BLO-Turp is the not so creative hyphenated slang for a mixture of boiled linseed oil (BLO) and turpentine that woodworkers often use in their projects for waterproofing and finishing their wares. Traditionally, any kind of wood features that are exposed to direct sunlight, weather, or get regular wear, would be treated seasonally with this 50/50 mixture. While this may be enough information for some of you to say “Hey that’s cool, I have some dry wood I could try wiping this on” and run off to experiment… I’m a nerd about the science of WHY its so useful, so I’m going to elaborate!
Both linseed oil and turpentine have a long history of use due to their naturally occurring properties. BLO is derived from flaxseed,and has a long history of being used in oil paints and for wood finishes.Raw linseed oil is at saturating dried wood grain and creating a beautiful waterproof coating that enhances the beauty of the wood grain as well, but it can take over a week to dry. Boiled linseed oil has all the same abilities but also contains a chemical additive which makes it skin over usually within 48 hours. The move away from using natural oil for wood treatments was partly due to this dry time and the seasonal maintenance, but also due to the potential for fungal growth in warm damp climates. Modern wood finishes eliminate all of those issues but are not always as good on the “natural” or “saturating” fronts.
Turpentine is made from conifer trees, specifically conifer resin, which the tree produces when it is wounded to prevent bugs and fungus getting in. This makes it a common ingredient in many natural pesticides. Turpentine was also traditionally used by artists and industrial manufacturers alike for thinning oil paints. In fact, turpentine was historically used in everything, no joke. Vics Vapo Rub. Shoe Polish. Lamp oil. Soap. Astringents. Laxatives. Metal polish. The list goes on and on…While you may be able to find “Turpentine” in big box stores, the truth is that REAL domestic turpentine is no longer made in the USA for various reasons including market demand, cheaper competing products (aka mineral spirits), and the near total deforestation of the long leaf pine forests in the US. Fake turps is commonly available.
While it is labeled “turpentine” it is actually an industrial chemical solvent.
It’s easy to tell real turpentine from fake, because fake turpentine stinks, in a very real / bad way that was actually introduced to it to protect anyone using it from breathing it too much. Real turpentine has a nice mild smell, like a Christmas tree.
So…. you combine the amazing wood saturating and refinishing qualities of the oil (that happens to be slow drying and susceptible to mildew) and add in some turpentine with its anti pest and fungal qualities and oil thinning ability, and you have yourself a wondrous wood finishing product that not only revives dried out wood grain, but it is thinned to suck the oil super deep into the grain, dry even faster, AND has natural pest and mildew prevention built right in!
Now, you might say, but if turpentine isn’t made in the U.S., this seems like it might get a little pricey. And yes, that is honestly an issue. You can still get it, but its much more expensive than your big box store paint thinner. A good source for real turpentine is American Rope and Tar. For the purist, or for anyone wanting to try this treatment on some interior surfaces or projects, its my recommended choice. You could also just treat with straight BLO if its an interior surface, it’ll just take a bit longer to cure. You can also use straight BLO on outside features, but again, it will dry slowly, and you should think about getting yourself some mildewcide or borates to avoid mildew and fungus.
HOWEVER. If you’re super set on a deep saturation of old dry wood for better waterproof protection, and you have wonderful ventilation in your shop or you can work outside, you can cut it with mineral spirits for that fast drying, deep saturating quality. It still won’t be mildew resistant, and it will stink to high heaven, but you can do it.
Another note. If your refinishing plans are actually to paint over old wood, this treatment is also helpful for your paint finish as well. Especially where you plan to use oil paint, if you paint directly over dry cracked wood, it will suck all of the oil out of the finish, and ruin your paint coating. Putting down a layer of BLO, BLO-turp, or some other BLO + thinner + mildewcide combination prior to your paint coatings will allow the paint to sit smoothly on top.
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