What is the most environmentally friendly way to paint/preserve wooden art or construction outdoors?

Question

Wood beams, whether pressure-treated or not, tend to be painted to help preserve them outdoors. Wooden art outdoors tends to be stained or coated in something to weatherize it. I am concerned that most of these paints and sealants are petroleum products that harm the environment in their production, if not also in their use on-site. I might be misunderstanding but I also think of waterproofing agents likely to introduce PFAS, a harmful 'forever chemical' into the local environment.

What are the most environmentally-friendly alternatives to preserve wood outdoors? 'Environmentally friendly' in terms of both off-site production and on-site use. Of course 'none' and 'less' are best, and using naturally rot-resistant materials like cedar and locust are great for that. If I have beams or a wood porch that has paint chipping and wood starting to decay, what can I coat it with to help preserve it? I think of "white wash" as what farmers used to do for wooden outbuildings before petroleum products were widely available, and perhaps that is the right answer - looking for some guidance here.

Answer 1

Our preferred solution here (on land and for seagoing wooden boats) is linseed oil based paints, or just plain (raw) linseed oil.

The oil soaks in the wood and therefore prevent water to soak into it just like the resin of some evergreens naturally does. If you add pigments or some minerals to it, you can increase UV protection by cutting the light. Linseed oil based paints need to be reapplied more often than chemical paints but they are natural and relatively harmless for the environment. It requires several layers and, depending on the wood you are coating and the weather, might take time until it is touch-dry. You can use raw linseed oil as a primer and dilute the oil with turpentine for the very first layer to help it soak better into the wood.

If you want to be sure what your paint actually contains, best is to mix it yourself. you will find plenty of tutorials online and the product is easily available.

The environmental friendliness depends of course of how and where the linseed oil was farmed but again, if you mix it yourself you can choose where you buy your ingredients.

On the wooden boats we often protect hardwoods with just several layers of raw linseed oil. Cooked linseed oils dry faster and leave a protective layer on the wood but the industrial oils sometimes contain other chemicals than just cooked oil.

You can also use pine tar the exact same way but I have less experience with that.

Answer 2

In Europe in mediaeval times, the external woodwork of timbered houses was painted with bulls' blood (hence the traditional dark red colour). Apparently it had to be bulls' blood and not pig, for example.

I can't find any data about how often it had to be repeated. I read that it had to be mixed with salt so it didn't coagulate or stink, but I expect there is much more to it than what I can see in Google.