- ThermoWood: No oiling required — ever. Leave untreated or oil every 5+ years for colour only.
- Siberian larch / Douglas Fir: No preservative needed. Oil every 3–5 years with UV-stable penetrating oil to maintain warm colour.
- Nordic spruce / pine: Must treat every 2–3 years with microporous preservative stain — not optional.
- Best time to oil: Spring (April–May) or early autumn (September–October) — dry overcast day, 8–25°C.
- Best products: Koopmans Houtolie or Owatrol H4 for larch and Douglas Fir. Remmers HK Stain for spruce.
- Never use: Fence paint, yacht varnish, or non-breathable film-forming coatings on exterior cladding.
The most common question about timber cladding maintenance — after "does it need treating?" — is "how do I actually do it?" The answer depends heavily on which species you have, what finish you want, and whether treatment is actually necessary at all. This guide gives you the honest, species-by-species picture: which cladding needs oiling, which products to use, how often to apply them, when to do it, and the step-by-step method for getting a consistent result on a UK exterior.
First — Does Your Cladding Actually Need Oiling?
| Species | Oil required? | Frequency | Purpose |
|---|---|---|---|
| ThermoWood | No — ever | Not needed | Zero maintenance — leave untreated or oil every 5+ yrs for colour retention only |
| Siberian Larch | No — optional | Every 3–5 years | Maintains warm honey-gold colour. Without oiling, weathers to silver-grey naturally |
| Douglas Fir | No — optional | Every 3–5 years | Maintains warm reddish-brown colour. Without oiling, weathers to silver-grey |
| Nordic Spruce | Yes — mandatory | Every 2–3 years | Biological protection essential — not optional. Spruce will fail without treatment |
| Charred Timber | No — ever (deep charred) | Not needed | Char layer provides all protection — zero maintenance. Brushed/stained variants benefit from oiling every 3–5 yrs |
If you have ThermoWood or deep charred timber — you do not need to oil it. Zero. If you have Siberian larch or Douglas Fir and you like the silver-grey weathered look — you do not need to oil it. If you have Nordic spruce — oiling or preservative treatment every 2–3 years is not optional, it is what keeps the cladding structurally sound. See our full timber cladding maintenance guide for species-specific detail.
Which Oil Product to Use — By Species
| Species | Recommended product | Type | Coverage |
|---|---|---|---|
| Siberian larch | Koopmans Houtolie | Penetrating linseed oil | ~8–12 m² per litre |
| Douglas Fir | Owatrol H4 | Penetrating waterproofing oil | ~10–15 m² per litre |
| ThermoWood (colour only) | Koopmans Houtolie | Penetrating linseed oil | ~10–15 m² per litre (TW absorbs less) |
| Nordic spruce — colour + protect | Remmers HK Stain | Microporous preservative stain | ~8–10 m² per litre |
| Nordic spruce — grey preserve | Remmers Grey Protect | Grey-toning preservative stain | ~8–10 m² per litre |
Never use standard fence paint, yacht varnish, alkyd gloss paint, or non-breathable film-forming coatings on exterior timber cladding. These products form a surface film that cannot breathe — as moisture moves in and out of the timber seasonally, the film blisters, cracks, and peels within 2–3 years, leaving the wood in a worse state than if it had never been treated. Always use penetrating oils or microporous stains specifically formulated for exterior timber.
When to Oil Timber Cladding — Timing and Conditions
Getting the timing right is as important as choosing the right product. Oiling in the wrong conditions produces uneven absorption, lap marks, and poor durability. The ideal conditions for oiling exterior timber cladding in the UK are a dry overcast day with temperatures between 8°C and 25°C, with no rain expected for at least 48 hours after application.
- Best months: April–May (spring) and September–October (early autumn)
- Avoid: July–August when strong direct sun causes rapid drying and lap marks
- Avoid: November–March when temperatures regularly fall below 5°C overnight
- Avoid: Any day with rain forecast within 48 hours of completion
- Avoid: Surfaces that are wet from dew, rain, or condensation — allow to dry fully first
- Avoid: Oiling in direct strong sunlight on south-facing elevations in summer
How to Oil Timber Cladding — Step by Step
Confirm dry weather for at least 48–72 hours after planned completion. Check the temperature is between 8°C and 25°C throughout the working day. Morning dew should be fully dried before starting — typically mid-morning.
Brush away loose dirt, cobwebs, and surface debris with a stiff brush. Where algae, green staining, or heavy soiling is present, wash with a dilute wood cleaner (follow manufacturer's dilution instructions). Pressure washing is effective but use low pressure — high pressure can raise the grain and damage softwood cladding. Allow to dry fully — typically 24–48 hours depending on conditions and exposure.
Check all fixings for rust staining — galvanised fixings will rust and stain the boards. Replace any corroded fixings with A4 stainless steel equivalents before oiling. Check for split, cracked, or damaged boards and repair or replace before oiling — oil will not hide or repair structural defects.
Stir or shake the oil product thoroughly before use and at regular intervals during application — particularly for pigmented oils and stains where pigment settles to the bottom. Unstirred pigmented products will give uneven colour.
Apply oil generously with a quality brush, short-pile roller, or pad applicator, working with the grain direction. Work in manageable sections — typically 2–3 boards wide — to maintain a wet edge and prevent lap marks forming. Apply to all accessible faces and end grain at reveals and cut ends.
Allow 15–30 minutes for the oil to absorb into the timber. Check for any unabsorbed pooling in grooves, shadow gaps, or low points. Wipe away any pools or drips with a clean lint-free cloth before they dry — dried oil pools leave visible marks that are difficult to remove.
On bare or very dry timber — first-time oiling or timber that has been stripped back — a second coat is recommended after the first coat has dried (typically 4–6 hours in good conditions). On previously oiled cladding in good condition with even colour, one coat is usually sufficient. Never apply a second coat before the first is dry.
Allow 24–48 hours for full cure before rain exposure. Do not wash the surface or allow standing water to contact the freshly oiled surface for at least 48 hours. In cooler autumn conditions, allow 48–72 hours for full cure.
Can You Oil Cladding That Has Already Gone Grey?
Yes — naturally durable timber that has greyed can be cleaned and re-oiled. The grey colour on naturally durable species such as larch and Douglas Fir is a surface photochemical process (UV degradation of lignin) and the timber beneath is typically still sound. To restore some warmth to the colour, clean with a wood cleaner or dilute oxalic acid solution to remove the grey surface layer, allow to dry fully for 24–48 hours, then apply a quality penetrating oil.
The result will not fully restore the original colour — some grey tone is permanent as the UV-degraded layer goes deeper than cleaning can remove — but it will add warmth, depth, and life back to the surface and significantly improve the appearance. For very heavily greyed or weathered cladding where the grain has opened significantly, light sanding with 80-grit paper before oiling produces better results.
Does timber cladding need oiling?
It depends on the species. ThermoWood and charred timber need no oiling at all. Siberian larch and Douglas Fir do not require oiling to stay durable — they are naturally durable — but oiling every 3–5 years maintains their warm colour. Nordic spruce must be treated every 2–3 years with a preservative stain or oil — it is not naturally durable and will fail without treatment.
What is the best oil for timber cladding in the UK?
For Siberian larch and Douglas Fir, Koopmans Houtolie or Owatrol H4 penetrating oil. For Nordic spruce, Remmers HK Stain microporous preservative stain. Never use fence paint, yacht varnish, or non-breathable coatings on exterior cladding — they will blister and peel within 2–3 years.
How often should timber cladding be oiled?
Siberian larch and Douglas Fir every 3–5 years if maintaining warm colour. Nordic spruce every 2–3 years with preservative stain. ThermoWood never. Exposed south-facing and coastal elevations need treatment more often than sheltered north-facing ones.
When is the best time to oil timber cladding in the UK?
Spring (April–May) and early autumn (September–October) are best. Avoid summer direct sun, winter temperatures below 5°C, and any day with rain forecast within 48 hours. Ideal conditions are a dry overcast day between 8°C and 25°C.
Can I oil timber cladding that has already gone grey?
Yes — clean with wood cleaner or dilute oxalic acid, allow to dry fully, then apply penetrating oil. The result won't fully restore original colour — some grey is permanent — but will add warmth and significantly improve appearance. Very weathered cladding benefits from light sanding first.
Timber Cladding Treatment Products — UK Stock
We stock Koopmans Houtolie, Owatrol H4, Remmers HK Stain, Remmers Grey Protect, and Koopmans Cover Line for all timber cladding species. All products available with nationwide delivery. Browse our full woodcare range or contact us for product advice on your specific species and condition.