Pine Tar to Treat Outdoor Wood

Yesterday I cleaned our deck and treated it with pine tar. I have been “experimenting” with pine tar to preserve outdoor wood for the past 5 years or so. I put “experimenting” in quotes because so far I've done no formal trials with control groups, no measurements or postmortems, I'm just trying it out to see how it goes. So far, I think it's working very well, and I'll be trying it in different ways going forward. Click through to see some before/after pictures of our deck.

Why pine tar?

Lots of reasons. I have a fair amount of experience with standard outdoor wood finishes and they almost all look great initially and don't age well at all. Some (many stains) look terrible immediately and get worse. So first of all, I'm on the lookout for something that works.

Second, the fact that it's a “natural” product is appealing. There's no petroleum in pine tar, which is produced by heating pine roots and other pine waste in a vacuum chamber and catching the thick liquid that oozes out as a result. Read more here: https://en.wikipedia.org/wiki/Pine_tar 

(There's also birch tar, made from birchbark with the same method.)

Third, although “natural” products are often less effective than their petroleum-derived or otherwise synthetic counterparts, pine tar was the wood preservative of choice for much of human history, even in maritime settings. Royal Navy sailors of the “Rule Britannia” era were called “tars” because pine tar, used to preserve rope, stained their hands.

Fourth, not only is pine tar natural, it has low toxicity, and in fact has been used as a topical antiseptic both for humans and livestock. Then there's dandruff and eczema . . . check it out if you don't believe me.

I have bought mine from a website called solvent free paint dot com for about 5 years now. Transactions have gone smoothly and shipping is prompt. Prices are not low, but not ridiculous, either, especially when you consider this is imported from Sweden. A 3-liter (.85-gallon) can costs $69, but it's more than enough to treat my 300 square foot deck, with about a quart left over. As the the Solvent Free Paint website directs, I thin the tar with about 30% linseed oil (that site also sells several types of Swedish and US-grown linseed oil). I also clean up with their linseed oil soap, a thick liquid soap that smells like linseed oil but does an excellent job of getting the pine tar out of my deck brush. 

I said above that so far my experience is good. It is. But guess what? Pine tar starts out looking great, and gradually fades. The good news, though, is that when it gets gray or dingy, you can simply wash the deck with soap and water, and apply more pine tar. That's what I did yesterday. I guess you do that with the other products, too, but I really love the way the “light” pine tar and linseed color the wood. Our deck is developing a patina, and the color gets warmer and more mellow with each application. I don't think I've ever seen treated yellow pine decking look quite this good. 

Our Georgia deck gets a lot of direct sunlight. Yesterday's treatment was the third one in 2 years. In Wisconsin, our deck is in the shade all day long, and its main challenge is moisture. That deck is 5 years old and has had 2 applications. So far, so good.

Here are more photos from yesterday:

Before

After

A More General View