Wood gutters have to be oiled regularly, or they can dry out and crack. They can also get saturated with water and rot. I don’t think I have ever seen wood gutters on a house without at least some rot! So, what are you supposed to coat your gutters with? Here are your choices with my personal recommendations.
Used motor oil always seems to be the favorite of the old-time do-it-your-selfer. What’s not to like? used motor oil is free. Motor oil actually works very well. The problem is that this type of oil can travel right through the gutter and out the other side. Once it comes out the other side, it will make the paint peel and then you won’t be able to get a new coat of paint to stick.
I used to routinely patch gutters with tar. Because every wood gutter contained at least some tar, I assumed tar was “All the rage.” Eventually I learned that tar locks in moisture and causes wood rot. I made a vow not to ever use roof cement for any application. It is so incredibly messy that if you get a small gob of this stuff on your floor, it will spread throughout your home like a virus. You won’t even know where it is coming from! As far as wood gutters go, tar is a product only used by amateurs. Some people coat all of their gutters with this stuff.
This category includes wood preservatives like Cuprinol Clear and WoodLife. These products work very well and last for years. You should reapply every 4 to 5 years.
Boiled linseed oil
I used to coat wood gutters with boiled linseed oil all the time. I thought this was the way to go since every respectable gutter expert said to use it. I began to notice that unboiled linseed oil dries into a film. This film will lock in moisture and potentially cause rot, just like tar does.
Unboiled (Raw) linseed
I think raw linseed oil is one of the best products to coat gutters with. Unlike the boiled, raw linseed oil does not contain solvents that cause it to dry and harden. When raw oil is applied to wood, it stays wet. It creates a seal that prevents moisture from getting trapped in the wood, while creating a barrier that keeps rain water out. If you regularly clean your gutters, unboiled linseed oil will last as long as Cuprinol Clear. Also it is cheap and easy to apply.
So what is my recommendation?
In my experience, Raw linseed oil is the way to go, with Cuprinol Clear coming in a close second. As far as roof cement is concerned, stay away from it.