Oiling is one of the most common protection methods for cedar decks in Canada. Unlike film-forming products that create a surface layer, oils penetrate wood fibres and nourish the wood from within.
Why oil exterior cedar
Western red cedar (Thuja plicata), widely used for decks in British Columbia and Ontario, has natural resistance to rot. That resistance comes from oils and resins present in new wood. With exposure to UV and freeze-thaw cycles, these natural compounds gradually evaporate.
Untreated wood turns grey within a few seasons. Greying does not necessarily mean structural damage, but it signals that the wood is losing its natural water-repellent properties.
Surface preparation
Thorough preparation determines how long the treatment will protect the wood. Product applied to poorly prepared wood adheres less well and breaks down faster.
Initial cleaning
Sweep the surface to remove debris, leaves, and accumulated moss. For decks with mould or algae deposits, a pressure washer set between 700 and 1,200 psi is suitable for cedar. Higher pressure risks eroding the soft sapwood fibres.
A sodium percarbonate cleaner diluted in water can be applied with a brush to brighten greyed wood. Rinse thoroughly after 15 to 20 minutes of contact.
Sanding
If the deck has raised fibres after cleaning, light sanding with 80 to 100 grit paper smooths the surface without removing too much material. Sand only in the direction of the grain.
Drying time
Wood must be completely dry before oil is applied. As a rule, wait at least 48 hours after cleaning in sunny conditions. In humid periods, this can extend to 72 to 96 hours. A wood moisture meter can confirm moisture content is below 15% before application.
Choosing an oil
Two main families of oils are used for exterior cedar in Canada:
Penetrating linseed or tung oils
These products absorb into wood cells and cure by oxidation. They protect against moisture while allowing the wood to breathe. Pure tung oil needs several thin coats but offers good water resistance.
Modified oils with UV agents
Formulations combining a plant base and UV filters slow greying caused by sun exposure. These products are especially recommended for south-facing decks in Quebec and Ontario, where summer sunlight is intense.
What to check on the label
- Compatibility with resinous species (cedar, pine, larch)
- Recommended drying time between coats
- Minimum application temperature (generally +10°C)
- Number of coats advised for new wood vs previously treated wood
Application
Applying with a wide brush (10 to 15 cm) or short-nap roller helps the product reach wood irregularities. An airless sprayer can be used on large areas but requires covering surrounding zones first.
Work board by board, following the grain. Avoid pooling at joints between boards; excess oil at these points encourages mould growth.
Number of coats
For new or recently sanded wood, two to three thin coats are usually recommended. Apply the second coat after the manufacturer’s drying window, typically between 4 and 24 hours depending on temperature.
Weather conditions
Apply in dry weather, sheltered from direct wind, at temperatures between +10°C and +28°C. Avoid days with high humidity (>80%) or rain forecast within 24 hours of application.
Maintenance frequency
Protection duration depends on deck exposure. A covered or partially shaded surface may last three to four years between treatments. A full-sun deck in provinces with strong sunlight, such as Alberta, often needs renewal every two years.
A simple test checks treatment condition: pour a few drops of water on the surface. If water beads, protection is still active. If water is absorbed within a minute, it is time to re-treat.
Last updated: May 1, 2026