Planning a deck stain job
Running out of stain halfway through a deck leaves lap marks where you start again with a new can, and buying far too much wastes money. A few measurements give a good estimate of how much you need.
What to measure
- Deck floor: length × width. For an L-shaped deck, split it into rectangles and add them.
- Railings: total length × height. The calculator counts this area once, which roughly covers both faces of the posts, rails and balusters with the gaps between them.
- Stairs: the number of steps × the stair width. Each step counts about 1.6 square feet per foot of width, for the tread, the riser and the stringers.
The calculation
Stain needed = total area × number of coats ÷ coverage per coat × (1 + extra for porous wood)
The number of cans is rounded up.
Example
A 16 × 12 foot deck (192 sq ft) with 40 feet of 3-foot railing and 4 steps 4 feet wide adds up to about 338 square feet. With two coats at 200 square feet per gallon and 10% extra, you need about 3.7 gallons: buy 4 one-gallon cans.
Typical coverage
| Product | Coverage per coat |
|---|---|
| transparent or toner | 200 to 300 sq ft per gallon |
| semi-transparent | 150 to 250 sq ft per gallon |
| solid color | 200 to 400 sq ft per gallon |
| rough or weathered wood | about half the smooth-wood value |
Getting a good finish
- Clean the deck with a deck cleaner and let it dry for 24 to 48 hours. Strip old peeling finishes.
- Test absorption by sprinkling water: if it beads, the wood is not ready.
- Check the weather: most stains need temperatures of about 50 to 90 °F and no rain for 24 to 48 hours.
- Work in sections of two or three boards along their whole length to avoid lap marks.
- Back-brush sprayed or rolled stain into the grain and wipe off any that has not soaked in after 15 to 20 minutes.
- Mix cans together in a bucket to keep the color even.
New wood
New pressure-treated lumber is often too wet to absorb stain. Many manufacturers suggest waiting a few weeks to a few months, until water soaks in. Kiln-dried lumber can usually be stained sooner.
How often to restain
Transparent stains often need a refresh every year or two, semi-transparent every two to three years, and solid stains every three to five years, more often on horizontal surfaces in full sun.