Wooden slatted blinds are kept in good condition by controlling moisture and UV exposure to the wood, as well as by regular cleaning and adjusting the mechanism that rotates the slats. The combination of damp, sunlight and friction in the fittings causes the most damage, exacerbated by the lack of a water-drainage slope, slats set too tightly and poor ventilation. Durability is ensured by the use of stable timber (KVH/BSH in the construction), a slat profile with a drip edge, and an OSMO oil finish, which should be reapplied when the surface becomes dull and absorbs water more quickly – usually every 2–3 seasons on a south-facing side.
What causes the most damage to wooden slatted blinds, and how can this be prevented in practice?
Movable wooden blinds deteriorate most rapidly not simply due to rain, but because of the combination of moisture, UV light and friction within the mechanism that rotates the slats. When this is compounded by a lack of a water drainage slope, incorrectly positioned fixing points and an enclosure that is too airtight with no ventilation, the wood begins to warp and the fittings become loose.
At Dąb Gaj Wood, we design these systems so that the wood has somewhere to release moisture, and so that the mechanism isn’t forced to work, because it’s the first to indicate that something is wrong.
If you plan to customised movable wooden blinds, make sure you ask straight away about the direction of water drainage, expansion joints and how the front edges of the slats are protected, as these are details that only become apparent after 2–3 seasons.
The most common installation error is fitting blinds under a cooker hood without a drip edge and without leaving a gap from the wall, which causes water to pool on the top edge and seep into the wood. Another classic mistake is setting the slats flush against one another for a full blackout effect, only to be surprised when, at the first change in humidity, they start to rub against each other and the rotating mechanism becomes stiff.
The third problem is the lack of inspection of anchors and steel connectors after the first winter, when the building’s structure and the timber settle into their new geometry.
What type of wood and finish ensure that wooden slatted blinds do not warp over the course of a season?
The stability of the slats depends not so much on the timber species itself as on controlled moisture content and the grade of the material; this is why KVH and BSH GL24 SI are used for structural components, whilst the profile of the slats is selected to ensure that water does not collect on the edges.
KVH is solid structural timber, kiln-dried and joined using micro-finger joints, whilst BSH GL24 SI is a laminated timber with a GL24 strength class, which retains its geometry and has lower internal stresses than a solid beam.
In practice: it is advisable to support frames and posts (e.g. for larger patio awnings) on a stable structural material, and to make the slats themselves from a profile with rounded edges and a distinct drip edge.
Scandinavian spruce is predictable and light, and takes oils and stains well, whilst larch provides a harder surface and naturally better durability, but can warp more if it is not properly dried and if the slat cross-section is too thick. That is why it is sometimes better to have a thinner lamella with a good profile than a thick plank, which retains moisture for a long time.
The choice of finish depends on whether you want a coating that works in harmony with the wood, or a hard, lacquer-like finish. OSMO Oil Extra penetrates the grain and does not flake off in patches, so renovation after 2–3 years usually involves simply washing the surface and applying another coat, without having to strip it back to the bare wood.
OSMO UV-Schutz-Öl works well against strong midday sun, as it slows down greying and stabilises the colour; wood stain is a good option if you want a specific shade and an even finish across the entire terrace façade.
How should you clean and maintain the slat rotation mechanism without damaging the fittings?
The slat rotation mechanism will only last a long time if it is kept clean, retains its installation clearances and is not subjected to strain caused by warped wood. If the blind starts to move more stiffly, do not simply lubricate it without checking; first remove any dirt and check that the slats are not rubbing against the guides.
First, I clean the slats and the areas around the fittings with a soft brush and water mixed with a mild detergent, without using a pressure washer directed at the bearings or joints. A pressure washer can force dirt and water into areas that are meant to stay dry, which can then lead to corrosion on bolts and steel fittings, even if they are galvanised.
Once it has dried, I check that there is no axial play at the pivot points, that the bolts haven’t come loose over the winter, and that the control arm isn’t twisted.
- Carry out seasonal maintenance twice a year: after winter and after the pollen season (spring/summer), as pollen from plants acts like an abrasive on the joints. Whilst you’re at it, adjust the angle at which the slats close so that they don’t slam against each other.
- If the manufacturer permits lubrication, use a product that is neutral to wood and oil-based finishes, rather than one that dissolves the oil or leaves a sticky film. A sticky film attracts dust, and after a month the mechanism will operate less smoothly than it did before servicing.
It’s also worth checking the ground fixings once a season: the galvanised anchor and steel connector are designed to bear wind loads, not to rely on a single bolt. When the blinds form part of a larger patio structure, I also check the main beam and any 18×18 cm support posts, as even the slightest twist in the frame can distort the alignment of the slats and force the mechanism to work harder.
When should you refinish an OSMO finish, and how can you do so without sanding down to the bare wood?
The OSMO oil finish should be renewed when the wood starts to lose its lustre and absorbs water more quickly, rather than only when it has turned grey and cracked. In practice, on south- and west-facing sides this is usually every 2–3 seasons, whilst on north-facing sides it is sometimes less frequent, as UV radiation has the greatest effect there.
Renovation without stripping means that the oil does not form a brittle crust like varnish, but penetrates the wood and can be built up with further layers. First, I clean the surface, removing any tarnish and greasy dirt, and then I leave it to dry completely, as oil applied to damp wood will trap moisture inside.
If there are localised nicks or fibres standing on end after the winter, it is sufficient to lightly sand them down with fine-grit sandpaper, but only in specific areas and without aggressively sanding the edge profile.
It is essential to protect the areas that absorb water most quickly: the front edges of the slats and the lower edges, where dew collects. I apply a thin but thorough coat of oil there, because a thick layer will become sticky and trap dirt, whereas a thin layer will be absorbed well and won’t cause the mechanism to stick.
If the blinds are close to the roofing material (polycarbonate, metal roof tiles, bituminous shingles or ceramic tiles), I also check for any persistent dripping from the edge of the roof, as this causes localised burning of the coating and dark water stains.
What should you check after installation and after the first winter to ensure your blinds last for years?
Most durability issues don’t arise in the workshop, but after the first winter, which is why a post-season check is just as important as a proper installation. At that point, you should check the frame alignment, the operation of the slats across the full range of angles, and ensure that water is not pooling at any point in the system.
Once the installation is complete, I check three things: whether the expansion gaps between the slats are maintained, whether the guides and pivot points are aligned, and whether the fixings to the subfloor are protected from moisture (spacer, washer, correct anchor).
If the blinds form part of a larger terrace enclosure, it’s also worth asking about the formalities: with certain configurations of roofing and side walls, restrictions such as building area limits may apply, and you may need to submit a building notification or apply for planning permission, and it is better to clarify this before placing an order rather than after installation.
When working on roofs supported by rafters and a main beam, I make sure that the roof pitch and the flashings do not direct water onto the louvres, because even the best oil-based coating cannot withstand constant flooding.
After the first winter, I carry out a brief check: tightening the fittings, adjusting the limit settings, assessing the coating on the sides most exposed to the sun, and checking that nothing is rubbing when the machine is in operation in freezing conditions and after a thaw.
If you want your awning to operate smoothly and look as good as new for years to come, please get in touch with Dąb Gaj Wood and ask about the maintenance schedule and the right OSMO oil for your decking.
Read also: Why are retractable wooden patio shutters better than awnings?
Frequently asked questions
How often should you service wooden blinds to prevent the mechanism from becoming stiff?
It is best to service the blinds twice a year: after winter and after the pollen season (spring/summer), as dust and dirt act like an abrasive on the joints. As part of the service, remove any dirt from the fittings, check for play and ensure the screws are tight, and adjust the closing angle of the slats so that they do not knock against each other. If the blind starts to feel stiff, first check whether the slats are rubbing against each other due to changes in humidity, rather than applying lubricant straight away.
Can I clean my wooden slatted blinds with a pressure washer?
It is best to avoid directing the pressure washer towards fittings, bearings and joints, as the water can force dirt into the mechanism and accelerate corrosion of steel components. It is safer to use a soft brush and water with a mild detergent, and only then dry everything thoroughly. If you do want to use a pressure washer, do so from a greater distance and never direct the jet at moving parts.
Which OSMO oil should I choose for the side of the terrace that gets a lot of sun, and how often should I reapply it?
OSMO UV-Schutz-Öl works well on south-facing surfaces, as it slows down greying and stabilises the colour of the wood. Renewal is usually required every 2–3 seasons, but the tell-tale signs are a loss of lustre and increased water absorption, rather than just noticeable greying. Before applying the next coat, wash the surface and allow it to dry completely so as not to trap moisture in the wood.
What should you do before installation to ensure the blinds drain properly and are well ventilated?
Ensure that the design allows for water to run off, includes drip edges and provides a gap from the wall, so that water does not pool on the upper edge or seep into the front of the slats. Ask for expansion joints and space for the wood to move to be left in place, as an installation that is too tight and lacks ventilation accelerates warping and friction within the mechanism. It is also worth ensuring that the fixings to the substrate are protected from moisture (using a spacer/washer and a suitable anchor), as this stabilises the geometry of the entire system.
What should you check after the first winter if the slats have started to rub or there is some play?
First, check the geometry of the frame, the guide rails and the pivot points, as even the slightest distortion in the structure can cause the slats to become misaligned. Next, check that the fittings and fastenings are tight and that the end stops are correctly set, as the building and the wood often settle into a new position after the winter. If the rubbing persists, also check for any areas where water is constantly dripping onto the shutters, as localised damp accelerates the movement of the wood and puts strain on the mechanism.