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Exterior Log Surfaces

Hirsirakentaminen


We recommend treating log surfaces as early in the building phase as possible, because sunlight breaks down the wood surface, quickly greying it and producing a downy consistency.  Dirt also sticks easily to a downy surface. Moisture makes the wood swell, and when it dries, there is considerable shrinkage. Moisture variations cause stresses that lead to the wood cracking over time. Moisture also promotes the growth of blue stain, mould and rot fungi. Primers and coatings protect the wood, reducing the effect of sunlight, moisture and fungi.

Massive logs

A structure built from massive round or planed logs requires good water vapour permeability of the coating, allowing the wood to dry. Round logs in particular swell and shrink a lot with moisture variations, and cracks form on their surfaces, often reaching all the way to the heartwood. These cracks pose a problem, as slanted rain can directly reach the wooden structure through them. The risk of rotting is greatest in the bottom-most logs that are not protected from the rain by the eaves.


We recommend treating massive logs with tinted semi-transparent wood finishes that do not form a film on the log surface that slows down drying. Examples of recommended products are the solvent-based Valtti Color, the waterborne Valtti Akvacolor or the Valtti Arctic, which provides a pearly lustre. If you want the surfaces to look opaque, or if you want to change a previously semi-transparent finished surface into a light surface, you can use the opaque Vinha.


Laminated log

Laminated logs are not made of massive timber; they comprise wooden lamellas (planed planks) glued together, with the heartwood on the outside. A laminated log does not expand and contract with moisture variation like a massive log, which also means that it will not crack. Laminated logs can be finished with all semi-transparent and opaque products with the exception of red ochre paints that cannot achieve good enough purchase on the smooth, planed surface.


Log balustrades

Patio balustrades made from logs are problematic with regard to the durability and finishing of the wood. A massive log balustrade expands and contracts very much according to variations in air humidity. Additionally, slanted rain will wet the balustrade from both sides, as the patio roof is often not long enough to protect the balustrade structures. The swelling and contracting of wood with moisture leads to cracks reaching all the way to the heartwood, allowing water to absorb directly into the wood. Thick massive wood dries extremely slowly, and the moisture content of the balustrades can easily remain above 25% for long periods. For this reason, the rotting risk of log balustrades is higher. We recommend coloured, semi-transparent wood finishes for treating log balustrades: Valtti Color, Valtti Akvacolor or Valtti Arctic.

We recommend building the balustrades from boards. Even the largest log building companies have switched their balustrade materials to plank boards.


Because the balustrades will always be subjected to more weather stress than wall surfaces, the maintenance interval of the finish is shorter than for wall surfaces. The condition of the surface must be regularly monitored and the maintenance treatments done in time. Snow and water stay on horizontal surfaces, which wears film-forming treatments (e.g. paints) and causes the surface to flake. We recommend building horizontal surfaces on a slight slope to allow for water removal. Roofing the patio also increases its service life and protects the horizontal surfaces.

Suggested maintenance treatment intervals:

  • semi-transparent wood finishes: 3 to 7 years
  • Vinha: 7 to 10 years
  • oil and acrylate paints (laminated log surfaces): 10 to 15 years