Douglas Fir Treatment Guide: The Best Sealants, Finishes & Stains & How To Apply Them

The best types of treatment for Douglas Fir for outdoor use

Thanks to its excellent natural durability, Douglas Fir can be left to weather naturally. However, moisture, humidity and the sun’s UV rays will eventually cause your timber to begin changing colour to a silvery-grey after around six months. After this, you may begin to see some level of surface mould build up, with potential for black spots.

This can be offset with a quality, non-film forming treatment. You have many options when finishing, sealing or staining Douglas Fir for outdoor use, which we would group into three categories depending on their appearance and the level of protection provided: transparent, semi-solid or a solid finish.

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Option 1: Transparent preservatives — to achieve a natural look whilst providing good protection

This is the least ‘intrusive’ type of treatment. Colourless, transparent preservatives result in very minimal change in immediate appearance, and allow the wood to naturally turn grey over time whilst providing decent protection against damage caused by moisture, bacteria and dirt — avoiding those dreaded black spots!

A good product falling into this category is Owatrol H4 Wood. It provides colourless, waterproof protection, allowing your Douglas Fir to eventually achieve the on-trend, rustic ‘grey look’ whilst guarding against the structural problems associated with leaving the wood completely untreated — we’re talking cracking and warping.

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These types of products are usually silicone free, so fantastic if you’re wanting to create a natural, sustainable space. As people increasingly seek to get ‘back to nature’ with their gardens, the weathered appearance that comes with this type of treatment can eventually provide a versatile, uncomplicated monochromatic backdrop to any outdoor area.

Water-repellent preservatives don’t usually last as long as the stronger types of finish which we’ll mention later — they typically require a recoating every couple of years. Be sure to check the product manufacturer’s guidelines on reapplication.

P.S. — don’t fancy waiting for your wood to turn grey? Want that rustic look for your Fir as soon as possible? You might like to look at a weathering accelerant instead. Si00x is a popular choice for speeding the greying process whilst sealing and protecting the timber.

Option 2: Semi-transparent stains— for strong protection that preserves & showcases the Douglas Fir’s beauty

The second category of finishes for Douglas Fir are semi-solid or semi-transparent oils. These provide a higher level of environmental protection for the wood and require less frequent reapplication, and they can be used to subtly alter the colour of the wood.

A quality semi-solid finish can actually enhance the Douglas Fir’s natural, wild and characterful grain pattern, helping it to ‘pop’, which is why we’re big fans of these types of finish.

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When shopping around for a quality stain for your Douglas Fir, be sure that the product is non-film forming. This means it won’t flake or peel.

Within the semi-transparent stain category, there are oil-based and water-based products.

A popular oil-based semi-transparent finish includes Owatrol Textrol HES. Available in a range of tints, from virtually clear to charcoal, you’re able to add a degree of customisation to the appearance of your Douglas Fir project. By penetrating the wood, it provides deep, long-lasting protection and doesn’t form a film.

As for water-based semi-transparent finishes, you’ve got Owatrol Aquadecks. This similarly penetrates the wood to seal and protect it without forming a film. You can choose from a number of different shades available (including honey, movingui, teak and even graphite grey). As it’s water-based, it is seen as more environmentally friendly.

Reapplication times for these types of finishes typically range from 2-4 years, but be sure to check the manufacturer’s guidelines.

Source: https://gardencourte.com
Categories: Outdoor