry weather.
- Check the forecast. Most stains need dry weather for a day or so after application and air above about 50 °F.
Drying and recoat times
An oil-based penetrating stain is typically touch-dry in about 4 hours and ready for a second coat, if one is needed, after about 24 hours at 77 °F. Cool or damp weather stretches those times. The drying and recoat calculator adjusts them for your conditions, and dry, recoat and cure explains the stages. Keep furniture and foot traffic off until the surface is dry, and heavy furniture off for longer.
How often to re-stain
Horizontal deck boards take the full force of sun, rain and feet, so they need recoating more often than the railings and far more often than vertical siding. Instead of a fixed schedule, watch the water test: when water stops beading and starts soaking in, it is time. Re-staining a deck that is still sound with a penetrating stain is a light job of cleaning and one coat; leaving it until the wood is grey and rough means more prep and more stain.
Hardwoods and composite
Dense tropical hardwoods such as ipe absorb very little, so ordinary deck stains sit on top and stay tacky. They take a penetrating oil made for dense hardwoods, applied thin and wiped, and its coverage is high. Composite and PVC decking is not stained at all; it is cleaned. If an old composite deck has faded, some manufacturers sell a coating for it, but check the decking maker’s guidance first, because a coating can void the warranty. Painted porch floors are a different system again, a floor enamel over primer, covered by the porch and floor paint calculator.
The same logic elsewhere
Fences, pergolas and wooden furniture follow the same rules: wood condition sets the coverage, and the product sets the coats. For a fence, see planning a fence stain and the fence stain calculator. For interior wood, such as trim, doors and furniture, the wood stain and finish calculator covers wiping stains and clear coats. For siding, see siding types and paint usage.
Common mistakes
- Planning with the “up to 300” on the can for a grey deck. Weathered wood takes far more.
- Forgetting the railings. They are often a quarter or more of the area.
- A second coat of penetrating stain that cannot soak in. It stays sticky and wears off in patches.
- Staining wet wood. The stain cannot penetrate; wait for the water test.
- Painting a deck to avoid re-staining. Paint on horizontal boards eventually peels and needs stripping.
- Staining in full, hot sun. It flashes off unevenly; stain in the shade or early in the day.